EP2318779A2

EP2318779A2 - Thermal energy storage device

Info

Publication number: EP2318779A2
Application number: EP09795271A
Authority: EP
Inventors: Songgang Qiu; Maurice A. White; David J. Yarger; Ross Galbraith
Original assignee: Infinia Corp
Current assignee: Infinia Corp
Priority date: 2008-07-10
Filing date: 2009-07-10
Publication date: 2011-05-11
Also published as: WO2010006319A2; WO2010006319A3; US20100212656A1; CN102149987A

Abstract

A thermal energy storage (“TES”) device including a vessel housing a continuous volume of a TES media, an input portion, an output portion, and a plurality of thermal energy transport members connected to the input portion and/or the output portion. The input portion receives thermal energy from a thermal energy source. The received thermal energy is transported by one or more of the thermal energy transport members to the output portion and/or the TES media for storage. One or more of the thermal energy transport members connected to the output portion transport stored thermal energy from the TES media to the output portion. The output portion is coupled to an external device, such as a Stirling engine, and configured to transfer thermal energy the external device. Optionally, selected ones of the thermal energy transport members connected to both the input and output portions may be insulated from the TES media.

Description

THERMAL ENERGY STORAGE DEVICE

CROSS REFERENCE TO RELATED APPLICATION(S)

The present application claims the benefit of U.S. Provisional Patent Application No. 61/079,787, filed July 10, 2008, which is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT The invention described herein was made under federally sponsored research and development with Department of the Navy contract no. N00014-07-M- 0409 and may be manufactured and used by or for the United States Government for governmental purposes without the payment of any royalties thereon.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention is directed generally to thermal energy storage devices.

Description of the Related Art

The Stirling engine was first described in an 1816 patent issued to a Scottish clergyman named Robert Stirling. Many variants of the Stirling cycle were implemented over the next century and applied to applications such as pumping water from mines, and powering ships. Stirling engines were even used as kerosene-fueled cooling fans available in early Sears catalogs. All such applications were later displaced by the advent of the electric motor and internal combustion ("IC") engine. Before Philips began to apply modern materials and thermodynamic analysis to the Stirling cycle in the 1940's, all Stirling machines operated with air at atmospheric pressure. The use of helium or hydrogen working fluid at significantly elevated charge pressure enabled major improvements in both efficiency and specific power. Philips, its licensees and others developed many versions of Stirling engines and coolers aimed at a wide range of applications, but outside of a few cryocooler applications, no significant commercialization has occurred. The primary reasons are the inherent life and reliability limitations imposed by the sliding seal in all kinematic Stirling machines (where piston and displacer motions are constrained by conventional crankshafts and related mechanisms), and the high cost that results from no engines having crossed the threshold from demonstration machines to high level production of an engine with comprehensive design for manufacture and assembly ("DFMA"). A typical Stirling engine includes a hot heat exchanger and a cold heat exchanger. Heat is supplied to the hot heat exchanger at a high temperature T_h and rejected to the environment at a low temperature T_c from the cold heat exchanger. A regenerator heat exchanger located between the hot heat exchanger and cold heat exchanger stores and delivers thermal energy to different parts of the cycle. In a two piston alpha configuration, a phase difference between two piston motions is used to extract net work from the cycle by having most of the gas in the hot region during the expansion phase (volume between the two pistons is increasing) and most of the gas in the cold region during the compression phase (volume between the two pistons is decreasing). Net positive cyclic work is applied to the pistons because cycle work output from expanding a hot gas is greater than negative cycle work input by compressing a cold gas. Inertia associated with the piston motions carries the engine through the compression work phase. Single acting alpha engines can only be implemented as kinematic machines since the resonant dynamic forces acting on free pistons cannot achieve a phase relationship that enables positive work output. Beta and gamma Stirling engine configurations both use a single power piston, but add a displacer piston to shuttle working gas between the hot and cold ends. The displacer motion does not change total cycle volume (except at a second order level resulting from the physical diameter of the displacer drive rod), but creates a pressure wave within the cycle working gas by shuttling gas through the heat exchangers so that most of the gas alternates between the hot and cold regions. This pressure wave applied to the power piston generates net cyclic work that causes the piston to reciprocate. Beta and gamma engine configurations can be implemented as either kinematic or free piston engines. Free-piston engines utilize different resonant dynamics of a lightly loaded displacer (that shuttles gas only through the heat exchangers) and the heavily loaded power piston (that extracts work from the engine cycle) to resonantly tune the system to achieve the proper strokes and phase relationship between piston and displacer motions. The difference between beta and gamma engine configurations is that in beta engine configurations, the displacer and power pistons are constrained to the same diameter so they can reciprocate within the same cylinder. In contrast, gamma engine configurations offer more design flexibility with the piston and displacer in separate cylinders. These engines are inherently single acting.

Traditional kinematic Stirling engines extract power from the Stirling cycle via mechanical linkages. They are complicated and expensive to build, and require a lubricated crankcase, piston and rod seals, and mechanical bearings that restrict performance and limit life. Power output is difficult to vary in a kinematic design, generally being accomplished by a complex system that pumps the helium or hydrogen working fluid back and forth between the engine and a storage reservoir to change the average working pressure in the engine. By contrast, free-piston Stirling engines

("FPSE"), such as those available from lnfinia Corporation of Houston, Texas ("Infinia"), include an independently mounted displacer and a power piston that is directly coupled to a linear alternator, both using virtually infinite life flexure bearings and clearance seals that do not require lubricants. Power can be varied over a wide range of output levels, while maintaining high efficiency by using the engine controller electronics to vary terminal voltage and, therefore, piston stroke. Free-piston Stirling engines may be configured to have a simple mechanical configuration that delivers a highly efficient, low or no maintenance product.

As explained above, a Stirling engine is powered by thermal energy. For continuous operation, a Stirling engine typically requires a continuous supply of thermal energy at its hot end. The thermal energy is used to maintain the high temperature T_h of the hot end. However, some sources of thermal energy are not continuous. For example, solar energy is intermittent. Further, some thermal energy sources may supply more energy than is required to operate the Stirling engine. Thus, a need exists for devices configured to store thermal energy for later use by a Stirling engine or other thermal energy consuming devices. The present application provides this and other advantages as will be apparent from the following detailed description and accompanying figures.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Figure 1 is a schematic illustrating an exemplary embodiment of a thermal energy storage ("TES") device.

Figure 2 is a schematic illustrating a first alternate embodiment of the TES device of Figure 1. Figure 3 is a schematic illustrating an electrothermal system incorporating the TES device of Figure 1.

Figure 4 is a side cross-sectional view of a second alternate embodiment of the TES device of Figure 1 for incorporation in the electrothermal system of Figure 3. Figure 5 is a perspective partial sectional view of a third alternate embodiment of the TES device of Figure 1 for incorporation in the electrothermal system of Figure 3.

Figure 6 is a plot illustrating total energy storage capacity of three TES medias compared to the energy storage in a typical prior art liquid salt storage system for troughs.

Figure 7 is phase diagram for the KF/NaF binary system.

Figure 8 is a perspective cutaway view of a fourth alternate embodiment of the TES device of Figure 1 configured for use with an external thermal energy source. Figure 9 is a perspective cutaway view of a fifth alternate embodiment of the TES device of Figure 1 configured for use with an external thermal energy source.

Figure 10 is a perspective cutaway view of a sixth alternate embodiment of the TES device of Figure 1 configured for use with an external thermal energy source. Figure 1 1 is a perspective cutaway view of a seventh alternate embodiment of the TES device of Figure 1 configured for use with an external thermal energy source.

Figure 12 is a perspective broken cutaway view of an eighth alternate embodiment of the TES device of Figure 1 configured for use with an internal thermal energy source.

Figure 13 is a perspective partial cutaway view of a drive system incorporating the TES device of Figure 12.

Figure 14 is an enlarged view of Figure 13 with the TES media, Sterling engine, and fuel tank omitted. Figure 15 is a perspective cutaway view of a ninth alternate embodiment of the TES device of Figure 1 configured for use with an internal thermal energy source.

Figure 16 is a perspective cutaway view of a tenth alternate embodiment of the TES device of Figure 1 configured for use with an internal thermal energy source. Figure 17 is an enlarged perspective cutaway view of a combustor subassembly of the TES device of Figure 16.

Figure 18 is a perspective cutaway view of an eleventh alternate embodiment of the TES device of Figure 1 configured for use with an internal thermal energy source.

Figure 19 is an enlarged perspective cutaway view of a combustor subassembly of the TES device of Figure 18.

Figure 20 is a schematic illustrating a twelfth alternate embodiment of the TES device of Figure 1 configured for use with an internal thermal energy source. Figure 21 provides three graphs illustrating model results: the topmost graph depicts the temperature of a TES media 1 10 over time; the middle graph depicts combustion temperature inside an internal combustor chamber over time; and the bottommost graph depicts temperature of combustion products ("Return") exiting from the internal combustor chamber and the temperature of the incoming fuel and oxidizer obtained via recuperation ("Recouperater") over time.

Figure 22 provides two graphs obtained from a model illustrating power flow through a TES device.

Figure 23 provides two graphs illustrating model results: the topmost graph shows energy accumulation and extraction from the TES media, and the bottommost graph shows transient JP10 fuel expenditure.

Figure 24 is a graph of combustor efficiency as a function of percentage of dilutent for embodiments of a TES device incorporating fins having different thermal conductivities.

Figure 25 is a graph of combustor efficiency as a function of combustor power for embodiments of a TES device incorporating different numbers of heat pipes.

Figure 26 is a block diagram of a method of controlling thermal energy storage in the TES device of Figure 1 based on a temperature of a heater head portion of a Stirling engine coupled to a thermal energy output portion of the TES device.

Figure 27 is a perspective view a receiver plate including temperature sensors for use with the electrothermal system of Figure 3.

Figure 28 is a block diagram of a method of controlling thermal energy storage in the TES device of Figure 1 by modifying the engine stroke of a Stirling engine coupled to the thermal energy output portion of the TES device. DETAILED DESCRIPTION OF THE INVENTION

OVERVIEW

The present application provides a thermal energy storage ("TES") and transfer device for storing thermal energy generated by a thermal energy source and transferring it to a different physical location. The stored thermal energy may be used at a later time by a recipient structure or device such as a thermal energy driven power generation device or any other device requiring thermal energy (e.g., a Stirling engine or a steam turbine). The TES device may be described as a buffering means for thermal energy supplied by a thermal energy source before the thermal energy is provided to the recipient structure or device. Thus, the TES device may be used to introduce a delay period between the generation of the thermal energy and its consumption by a thermal energy driven power generation device. Alternatively, the TES device may be configured to provide thermal energy to a thermal energy driven power generation device without introducing a delay. As will be described below, the TES device may be adapted for use with various thermal energy sources as well as various recipient structures or devices, including various thermal energy driven power generation devices.

Figure 1 provides a block diagram illustrating an exemplary TES device 10. The TES device 10 includes a vessel 90 defining a sealed interior chamber 100 housing a TES media 1 10 (discussed in detail below). Depending upon an amount of thermal energy stored by the TES media 110, the TES media housed inside the interior chamber 100 may be either a solid or a liquid. The vessel 90 is configured to withstand repeated freezing and thawing cycles of the TES media 1 10. The vessel 90 has a thermal energy input portion 102 and a thermal energy output portion 104.

The thermal energy input portion 102 and the thermal energy output portion 104, are each configured to transfer heat through at least one heat transfer mode (e.g., conduction and/or convection). By way of a non-limiting example, the thermal energy input portion 102 and/or the thermal energy output portion 104 may be implemented as a simple conductor. Alternatively, the thermal energy input portion 102 and/or the thermal energy output portion 104 may be implemented as a heat pipe (described below) or similar structure. Thermal energy (illustrated as arrow "A1 ") is transferred to the thermal energy input portion 102 of the TES media 110 from a thermal energy source 130. The thermal energy source 130 may be external to the interior chamber 100 of the vessel 90 or alternatively, housed inside the interior chamber 100. The thermal energy source 130 may be implemented using any suitable heat source.

The thermal energy (illustrated as arrow "A1 ") transferred to the thermal energy input portion 102 heats the TES media 1 10 housed inside the interior chamber 100. The TES device 10 includes one or more heat transporting members or means 140 configured to transfer heat via at least one heat transfer mode (e.g., conduction and/or convection). By way of a non-limiting example, the heat transporting means 140 may be implemented as simple conductors (e.g., solid rods of thermally conductive material).

Alternatively, the heat transporting means 140 may be implemented as one or more conventional heat pipes. Heat pipes transfer thermal energy from a hotter location to a cooler location. Heat pipes may be configured to perform this function even when a small difference in temperature exists between the hotter location and cooler location. At the hotter location, heat pipes have a hot interface and at the cooler location, heat pipes have a cold interface. Heat pipes also have a liquid tight interior void (e.g., a channel or chamber) that houses a working fluid defined by an outer sidewall constructed from a material having a high thermal conductivity. Inside the interior void, the working fluid is housed in a partial vacuum having a pressure near or below the vapor pressure of the working fluid. Thus, inside the interior void, a portion of the working fluid in a liquid phase and a portion of the working fluid in a gas phase. In other words, the working fluid is in a saturated phase that includes a saturated liquid and saturated vapor.

Inside the interior void, thermal energy is transferred from the hot interface to the cold interface via a process referred to as two-phase convection. Specifically, inside a heat pipe, at the hot interface, the working fluid evaporates to form a saturated vapor. The portion of the heat pipe in which the working fluid evaporates may be referred to as an evaporator. The evaporated working fluid flows as a gas toward the cold interface whereat it condenses back into a liquid. The portion of the heat pipe in which the working fluid condenses may be referred to as a condenser. The liquid working fluid then returns to the hot interface. By way of an example, the interior void of the heat pipe may include wicks that move the liquid working fluid by capillary action back to the hot interface whereat the working fluid may evaporate again. Alternatively, gravity or some other force may be used to return the liquid working fluid back to the hot interface whereat the working fluid may evaporate again. Thus, inside the interior void, the working fluid repeated cycles between the gas phase and the liquid phase as well as between the hot interface and the cold interface.

A heat pipe need not have any particular shape. For example, a heat pipe may have an elongated extruded shape (e.g., a hollow cylindrical shape), a non- elongated shape (e.g., a hollow disk shape), and the like. As is appreciated by those of ordinary skill in the art, a heat pipe may transport thermal energy along a single direction or multiple directions. In implementations that transport thermal energy in multiple directions, the hot interface and the cold interface may change physical locations on the heat pipe as the temperatures at the hotter location and/or the cooler location change. Thus, the flow direction of thermal energy through the heat pipe may change in response to changing temperatures at the hotter location and/or the cooler location.

In addition to transferring thermal energy via two-phase convention, a heat pipe may transfer thermal energy via conduction. For example, as mentioned above, the interior void of the heat pipe is defined by an outer sidewall constructed from a thermally conductive material. The outer sidewall will conduct thermal energy to surrounding media (e.g., the TES media 1 10) and/or structures (e.g., thermal energy output portion 104).

The heat transporting means 140 are illustrated as heat pipes 140A, 140B, 140C, 140D, and 140E, disposed inside the TES media 110. The heat pipes 140A--140E transfer thermal energy stored in the TES media to the thermal energy output portion 104 of the vessel 90. The heat pipes 140A--140E may be configured to transport thermal energy to the thermal energy output portion 104 from the TES media 110 and to transport thermal energy from the thermal energy output portion 104 to the TES media 1 10. In other words, the heat pipes 140A--140E may provide bidirectional thermal energy flow. The direction in which thermal energy flows may be determined based upon which of the thermal energy output portion 104 and the TES media 1 10 is hotter. If the thermal energy output portion 104 is hotter than the TES media 1 10, the heat pipes 140A--140E will transport thermal energy from the thermal energy output portion 104 to the TES media 110. On the other hand, if the TES media 1 10 is hotter than the thermal energy output portion 104, the heat pipes 140A-- 140E will transport thermal energy from the TES media 1 10 to the thermal energy output portion 104. Alternatively, the heat pipes 140A-140E may be configured to transport thermal energy in only a single flow direction from TES media 110 to the thermal energy output portion 104. Optional conductive fins (e.g., fins 836 illustrated in Figure 8 attached to heat transporting means 810B) may be attached to, or interfaced with, the heat transporting means 140. In certain circumstances, the conductive fins may improve the performance of the TES device 10. The heat pipes 140A--140E and/or other components of the TES device 10 may include appropriate insulation to affect heat transfer for a desired purpose. The heat pipes 140A--140E may be configured to provide variable thermal energy transfer so that the flow of thermal energy inside the TES device 10 can be modified depending upon thermal energy needs.

The TES device 10 may include sensors "HF1 ," "HF2," and "HF3." The sensors "HF1 ," "HF2," and "HF3" are positioned in locations where the TES media freezes last as the thermal energy is extracted therefrom. The sensors "HF1 ," "HF2," and "HF3" are also positioned in locations where the TES media melts last as the thermal energy is stored therein. When the vessel 90 has a generally cylindrical shape, one or more sensors "HF1 " are arranged inside the interior chamber 100 in a location adjacent the thermal energy input portion 102, one or more sensors "HF2" are arranged inside the interior chamber 100 in a location adjacent the thermal energy output portion 104, and one or more sensors "HF3" are arranged inside the interior chamber 100 along its central axis extending between the thermal energy input portion 102 and thermal energy output portion 104. The sensors "HF1 ," "HF2," and "HF3" are configured to measure temperature information and transmit that information. When the last region of TES media 110 to freeze, freezes or the last region of TES media to melt, melts, the temperature of the TES media 110 can be measured and the energy content of the TES media determined.

While not illustrated in Figure 1 , one or more of the heat transporting means 140 may be connected to the thermal energy input portion 102 and configured to transfer thermal energy from the thermal energy input portion 102 to the TES media 1 10. By way of a non-limiting example, the heat pipes 140A--140E may extend from the thermal energy input portion 102 into the TES media 1 10. In such an embodiment, the heat pipes 140A--140E may be configured to transport thermal energy from the thermal energy input portion 102 to the TES media 1 10 and to transport thermal energy to the thermal energy input portion 102 from the TES media 1 10. In other words, the heat pipes 140A-140E may provide bidirectional thermal energy flow. As explained above, the direction in which thermal energy flows may be determined based upon which of the thermal energy input portion 102 and the TES media 1 10 is hotter. If the thermal energy input portion 102 is hotter than the TES media 1 10, the heat pipes 140A--140E will transport thermal energy from the thermal energy input portion 102 to the TES media 1 10. On the other hand, if the TES media 1 10 is hotter than the thermal energy input portion 102, the heat pipes 140A--140E will transport thermal energy from the TES media 1 10 to the thermal energy input portion 102. Alternatively, the heat pipes 140A--140E may be configured to transport thermal energy in only a single flow direction, i.e., from the thermal energy input portion 102 to the TES media 1 10.

By way of yet another alternate embodiment, one or more of the heat transporting means 140 may be connected between the thermal energy input portion 102 and the thermal energy output portion 104. By way of a non-limiting example, the heat pipes 140A--140E may extend from the thermal energy input portion 102 to the thermal energy output portion 104. The heat pipes 140A--140E may be configured to transport thermal energy directly from the thermal energy input portion 102 to the thermal energy output portion 104 and to transport thermal energy directly to the thermal energy input portion 102 from the thermal energy output portion 104. In other words, the heat pipes 140A--140E may provide bidirectional thermal energy flow. As explained above, the direction in which thermal energy flows may be determined based upon which of the thermal energy input portion 102 and the thermal energy output portion 104 is hotter. If the thermal energy input portion 102 is hotter than the thermal energy output portion 104, the heat pipes 140A--140E will transport thermal energy from the thermal energy input portion 102 to the thermal energy output portion 104. On the other hand, if the thermal energy output portion 104 is hotter than the thermal energy input portion 102, the heat pipes 140A--140E will transport thermal energy from the thermal energy output portion 104 to the thermal energy input portion 102. Alternatively, the heat pipes 140A--140E may be configured to transport thermal energy in only a single flow direction, i.e., from the thermal energy input portion 102 to the thermal energy output portion 104.

In embodiments in which the heat pipes 140A--140E are connected between the thermal energy input portion 102 and the thermal energy output portion 104, the heat pipes 140A--14OE may pass through the TES media 1 10 or may be insulated therefrom. If the heat pipes 140A--140E pass through the TES media 1 10, at least a portion of the thermal energy transported by the heat transporting means 140 may be transferred to the TES media 1 10 and stored thereby. If the heat pipes 140A-140E are configured to provide bidirectional thermal energy flow. The direction in which thermal energy flows may be determined based upon which of the thermal energy input portion 102, the thermal energy output portion 104, and the TES media 1 10 is hotter. If the thermal energy input portion 102 is hotter than the thermal energy output portion 104 and the TES media, the heat pipes 140A--140E will transport thermal energy from the thermal energy input portion 102 through the TES media 110 to the thermal energy output portion 104. On the other hand, if the thermal energy output portion 104 is hotter than the thermal energy input portion 102 and the TES media 1 10, the heat pipes 140A--140E will transport thermal energy from the thermal energy output portion 104 through the TES media 1 10 to the thermal energy input portion 102. Alternatively, if the TES media 110 is hotter than both the thermal energy input portion 102 and the thermal energy output portion 104, the heat pipes 140A--140E will transport thermal energy from the TES media 1 10 to both the thermal energy output portion 104 and the thermal energy input portion 102.

Optionally, insulation (not shown) may be used to insulate the heat transporting means 140 and limit the amount of thermal energy transferred from the heat transporting means 140 to the TES media 110.

The thermal energy output portion 104 includes a heat delivery assembly 150 having an inside surface 145 spaced inwardly from an outside surface 160. The heat delivery assembly 150 may be implemented as a vapor chamber, heat pipe, and the like. The heat delivery assembly 150 includes a liquid tight internal chamber 165 at least partially defined between the spaced apart inside and outside surfaces 145 and 160. A two-phase compound or working fluid 167, such as sodium, helium, mercury, zinc, indium, ammonia, alcohol, methanol, water, steam, air, and the like, is housed inside the internal chamber 165. Inside the internal chamber 165, the heat delivery assembly 150 may condense and wick the working fluid 167 much like a conventional heat pipe (discussed above).

As mentioned above, one or more heat transporting means 140 are affixed to the inside surface 145 and configured to transfer thermal energy from the TES media 1 10 to the inside surface 145 of the heat delivery assembly 150. In particular embodiments, the heat pipes 140A-140E are in two-phase fluidic communication with the thermal working fluid 167 of the heat delivery assembly 150. The inside surface 145 is heated by the thermal energy originating from the heat transporting means 140 and/or the TES media 1 10. The heated inside surface 145 heats the working fluid 167 inside the internal chamber 165 of the heat delivery assembly 150. Then, the heated working fluid 167 heats the outside surface 160 of the heat delivery assembly 150. Thermal energy transferred to the inside surface 145 of the heat delivery assembly 150 by the heat transporting means 140 and/or the TES media 1 10 is comingled inside the internal chamber 165 of the heat delivery assembly 150 to produce a relatively uniform temperature and heat flux along the outside surface 160.

Thermal energy (illustrated as arrow "A2") is transferred from the outside surface 160 to a recipient structure or device 170, such as a thermal energy driven power generation device. Thus, the outside surface 160 of the heat delivery assembly 150 is a heat-exchange surface. The recipient structure or device 170 may include any suitable device requiring heat energy. Non-limiting examples of suitable recipient structures or devices for use with the TES device 10 include an engine, a Stirling engine, a generator, a heat exchanger, and the like.

In alternate embodiments (not shown), the heat delivery assembly 150 may be omitted from the thermal energy output portion 104 of the vessel 90. In such embodiments, the thermal energy output portion 104 may include at least a portion of an outside surface of the interior chamber 100, which serves as a heat exchange surface. One or more of the heat transporting means 140 are affixed to the portion of the outside surface of the interior chamber 100 and transfer thermal energy from the TES media 1 10 to the portion of the outside surface of the interior chamber 100. The recipient structure or device 170 may be coupled to the portion of the outside surface of the interior chamber 100 and configured to receive thermal energy therefrom.

In embodiments in which the thermal energy source 130 is external to the interior chamber 100, the interior chamber 100 may include a heat receiving outside surface 180. In such embodiments, the outside surface 160 of the heat delivery assembly 150 and the heat receiving outside surface 180 are both heat-exchange surfaces. The outside surface 160 of the heat delivery assembly 150 can be configured in any manner appropriate for effecting an interface between the vessel 90 and the recipient structure or device 170. Similarly, the heat receiving outside surface 180 can be configured in any manner appropriate for effecting an interface between the vessel 90 and the thermal energy source 130. For example, one or both of these surfaces could be configured with fins, heat exchangers, heat exchangers that utilize a liquid, conduction means, and the like. Further, one or both of these surfaces may include a portion of one or more of the heat transporting means 140.

In particular embodiments described below, the outside surface 160 of the heat delivery assembly 150 is substantially planar. In such embodiments, the substantially planar outside surface 160 of the heat delivery assembly 150 may be configured to be coupled to a substantially planar or flat heater head of a Stirling engine.

The TES device 10 may be characterized as transferring thermal energy from a first location or region (e.g., the thermal energy source 130) to a second region (e.g., the recipient structure or device 170). Further, as mentioned above, because the transfer of thermal energy may be delayed by the TES media 1 10, depending upon the implementation details, particular embodiments of the TES device 10 may be used to buffer thermal energy as it is transferred between the first and second regions. The TES device 10 may be utilized as a thermal capacitor in any system requiring uniform application of heat flux from a non-uniform first region to the second region.

By way of non-limiting examples, the TES device 10 may be configured to perform one or more of the following functions:

• transfer thermal energy from the thermal energy input portion 102 through the interior chamber 100 housing the TES media 1 10 to the thermal energy output portion 104;

• transfer thermal energy from the thermal energy input portion 102 to the TES media 1 10 for storage;

• buffer thermal energy to lessen an amount by which rates of heat transfer vary for the thermal energy entering the TES device 10 and/or the thermal energy exiting the TES device 10;

• transfer thermal energy out of the TES device 10 such that the outside surface 160 of the heat delivery assembly 150 is ideally isothermal;

• eliminate local high temperature regions, also known as hot spots, in the outside surface 160 of the heat delivery assembly 150;

• smooth heat transfer provided to the recipient structure or device 170; • transfer thermal energy from the thermal energy input portion 102 to only the TES media 1 10; and

• control the rate at which thermal energy is transferred to the thermal energy output portion 104 from the TES media 1 10 and/or the thermal energy input portion 102.

The recipient structure or device 170 may be implemented as a prime mover configured to convert thermal energy to mechanical power, pneumatic power, hydraulic power, electrical power, and the like. Often, a prime mover will have a temperature range of peak efficiency. Because the TES device 10 can be operated with the TES media 1 10 in a saturated condition, latent heat can be delivered to the prime mover ideally isothermally at a desired temperature. If it is desirable to extract thermal energy stored in the TES media 110 for use with the prime mover, the sensible heat transfer could also be used once an appropriate temperature gradient is established.

The thermal energy source 130 may be implemented as a single heat source or multiple separate heat sources. For example, the TES device 10 may be configured for use with a single heat source, such as radiant solar energy or solar power. Alternatively, the TES device 10 may be configured for use with a multimode heat source that includes both solar power and heat developed from combustion. The thermal energy source 130 may be implemented using geothermal energy, or any other source of high-grade heat, alone or in a combination. Through application of ordinary skill in the art to the present teachings, the geometry of the TES device 10 could be altered to accommodate any thermal energy source or recipient structure or device requiring heat transfer.

TES MEDIA

The TES media 1 10 is a phase change material ("PCM"). Using latent heat of fusion of the phase change TES media 1 10 in the TES device 10 may improve the specific weight and volume relative to a TES device using a single-phase TES media. Thus, the TES device 10 may be incorporated in an integrated source/TES/sink module (e.g., an electrothermal system 300 illustrated in Figure 3). In a source/TES/sink module, the source refers to an energy input, including solar, combustion, or waste heat streams. The sink refers to energy extraction, including industrial process heat, water heating, and heat engines (e.g., a Stirling engine). There are many pure and eutectic salts, mostly alkali halides, with attractive properties for use as the TES media 1 10. Selection of the TES media 110 depends on matching its melting point to the application, namely, the temperature range desired at the heat sink. The TES device 10 may be configured to provide nearly isothermal heat transfer during the solidification phase of heat extraction. Also, depending on the acceptable operating temperature range of the heat sink, sensible heat may be extracted from the two-phase TES media 110 in its liquid and solid phases near its melting temperature. The TES device 10 may be utilized as a thermal capacitor in any system requiring uniform application of heat flux to a sink from a nonuniform source.

The TES media 1 10 serves two functions. First, the TES media functions as a heat transfer medium between the thermal energy input portion 102 and the thermal energy output portion 104. Second, the TES media 1 10 stores thermal energy and provides that stored thermal energy to the thermal energy output portion 104 when the thermal energy input portion 102 is not receiving thermal energy from the thermal energy source 130. The TES media 1 10 used may have a high melting temperature, and high latent heat of fusion. For example, eutectic salts may be used. By way of non-limiting examples, mixtures of LiF/NaF/MgF₂, LiF/NaF, NaF/NaCI, and the like may be used. These mixtures have a relatively high heat of fusion and a melting temperature of about 1200 ⁵F.

While the above mentioned TES medias are suitable for this application, there are alternative materials available for achieving high energy storage. For example, Li, LiOH, LiH, LiF/CaF₂, LiF, NaF, CaF₂, and MgF₂ may be used.

Particular implementations are configured such that the recipient structure or device 170 operates within a temperature range of about 1800 ⁵F to about 900 ⁵F. For example, a Stirling engine may be configured to operate efficiently within this temperature range. In such implementations, lithium hydride ("LiH") may be a desirable material because of its specific (fusion) energy and energy available over the designated temperature range of about 1800 ⁵F to about 900 ⁵F. The heat of fusion of LiH is nearly three times that of the LiF/NaF/MgF₂ eutectic. Moreover, its high heat capacity gives LiH an exceptionally high sensible heat addition over the temperature range of about 1800 ⁵F to about 900 ⁵F. On a volume basis, the above-mentioned TES medias are more balanced and somewhat equivalent. Of TES medias exhibiting a reasonable melting temperature, LiF appears to stand out as the best performing material for both energy density during fusion and over the temperature range of about 1800 ⁵F to about 900 ⁵F. The heat of fusion per volume of LiH is not one of the top-performers in this case, owing to its low density, but LiH still provides the second best energy density over the temperature range of about 1800 ⁵F to about 900 ⁵F, again due to its high heat capacity. The LiF/NaF/MgF2 eutectic rates fairly well in this case, offering almost the same performance as LiH. However, depending upon implementation details, single compounds such as LiH or LiF may be easier to prepare and implement.

Different values for the heat of fusion and melting temperature of LiF/NaF/MgF₂ eutectic are known in the art: one based on thermochemical property data provided by lnfinia Corporation of Houston, Texas ("Infinia"); and another provided by an extensive NASA study. The thermochemical property data provides slightly better TES performance. Nevertheless, it is believed the chemical composition of the eutectics used to obtain these properties is the same.

If the interior chamber 100 of the vessel 90 has a volume of about 0.545 ft³. Table A1 below lists the material weights and available energies from various TES medias, including LiH, LiF, and the LiF/NaF/MgF2 eutectic. As shown in Table A1 , by using LiH, the weight could be reduced by 50 Ib in comparison to the LiF/NaF/MgF₂ eutectic, without a significant change in energy storage.

Table A1

Tables A2 and A3 below list additional properties of materials suitable for use as the TES media 1 10.

Table A2

Table A3

Fluoride salts (e.g., LiF, NaF, and MgF2) are reasonably safe to use and handle in most environments. These materials are inherently stable as indicated by their high melting temperature. They are not combustible, cannot explode, and have low reactivity at ambient conditions. A few of them are considered to be a moderate health hazard and/or moderately toxic, and thus require a reasonable amount of personal protection (e.g., goggles, gloves, lab smock, respirator or fume hood), when using. The fluoride salts can be irritants to the skin and airways, and should never be eaten (although NaF is a very minor ingredient in some toothpaste brands).

Table A4 below summarizes National Fire Protection Association ("NFPA") and Hazardous Materials Identification System ("HMIS") ratings given to LiF, NaF, MgF₂, and LiH by most MSDS listings. Each rating system provides a score of 0- 4 in three specific categories with "0" generally representing no special hazards and "4" used for severe or extreme hazard potential.

Table A4 According to Table A4, the fluoride salts present a fairly low hazard overall. Further, shipping and general handling of the fluoride salts at room temperature does not appear to pose any special risks or measures. Many of the potential heath hazards associated with the fluoride salts (1 -2 ratings) are due to applications where they are used/handled as a fine powder. Powders generally have higher hazards because of their high surface area (and thus reactivity) and the ease in which they can be inhaled and/or ingested. It is unlikely, however, that the TES media 1 10 would be in a powder form. As a thermal storage or heat transfer material, the TES media 1 10 may be most efficient when used as a continuous solid or liquid mass.

Another common warning for these materials is the possible release of hydrogen fluoride, hydrofluoric acid, or fluorine gases under circumstances such as extremely high temperatures (prompting decomposition) or exposure to water at high temperature. However, this cannot occur if the TES media 1 10 is stored in a water-free sealed container/vessel, and held below all but extreme (>2500 ⁵F) temperatures, as would be the case for the TES media 110 used in the TES devices described herein (e.g., the TES device 10). However, it may not be crucial that the TES media 1 10 be completely dry before use to prevent the formation of the gases mentioned above. Naturally, corrosion of the vessel 90 should be limited and kept to a minimum. LiH may be the most hazardous material mentioned above for use as the TES media 1 10. This is due to LiH's high reactivity with water, which results in the production of highly flammable hydrogen gas, and highly irritating lithium hydroxide (LiOH) and lithium oxide (Li₂O) solids. By itself, however, LiH is very stable, and does not decompose unless heated above 1800 ⁵F (where it breaks down to Li metal and H₂ gas). Even then, the decomposition reaction is not exothermic, requiring continued energy input to sustain it. Note in Table A4 above, LiH is given a NFPA flammability rating covering a range of 0 to 4. This depends on the reporting source. Apparently some suppliers/manufacturers consider only whether the material itself is flammable (LiH is not flammable), or whether its potential water- reaction byproducts (hydrogen) are flammable (hydrogen is flammable). This inconsistency obviously leads to some confusion in MSDS interpretation.

In the same way, the health hazard rating of 3 for LiH is due to the water reaction products of LiOH and Li₂O, two very irritating and caustic substances to the skin and airways.

ARL has used LiH in experimental testing both as a hydrogen generating material and in a limited TES study. In both programs, LiH was used repeatedly in a solid and a molten state without incident. Primary precautions taken when handling LiH included keeping it away from water or humid ambient air, and avoiding the creation of LiH dust. Typically, LiH was handled/transferred inside an argon atmosphere glove box at the steam plant. When this was not practical, an argon purge was kept above open LiH containers, and respirators and protective gloves were worn when handling.

TES medias and materials are typically used in high-temperature, long- endurance applications. Thus, corrosion and durability of their containment vessel is certainly a critical issue. Although the data is far from complete, studies by NASA and lnfinia show that common austenitic stainless steels hold up fairly well to molten fluoride salts, as does the some of the nickel-based lnconels and Hastelloys. The chromium component in these metals appears to be most vulnerable as CrF₂ and CrF₃ compounds are predicted to form at higher equilibrium concentrations than other metal fluorides. As already mentioned, the NASA study also showed the importance of removing residual water from the salts prior to loading in sealed vessels. This reduces the potential to make hydrogen fluoride at high temperature, a very reactive material to almost all materials including metals. Investigations of LiH performed by ARL were conducted exclusively in 316 stainless steel vessels. Although total exposure time in the molten state was relatively short (hours), the vessels never showed any visual signs of surface degradation or weakening. The vessel 90 may be constructed from a stainless steel, such as 304 stainless steel, 316 stainless steel, and the like. However, the material used to construct the vessel 90 should be analyzed for corrosion and stress cracking as appropriate.

Alkali halide salts and salt eutectics offer many advantages when used as the TES media 110 in the TES device 10. Such salts have high latent heat of fusion and good sensible heat capacity, resulting in very high energy storage density. They are relatively benign to work with, can function through thousands of melt/freeze cycles without degradation, and cause negligible corrosive attack on conventional stainless steel containment. Depending upon the implementation details, it may also be possible to "recharge" the TES device 10 more rapidly than conventional electrochemical batteries by heating and re-melting the TES media 110 at a high heat transfer rate.

A challenge when designing a TES system (such as the TES device 10) is providing for effective heat transfer from the thermal energy source 130 to the TES media 1 10 (e.g., salt) and from the TES media 110 to the recipient structure or device 170, while maintaining the TES device 10 at a uniform temperature and avoiding large temperature gradients during the heat addition process and heat delivery process. The TES media 1 10 properties that create this challenge are its relatively low thermal conductivity when in the solid phase, and the higher density of the solid phase when compared to the liquid phase. For example, the solid phase may be about 20%-25% denser than the liquid phase. As the liquid-phase TES media 1 10 (e.g., salt) is cooled by the recipient structure or device 170, the mass fraction of liquid TES media relative to solid TES media, will begin to change in the region best connected thermally to the recipient structure or device 170 via one or more of the heat transporting means 140. Earlier analyses have shown that, for particular embodiments, the TES media 1 10 should be no more than one to two inches from one of the heat transporting means 140. Heat pipes (e.g., the heat pipes 140A--140E) have been shown to offer adequate heat transport capability to effectively couple the TES media 1 10 to the recipient structure or device 170. This heat transport capability can be modified by the inclusion of optional conductive fins. The latent heat of melting the solid TES media 1 10 at a fixed temperature is much larger than the sensible heat extracted from the liquid TES media over a particular temperature range (e.g., about 1800 °F to about 900 ⁰F). This same principle is utilized for prior art trough TES systems. If a melting point near the peak efficiency temperature of the recipient structure or device 170 is used, most of the time the TES device 10 is operating at near optimum conditions for the recipient structure or device 170. The TES device 10 may serve as a thermal energy buffer that can maintain a relatively constant heat flux for the thermal energy output portion 104. With this relatively constant heat flux, undesirable "hot spots" can be prevented. The TES media 1 10 may be selected based on the desired operating conditions of the recipient structure or device 170. For example, the TES media 1 10 selected may be based on the particular embodiment of the TES device in which the TES media is to be used.

Typical TES medias in the form of salts, or eutectic salts, have a low thermal conductivity. This poses a practical difficulty during operation of the TES device 10 because the TES media 110 is stored as a bulk material within the interior chamber 100 of the vessel 90. For both sensible and latent heat transfer, arrangements of prior art thermal energy transport structures can be ineffective at transferring heat into and out of the bulk TES media 1 10 uniformly. This problem may be compounded by TES medias that undergo a volumetric change when changing phase. Volumetric changes in TES medias in the range 30% are typical.

The poor thermal conductivity of many TES medias, volumetric changes caused by phase changes, means for adding or extracting heat from the TES medias, and voids present in solid or low quality TES medias have created challenges and poor heat transfer and overall performance in prior art TES devices that include thermal energy transport structures. Some prior art devices, such as the one described in U.S. Patent No. 5,1 13,659 issued to Baker et al. on May 19, 1992, have tried to overcome these problems by storing TES media in small cells or canisters disposed about a thermal energy transport structure. However, this approach also has drawbacks. For example, the structure does not permit an appreciable amount of thermal capacitance or storage. Additionally, the introduction of an intermediary canister negatively affects heat transfer to the media due contact resistance and convection losses.

During steady-state operation, the heat transporting means 140 (e.g., the heat pipes 140A-- 140E) may each be considered ideally isothermal. Depending upon the configuration and arrangement of the heat transporting means 140, this can allow for uniform heat transfer to the bulk TES media 1 10 stored in the interior chamber 100 of the vessel 90 for purposes of adding or extracting latent or sensible heat. For uniform heat transfer to occur, the heat transporting means 140 (e.g., the heat pipes 140A--140E) may be configured to reduce or eliminate the presence of solid masses in the TES media 1 10 during certain modes of operation.

In certain circumstances, it is desirable for the TES media 1 10 to undergo a complete phase change. To transition the TES media 110 from a solid to a liquid, sensible heat is first transferred into the TES media 1 10. Then, latent heat is transferred into the TES media 1 10. Optionally, the liquid TES media 1 10 may be heated further by the addition of more sensible heat. Thus, to store thermal energy in the TES media 1 10, it may be necessary to transition all or a portion of the TES media from a solid to a liquid.

To extract all of the heat energy present in the TES media 1 10, it may be necessary to transition the TES media 110 from a liquid to a solid. This would require transferring the latent heat from TES media 1 10, which causes the phase change from liquid to solid. Then, remaining sensible heat may be extracted from the TES media 1 10 provided an appropriate temperature gradient exists. As is appreciated by those of ordinary skill in the art, before the latent heat is extracted, the liquid TES media 1 10 may be storing some sensible heat. When this is the case, the media is a single-phase liquid and not saturated. The sensible heat may be transferred from the single-phase liquid TES media 1 10 before the latent heat is extracted.

Some exemplary implementations of the TES device 10 will now be described.

HYBRID MODE EMBODIMENT

Figure 2 depicts a TES device 200 configured for use with the thermal energy source 130 implemented as a first thermal energy source 208 and a second thermal energy source 210. Like reference numerals have been used to identify like structures in Figures 1 and 2. The TES device 200 illustrated is configured to operate in a hybrid mode. By way of a non-limiting example, the first and second thermal energy sources 208 and 210 may each be implemented as a solar power source, a combustor, a geothermal source, any other source of high-grade heat, or the like. Through application of ordinary skill in the art to the present teachings, the geometry of the TES device 10 may be altered to accommodate any thermal energy source or recipient structure or device requiring heat transfer.

In the TES device 200, thermal energy is transferred to the TES media 1 10 from the first and second thermal energy sources 208 and 210 in different directions (identified by arrows "A1" and "A3," respectively). If the thermal energy source 210 is external to the interior chamber 100, the thermal energy source 210 may transfer thermal energy to the TES media 1 10 via a heat exchange surface 220. By way of non-limiting examples, different thermal energy sources may be used to add thermal energy to the TES device 200 along different planes, axes, or directions. The amount of thermal energy transferred into the TES device 200 from the thermal energy source 208 and/or the thermal energy source 210 may be controlled as needed. In Figure 2, the recipient structure or device 170 is illustrated as a prime mover 230.

SOLAR ELECTROTHERMAL SYSTEM EMBODIMENT Turning to Figure 3, the TES device 10 may be configured to receive thermal energy and dispatch it to any suitable thermal load. For example, thermal energy generated by the sun 280 may be supplied to the thermal energy input portion 102 of the TES device 10. The thermal energy input portion 102 of the TES device 10 may be coupled to a heat pump, a steam turbine, a tri-generation machine, and the like. Alternatively, the thermal energy input portion 102 of the TES device 10 may be coupled to a device configured to generate mechanical power from thermal energy for a variety of purposes.

Turning to Figure 3, the TES device 10 may be integrated into an electrothermal system 300. For ease of illustration, like reference numerals have been used to identify like structures in Figures 1 and 3. Desirable features of a solar power based electrothermal system include the ability to provide electricity in a dispatchable manner and the ability to provide electricity during cloud transient and non-daylight hours. Because the TES device 10 is capable of storing thermal energy for later use and providing that stored thermal energy at a predetermined rate, the TES device 10 may be used to help achieve these desirable features in the electrothermal system 300.

The electrothermal system 300 includes a heat module 312 and a power module 314. In the embodiment illustrated, the heat module 312 is implemented as a Stirling engine 315, which may be configured to efficiently extract energy stored in the TES media 1 10. The heat module 312 may also receive thermal energy directly from the thermal energy input portion 102 and/or from one or more external thermal energy sources (not shown).

A Stirling engine converts heat or thermal energy into mechanical power by alternately compressing and expanding a fixed quantity of working fluid or other gas (i.e., hydrogen, helium, and air) at different temperatures. Thermal energy is supplied to a hot heat exchanger portion or heater head portion 315A of the Stirling engine 315 at a high temperature T_h and rejected to the environment from a cold heat exchanger portion 315B at a low temperature T_c. The working fluid is generally compressed in a colder portion 315C of the Stirling engine 315 and expanded in a hotter portion 315D resulting in a net conversion of heat into work. The functionality and components of Stirling engines are well known in the art and will not be described in further detail.

To convert mechanical movement to electrical power, the Stirling engine 315 may be coupled to or integrated with the power module 314. For example, the Stirling engine 315 may include a displacer 316 and a working fluid 318 in fluid communication with a power piston 320, which is part of the power module 314. The power piston 320 of the power module 314 may be connected to a conventional linear electrodynamic system 322 through a shaft 323 coupled to a mover 324. The linear electrodynamic system 322 further includes a stator 326 and a paired electrical line 328 to furnish or receive electrical power. Movement of the mover 324 relative to the stator 326 creates an electrical current that may be carried by the paired electrical line 328 to power one or more external electrical devices 330. Several alternate Stirling engine configurations are known in the art, and the present disclosure is not limited to use with any particular implementation of the Stirling engine.

Once the Stirling engine 315 is started, control may be accomplished by controlling the engine's output. For example, if as in Figure 3, the Stirling engine 315 is outputting alternating current ("AC"). The Stirling engine 315 may be controlled by controlling its AC output. For an lnfinia free-piston Stirling engine, engine stroke is inversely correlated to the temperature of the heater head portion 315A for any fixed heat transfer rate applied to the heater head portion 315A. Stroke refers to peak-to- peak amplitude of a piston or displacer's linear motion. Thus, stroke refers to the peak- to-peak amplitude of the linear motion of the mover 324 relative to the stator 326. This generally occurs about a mean position. Since engine stroke is directly correlated to the amplitude of the voltage at the rectifier input, by varying amplitude, the temperature of the heater head portion 315A may be controlled. Thus, by controlling the movement of the mover 324 relative to the stator 326, the temperature of the heater head portion 315A may be controlled.

The electrothermal system 300 includes one or more sensors 327A, 327B, and/or 327C configured to sense temperature information from which heat flux may be determined. The sensors 327A, 327B, and/or 327C are positioned at locations where thermal energy is delivered to or received from the TES device 10.

The sensors 327A are placed on the heater head portion 315A of the Stirling engine 315 in a sufficiently cool location or safe zone (i.e., one that allows high sensor reliability) may be used to provide feedback to a stroke regulator or controller 329. Alternatively, the sensors 327A may be placed on the outside surface 160 of the heat delivery assembly 150. The sensors 327A collect temperature information that provides a proxy for heater head temperature. Carnot efficiency for the Stirling engine 315 increases as the temperature of the heater head portion 315A increases. If thermal energy available to the heater head portion 315A is held constant, as stroke increases, the temperature of the heater head portion 315A is drawn down or decreases. On the other hand, if thermal energy available to the heater head portion 315A is held constant, as stroke decreases, the temperature of the heater head portion 315A increases.

The sensors 327A transmit temperature information to the controller 329, which the controller 329 uses to determine a stroke setting. The controller 329 may determine a stroke setting that is optimal for a given operational parameter. The controller 329 is coupled to the mover 324 and configured to determine its stroke and thereby the temperature of the heater head portion 315A.

The heater head portion 315A of the Stirling engine 315 is connected to the outside surface 160 of the heat delivery assembly 150 of the TES device 10. The outside surface 160 of the heat delivery assembly 150 transfers thermal energy to the heater head portion 315A of the Stirling engine 315, which drives the displacer 316 and the power piston 320 and generates an electrical current in the electrical line 328.

The electrothermal system 300 includes a concentrator 340, such as a parabolic dish or mirror that concentrates solar energy on an absorber 350. The concentrator 340 may be mounted on a chassis/stand 360 and positioned by a tracking drive 362. By way of a non-limiting example, the concentrator 340 may be a modified or unmodified 3-kW solar dish sold by Infinia. The absorber 350 may be a component of the thermal energy input portion 102 of the TES device 10. For example, the absorber 350 may be the heat receiving outside surface 180 of the TES device 10. Alternatively, the absorber 350 may be another structure configured to transfer absorbed solar energy to the thermal energy input portion 102 of the TES device 10. Optionally, the electrothermal system 300 may include a solar thermal receiver 370 adjacent the thermal energy input portion 102 of the TES device 10 configured to receive radiant solar energy from the concentrator 340. The receiver 370 may include a receiver plate 373 having an aperture 374 formed therein configured to reduce losses of the solar energy concentrated on the absorber 350. As mentioned above, the absorber 350 may be the heat receiving outside surface 180 of the TES device 10. Alternatively, the absorber 350 may be a component of the receiver 370. By way of a non-limiting example, the electrothermal system 300 may be constructed by modifying a 3-kW commercial Dish Stirling Concentrated Solar Power ("CSP") system sold by lnfinia to incorporate the TES device 10 between the receiver 370 and the Stirling engine 315. Referring to Figure 26, a method 2600 that may be performed by the controller 329 (see Figure 3) is provided. At first block 2610, the sensors 327A (see Figure 3) sense temperature information from the heater head portion 315A of the Stirling engine 315 (see Figure 3) and transmit the temperature information to the controller 329 (see Figure 3). At decision block 2620, the controller 329 determines whether the heater head portion 315A is too hot based on the temperature information received from the sensors 327A.

If the heater head portion 315A is too hot, the decision in decision block 2620 is "YES" and at block 2630, the controller 329 directs the Stirling engine 315 to increase its stroke thereby cooling the heater head portion 315A. In turn, the heater head portion 315A will cool the thermal energy output portion 104 of the TES device 10.

At decision block 2640, whether the new cooler temperature of the thermal energy output portion 104 is less than the temperature of the TES media 1 10 is determined. If the new cooler temperature of the thermal energy output portion 104 is less than the temperature of the TES media 1 10 inside the interior chamber 100 of the vessel 90, the decision in decision block 2640 is "YES" and at block 2650, the heat transporting means 140 will transport stored thermal energy from the TES media 1 10 to the thermal energy output portion 104. In turn, the thermal energy output portion 104 will transfer the received thermal energy to the heater head portion 315A. Thus, the heater head portion 315A receives thermal energy previously stored in the TES media 1 10. Then, the method 2600 returns to block 2610.

If the new cooler temperature of the thermal energy output portion 104 is not less than the temperature of the TES media 1 10 inside the interior chamber 100 of the vessel 90, the decision in decision block 2640 is "NO," and the method 2600 advances to decision block 2655.

At decision block 2655, whether the new cooler temperature of the thermal energy output portion 104 is greater than the temperature of the TES media 1 10 is determined. If the new cooler temperature of the thermal energy output portion 104 is greater than the temperature of the TES media 1 10 inside the interior chamber 100 of the vessel 90, the decision in decision block 2655 is "YES" and at block 2660, the heat transporting means 140 will transport stored thermal energy from the thermal energy output portion 104 to the TES media 1 10 for storage. This will cool the thermal energy output portion 104 and cause the heater head portion 315A to transfer thermal energy to the thermal energy output portion 104 thereby cooling the heater head portion 315A. Then, the method 2600 returns to block 2610.

If the new cooler temperature of the thermal energy output portion 104 is not greater than the temperature of the TES media 1 10 inside the interior chamber 100 of the vessel 90, the decision in decision block 2655 is "NO," and the method 2600 returns to block 2610.

If the heater head portion 315A is not too hot, the decision in decision block 2620 is "NO," and the method 2600 advances to decision block 2675. At decision block 2675, the controller 329 determines whether the heater head portion 315A is too cool based on the temperature information received from the sensors 327A. If the heater head portion 315A is too cool, the decision in decision block

2675 is "YES," and at block 2680, the controller 329 directs the Stirling engine 315 to decrease its stroke thereby heating the heater head portion 315A. In turn, the heater head portion 315A will heat the thermal energy output portion 104 of the TES device 10. At decision block 2685, whether the new hotter temperature of the thermal energy output portion 104 is greater than the temperature of the TES media 1 10 is determined. If the new hotter temperature of the thermal energy output portion 104 is greater than the temperature of the TES media 110 inside the interior chamber 100 of the vessel 90, the decision in decision block 2685 is "YES" and at block 2688, the heat transporting means 140 will transport thermal energy from the thermal energy output portion 104 to the TES media 1 10 for storage thereby. This will cool the thermal energy output portion 104 and cause the heater head portion 315A to transfer thermal energy to the thermal energy output portion 104 thereby cooling the heater head portion 315A. Then, the method 2600 returns to block 2610.

If the new hotter temperature of the thermal energy output portion 104 is not greater than the temperature of the TES media 1 10 inside the interior chamber 100 of the vessel 90, the decision in decision block 2685 is "NO," and the method 2600 advances to decision block 2690. At decision block 2690, whether the new hotter temperature of the thermal energy output portion 104 is less than the temperature of the TES media 1 10 is determined. If the new hotter temperature of the thermal energy output portion 104 is less than the temperature of the TES media 1 10 inside the interior chamber 100 of the vessel 90, the decision in decision block 2690 is "YES" and at block 2695, the heat transporting means 140 will transport stored thermal energy from the TES media 110 to the thermal energy output portion 104. In turn, the thermal energy output portion 104 will transfer the thermal energy to the heater head portion 315A. Thus, the heater head portion 315A receives thermal energy previously stored in the TES media 1 10. Then, the method 2600 returns to block 2610. If the new hotter temperature of the thermal energy output portion 104 is not less than the temperature of the TES media 1 10 inside the interior chamber 100 of the vessel 90, the decision in decision block 2690 is "NO," and the method 2600 returns to block 2610.

If the heater head portion 315A is not too cool, the decision in decision block 2675 is "NO," and the method 2600 returns to block 2610. The sensing performed in block 2610 may be performed periodically or at random intervals.

Returning to Figure 3, the sensors 327B may be placed on the heat receiving surface 180 of the TES device 10 in a sufficiently cool location or safe zone (i.e., one that allows high sensor reliability). In the embodiment illustrated, the sensors 327B are positoned on the absorber 350. In such an embodiment, the sensors 327B may be configured to take advantage of the conductivity of the absorber 350.

Referring to Figure 27, optionally, the sensors 327C may be placed on the receiver plate 373 and used to measure the heat flux of thermal energy entering the thermal energy input portion 102 of the TES device 10. As mentioned above, the sensors 327A are placed on the heater head portion 315A of the Stirling engine 315 or the outside surface 160 of the heat delivery assembly 150. Thus, the difference in heat flux measured between the sensors 327A and 327B may be used to calculate the thermal energy stored in the TES media 110 over time. Further, the difference in heat flux measured between the sensors 327C and 327B may be used to calculate the thermal energy stored in the TES media 110 over time. In other words, by monitoring difference in an input rate a which heat is entering the thermal energy input portion 102 and an output rate at which heat is exiting the thermal energy output portion 104, the controller 329 may determine an amount of thermal energy stored by the TES media 1 10.

The flux sensors transduce heat flux using measuring temperature. This is used to establish a thermal gradient to measure heat transfer. For certain embodiments, the sensors 327A, 327B, and 327C may be located so that they are not operated over-temperature. While exemplary locations for the sensors 327A, 327B, and 327C have been illustrated, through application of ordinary skill in the art to the present teachings alternate locations may be determined that are also suitable for determining the difference in the rate of heat transfer into and out of the TES device 10 and such embodiments are also within the scope of the present teachings. Further, as explained above, the TES device 10 includes sensors "HF1 ,"

"HF2," and "HF3" that sense temperature information inside the interior chamber 100 of the vessel 90. The sensors "HF1 ," "HF2," and "HF3" may be coupled to the controller 329 and configured to transmit temperature information to the controller 329. The sensors "HF1 ," "HF2," "HF3," 327A, 327B, and/or 327C may be communicatively connected to the controller 329 via wired and/or wireless connections.

As mentioned above, when the last region of TES media 1 10 to freeze, freezes or the last region of TES media to melt, melts, the temperature of the TES media 1 10 can be measured and the energy content of the TES media determined. These points in time may be used as starting time for a method 2800 illustrated in Figure 28. The method 2800 may be performed by the controller 329 (see Figure 3).

At first block 2810, the sensors 327A, 327B, and/or 327C sense temperature information and transmit that temperature information to the controller 329 (see Figure 3). The controller 329 monitors this temperature information and in block 2820, uses it to calculate an amount of thermal energy stored in the TES device 10. In block 2830, the sensors "HF1 ," "HF2," and "HF3" sense temperature information inside the interior chamber 100 of the vessel 90, transmit that temperature information to the controller 329 (see Figure 3), and the controller 329 uses that temperature information to determine the temperature of the TES media 1 10 inside the vessel 90 (see Figure 3).

At decision block 2840, the controller 329 determines whether the amount of thermal energy stored in the TES device 1 10 (calculated in block 2820) exceeds a predetermined threshold value. If the amount of thermal energy stored in the TES device 110 exceeds the predetermined threshold value, the decision in decision block 2840 is "YES," in block 2850, the controller 329 directs the Stirling engine 315 to increase its stroke to cool the heater head portion 315A to below the temperature of the TES media 1 10 (determined in block 2830). In turn, the heater head portion 315A will cool the thermal energy output portion 104 of the TES device 10.

Then, in block 2860, the heat transporting means 140 will transport stored thermal energy from the TES media 1 10 to the thermal energy output portion 104. In turn, the thermal energy output portion 104 will transfer the thermal energy to the heater head portion 315A. Thus, the heater head portion 315A receives thermal energy previously stored in the TES media 1 10. Then, the method 2800 returns to block 2810. If the amount of thermal energy stored in the TES device 1 10 is less than the predetermined threshold value, the decision in decision block 2840 is "NO," and in block 2870, the controller 329 directs the Stirling engine 315 to decrease its stroke to heat the heater head portion 315A to above the temperature of the TES media 110 (determined in block 2830). In turn, the heater head portion 315A will heat the thermal energy output portion 104 of the TES device 10. Then, the heat transporting means 140 will transport thermal energy from the thermal energy output portion 104 to the TES media 1 10 for storage thereby. Then, the method 2800 returns to block 2810.

The predetermined threshold value may be based at least in part on a quantity of thermal energy required to operate the Stirling engine 315 for a predetermined period of time. For example, the predetermined threshold value may be set equal to the amount of thermal energy required to operate the Stirling engine 315 for a predetermined amount of time (e.g., 2 hours, 3 hours, 4 hours, 6 hours, etc.). Figure 4 illustrates an embodiment of a TES device 400 that may be integrated into the electrothermal system 300 described above. For ease of illustration, like reference numerals have been used to identify like structures in Figures 3 and 4. The TES media 1 10 used in the TES device 400 may include one or more stable TES salts with high melting points in the range of about 600°Cto about 700°C to maximize energy storage density by utilizing both the latent heat of fusion and sensible heat capacity over a wide range of operating temperatures. To prevent freezing of the TES media 1 10, the TES device 400 may be constructed and operated without pumps, valves, or parasitic heat loads.

The thermal energy input portion 102 of the TES device 400 includes a heat receiving assembly 404. In the embodiment illustrated, the heat receiving assembly 404 includes the absorber 350 and an internal wall 406 spaced inwardly from the absorber. The heat receiving assembly 404 may include an internal chamber 407 housing a working fluid 408, such as sodium, helium, mercury, zinc, indium, ammonia, alcohol, methanol, water, steam, air, and the like. As is appreciated by those of ordinary skill in the art, the internal chamber 407 of the heat receiving assembly 404 may contain a wicked structure that provides substantially identical functionality to that provided by a wick in a conventional heat pipe (described above). In this particular embodiment, the heat receiving assembly 404 functions as a conventional heat pipe. The heat receiving assembly 404 may be implemented as a heat pipe, a vapor chamber, and the like. Alternatively, the heat receiving assembly 404 may be configured to transfer thermal energy only by conductance. The TES device 400 includes two separate sets of annular, or cylindrical shell-shaped heat transporting means 41 OA and 41 OB. The first set of heat transporting means 410A interleave with the second set of heat transporting means 410B in an alternating arrangement. The first set of heat transporting means 410A is spaced apart from the second set of heat transporting means 410B with TES media 1 10 disposed therebetween. However, in alternate embodiments, a single set of cylindrical shell-shaped heat transporting means (not shown) may connect the thermal energy input portion 102 directly to the thermal energy output portion 104.

The first set of heat transporting means 410A extends from the thermal energy input portion 102 of the TES device 400 into the TES media 1 10 but stop short of the thermal energy output portion 104. Solar flux concentrated by the concentrator 340 (see Figure 3) on the absorber 350 is transported into the TES media 1 10 by the first set of heat transporting means 41 OA, which are illustrated as being a plurality of concentrically arranged annular shaped heat pipes 412A to 412D. Each of the annular shaped heat pipes 412A to 412D has an internal channel 414 defined between a first heat conducting annular sidewall 416 space apart from a second heat conducting annular sidewall 418. Each of the internal channels 414 has an open end portion 420 in communication with the internal chamber 407 of the heat receiving assembly 404. Thus, the working fluid 408 may travel within and between the internal channels 414 of the first set of heat transporting means 41 OA and the internal chamber 407 of the heat receiving assembly 404.

The thermal energy output portion 104 of the TES device 400 includes a heat delivery assembly 450 substantially identical to the heat delivery assembly 150 (see Figure 1 ). The heat delivery assembly 450 has an inside surface 451 spaced inwardly from an outside surface 460. In the embodiment illustrated, the outside surface 460 is a heat exchange surface substantially similar to the outside surface 160 (see Figure 1 ). The heat delivery assembly 450 may be implemented as a vapor chamber, heat pipe, and the like. The heat delivery assembly 450 includes a liquid tight internal chamber 465 at least partially defined between the spaced apart inside and outside surfaces 451 and 460. A two-phase compound or working fluid 467, such as sodium, helium, mercury, zinc, indium, ammonia, alcohol, methanol, water, steam, air, and the like, is housed inside the internal chamber 465. Inside the internal chamber 465, the heat delivery assembly 450 may condense and wick the working fluid 467 much like a conventional heat pipe (discussed above). However, in alternative embodiments (not shown), the heat delivery assembly 450 may be configured to transfer thermal energy only by conductance.

The second set of heat transporting means 410B extends from the thermal energy output portion 104 of the TES device 400 into the TES media 1 10 but stop short of the thermal energy input portion 102. The second set of heat transporting means 41 OB are illustrated as a plurality of concentrically arranged annular shaped heat pipes 432A to 432C. Each of the annular shaped heat pipes 432A to 432C has an internal channel 434 defined between a first heat conducting annular sidewall 436 space apart from a second heat conducting annular sidewall 438. Each of the internal channels 414 has an open end portion 440 in communication with the internal chamber 465 of the heat delivery assembly 450 of the thermal energy output portion 104 of the TES device 400. Thus, the working fluid 467 may travel within and between the internal channels 434 of the second set of heat transporting means 410B and the internal chamber 465 of the heat delivery assembly 450. In the embodiment illustrated, the outside surface 460 of the heat delivery assembly 450 includes a portion of the heater head portion 315A of the Stirling engine 315 (see Figure 3). This configuration may provide uniform heating of the heater head portion 315A because condensation of the working fluid 467 occurs at approximately isothermal conditions. Uniform heating may improve the system efficiency of the Stirling engine 315 if heat transfer to the Stirling engine occurs at a peak cycle temperature of the Stirling engine (e.g., about 600°C to about 700°C)rather than over a non-uniform range of temperatures. Further, the entire heater head portion 315A may be heated to the peak allowable metal temperature rather than to a lower weighted average temperature. This has the added benefit of reducing localized thermal stresses that result from thermal gradients. The heater head portion 315A may include an annular flange 470 accessible outside the electrothermal system 300 (see Figure 3). The flange 470 may be used to achieve a significant efficiency improvement: external heating of the backside of the heater head portion 315A. This may reduce temperature drops between the heat source (i.e., the TES device 10) and the engine working fluid (not shown) because (depending upon the implementation details) a majority portion of the heater head portion 315A may be heated from two sides rather than just one. Any of the above factors may increase the peak average gas temperature inside the heater head portion 315A, which will increase the Carnot efficiency and therefore the practical operating efficiency of the Stirling engine 315 (see Figure 3).

The heater head portion 315A may be welded or brazed to the TES device 400 so the weight of the TES device 400 may be structurally supported by the Stirling engine 315. The heater head portion 315A may include a braze lip or weld lip 472 that may be weldable to the vessel 90 of the TES device 400. In other words, in the embodiment illustrated, the thermal energy output portion 104 of the TES device 400 is integrally formed with the heater head portion 315A of the Stirling engine 315 (see Figure 3). However, this is not a requirement.

Figure 5 illustrates an embodiment of a TES device 500 in which the outside surface 460 of the heat delivery assembly 450 and the heater head portion 315A of the Stirling engine 315 (see Figure 3) are implemented as separate components. For ease of illustration, like reference numerals have been used to identify like components of Figures 4 and 5. The thermal energy output portion 104 of the vessel 90 may be coupled to the heater head portion 315A of the Stirling engine 315 using any method known in the art. For example, the outside surface 460 of the heat delivery assembly 450 may be welded, or bolted to the heater head portion 315A of the Stirling engine 315. In this embodiment, the outside surface 460 of the heat delivery assembly 450 is substantially planar. The heater head portion 315A of the Stirling engine 315 is also substantially planar or flat. However, in alternate embodiments, such as the TES device 10 illustrated in Figure 3, the outside surface 160 of the heat delivery assembly 150 may be concave to engage with the heater head portion 315A of the Stirling engine 315, which is illustrated as having a convex shape. Returning to Figure 4, as mentioned above, the heat module 312 (see Figure 3) and the power module 314 (see Figure 3) may have an operating temperature within a range of about 600°C to about 700°C. In such embodiments, the TES device 400 may be configured for use with a TES media 1 10 that undergoes melt-freeze cycles within the range of about 600° C to about 700°Cthereby harnessing the latent heat storage of the TES media 1 10 and avoiding any complicated pumped loops or freezing/maintenance issues. Heat may be transported from the TES media 1 10 to the heater head portion 315A as needed for electricity production by the second set of heat transporting means 410B.

The TES device 400 can be configured to provide a high performance thermal storage system that successfully transports the heat to and from the phase change TES media 1 10 so that the latent heat of fusion and sensible heat can be stored over a wide range of temperatures. The TES device 400 may be configured to provide several hours of Stirling engine operation on demand. The TES device 400 may be configured so that it increases the size and weight of the commercial 3-kW lnfinia solar heat drive by no more than a desired amount. The electrothermal system 300 (see Figure 3) may be configured to operate during cloud transients and to provide dispatchable power for four to seven hours after sunset.

The Stirling engine 315 (see Figure 3) may be operated with a reduced output or in a stall mode during part of the day to divert some of the thermal energy from operating the Stirling engine 315 to instead heating the TES media 1 10. For example, if four hours of post-sunlight operating time is desired, the heat equivalent of four hours of normal Stirling engine 315 operation may be diverted from operating the engine to heating the TES media 1 10.

Alternatively, the thermal capacity of the concentrator 340 may be increased to increase the amount of thermal energy supplied to the TES device 400. The amount of thermal energy supplied to the TES device 400 may be adequate to provide for sufficient thermal energy in the TES media 1 10 and at the same, provide sufficient thermal energy to operate the Stirling engine 315 at full output for the day. For example, assuming a nominal 10-hour daily operating period, the effective area of the concentrator 340 implemented as a solar dish sold by lnfinia may be increased 40% to provide adequate thermal energy for simultaneous engine operation and TES storage. Such an increase in effective area may be achieved by increasing the diameter of the solar dish from its current diameter of about 4.8 m to a new diameter of about 5.7 m. The TES media 1 10 may be implemented using a combination of environmentally benign salts that undergo a phase change at operating temperatures, and small quantities of either sodium or potassium metals within the vessel 90. The salts may include KF/NaF and/or NaF/NaCI eutectic mixtures in quantities of approximately 10 to 1000 lbs. These salts may be sealed inside the vessel 90 for the life of the TES device 400. Should a breach occur in the vessel 90, the salts are unreactive but fluoride poisoning can occur if consumed internally. Appropriate precautions would be taken to insure that exposure was minimized. While sodium and potassium in the metallic form are considered very reactive, the TES device 400 may be configured to use a small amount (e.g., approximately 30 grams) of these substances to effect the heat transfer.

Returning to Figure 3, to achieve the maximum benefits of operation afforded by the TES device 10 in the electrothermal system 300 (such as a standalone CSP system), a larger concentratorthan would be used to operate of the Stirling engine 315 without the TES device 10 may be used to collect thermal energy to operate the Stirling engine 315 (e.g., a 3-kW Stirling engine) during the day as well as to expand engine operation time beyond daylight hours. The power output of the electrothermal system 300 may be increased by using an oversized concentrator 340 (e.g., a dish) to collect thermal energy that may be converted to electricity during nighttime or cloudy periods. Depending upon the implementation details, this increase in power production may be greater than the capital cost of including TES, thus increasing the value of the electrothermal system as an asset.

As mentioned above, the TES device 10 may be configured without pump loops that pump the TES media 110. In such embodiments, the TES device 10 will not experience the same maintenance issues associated with prior art centralized trough and power tower electrothermal systems. Multiple electrothermal systems 300 may be collocated in an array (not shown). For example, two to thousands of the electrothermal systems 300 may be aggregated into an array (not shown). Because the TES device 10 does not include any pumps or pump any fluids, problems associated with high temperature pumps and frozen loops will not render multiple electrothermal systems 300 within an array nonoperational. Should a problem occur, only one electrothermal system 300 in the array will experience issues, allowing the remaining electrothermal systems to continue operating. Thus, if only one electrothermal system 300 in an array is rendered nonoperational, the nonoperational electrothermal system will have little impact on the overall power production of the array.

Maintaining optical accuracy of the concentrated solar energy on the heater head portion 315A of a Stirling engine 315 can be expensive because the heater head portion needs to be heated uniformly to avoid hot spots that cause thermal stress. By incorporating the TES device 10 between the heater head portion 315A and the receiver 370, the heater head portion 315A is decoupled from the receiver 370, allowing more variability of the solar flux at the receiver 370 and/or absorber 350 without causing thermal stress on the heater head portion 315A. Further, the TES device 10 stores the heat and delivers it to the heater head portion 315A of the Stirling engine 315 uniformly. This lowers the optical accuracy requirements of the concentrator 340 and may reduce costs related to the concentrator 340, the chassis/stand 360, the tracking drive 362, the heater head portion 315A, as well as a variety of other subsystems of the electrothermal system 300 relative to prior art electrothermal systems.

Because the heater head portion 315A may be heated uniformly by the TES device 10, the entire electrothermal system 300 may be operated at higher heat flux than prior art electrothermal systems. Without the TES device 10, the heater head portion of a Stirling engine may characterized as operating at an average temperature, but some spots along the heater head portion 315A will be about 500 °C others will be about 650 °C. Thus, if one were to try to increase the average temperature to about 650°C some portions of the heater head portion 315A would be hotter than 650 °C. Those portions are referred to as "hot spots." If hot spots are minimized, the temperature of the entire heater head portion 315A can be maintained at a uniform temperature (e.g., about 650C), which may increase power output and efficiency. By way of a non-limiting example, initial calculations related to the impact of incorporating the TES device 10 in the electrothermal system 300 have determined an overall system cost reduction of as much as 20%.

Solar TES is typically associated with trough TES systems and central receiver TES systems. Trough TES systems include several candidate approaches with widely varying stages of development. The LUZ SEGS I trough, using the primary mineral oil heat transfer fluid (HTF) in hot and warm tanks, provided 3 hours of daily direct energy storage capacity between 1985 and 1999. The 10-MW Solar 2 central receiver system demonstrated the viability of molten salt TES in the late 1990's. These and most other direct and indirect solar TES systems use sensible heat capacity stored in the liquid state, are relatively inefficient with typical solar to electric efficiencies of 15- 20%, require complex pumping systems, and typically require large installations with plant sizes in the tens or hundreds of MW to be economically viable. Molten salt systems should avoid salt freezing. The entire system should be shut down with any freezing or when a component within the TES requires maintenance or fails. Phase change materials, which provide a large increase in energy storage density by utilizing the latent heat of fusion, are typically used only for low temperature storage in space heating and water heating applications.

In contrast, the electrothermal system 300 uses a PCM (the TES media 1 10) that is closely integrated with the Stirling engine 315 and the solar energy absorber 350 (and optionally, the receiver 370). The vessel 90 of the TES device 10 may be hermetically sealed and maintenance free. The TES device 10 may be characterized as a passive heat transport system that does not require insulated pumps, fittings, or other components to transport hot fluid. The TES device 10 is unaffected by ambient temperature levels or melt-freeze cycles. The electrothermal system 300 may be incorporated into an array of like electrothermal systems 300. In such an array, any problem that develops will negatively affect only a single electrothermal system 300.

Utilization of the latent heat of fusion in a TES device greatly improves the specific weight and volume relative to single phase TES systems and enables the practical use of an integrated receiver/TES/engine module. Figure 6 provides a quantitative comparison of the total energy storage capacity of three candidate TES medias to the energy storage in a typical prior art liquid salt storage system for troughs. The stored energy in W-hr/l is plotted over a range from the minimal functional operating temperature of 250°C for the lnfinia 3-kW engine to its maximum operating temperature in a range of about 700° C to about750°C.

Lithium salts generally have the best energy storage density but are also relatively quite expensive. Therefore, a non-lithium NaF/NaCI alternative is illustrated for comparison. While the NaF/NaCI alternative provides only about half the total volumetric storage capacity of LiH, the NaF/NaCI alternative still provides about five times the volumetric storage capacity of the liquid-phase NaNO₃/KNO₃ salt used in a "high temperature" advanced trough TES test loop by ENEA in Spain, in which the salt tanks operate at 270° C and 550° C. There are many pure and eutectic salts, mostly alkali halides, with attractive properties that may be used to implement the TES media 1 10.

The KF/NaF phase equilibrium depicted in Figure 7 is typical and illustrates key properties of a eutectic binary salt. Pure KF melts at 856° C and pure NaF melts at 990° C. As the salts are mixed, the melting point is depressed, reaching a minimum of about 710°C at the eutectic point of 40 Mol% KF and 60 Mol% NaF. For a non-eutectic mixture, as the solid mixture temperature is increased some eutectic liquid will form when the temperature reaches about 710°C, but some will remain solid until it reaches the temperature of the upper curve in Figure 7 corresponding to the given MoI fraction. If the mixture is a proper eutectic ratio, all melting will occur at precisely 710°C. This results in extended operation using the latent heat of fusion at the eutectic melt temperature, but a comparable amount of energy from sensible heat capacity is extracted by operating over a wide temperature range as illustrated in Figure 6. The conversion efficiency will decrease as the temperature drops, but the 3-kW engine will continue to generate useful kWh of energy down to at least 250° C For the lnfinia 3-kW Stirling engine interface, it is advantageous to select a TES media with a melting point in a range of about 600°C to about700°C range so that the extended operation during phase change is near the peak efficiency. Depending on the temperature drop from the TES media 1 10 to the heater head portion 315A, and the peak temperature of the heater head portion 315A when uniformly heated, it may be possible to select a TES media with a melting point substantially above 700° C.

Implementation challenges include low TES media thermal conductivities and a large volume increase during melting. With the variable orientation angle of a solar tracking system, heat transfer to and from the TES media 110 should be available in all regions of the vessel 90 for all orientations of the vessel, with sufficient heat transfer area between the heat transporting means 140 (e.g., the first and second sets of heat transporting means 410A and 410B illustrated in Figure 4) and the TES media 1 10 to maintain an adequate TES media interface. However, the first and second sets of heat transporting means 410A and 410B illustrated in Figure 4 may be used to effectively maintain reasonable temperature drops.

The size of the TES device 10, the receiver 370, the concentrator 340, and other components of the system 300 may be determined based on operating parameters, such as a duration over which the Stirling engine 315 is to operate on power extracted from the TES media 1 10 after the thermal energy source 130 (see Figure 1 ) has stopped supplying thermal energy to the TES media. For example, the electrothermal system 300 may be configured for one hour, two hours, three hours, four hours, etc. of use. By way of a non-limiting example, for one hour of use, the TES device 10 may extend axially outwardly about 7 inches from the heater head portion 315A and have a diameter of about 10 inches. By way of another non-limiting example, for four hours of use, the TES device 10 may extend axially outwardly about 1 1 inches from the heater head portion 315A and have a diameter of about 16 inches.

EMBODIMENTS FOR USE WITH EXTERNAL THERMAL ENERGY SOURCES The TES device 400 (see Figure 4) and the TES device 500 (see Figure

5) described above as for use with the electrothermal system 300 (see Figure 3) may be characterized as TES devices for use with external thermal energy sources (e.g., the solar energy concentrator 340 depicted in Figure 3). Figures 8 — 1 1 also provide TES devices configured for use with external thermal energy sources (e.g., the solar energy concentrator 340 depicted in Figure 3, a geothermal thermal energy source, any sufficient high-grade heat source, and the like). Further, through application of ordinary skill in the art, the TES devices illustrated in Figures 8 — 11 may be incorporated in the electrothermal system 300 depicted in Figure 3.

Figure 8 illustrates a TES device 800. For ease of illustration, like reference numerals have been used to identify like structures in Figures 1 and 8. The TES media 1 10 (see Figure 1 ) used in the TES device 800 may include any TES media described above as suitable for use in the TES device 400 (see Figure 4). To prevent freezing of the TES media 1 10, the TES device 800 may be constructed and operated without pumps, valves, or parasitic heat loads. An optional insulating member 802 may be disoosed about the outside of the vessel 90. The thermal energy input portion 102 of the TES device 800 includes a heat receiving assembly 804 including the heat receiving outside surface 180 of the thermal energy input portion 102, an internal wall 806 spaced inwardly from the heat receiving outside surface 180, and an internal chamber 807 at least partially defined between the heat receiving outside surface 180 and the internal wall 806. The heat receiving assembly 804 may be implemented as a vapor chamber, heat pipe, and the like. The internal chamber 807 of the heat receiving assembly 804 may house a working fluid 808, such as sodium, helium, mercury, zinc, indium, ammonia, alcohol, methanol, water, steam, air, and the like. As is appreciated by those of ordinary skill in the art, the internal chamber 807 of the heat receiving assembly 804 may contain a wicked structure that provides substantially identical functionality to that provided by a wick in a conventional heat pipe (described above). In this particular embodiment, the heat receiving assembly 804 functions as a conventional heat pipe transferring thermal energy via two-phase convention with or without conduction. In particular embodiments, the input energy portion 102 may transport thermal energy via conduction alone.

The TES device 800 includes two separate sets of heat transporting means 81 OA and 81 OB. The first set of heat transporting means 81 OA a spaced apart from the second set of heat transporting means 810B with TES media 1 10 disposed therebetween. The first set of heat transporting means 81 OA are distributed within the interior chamber 100 between the second set of heat transporting means 810B.

The first set of heat transporting means 810A extends from the internal wall 806 of the heat receiving assembly 804 into the interior chamber 100 housing the TES media 1 10 but stops short of the thermal energy output portion 104. Thermal energy transferred to the heat receiving assembly 804 of the thermal energy input portion 102 is transported into the TES media 1 10 by the first set of heat transporting means 810A, which are illustrated as being a plurality of elongated cylindrically shaped heat pipes 812. Each of the heat pipes 812 has an internal channel 814 and in particular embodiments may contain a plurality of radially outwardly extending conductive fins 816. In particular embodiments, the optional fins may be oriented at a clocking angle that would provide optimal heat transfer to and from the TES media. A closed end portion 820 of each of the internal channels 814 abuts the internal wall 806 of the heat receiving assembly 804. Thus, the working fluid 808 may travel inside the heat receiving assembly 804 but not within the internal channels 814 of the first set of heat transporting means 81 OA. In particular embodiments, the first set of heat transporting means 810A may be in fluidic communication with the internal chamber 807 of the heat receiving assembly 804. In particular embodiments, the first set of heat transporting means 810A may be in conductive communication with the heat receiving assembly 804.

The thermal energy output portion 104 of the TES device 800 includes a heat delivery assembly 850 substantially identical to the heat delivery assembly 150 (see Figure 1 ). The heat delivery assembly 850 has an inside surface 851 spaced inwardly from an outside surface 860. In the embodiment illustrated, the outside surface 860 is a heat exchange surface substantially similar to the outside surface 160 (see Figure 1 ). The heat delivery assembly 850 may be implemented as a vapor chamber, heat pipe, and the like. The heat delivery assembly 850 includes a liquid tight internal chamber 865 at least partially defined between the spaced apart inside and outside surfaces 851 and 860. A two-phase compound or working fluid 867, such as sodium, helium, mercury, zinc, indium, ammonia, alcohol, methanol, water, steam, air, and the like, is housed inside the internal chamber 865. Inside the internal chamber 865, the heat delivery assembly 850 may condense and wick the working fluid 867 much like a conventional heat pipe (discussed above). However, in alternative embodiments (not shown), the heat delivery assembly 850 may be configured to transfer thermal energy only by conductance.

The second set of heat transporting means 810B extends from the inside surface 145 of the heat delivery assembly 850 of the thermal energy output portion 104 into the interior chamber 100 for housing the TES media 1 10 but stops short of the thermal energy input portion 102. The second set of heat transporting means 810B are illustrated as being a plurality of elongated cylindrically shaped heat pipes 832. Each of the heat pipes 832 has an internal channel 834 and a plurality of radially outwardly extending fins 836. A closed end portion 840 of each of the internal channels 834 abuts the inside surface 851 of the heat delivery assembly 850. Thus, the working fluid 867 may travel within the heat delivery assembly 850 but not within the internal channels 834 of the second set of heat transporting means 810B. In particular embodiments, the second set of heat transporting means 810B may be in fluidic communication with the internal chamber 865 of the heat delivery assembly 850. In particular embodiments, the second set of heat transporting means 810B may be in conductive communication with the heat delivery assembly 850. Figure 9 illustrates a TES device 900. For ease of illustration, like reference numerals have been used to identify like structures in Figures 1 and 9. The TES media 1 10 (see Figure 1 ) used in the TES device 900 may include any TES media described above as suitable for use in the TES device 400 (see Figure 4). The TES device 900 may be constructed and operated without pumps, valves, or parasitic heat loads. An optional insulating member 902 may be disposed about the outside of the vessel 90. The insulating member 902 may be constructed from any material suitable for constructing the insulating member 802 illustrated in Figure 8 and described above. The thermal energy input portion 102 of the TES device 900 includes a heat receiving assembly 904 including the heat receiving outside surface 180 of the thermal energy input portion 102, an internal wall 906 spaced inwardly from the heat receiving outside surface 180, and an internal chamber 907 at least partially defined between the heat receiving outside surface 180 and the internal wall 906. The heat receiving assembly 904 may be implemented as a vapor chamber, heat pipe, and the like. The heat receiving assembly 904 may house a working fluid 908, such as sodium, helium, mercury, zinc, indium, ammonia, alcohol, methanol, water, steam, air, and the like. As is appreciated by those of ordinary skill in the art, the interior of the internal chamber 907 of the heat receiving assembly 904 may contain a wicked structure that provides substantially identical functionality to that provided by a wick in a conventional heat pipe (described above). In this particular embodiment, the heat receiving assembly 904 functions as a conventional heat pipe.

The thermal energy output portion 104 of the TES device 900 includes a heat delivery assembly 950 substantially identical to the heat delivery assembly 150 (see Figure 1 ). The heat delivery assembly 950 has an inside surface 951 spaced inwardly from an outside surface 960. In the embodiment illustrated, the outside surface 960 is a heat exchange surface substantially similar to the outside surface 160 (see Figure 1 ). The heat delivery assembly 950 may be implemented as a vapor chamber, heat pipe, and the like. The heat delivery assembly 950 includes a liquid tight internal chamber 965 at least partially defined between the spaced apart inside and outside surfaces 951 and 960. A two-phase compound or working fluid 967, such as sodium, helium, mercury, zinc, indium, ammonia, alcohol, methanol, water, steam, air, and the like, is housed inside the internal chamber 965. Inside the internal chamber 965, the heat delivery assembly 950 may condense and wick the working fluid 967 much like a conventional heat pipe (discussed above). However, in alternative embodiments (not shown), the heat delivery assembly 950 may be configured to transfer thermal energy only by conductance.

The TES device 900 includes a single set of spaced apart heat transporting means 910 that are distributed within the interior chamber 100 housing the TES media 1 10 (see Figure 1 ). Each of the heat transporting means 910 extend between the thermal energy input portion 102 and the thermal energy output portion 104. In the embodiment illustrated, the heat transporting means 910 extend from the internal wall 906 of the heat receiving assembly 904 through the interior chamber 100 to the inside surface 951 of the heat delivery assembly 950 of the thermal energy output portion 104.

The heat transporting means 910 are illustrated as being a plurality of elongated cylindrically shaped heat pipes 912. Each of the heat pipes 912 has an internal channel 914 and a plurality of radially outwardly extending fins 916. A first closed end portion 920 of each of the internal channels 914 abuts the internal wall 906 of the heat receiving assembly 904 and a second closed end portion 922 of each of the internal channels 914 abuts the inside surface 951 of the heat delivery assembly 950. Thus, the working fluid 908 may travel inside the heat receiving assembly 904 but not within the internal channels 914 of the heat transporting means 910 and the working fluid 967 may travel within the heat delivery assembly 950 but not within the internal channels 914 of the heat transporting means 910. In particular embodiments, the heat transporting means 910 may be in fluidic communication with the internal chamber 907 of the heat receiving assembly 904 and/or the internal chamber 965 of the heat delivery assembly 950. In particular embodiments, the heat transporting means 910 may be in conductive communication with the heat receiving assembly 904 and/or the heat delivery assembly 950.

Figure 10 illustrates a TES device 1000 configured to provide thermal energy to the thermal energy output portion 104 before a portion of the thermal energy is transported to the TES media 1 10 (see Figure 1 ) for storage. For ease of illustration, like reference numerals have been used to identify like structures in Figures 1 and 10. The TES media 1 10 (see Figure 1 ) used in the TES device 1000 may include any TES media described above as suitable for use in the TES device 400 (see Figure 4). The TES device 1000 may be constructed and operated without pumps, valves, or parasitic heat loads. The interior chamber 100 of the vessel 90 of the TES device 1000 includes a central portion "C1 " surrounded by a perimeter portion "P1." The vessel 90 includes an annular shaped interior insulated channel 1002 extending along the perimeter portion "P1 " of the interior chamber 100. The interior insulated channel 1002 may be segregated from the remainder of the interior chamber 100 by a continuous sidewall or divider 1005. The TES media 110 (see Figure 1 ) is housed inside the central portion "C1 " of the interior chamber 100 but not inside the interior insulated channel 1002. Optionally, the interior insulated channel 1002 may be filled with an insulating material 1003, such as air, an insulating ceramic, and the like. The thermal energy input portion 102 of the TES device 1000 includes a heat receiving assembly 1004, includingthe heat receiving outside surface 180 of the thermal energy input portion 102, an internal wall 1006 spaced inwardly from the heat receiving outside surface 180, and an internal chamber 1007 at least partially defined between the heat receiving outside surface 180 and the internal wall 1006. The heat receiving assembly 1004 may be implemented as a vapor chamber, heat pipe, and the like. The heat receiving assembly 1004 may house a working fluid 1008, such as sodium, helium, mercury, zinc, indium, ammonia, alcohol, methanol, water, steam, air, and the like. As is appreciated by those of ordinary skill in the art, the internal chamber 1007 of the heat receiving assembly 1004 may contain a wicked structure that provides substantially identical functionality to that provided by a wick in a conventional heat pipe (described above). In this particular embodiment, the heat receiving assembly 1004 functions as a conventional heat pipe.

The TES device 1000 includes a first set of spaced apart heat transporting means 1010A and a second set of spaced apart heat transporting means 101 OB. Each of the heat transporting means of the first and second sets 101 OA and 1010B are spaced apart from one another and distributed within the interior chamber 100. The heat transporting means of the first and second sets 101 OA and 101 OB may be spaced apart from one another and distributed within the interior chamber 100 to optimize heat transfer to and from the TES media 1 10. The first set of heat transporting means 101 OA reside inside the interior insulated channel 1002 and the second set of heat transporting means 1010B reside outside the interior insulated channel 1002.

The thermal energy output portion 104 of the TES device 1000 includes a heat delivery assembly 1050 substantially identical to the heat delivery assembly 150 (see Figure 1 ). The heat delivery assembly 1050 has an inside surface 1051 spaced inwardly from an outside surface 1060. In the embodiment illustrated, the outside surface 1060 is a heat exchange surface substantially similar to the outside surface 160 (see Figure 1 ). The heat delivery assembly 1050 may be implemented as a vapor chamber, heat pipe, and the like. The heat delivery assembly 1050 includes a liquid tight internal chamber 1065 at least partially defined between the spaced apart inside and outside surfaces 1051 and 1060. A two-phase compound or working fluid 1067, such as sodium, helium, mercury, zinc, indium, ammonia, alcohol, methanol, water, steam, air, and the like, is housed inside the internal chamber 1065. Inside the internal chamber 1065, the heat delivery assembly 1050 may condense and wick the working fluid 1067 much like a conventional heat pipe (discussed above). However, in alternative embodiments (not shown), the heat delivery assembly 1050 may be configured to transfer thermal energy only by conductance.

Each of the first set of spaced apart heat transporting means 1010A extend between the thermal energy input portion 102 and the thermal energy output portion 104. In the embodiment illustrated, the first set of spaced apart heat transporting means 1010A extend from the internal wall 1006 of the heat receiving assembly 1004 through the insulated interior channel 1002 of the interior chamber 100 to the inside surface 1051 of the heat delivery assembly 1050 of the thermal energy output portion 104. The insulated interior channel 1002 limits the amount of thermal energy that can be transferred from the first set of spaced apart heat transporting means 101 OA to the TES media 110 (see Figure 1 ) inside the central portion "C1 " of the interior chamber 100. Because the amount of thermal energy transferred to the TES media 1 10 (see Figure 1 ) is limited, more of the thermal energy received by the thermal energy input portion 102 may be transmitted directly to the thermal energy output portion 104 by the first set of heat transporting means 101 OA.

The first set of heat transporting means 1010A are illustrated as being a plurality of elongated cylindrically shaped heat pipes 1012. Each of the heat pipes 1012 has an internal channel 1014. A first closed end portion 1020 of each of the internal channels 1014 passes through the internal wall 1006 of the heat receiving assembly 1004 to dispose at least a portion 1020A of the first closed end portion 1020 of each of the internal channels 1014 inside the internal chamber 1007 of the heat receiving assembly 1004. A second closed end portion 1022 of each of the internal channels 1014 passes through the inside surface 1051 of the heat delivery assembly 1050 to dispose at least a portion 1022A of the second closed end portion 1022 of each of the internal channels 1014 inside the internal chamber 1065 of the heat delivery assembly 1050. Thus, the working fluid 1008 may travel inside the internal chamber 1007 of the heat receiving assembly 1004 but not within the internal channels 1014 of the first set of heat transporting means 101 OA and the working fluid 1067 may travel within the internal chamber 1065 of the heat delivery assembly 1050 but not within the internal channels 1014 of the first set of heat transporting means 101 OA.

The second set of heat transporting means 1010B extends from the inside surface 1051 of the heat delivery assembly 1050 of the thermal energy output portion 104 into the central portion "C1 " of the interior chamber 100 housing the TES media 1 10 but stops short of the internal wall 1006 of the heat receiving assembly 1004 of the thermal energy input portion 102. The second set of heat transporting means 1010B are distributed within the central portion "C1 " of the interior chamber 100 outside the insulated interior channel 1002. The second set of heat transporting means 1010B may be distributed within the central portion "C1 " of the interior chamber 100 in such a way as to optimize the performance of the TES module 1000.

The second set of heat transporting means 1010B are illustrated as being a plurality of elongated cylindrically shaped heat pipes 1032. Each of the heat pipes 1032 has an internal channel 1034. Optionally, the heat pipes 1032 may include a plurality of radially outwardly extending fins (not shown). A closed end portion 1040 of each of the internal channels 1034 passes through the inside surface 1051 of the heat delivery assembly 1050 to dispose at least a portion 1040A of the closed end portion 1040 of each of the internal channels 1034 inside the internal chamber 1065 of the heat delivery assembly 1050. Thus, the working fluid 1067 may travel within the heat delivery assembly 1050 but not within the internal channels 1034 of the second set of heat transporting means 101 OB.

After thermal energy has been transported to the thermal energy output portion 104 by the first set of heat transporting means 1010A, the second set of heat transporting means 1010B transport a portion of the thermal energy not being used by the recipient structure or device 170 (see Figure 1 ), such as the Stirling engine 315 (see Figure 3) to the TES media 1 10 (see Figure 1 ) for storage thereby. In this manner, the thermal energy received by the thermal energy input portion 102 may be transported immediately to the thermal energy output portion 104 for immediate use and a portion of this thermal energy transported back to the TES media 1 10 (see Figure 1 ) for future use. Figure 1 1 illustrates a TES device 1 100 configured to provide thermal energy to the thermal energy output portion 104 before a portion of the thermal energy is transported to the TES media 1 10 (see Figure 1 ) for storage. For ease of illustration, like reference numerals have been used to identify like structures in Figures 1 and 1 1. The TES media 1 10 (see Figure 1 ) used in the TES device 1100 may include any TES media described above as suitable for use in the TES device 400 (see Figure 4). The TES device 1100 may be constructed and operated without pumps, valves, or parasitic heat loads.

The interior chamber 100 of the vessel 90 of the TES device 1 100 includes a central portion "C2" surrounded by a perimeter portion "P2." The vessel 90 includes an interior insulated channel 1102 in its central portion "C2." The TES media 1 10 (see Figure 1 ) is housed inside a portion 1 103 of the interior chamber 100 outside the interior insulated channel 1 102. Optionally, the interior insulated channel 1 102 may be filled with an insulating material 1 101 , such as air, an insulating ceramic, and the like. The interior insulated channel 1 102 may be segregated from the portion 1 103 of the interior chamber 100 by a continuous sidewall or divider 1 105.

The thermal energy input portion 102 of the TES device 1 100 includes a heat receiving assembly 1104 includingthe heat receiving outside surface 180 of the thermal energy input portion 102, an internal wall 1 106 spaced inwardly from the heat receiving outside surface 180, and an internal chamber 1 107 at least partially defined between the heat receiving outside surface 180 and the internal wall 1 106. The heat receiving assembly 1 104 may be implemented as a vapor chamber, heat pipe, and the like. The internal chamber 1 107 of the heat receiving assembly 1104 may house a working fluid 1 108, such as sodium, helium, mercury, zinc, indium, ammonia, alcohol, methanol, water, steam, air, and the like. As is appreciated by those of ordinary skill in the art, the internal chamber 1 107 of the heat receiving assembly 1 104 may contain a wicked structure that provides substantially identical functionality to that provided by a wick in a conventional heat pipe (described above). In this particular embodiment, the heat receiving assembly 1004 functions as a conventional heat pipe. The TES device 1 100 includes a first set of spaced apart heat transporting means 1 1 10A and a second set of spaced apart heat transporting means 1 1 10B. Each of the heat transporting means of the first and second sets 11 10A and 1 1 10B are spaced apart from one another and distributed within the interior chamber 100. The heat transporting means of the first and second sets 11 10A and 1 1 10B may be spaced apart from one another and distributed within the interior chamber 100 to optimize heat transfer to and from the TES media. The first set of heat transporting means 1 1 10A reside inside the interior insulated channel 1 102 and the second set of heat transporting means 11 10B reside outside the interior insulated channel 1 102. The thermal energy output portion 104 of the TES device 1 100 includes a heat delivery assembly 1150 substantially identical to the heat delivery assembly 150 (see Figure 1 ). The heat delivery assembly 1 150 has an inside surface 1151 spaced inwardly from an outside surface 1 160. In the embodiment illustrated, the outside surface 1 160 is a heat exchange surface substantially similar to the outside surface 160 (see Figure 1 ). The heat delivery assembly 1 150 may be implemented as a vapor chamber, heat pipe, and the like. The heat delivery assembly 1 150 includes a liquid tight internal chamber 1 165 at least partially defined between the spaced apart inside and outside surfaces 1 151 and 1160. A two-phase compound or working fluid 1 167, such as sodium, helium, mercury, zinc, indium, ammonia, alcohol, methanol, water, steam, air, and the like, is housed inside the internal chamber 1 165. Inside the internal chamber 1 165, the heat delivery assembly 1 150 may condense and wick the working fluid 1 167 much like a conventional heat pipe (discussed above). However, in alternative embodiments (not shown), the heat delivery assembly 1150 may be configured to transfer thermal energy only by conductance. Each of the first set of spaced apart heat transporting means 11 10A extend between the thermal energy input portion 102 and the thermal energy output portion 104. In the embodiment illustrated, the first set of spaced apart heat transporting means 1 1 10A extend from the internal wall 1 106 of the heat receiving assembly 1004 through the insulated interior channel 1102 of the interior chamber 100 to the inside surface 1151 of the heat delivery assembly 1 150 of the thermal energy output portion 104. The insulated interior channel 1 102 limits the amount of thermal energy that can be transferred from the first set of spaced apart heat transporting means 1 1 10A to the TES media 1 10 (see Figure 1 ) inside the portion 1 103 of the interior chamber 100. Because the amount of thermal energy transferred to the TES media 1 10 (see Figure 1 ) is limited, more of the thermal energy received by the thermal energy input portion 102 may be transmitted directly to the thermal energy output portion 104 by the first set of heat transporting means 1 1 10A.

The first set of heat transporting means 1 110A are illustrated as being a plurality of elongated cylindrically shaped heat pipes 1 1 12. Each of the heat pipes 1 1 12 has an internal channel 1 1 14. A first closed end portion 1 120 of each of the internal channels 1 1 14 passes through the internal wall 1 106 of the heat receiving assembly 1 104 to dispose at least a portion 112OA of the first closed end portion 1 120 of each of the internal channels 1 1 14 inside the heat receiving assembly 1104. A second closed end portion 1 122 of each of the internal channels 1 114 passes through the inside surface 1 151 of the heat delivery assembly 1 150 to dispose at least a portioni 122A of the second closed end portion 1 122 of each of the internal channels 1 1 14 inside the heat delivery assembly 1150. Thus, the working fluid 1 108 may travel inside the internal chamber 1107 of the heat receiving assembly 1 104 but not within the internal channels 1 1 14 of the first set of heat transporting means 1 1 10A and the working fluid 1 167 may travel within the internal chamber 1 165 of the heat delivery assembly 1 150 but not within the internal channels 1 114 of the first set of heat transporting means 1 1 10A.

The second set of heat transporting means 11 10B extends from the inside surface 1 151 of the heat delivery assembly 1150 of the thermal energy output portion 104 into the portion 1 103 of the interior chamber 100 housing the TES media 1 10 but stops short of the internal wall 1 106 of the heat receiving assembly 1104 of the thermal energy input portion 102. The second set of heat transporting means 1 1 10B are distributed within the portion 1103 of the interior chamber 100 outside the insulated interior channel 1102.

The second set of heat transporting means 11 10B are illustrated as being a plurality of elongated cylindrically shaped heat pipes 1 132. Each of the heat pipes 1 132 has an internal channel 1 134. Optionally, the heat pipes 1 132 may include a plurality of radially outwardly extending fins (not shown). A closed end portion 1 140 of each of the internal channels 1 134 passes through the inside surface 1 151 of the heat delivery assembly 1 150 to dispose at least a portioni 140A of the closed end portion 1 140 of each of the internal channels 1 134 inside the heat delivery assembly 1 150. Thus, the working fluid 1 167 may travel within the heat delivery assembly 1 150 but not within the internal channels 1 134 of the second set of heat transporting means 1 1 10B. After thermal energy has been transferred to the thermal energy output portion 104 by the first set of heat transporting means 1 1 10A, the second set of heat transporting means 1 1 10B transport a portion of the thermal energy not being used by the recipient structure or device 170 (see Figure 1 ), such as the Stirling engine 315 (see Figure 3) to the TES media 1 10 (see Figure 1 ) for storage thereby. In this manner, the thermal energy received by the thermal energy input portion 102 may be transported immediately to the thermal energy output portion 104 for immediate use and a portion of this thermal energy transported back to the TES media 1 10 (see Figure 1 ) for future use. Thus, the TES devices 1000 and 1 100 illustrated in Figures 10 and 1 1 , respectively, are configured to transfer heat to the recipient structure or device 170 (see Figure 1 ) without first storing thermal energy in the TES media 110 (see Figure 1 ) or alternatively, to store only a limited amount of thermal energy in the TES media 1 10 as the thermal energy is provided to the recipient structure or device 170. For example, the TES devices 1000 and 1 100 can be configured to store only thermal energy in excess of what is required by the recipient structure or device 170 (e.g., the Stirling engine 315 depicted in Figure 3) to function. In such embodiments, only a limited amount of thermal energy is transferred to the TES media 110 (see Figure 1 ). Such embodiments may be characterized as being dual-mode because they have the ability to (1 ) store thermal energy in the TES media 110 and (2) transport the thermal energy to the thermal energy output portion 104. The TES devices 1000 and 1 100 may be constructed as is a factory-sealed maintenance-free modules.

INTERNAL COMBUSTOR EMBODIMENT Figures 12 — 20 illustrate embodiments of TES devices for use with internal thermal energy sources, such as a combustor. Figure 12 provides an isometric cutaway illustration of an embodiment of a TES device 1200 having a TES subassembly 1210 (which may be optionally integrated with the heater head portion 315A), and a combustor subassembly 1212. In this embodiment, the thermal energy input portion 102 includes the combustor subassembly 1212, which provides thermal energy to be stored by the TES media 1 10 (see Figure 1 ). The TES subassembly 1210 extracts the thermal energy stored in the TES media 110 (see Figure 1 ) and provides the extracted thermal energy to the recipient structure or device 170 (see Figure 1 ) via the thermal energy output portion 104. The TES subassembly 1210 has a housing 1220 defining a hollow interior region 1222 configured to store the TES media 110 (see Figure 1 ). To provide a better view of structures inside the TES subassembly 1210, the TES media 1 10 has been omitted from Figure 12, but may be viewed in Figure 13. The housing 1220 has a generally cylindrical outer shape. However, this is not a requirement and embodiments in which the housing 1220 has a different outer shape, such as square, rectangular, hexagonal, and the like are also within the scope of the present disclosure. By way of a non-limiting example, the housing 1220 may have a diameter "D" of about 15 inches and a length "L" of about 15 inches. The housing 1220 has an open end portion 1226 configured to receive the combustor subassembly 1212, which may be affixed therein. By way of a non-limiting example, the combustor subassembly 1212 may be non-removably affixed to the housing 1220 using conventional metal bonding techniques known in the art. The combustor subassembly 1212 extends into the hollow interior region 1222 configured to store the TES media 110 (see Figure 1 ). The housing 1220 may be implemented as an outer cylindrical shell that has a weld lip (not shown) at its open end portion 1226 to interface with the combustor subassembly 1212.

Opposite the open end portion 1226, the housing 1220 has a closed-end portion 1228. A heat delivery assembly 1230 that performs the function as the heat delivery assembly 150 (see Figure 1 ) is formed in the closed-end portion 1228 of the housing 1220. The heat delivery assembly 1230 may be implemented as a vapor chamber, heat pipe, and the like. Alternatively, the heat receiving assembly 1230 may be configured to transfer thermal energy only by conductance.

In the embodiment illustrated, the heat delivery assembly 1230 has been implemented as a heat pipe. The heat delivery assembly 1230 includes an interior sidewall 1232 spaced apart from an external sidewall 1234 with an internal chamber 1235 at least partially defined therebetween. In this embodiment, the thermal energy output portion 104 includes the heat delivery assembly 1230 and its interior and exterior sidewalls 1232 and 1234. The interior sidewall 1232 has a perimeter portion 1233 adjacent the housing 1220. Optionally, the interior sidewall 1232 includes a plurality of spaced apart through-holes 1240. The external sidewall 1234 may include the heater head portion 315A.

The external sidewall 1234 may include a ring shaped transition member disposed about the heater head portion 315A. The housing 1220 may be welded or brazed to the perimeter portion 1233 of the interior sidewall 1232 and the ring shaped transition member. The optional heater head portion 315A and/or ring shaped transition member may include weld lips (not shown) that may be used to weld the housing 1220 thereto. The interior sidewall 1232 and optionally exterior sidewall 1234 include one or more fill ports 1236. The TES subassembly 1210 includes a plurality of heat transporting means 1258 illustrated as hollow cylindrically shaped heat pipes 1260 that extend from the interior sidewall 1232 toward the combustor subassembly 1212 and into the TES media 1 10 (see Figure 1 ). In embodiments in which the interior sidewall 1232 includes the plurality of spaced apart through-holes 1240, each of the plurality of heat pipes 1260 may terminate at one of the through-holes 1240. The plurality of heat pipes 1260 may plug the through-holes 1240 preventing the TES media 1 10 from entering the heat delivery assembly 1230 through the through-holes 1240. The heat pipes 1260 terminate at the through-holes 1240 of the interior sidewall 1232. The TES media 1 10 (see Figure 1 ) is sealed inside the hollow interior region 1222 between the housing 1220, the combustor subassembly 1212 (which closes the open end portion 1226 of the housing 1220), and the interior sidewall 1232 of the heat delivery assembly 1230.

External devices, such as the recipient structure or device 170 (see Figure 1 ), which may include the Stirling engine 315 (see Figure 3) may be coupled to the heat delivery assembly 1230 to receive thermal energy therefrom. As discussed above with respect to other embodiments, the heater head portion 315A of the Stirling engine 315 (see Figure 3) may be integrally formed with the outside surface 1234 of the heat delivery assembly 1230. Alternatively, the heater head portion 315A and the outside surface 1234 of the heat delivery assembly 1230 may be separate components coupled together to effect heat transfer therebetween.

The combustor subassembly 1212 will now be described. As mentioned above, the combustor subassembly 1212 is disposed inside the open end portion 1226 of the housing 1220 and extends into the hollow interior region 1222 configured to store the TES media 110 (see Figure 1 ).

The combustor subassembly 1212 includes an internal combustor chamber 1280 configured to be disposed inside and at least partially surround by the TES media 1 10 (see Figure 1 ). The internal combustor chamber 1280 has one or more inlets 1282 through which a fuel and oxygen mixture enter the internal combustor chamber 1280. By way of a non-limiting example, the internal combustor chamber 1280 may have a generally cylindrical shape. By way of another non-limiting example, the internal combustor chamber 1280 may have a diameter of about 2 inches and a length of about 6 inches. The internal combustor chamber 1280 has one or more outlets 1284 through which combustion products exit the internal combustor chamber. To channel the combustion products away from the internal combustor chamber 1280, the combustor subassembly 1212 includes a first plurality of flow passages 1290, and one or more annular exhaust passageways (e.g., an inner annular exhaust passageway 1294A and an outer annular exhaust passageway 1294B) disposed inside the hollow interior region 1222 of the housing 1220 of the TES subassembly 1210 and extending through the TES media 1 10 (see Figure 1 ). In the embodiment illustrated, the first plurality of flow passages 1290 extend radially away from the internal combustor chamber 1280. Each of the annular exhaust passageways 1294A and 1294B is arranged around and spaced apart from the internal combustor chamber 1280. In the embodiment illustrated in Figure 12, the combustor subassembly 1212 includes the inner annular exhaust passageway 1294A and the outer annular exhaust passageway 1294B. However, embodiments include a single annular exhaust passageway or more than two annular exhaust passageways are also within the scope of the present teachings. By way of a non-limiting example, the inner annular exhaust passageway

1294A may be approximately 7 inches from the center of the internal combustor chamber 1280 and the outer annular exhaust passageway 1294B may be approximately 12 inches from the center of the internal combustor chamber. The inner and outer annular exhaust passageways 1294A and 1294B have exit apertures 1296A and 1296B, respectively, through which combustion products may exit the combustor subassembly 1212 of the TES device 1200.

The combustor subassembly 1212 illustrated also includes a second plurality of flow passages 1300 that interconnect the inner and outer annular exhaust passageways 1294A and 1294B. The second plurality of flow passages 1300 are disposed inside the hollow interior region 1222 of the housing 1220 of the TES subassembly 1210 and extend through the TES media 1 10 (see Figure 1 ). The first and second plurality of flow passages 1290 and 1300 each have heat conducting sidewalls "S1." The inner and outer annular exhaust passageways 1294A and 1294B are each defined between a pair of spaced apart heat conducting sidewalls "S2" and "S3." The heat conducting sidewalls "S1 ," "S2," and "S3" are in direct contact with the TES media 1 10 (see Figure 1 ) stored inside the hollow interior region 1222 of the housing 1220.

The combustion products exit the internal combustor chamber 1280 through the outlets 1284 flow through the TES subassembly 1210 of the TES device 1200 along radial or annular combustion gas flow paths. Specifically, each of the first plurality of flow passages 1290 connects the outlets 1284 of the internal combustor chamber 1280 to the inner annular exhaust passageway 1294A. The first plurality of radially extending flow passages 1290 transport the combustion products radially outward away from the internal combustor chamber 1280 and into the inner annular exhaust passageway 1294A. This approach may be configured to offer excellent heat transfer characteristics that can be manufactured in a straightforward manner with mostly loose tolerances and simple integration. In the embodiment illustrated, the first plurality of flow passages 1290 are implemented as an array of rectangular cross- section ducts. The total cross-sectional area of the first plurality of flow passages 1290 may be approximately equal to the cross-sectional area of the internal combustor chamber 1280.

A portion of the combustion products flowing radially outwardly through the first plurality of flow passages 1290 flows into the inner annular exhaust passageway 1294A and exits the inner annular exhaust passageway through the exit aperture 1296A. The remainder of the combustion products continue radially outward through the second plurality of flow passages 1300, enter and travel through the outer annular exhaust passageway 1294B, and exit the inner annular exhaust passageway through the exit aperture 1296B. The first and second plurality of flow passages 1290 and 1300 may be configured so that the pressure inside the inner and outer annular exhaust passageways 1294A and 1294B adjacent the second plurality of flow passages 1300 is substantially equal. For example, in the embodiment illustrated, the combustor subassembly 1212 includes twice as many flow passages 1300 in the second plurality as in the first plurality of flow passages 1290. Each of the second plurality of flow passages 1300 has the same cross-sectional area as each of the first plurality of flow passages 1290. This arrangement causes the pressure inside the inner and outer annular exhaust passageways 1294A and 1294B adjacent the second plurality of flow passages 1300 to be substantially equal. The average combined cross-sectional flow area of both the inner and outer annular exhaust passageways 1294A and 1294B may be substantially equal to the cross-sectional area of the internal combustor chamber 1280. Each of the inner and outer annular exhaust passageways 1294A and 1294B may taper, becoming larger near the exit apertures 1296A and 1296B. For example, adjacent the second plurality of flow passages 1300, the inner and outer annular exhaust passageways 1294A and 1294B may have a maximum width of about 0.10 inches and at the exit apertures 1296A and 1296B, the inner and outer annular exhaust passageways 1294A and 1294B, respectively, may each have a minimum width of about 0.02 inches. The combustion products enter each of the inner and outer annular exhaust passageways 1294A and 1294B at a temperature of about 1500 K (1227 C), and exit the combustor subassembly 1212 through the exit apertures 1296A and 1296B at a temperature of about 1000 K (727°C). Heat transfer effectiveness is approximately proportional to the inverse of the width of the inner and outer annular exhaust passageways 1294A and 1294B. By tapering the inner and outer annular exhaust passageways 1294A and 1294B, the sidewalls "S2," and "S3" of the inner and outer annular exhaust passageways 1294A and 1294B may have an approximately uniform temperature and heat flux along their portion of the combustion gas flow path as the temperature difference driving the heat transfer decreases. The combustor subassembly 1212 illustrated includes three washer- shaped flat disk sections 1270A, 1270B, and 1270C. The disk section 1270A closes off the space between the internal combustor chamber 1280 and inner exit aperture 1296A. The disk section 1270B closes off the space between the inner and outer exit apertures 1296A and 1296B. The disk section 1270C closes off the space between the outer exit aperture 1296B and the outer cylindrical housing 1220. The combustor subassembly 1212 may be constructed mainly from sheet metal parts that are individually straightforward to fabricate. Such components may be brazed or welded together to produce a rugged combustor subassembly 1212. As mentioned above, the housing 1220 may include the weld lip (not shown) at its open end portion 1226 that may be welded or brazed to the disk section 1270C along its perimeter.

The heat flows that melt and super-heat the TES media 110 (see Figure 1 ) originate from the flow of combustion products as they exit the internal combustor chamber 1280 and travel through the inner and outer annular exhaust passageways 1294A and 1294B. The sidewalls "S2" and "S3" of the first and second plurality of flow passages 1294A and 1294B are heated by the flow of combustion products and transfer at least a portion of their acquired thermal energy to the TES media 1 10 (see Figure 1 ).

Heat transferred across the sidewalls "S2" and "S3" heats and melts adjacent regions of the TES media 1 10 (see Figure 1 ). Without other heat transfer means, these regions of the TES media 1 10 (see Figure 1 ) would become overheated while the heat delivery assembly 1230 (and the optional heater head portion 315A) and nearby TES media regions would remain relatively cool. This undesirable situation may be prevented by the heat pipes 1260 arranged inside the TES subassembly 1210. In the embodiment illustrated, the heat pipes 1260 have a generally tubular shape with a circular cross-sectional shape. However, this is not a requirement.

In the embodiment illustrated, the heat pipes 1260 each extend into the combustor subassembly 1212 and have a closed-end portion 1320 terminating inside the combustor subassembly 1212. When the internal combustor chamber 1280 is operating (i.e., during a heating cycle), the closed-end portions 1320 of the heat pipes 1260 in the TES media 1 10 (see Figure 1 ) adjacent the combustor subassembly 1212 transfer heat from that region to the heat delivery assembly 1230, and also to the portions of the TES media 1 10 (see Figure 1 ) remote from the combustor subassembly 1212. When the internal combustor chamber 1280 is not operating (e.g., during a cooling cycle), the entire length of each of heat pipes 1260 may transfer heat from the TES media 1 10 (see Figure 1 ) to the heat delivery assembly 1230.

In the embodiment illustrated, the heat pipes 1260 are arranged in a pattern of concentric rings that include a first ring "FM A" that extends into the combustor subassembly 1212 between the internal combustor chamber 1280 and the inner annular exhaust passageway 1294A, and a second ring "R2A" that extends into the combustor subassembly 1212 between the inner and outer annular exhaust passageways 1294A and 1294B. Thus, each of the rings "FM A" and "R2A" is adjacent to and receives thermal energy from at least one of the internal combustor chamber 1280, the inner annular exhaust passageway 1294A, and the outer annular exhaust passageway 1294B.

By way of a non-limiting example, the first ring "FM A" may include eight heat pipes 1260 located at approximately 45 degree intervals at about 4.5 inches from the center of the housing 1220, and the second ring "R2A" may include 16 heat pipes at approximately 22.5 degree intervals at about 9.5 inches from the center of the housing 1220. An optional third ring (not shown) may include 20 heat pipes at approximately 18 degree intervals at about a 13.5 inches from the center of the housing 1220. These spacing intervals were selected to provide approximately two inch on-center spacing between the heat pipes 1260 within the TES media 1 10 (see Figure 1 ). This spacing ensures that no portion of the TES media 1 10 (see Figure 1 ) is much more than an inch from the nearest heat pipe 1260 (i.e., a heat removal location).

However, please note, this spacing is not provided near the center of the housing 1220 inward of the internal combustor chamber 1280. The exception in this central region does not pose a problem because as the TES media 110 (see Figure 1 ) freezes around the heat pipes 1260 and its volume shrinks, any residual liquid in the central region will work its way by gravity to areas close to heat pipes 1260. If the central region were to present a problem during heating or cooling, a heat pipe (not shown) can be added that extends from the internal combustor chamber 1280 or a location adjacent the internal combustor chamber 1280 through the TES media to the heat delivery assembly 1230.

When the TES device 1200 is constructed, the TES media 110 (see Figure 1 ), which may be a solid salt, is inserted into the hollow interior region 1220 of the TES subassembly 1210 before the exterior surface 1234 of the heat delivery assembly 1230 is affixed inside the closed end portion 1228 of the housing 1220. In the embodiment illustrated, the TES media 1 10 (see Figure 1 ) is poured inside the hollow interior region 1220 through the fill port 1236. A measured mass of solid TES media (and optionally a getter material such as aluminum granules if determined to be needed) is poured through the fill port 1236 in until the hollow interior region 1222 is completely filled with TES media. Based on the known density ratio of liquid to solid salt and the selected volumetric safety margin, a measured mass of the salt is removed to accommodate the volume change caused by melting. After that, the filler port 1236 is cleaned thoroughly and a fill plug 1238 is affixed inside the filler port 1236 to seal the hollow interior region 1222 of the TES subassembly 1210. Then, the plug 1238 traps the TES media 1 10 (see Figure 1 ) inside the hollow interior region 1222. By way of a non-limiting example, the plug 1238 may be affixed inside the filler port 1236 by welding the plug inside the fill port 1236. Next, the heater head portion 315A may be welded to the ring shaped transition member of the exterior surface 1234 of the heat delivery assembly 1230. Optionally, an appropriate quantity of heat pipe working fluid 1242 (e.g., sodium) may be added through the filler port (not shown) in the ring shaped transition member. Then, the filler port (not shown) is sealed by inserting a plug (not shown) in the filler port. The plug may be affixed inside the filler port using any method suitable for affixing the plug 1238 in the filler port 1236. It may be desirable to add heat pipe wicks (not shown) to the components in contact with the heat pipe working fluid. The heat pipe wicks (not shown) may be formed in the interior of the heat pipes 1260 by a knurling process. The heat pipe wicks may include a screen or granular wicking material added to the other components. Effectiveness of Stirling engines (e.g., the Stirling engine 315 depicted in

Figure 3) may be improved by intimate thermal communication between a heat source (e.g., a hydrocarbon/oxygen combustor) and the hot end of the Stirling engine. The ability to maintain a nearly constant temperature at the value deemed optimum is also of importance. The combustor subassembly 1212 may be used as either a constant or intermittent heat source to maintain the two-phase, constant-temperature state of the TES media 1 10 (see Figure 1 ).

By way of a non-limiting example, the TES device 1200 may be incorporated into an undersea vehicle and used to power the vehicle. In such embodiments, the internal combustor chamber 1280 may be configured to burn JP5, JP8, JP10, and the like. The use of strategic hydrocarbon fuels such as JP5, JP8, or JP10 in unmanned undersea vehicles ("UUVs") is of interest to the U.S. Navy because of the potential for very large range travel when used with compact oxygen storage/generation, or for snorkeling. This is especially the case when high efficiency energy converters such as fuel cells or Stirling engines are used. An additional benefit is that the vehicle may go to near the surface of the water to run the combustor subassembly 1212 at a lower exhaust pressure (and therefore higher efficiency) to thermally "charge" the TES media 110 (see Figure 1 ) which may then be used to supply a constant temperature closed heat source when the vehicle is underwater. It would also be possible to run the combustor subassembly 1212 to charge the TES media 110 (see Figure 1 ) when the vehicle is at the surface, and thus negate the need for carrying oxidizer onboard the vehicle.

Figures 13 and 14 provide illustrations a drive system 1400 that may be used to power a vehicle, such as an underwater vehicle. The drive system 1400 includes the TES device 1200 coupled to a fuel tank 1410 and an oxygen tank 1412. The fuel tank 1410 is disposed about the heater head portion 315A of the Stirling engine 315. Figure 13 depicts the internal combustor chamber 1280 embedded inside the TES media 1 10. The internal combustor chamber 1280 receives fuel from the fuel tank 1410 and oxygen from the oxygen tank 1412 and burns them to produce thermal energy that is transferred to the TES media 1 10 for storage. The heat pipes 1280 transport the stored thermal energy to the heater head portion 315A where it powers the Stirling engine 315.

Figure 15 an alternate embodiment of a TES device 1500 for use with a combustor. The TES device 1500 has a TES subassembly 1510, and a combustor subassembly 1512. In this embodiment, the thermal energy input portion 102 includes the combustor subassembly 1512, which provides thermal energy to be stored by the TES media 1 10 (see Figure 1 ). The TES subassembly 1510 extracts the thermal energy stored in the TES media 1 10 (see Figure 1 ) and provides the extracted thermal energy to the recipient structure or device 170 (see Figure 1 ) via the thermal energy output portion 104.

The TES subassembly 1210 has a housing 1520 defining a hollow interior region 1522 configured to store the TES media 1 10 (see Figure 1 ). To provide a better view of structures inside the TES subassembly 1510, the TES media 1 10 has been omitted from Figure 15. The housing 1520 has a generally cylindrical outer shape. However, this is not a requirement and embodiments in which the housing 1520 has a different outer shape, such as square, rectangular, hexagonal, and the like are also within the scope of the present disclosure.

The housing 1520 may be substantially similar to the housing 1220 (see Figure 12) and may be coupled to the combustor subassembly 1512 in any manner described above as suitable for coupling the combustor subassembly 1212 (see Figure 12) to the housing 1220 (see Figure 12). The combustor subassembly 1512 extends into the hollow interior region 1522 configured to store the TES media 1 10 (see Figure

1 )-

The TES subassembly 1510 also includes a heat delivery assembly 1530 that functions in a manner substantially similar to that of the heat delivery assembly 1230 (see Figure 12). External devices, such as the recipient structure or device 170 (see Figure 1 ), which may include the Stirling engine 315 (see Figure 3) may be coupled to the heat delivery assembly 1530 to receive thermal energy therefrom. In the embodiment illustrated, the heat delivery assembly 1530 is not integrally formed with the heater head portion 315A (see Figure 4) of the Stirling engine 315 (see Figure 3). However, embodiments in which the heat delivery assembly 1530 is integrally formed with the heater head portion 315A (see Figure 4) of the Stirling engine 315 (see Figure 3) are within the scope of the present teachings. The heat delivery assembly 1530 is defined between an interior sidewall 1532 spaced apart from an external sidewall 1534. In this embodiment, the thermal energy output portion 104 includes the heat delivery assembly 1530 and its interior and exterior sidewalls 1532 and 1534. The interior sidewall 1532 and optionally exterior sidewall 1534 include one or more fill ports (not shown) substantially similar to the fill port 1236 (see Figure 12). Optionally, the interior sidewall 1532 includes a plurality of spaced apart through-holes 1540. An optional collar 1542 may be disposed about each of the through-holes 1540.

The TES media 1 10 (see Figure 1 ) is sealed inside the hollow interior region 1522 between the housing 1520, the combustor subassembly 1512, and the interior sidewall 1532 of the heat delivery assembly 1530. The TES subassembly 1510 includes a plurality of heat transporting means 1558 illustrated as hollow cylindrically shaped heat pipes 1560 that extend from the interior sidewall 1532 toward the combustor subassembly 1512 and into the TES media 1 10 (see Figure 1 ). In embodiments in which the interior sidewall 1532 includes the plurality of spaced apart through-holes 1540, each of the plurality of heat pipes 1560 may extend into or terminate at one of the through-holes 1540. In the embodiment illustrated, the heat pipes 1560 are received inside the collars 1542 and each partially extend into the heat delivery assembly 1530. Thus, the heat pipes 1560 plug the through-holes 1240 and prevent the TES media 110 from entering the heat delivery assembly 1530 through the through-holes 1540.

The combustor subassembly 1512 includes an internal combustor chamber 1580 configured to be disposed inside and at least partially surround by the TES media 1 10 (see Figure 1 ). The internal combustor chamber 1580 may be substantially identical to the internal combustor chamber 1280 (see Figure 12). The internal combustor chamber 1580 has one or more inlets 1582 through which a fuel and oxygen enter the internal combustor chamber 1580. The internal combustor chamber 1580 also has one or more outlets 1584 through which combustion products exit the internal combustor chamber. To channel the combustion products away from the internal combustor chamber 1580, the combustor subassembly 1212 has a plurality of flow passages 1590, and one or more annular exhaust passageways (e.g., an annular exhaust passageway 1594) disposed inside the hollow interior region 1522 of the housing 1520 of the TES subassembly 1510 and extending through the TES media 110 (see Figure 1 ). In the embodiment illustrated, the flow passages 1590 extend radially away from the internal combustor chamber 1580. The annular exhaust passageway 1594 is arranged around and spaced apart from the internal combustor chamber 1580. The annular exhaust passageway 1594 has an exit aperture 1596 through which combustion products may exit the combustor subassembly 1512 of the TES device 1500. In the embodiment illustrated in Figure 15, the combustor subassembly 1512 includes only the annular exhaust passageway 1594. However, embodiments include two or more annular exhaust passageways are also within the scope of the present teachings. The flow passages 1590 are substantially similar to the first flow passages

1290 (see Figure 12) of the TES device 1200 (see Figure 12). Similarly, the annular exhaust passageway 1594 may be substantially similar to the inner annular exhaust passageway 1294A (see Figure 12) of the TES device 1200. However, the annular exhaust passageway 1594 is configured to transport all of the combustion products away from the internal combustor chamber 1580 instead of only a portion of the combustion products. Further, unlike the inner annular exhaust passageway 1294A, the annular exhaust passageway 1594 is not connected to a second set of flow passages. The annular exhaust passageway 1594 is defined between a pair of spaced apart heat conducting sidewalls "S4" and "S5." The heat conducting sidewalls "S4" and "S5" are in direct contact with the TES media 1 10 (see Figure 1 ) stored inside the hollow interior region 1522 of the housing 1520.

The flow passages 1590 connect the outlets 1584 of the internal combustor chamber 1580 to the annular exhaust passageway 1594. The radially extending flow passages 1590 transport the combustion products radially outward away from the internal combustor chamber 1580 and into the annular exhaust passageway 1594. The combustion products travel through the annular exhaust passageway 1594, and exit the annular exhaust passageway through the exit aperture 1596. As the combustion products travel through the annular exhaust passageway 1594, the combustion product heat the heat conducting sidewalls "S4" and "S5." The combustor subassembly 1512 includes an annular shaped heat pipe

1598 having a pair of spaced apart heat conducting sidewalls "S6" and "S7." The sidewall "S7" is adjacent the sidewall "S4" of the annular exhaust passageway 1594. The sidewall "S7" may be spaced apart from or in face-to-face engagement with the sidewall "S4." The sidewall "S7" receives thermal energy from the sidewall "S4" and transports that thermal energy into the TES media 1 10 (see Figure 1 ). In the embodiment illustrated, the annular shaped heat pipe 1598 extends from the annular exhaust passageway 1594 toward the heat delivery assembly 1530 but does not contact the heat delivery assembly 1530. In alternate embodiments (not illustrated), the annular shaped heat pipe 1598 may be in contact with the heat delivery assembly 1530 and configured to transport thermal energy thereto.

The heat pipes 1560 each extend from the heat delivery assembly 1530 into the combustor subassembly 1512 between the flow passages 1590 and each have a closed-end portion 1600 terminating inside the combustor subassembly 1612. When the internal combustor chamber 1580 is operating (i.e., during a heating cycle), the closed-end portions 1600 of the heat pipes 1560 adjacent the combustor subassembly 1512 transfer heat from the internal combustor chamber 1580 to the heat delivery assembly 1530. When the internal combustor chamber 1580 is not operating (e.g., during a cooling cycle), the entire length of each of heat pipes 1560 may transfer heat from the TES media 1 10 (see Figure 1 ) to the heat delivery assembly 1530.

In the embodiment illustrated, the heat pipes 1560 are arranged in a pattern of concentric rings that include a first ring "FM B" that extends into the combustor subassembly 1512 between the internal combustor chamber 1580 and the annular shaped heat pipe 1598, and a second ring "R2B" that extends into the combustor subassembly 1512 between the annular shaped heat pipe 1598 and the housing 1520. The heat pipes 1560 of the first ring "FM B" extend between the flow passages 1590. Thus, each of the rings "FM B" and "R2B" is adjacent to and receives thermal energy from at least one of the internal combustor chamber 1280, the annular exhaust passageway 1594, the annular shaped heat pipe 1598, and the flow passages 1590. A working fluid (not shown) may be disposed inside the heat pipes 1560 and/or the annular exhaust passageway 1594. It may be desirable to add heat pipe wicks (not shown) to the components in contact with the heat pipe working fluid. The heat pipe wicks may be formed in the interior of the heat pipes 1560 by a knurling process. The heat pipe wicks may include a screen or granular wicking material added to the other components.

Figure 16 depicts an alternate embodiment of a TES device 1700 for use with a combustor. The TES device 1700 has a TES subassembly 1710, and a combustor subassembly 1712. In this embodiment, the thermal energy input portion 102 includes the combustor subassembly 1712, which provides thermal energy to be stored by the TES media 1 10 (see Figure 1 ). The TES subassembly 1710 extracts the thermal energy stored in the TES media 110 (see Figure 1 ) and provides the extracted thermal energy to the recipient structure or device 170 (see Figure 1 ) via the thermal energy output portion 104. The TES subassembly 1710 has a housing 1720 defining a hollow interior region 1722 configured to store the TES media 1 10 (see Figure 1 ). To provide a better view of structures inside the TES subassembly 1510, the TES media 1 10 has been omitted from Figure 17. The housing 1720 has a generally cylindrical outer shape. However, this is not a requirement and embodiments in which the housing 1720 has a different outer shape, such as square, rectangular, hexagonal, and the like are also within the scope of the present disclosure.

The housing 1720 has an open end portion 1726 to which the combustor subassembly 1712 is coupled. The open end portion 1726 includes a weld lip 1727 and the combustor subassembly 1712 includes a corresponding weld lip 1728. The combustor subassembly 1712 may be coupled to the housing 1720 by welding the weld lip 1728 to the weld lip 1727.

The TES subassembly 1710 includes a heat delivery assembly 1730 that functions in a manner substantially similar to that of the heat delivery assembly 1230 (see Figure 12). External devices, such as the recipient structure or device 170 (see Figure 1 ), which may include the Stirling engine 315 (see Figure 3) may be coupled to the heat delivery assembly 1730 to receive thermal energy therefrom. In the embodiment illustrated, the heat delivery assembly 1730 is not integrally formed with the heater head portion 315A (see Figure 4) of the Stirling engine 315 (see Figure 3). However, embodiments in which the heat delivery assembly 1730 is integrally formed with the heater head portion 315A (see Figure 4) of the Stirling engine 315 (see Figure 3) are within the scope of the present teachings.

The heat delivery assembly 1730 is defined between an interior sidewall 1732 spaced apart from an external sidewall 1734. In this embodiment, the thermal energy output portion 104 includes the heat delivery assembly 1730 and its interior and exterior sidewalls 1732 and 1734. The interior sidewall 1732 and optionally exterior sidewall 1734 include one or more fill ports 1735 substantially similar to the fill ports 1236 (see Figure 12), respectively. Optionally, the interior sidewall 1732 includes a plurality of spaced apart through-holes 1740. An optional collar 1742 may be disposed about each of the through-holes 1740. The TES media 1 10 (see Figure 1 ) is sealed inside the hollow interior region 1722 between the housing 1720, the combustor subassembly 1712, and the interior sidewall 1732 of the heat delivery assembly 1730. The TES subassembly 1710 includes a plurality of heat transporting means 1758 illustrated as hollow cylindrically shaped heat pipes 1760 that extend from the interior sidewall 1732 toward the combustor subassembly 1712 and into the TES media 1 10 (see Figure 1 ). In embodiments in which the interior sidewall 1732 includes the plurality of spaced apart through-holes 1740, each of the plurality of heat pipes 1760 may extend into or terminate at one of the through-holes 1740. In the embodiment illustrated, the heat pipes 1760 are received inside the collars 1742. Thus, the heat pipes 1760 plug the through-holes 1740 and prevent the TES media 1 10 from entering the heat delivery assembly 1730 through the through-holes 1740.

Turning to Figure 17, the combustor subassembly 1712 has a partially hollow interior 1730 divided into hollow regions 1732 by a plurality of branching channels 1734. The branching channels 1734 may be implemented as fractal heat exchangers. The hollow regions 1732 are each configured to store an additional quantity of the TES media 1 10 (see Figure 1 ).

Each of the branching channels 1734 has a first substantially linear portion 1734A, a branching portion 1734B, a second substantially linear branched portion 1734C, and a third substantially linear branched portion 1734D. The branching portion 1734B connects the first substantially linear portion 1734A to the second and third substantially linear branched portions 1734C and 1734D.

The hollow regions 1732 are defined between the second and third substantially linear branched portions 1734C and 1734D as well as between adjacent branching channels 1734. Each of the first substantially linear portion 1734A, the second substantially linear branched portion 1734C, and the third substantially linear branched portion 1734D has an exit aperture 1736 formed in an outside portion 1738 of the combustor subassembly 1712.

The combustor subassembly 1512 includes an internal combustor chamber 1780 configured to be disposed inside and at least partially surround by the TES media 1 10 (see Figure 1 ). The internal combustor chamber 1780 may be substantially identical to the internal combustor chamber 1780 (see Figure 12). The internal combustor chamber 1780 has one or more inlets 1782 through which a fuel and oxygen enter the internal combustor chamber 1780. The internal combustor chamber 1780 also has one or more outlets 1784 through which combustion products exit the internal combustor chamber.

The branching channels 1734 are configured to direct all of the combustion products away from the internal combustor chamber 1780. The first substantially linear portions 1734A each connect one of the outlets 1784 of the internal combustor chamber 1780 to the branching portion 1734B. The combustion products flow from the outlets 1784 into the first substantially linear portions 1734A. The outlets 1784 and/or the branching channels 1734 may be configured such that equal amounts of the combustion products flow into each of the branching channels 1734. At least a portion of the combustion products flow through each of the first substantially linear portions 1734A toward the outside portion 1738 of the combustor subassembly 1712 and exit the combustor subassembly 1512 through the exit aperture 1736 of the first substantially linear portions 1734A.

The branching portion 1734B connects the first substantially linear portion 1734A to the second and third substantially linear branched portions 1734C and 1734D. A remainder of the combustion products flow from each of the first substantially linear portions 1734A into the branching portion 1734B connected thereto. Then, the remainder of the combustion products flow from the branching portion 1734B into the second and third substantially linear branched portions 1734C and 1734D. The branching channels 1734 may be configured such that equal amounts of the combustion products flow into each of the second and third substantially linear branched portions 1734C and 1734D. Finally, the remainder of the combustion products flow through the second and third substantially linear branched portions 1734C and 1734D toward the outside portion 1738 of the combustor subassembly 1712 and exit the combustor subassembly 1512 through the exit apertures 1736 of the second and third substantially linear branched portions 1734C and 1734D.

Thus, the branching channels 1734 may be characterized as directing the combustion products radially outward away from the internal combustor chamber 1780 and out the exit apertures 1736. The combustion products heat the TES media 1 10 (see Figure 1 ) in the hollow regions 1732 as they flow through the branching channels 1734.

Each of the branching channels 1734 may be configured to conduct substantially identical amounts of thermal energy from the combustion products into the TES media 1 10. The second and third substantially linear branched portions 1734C and 1734D may be configured to conduct substantially identical amounts of thermal energy from the combustion products to the TES media 1 10. The first substantially linear portion 1734A, the second substantially linear branched portion 1734C, and the third substantially linear branched portion 1734D may be implemented as balanced heat exchangers configured to deliver substantially identical amounts of thermal energy from the combustion products to the TES media 1 10. Further, the first substantially linear portion 1734A, the second substantially linear branched portion 1734C, and the third substantially linear branched portion 1734D may be configured to provide more thermal energy to portions of the TES media 1 10 located closer to the perimeter portion of the vessel 90 whereat the volume of TES media 110 increases.

The heat pipes 1760 each extend from the heat delivery assembly 1730 into the hollow regions 1732 of the combustor subassembly 1712. Each of the heat pipes 1760 has a closed-end portion 1790 terminating inside one of hollow regions 1732 of the combustor subassembly 1712. When the internal combustor chamber 1780 is operating (i.e., during a heating cycle), the closed-end portions 1790 of the heat pipes 1760 adjacent the combustor subassembly 1712 transfer heat from the internal combustor chamber 1780 to the heat delivery assembly 1730. When the internal combustor chamber 1780 is not operating (e.g., during a cooling cycle), the entire length of each of heat pipes 1760 may transfer heat from the TES media 1 10 (see Figure 1 ) to the heat delivery assembly 1730.

A working fluid (not shown) may be disposed inside the heat pipes 1760. It may be desirable to add heat pipe wicks (not shown) to the components in contact with the heat pipe working fluid. The heat pipe wicks may be formed in the interior of the heat pipes 1760 by a knurling process. The heat pipe wicks may include a screen or granular wicking material added to the other components.

Figures 18 and 19 depict an alternate embodiment of a TES device 1800 for use with a combustor. The TES device 1800 includes a combustor subassembly 1812 coupled to the TES subassembly 1710. The TES device 1800 is substantially similar to the TES device 1700 (see Figures 16 and 17). However, the combustor subassembly 1812 differs from the combustor subassembly 1712 of the TES device 1700 with respect to the interiors of the interiors of the branching channels 1734 and their exit aperture 1736. For ease of illustration, like reference numerals have been used to identify like components in the Figures 16 — 19. In the combustor subassembly 1812, each of the branching channels 1734 includes the first substantially linear portion 1734A, the branching portion 1734B, the second substantially linear branched portion 1734C, and the third substantially linear branched portion 1734D. The branching portion 1734B connects the first substantially linear portion 1734A to the second and third substantially linear branched portions 1734C and 1734D. The hollow regions 1732 are defined between the second and third substantially linear branched portions 1734C and 1734D as well as between adjacent branching channels 1734. Each of the first substantially linear portion 1734A, the second substantially linear branched portion 1734C, and the third substantially linear branched portion 1734D has an plurality of exit apertures 1820 formed in an outside portion 1822 of the combustor subassembly 1812.

Inside at least a portion of the first substantially linear portion 1734A, the second substantially linear branched portion 1734C, and the third substantially linear branched portion 1734D, each of the branching channels 1734 may include a filler member 1830 adjacent the plurality of exit apertures 1820 that at least partially fills the interior of the branching channel. The filler member 1830 illustrated includes grooves 1832 aligned with each of the exit apertures 1820 to provide a flow path for the combustion products away from the outlets 1784 of the internal combustor chamber 1780 and toward the outside portion 1822 of the combustor subassembly 1812.

A portion 1840 of each of the branching channels 1734 adjacent to the filler member 1830 allows the combustion products to flow radially from one of the outlets 1784 of the internal combustor chamber 1780 into the first substantially linear portion 1734A, from the first substantially linear portion 1734A into the branching portion 1734B, and then from the branching portion 1734B into the second and third substantially linear branched portions 1734C and 1734D.

The rate of flow of the combustion products through the exit apertures 1820 may be determined at least in part by the size of the grooves 1832. Thus, the grooves 1832 may be configured to limit the outward flow of the combustion products from the combustor subassembly 1812. Further, the size of the exit apertures 1820 may be used to control the flow of combustion products from the combustor subassembly 1812. In the embodiment illustrated, the exit apertures 1820 increase in size radially away from the internal combustor chamber 1780. MODEL RESULTS

Figure 20 depicts a TES device 2000 having an internal combustor chamber 2010 embedded inside the TES media 1 10. The TES media 1 10 and the internal combustor chamber 2010 are both disposed inside a TES media storage tank 2015. The internal combustor chamber 2010 has an inlet 2012 through which the internal combustor chamber 2010 received oxygen and JP fuel. The internal combustor chamber 2010 burns oxygen and JP fuel to produce combustion products. A diluent consisting of the combustion products was also added at the inlet 2012. In this embodiment, the combustor gas flow is reversed to allow the combustor products to exit the internal combustor chamber 2010 through the inlet 2012 at the axial location through which the oxygen and JP fuel entered the internal combustor chamber 2010.

The TES device 2000 includes a heat delivery assembly 2030 substantially similar to the heat delivery assembly 150 (see Figure 1 ) described above. Heat transferred to the heat delivery assembly 2030 may be provided to external devices such as the heater heat portion 315A (see Figure 4) of the Stirling engine 315 (see Figure 4). Alternatively, the heater heat portion 315A (see Figure 4) of the Stirling engine 315 (see Figure 4) may be formed integrally with the heat delivery assembly 2030.

The TES device 2000 includes a plurality of heat pipes 2040 that extend from the heat delivery assembly 2030 through the TES media 110. Each of the heat pipes 2040 may have at least one fin 2020 that extends toward the internal combustor chamber 2010. The heat pipes 2040 and fins 2020 are heated by the thermal energy transferred to the TES media 1 10 across combustor boundaries (e.g., across a sidewall of the internal combustor chamber 2010). The fins 2020 may contact the internal combustor chamber 2010 to be heated directly by the internal combustor chamber. The TES device 2000 also includes one or more heat pipes 2042 that extend between the heat delivery assembly 2030 and the internal combustor chamber 2010 and transport thermal energy from the internal combustor chamber 2010 directly to the heat delivery assembly 2030. Fins 2050 extend from the heat pipe 2042 into the TES media 1 10. Thermal energy is transferred from the heat pipe 2042 into the TES media 1 10 by the fins 2050.

Two types of models were developed to model the behavior of the TES device 2000. In both models, the TES media 1 10 modeled was a eutectic salt storage medium. The first model is a first-order model created using the MatLab Simulink environment. This model breaks the internal combustor chamber 2010 into three main sections, a combustion section, a mixing section, and a flow return section, and uses a lumped parameter model for the TES media 1 10. This model may be used to evaluate the effects of the internal combustor chamber 2010 and TES size; number, size, and thermal characteristics of heat transfer fins and/or heat pipes; the thermodynamic properties of different TES medias; and combustor power on combustor efficiency and the time required for thermal charge up.

The second model employs a finite volume representation of the internal combustor chamber 2010 and the TES media 110 and uses CFD to couple the chemical reaction with the heat transfer of the internal combustor chamber 2010 to the phase change behavior of the TES media 1 10. This model may be used to evaluate specific elements of the combustor design, as well as the specific placement of the internal combustor chamber 2010, Stirling engine fins, and heat pipes 2040 and 2042 to guarantee uniform volumetric energy transfer from the internal combustor chamber 2010 to the TES media 1 10 and thence to the Stirling hot side (e.g., the heater head portion 315A depicted in Figure 4).

The following is a basic equation for modeling bulk transient behavior of the TES media 1 10:

VJESPTES d hjEs/dt = Astirlmg hstιr_TES (Tstirling — TJES) +

∑ hcomb_Stage {Acomb_Stage (Tstage — TjES ) + (1 )

NFIΠS AFIΠS HFins(Tstage — TjES )} where the fin thermal efficiency OW') is modeled by the following expression:

HFm =

The temperature of the TES media is related to the enthalpy by the following expression:

If hjES <= Cp TES (TMP TES - TR_Θf) then TIES = h_TEs / CP TES + T_Ref

If Cp TES (TMP TES ^■ TR_Θf) < hjES < Cp jES (TMP TES " Tpjef) + I1FG_TES ,„,.

If Cp TES (TMP_TES " TRef) + I1FG_TES <= hjES then TIES = (IITES - h_FG_τEs) / CP TES + T_Ref Energy is transferred to the TES media 1 10 directly from the body of the internal combustor chamber 2010 and the fins 2020. As mentioned above, the internal combustor chamber 2010 was broken up into three virtual sections; the combustion section, the mixing section, and the return passage section. The combustion section contains the energy addition due to the chemical reaction, and the mixing section accounts for the temperature reduction caused by the addition of recycled combustion products for cooling. The return section refers to a designer specified number of reverse flow passages that redirect the combustion products out of the TES media 1 10. The term "thermal element" ("TE") refers to the solid combustor housing associated with each section, and is modeled thermally by the following equation:

VTEPTECP TE d TjE/dt = Acjnt hc_TE (Tc - TJE) + hcomb_Stage {Acomb_Stage /^\

(TIES - T_TE ) + N_Fιns A_Fιns ηFιns(Tτ_Es - T_TE )} ^ ^;

The combustor gas temperatures are obtained from a steady flow 1 st-law energy balance. A transient formulation was not used because it was assumed that the time scale associated with the change in gas temperature is very fast relative to that of the combustor walls or the TES media 110. For the combustion zone section the following equation was used: mo2 Cp_o2 (T|N_O2 - TR_Θf) + rriHc [ C-P HC (TIN_HC - TR_Θf) + HR_XΠ ] + mo CP D

(T|N_D - Tptef) = mH2O Cp_H2O (Tc - Tptef) + ITICO2 Cp_cO2 (Tc - Tptef) + mo

(5)

CP D (Tc — TR_Θf) + Acjnt hcjnt (Tc — TJE) + Acjnt l^"lRad (TRad — TJE)

Where h_RAD = σε(T_TE + T_Rad) (T_TE ² + T_Rad ²) (₆)

The CFD modeling of the Stirling engine heat source is accomplished via the CFD code CFDS-FLOW3D. This code has been used extensively by ARL for over 15 years, and has been modified at ARL to model the burning of hydrocarbon fuels such as JP5, JP8 and JP10; as well as to perform melting and freezing simulations. CFDS-FLOW3D has been used for the current application to model the heating of a phase-change TES storage medium via the burning of a hydrocarbon/oxygen in an attached combustor. The model incorporates chemical reaction, conjugate heat transfer through the internal combustor chamber 2010 to the TES media 1 10, phase change in the TES media, and extended surface heat transfer submodels. The model is run in a transient mode, so that the amount of energy stored in the TES media 1 10 increases with time. Model results for the behavior of the internal combustor chamber 2010 and the TES media 1 10 are illustrated in Figures 21 — 25. In Figures 21 — 25, the TES media 1 10 used was LiF/NaF/MgF₂ eutectic. LiF/NaF/MgF₂ eutectic has the following properties:

Melting Point 966 K

Heat Of Fusion 690 kJ/kg

Density 2600 kg/m³

Thermal Conductivity 1 1.3 W/m K Specific Heat 1.549 kJ/kg K

Figure 21 shows the behavior of the TES device 2000 (see Figure 20) at various temperatures of interest. Figure 21 includes three graphs. The topmost graph depicts the temperature of the TES media 1 10 (see Figure 20) over time. The middle graph depicts the combustion temperature inside the internal combustor chamber 2010 (see Figure 20) over time. The bottommost graph depicts the temperature of the combustion products ("Return") exiting from the internal combustor chamber 2010 (see Figure 20) and the temperature of the incoming fuel and oxidizer obtained via recuperation ("Recouperater") over time.

Plateaus 21 10 in the combustion temperature indicate periods during which the internal combustor chamber 2010 (see Figure 20) was operating or "turned on" and heating the TES media 1 10. A thermostat model was incorporated in the model. For these calculations, the internal combustor chamber 2010 (see Figure 20) was "turned on" when the temperature of the TES media fell to 10 K below the freezing/melting point of the TES media 1 10, and "turned off" when the temperature was 10 K above the freezing/melting point of the TES media 1 10. This logic produces blips 2120 in the TES temperature.

Figure 22 illustrates power flow through the TES device 2000. Under the conditions described above, the internal combustor chamber 2010 (see Figure 20) intermittently produces 60 kW of power (plateaus 2210), which may be used to produce a nominal steady flow of 3 kW of power (line 2220) from the Stirling engine 315 depicted in Figure 3 (assuming a thermodynamic efficiency of 40%).

The top portion of Figure 23 shows the energy accumulation and extraction from the TES media 1 10 (see Figure 20), and the bottom portion of Figure 23 shows the transient JP10 fuel expenditure. Figures 24 and 25 illustrate the capability of the 1 st-order model to perform design assessments. Figure 24 illustrates the overall combustor efficiency dependence on the amount of recycled combustion products used as a diluent. For the greatest efficiency, it is desirable to run the internal combustor chamber 2010 at the maximum temperature possible. This desire is tempered by the requirements of diluent addition to protect the internal combustor chamber 2010 (and possibly other components of the TES device 2000) from melting or other forms of thermal damage.

Figure 24 also shows the manner with which efficiency increases with increases in the thermal conductivity of the heat transfer surfaces (e.g., the fins 2020). The normalized baseline conductivity (i.e., relative fin conductivity = 1 ) is that of copper. A value 1/1 Oth of the normalized baseline (i.e., relative fin conductivity = 0.1 ) is appropriate for stainless steel, and shows a substantial drop in efficiency. Increasing the effective thermal conductivity by a factor of 10-100 may be achieved by the use of heat pipes (e.g., the heat pipes 2040 and/or 2042). While improvement in efficiency is observed for a 10-fold increase in conductivity (i.e., relative fin conductivity = 10), the curve for the 100-fold increase in conductivity (i.e., relative fin conductivity = 100) indicates improvements in conductivity start producing a diminishing "return on investment."

Figure 25 illustrates the overall combustor efficiency dependence on the operating power of the internal combustor chamber 2010. Higher power levels are needed if rapid thermal charging of the TES media 1 10 is required, while lower levels (equal to that drawn by the Stirling engine 315) are used if the internal combustor chamber 2010 is to run continuously. The significance of the results in Figure 25 is that it shows a clear optimum operating power may be predicted for a specific combustor design/geometry. If the power level is too high for the internal combustor chamber

2010, then there is excess thermal energy in the stream of combustion products exiting the internal combustor chamber 2010. If the power level is too low, then energy is not being transferred to the TES media 1 10 effectively.

The results of Figure 25 also show that higher efficiency is obtained as the number of heat pipes attached to the internal combustor chamber 2010 is increased. However, a similar caveat as was stated for Figure 24 is appropriate here; at some point increasing the number of heat pipes produces an impractically small improvement in efficiency. The location/magnitude of the optimum power level also appears to decrease, with reduced effectiveness in energy transfer to the TES media 1 10.

Calculations were also performed using lithium hydride ("LiH") as the TES media 1 10. This material was chosen for its superior energy storage qualities and in particular its large heat of fusion and specific heat on a mass basis. LiH has the following properties:

Melting Point 962.2 K

Heat Of Fusion 2842 kJ/kg

Density 820 kg/m³

Thermal Conductivity 1.38 W/m/K Specific Heat 2.562 kJ/kg/K

Thus, the melting point of LiH is about 962 K, which is slightly less than that of the LiF/NaF/MgF₂ eutectic, which is about 966 K. The specific heat and latent heat of fusion of LiH exceed those of the LiF/NaF/MgF₂ eutectic by factors of 4.3 and 4.1 , respectively. The energy density of LiH (between about 960 K and about 1240 K) is also greater, though only 1.03 times that of the LiF/NaF/MgF₂ eutectic. The principal benefit of the LiH relative to the LiF/NaF/MgF₂ eutectic is its low density. The solid/molten specific gravities of LiH and LiF/NaF/MgF₂ are 0.82/0.55 and 2.8/2.0, respectively. Ballasting requirements for the LiH system are less stringent. The temperature and power flow characteristics indicate that the LiH media yields a 20% increase in duration (which for a vehicle means an increase in travel range) relative to the LiF/NaF/MgF₂ eutectic.

The previous calculations were made using a thermostat controller that maintains the TES media 1 10 in a two-phase state. Additional energy would be available if the TES media 1 10 were heated to a temperature well into its liquid state. To employ this method of operation, a controller (not shown) may be used by the Stirling engine 315 (see Figure 3) to limit the heat input to be substantially similar to what it would receive from a two-phase TES media. In the model, because the boiling temperature of LiH is 1245 K, the controller (not shown) was modified to turn off the internal combustor chamber 2010 when the TES media 1 10 temperature reached 1240 K. The temperature and powering performance of this combined latent and sensible heat system demonstrated an increase in range relative to the LiF/NaF/MgF₂ eutectic and LiH media by 47% and 24%, respectively, because of the relatively low LiH boiling point. The boiling point of the LiF/NaF/MgF₂ eutectic is not well known, but assumed to be approximately equal to 1950 K (based on the boiling point of LiF). It is not reasonable to heat the TES media 1 10 to near this temperature because of the danger of damaging the internal combustor chamber 2010, heat transfer surfaces (e.g., fins 2020), and the TES media storage tank 2015. If the maximum temperature of the TES media 1 10 is limited to about 1600 K, the increase in range relative to the two- phase eutectic system was approximately equal 43 % (still less than that observed with LiH).

In the model, the internal combustor chamber 2010 was one inch in diameter and 4 inches long. Combustion products exited the internal combustor chamber 2010 via exhaust ducts similar to those illustrated in Figure 12 (e.g., the first plurality of flow passages 1290, the second plurality of flow passages 1300, the inner annular exhaust passageway 1294A, and the outer annular exhaust passageway 1294B). At the head (i.e., the portion facing the heat delivery assembly 2030) of the internal combustor chamber 2010, the combustion products were returned (i.e., left the TES device 2000) via four ducts (not shown) that were about 0.5 inches high and had a circumferential width of 40 degrees. Thus, the total travel length of the combustion gas was about 8 inches. The inlet gas flow consisted of 50 Ibm/hour of JP8 jet fuel, 172 Ibm/hr of oxygen and 1240 Ibm/hour of combustion products at a temperature of 485 F. The combustor pressure was at 450 psi. These flow conditions were used to produce a nominal combustor power of 64 kW with 7.5 kW transferred to the Stirling hot end (e.g., the heater head portion 315A depicted in Figure 4). The combustor walls were constructed from stainless steel.

Returning to Figure 20, inside the TES media storage tank 2015, the TES media 1 10 has a diameter of about 10 inches and extends past the head of the internal combustor chamber 2010 about 12 inches. The TES media 110 was heated via heat transfer across the walls of the internal combustor chamber 2010, and via the heat pipe 2042, which has a diameter of about 0.4 inches and extends along the center of the TES media 1 10. The heat pipe 2042 was assumed to be an excellent conductor, and its temperature was taken to be the temperature of the combustion products at the head of the internal combustor chamber 2010. To further enhance heat transfer, eight fins 2050 extended out from the heat pipe 2042 to the outer edge of the TES media 1 10. The fins 2050 were assumed to be made of copper. The heat transfer from the fins 2050 to the TES media 1 10 was calculated using classical one-dimension heat transfer theory as described by lncropera and Dewitt

When the TES media 1 10 was LiF-NaF-MgF₂, as a starting condition, the TES media was initially at a uniform temperature of 900 K. Thus, the analysis began assuming that the TES media 1 10 had previously experienced a number of heating/cooling cycles. The TES media 1 10 quickly reached melting temperature, but the melting process was slow due to the heat of fusion. When the TES media 110 is at its melting point, energy added by the internal combustor chamber 2010 is absorbed by the phase change of the TES media 110 from a solid to a liquid. Thus, a molten volume of the TES media 1 10 increases and a solid volume decreases as the TES media melts.

An analysis of the release of energy stored by the LiF-NaF-MgF₂ eutectic to run the Stirling engine 315 (see Figure 3) was performed. For this portion of the analysis, it was assumed that the internal combustor chamber 2010 was not operating and so heat was not added to the TES media 1 10 during this time. The initial condition for the LiF-NaF-MgF₂ eutectic was taken to be uniform at 1100 K, so that the TES media 1 10 was completely molten. It was assumed that at this point, the temperature at the head of the eutectic section (adjacent the internal combustor chamber 2010) was at 900 K, and heat transfer occurred between the LiF-NaF-MgF₂ eutectic and the head. Heat transfer was via eight heat pipes 2040 located at the outer radius of the LiF-NaF-MgF₂ eutectic. The heat pipes 2040 extended down the entire length of the TES media storage tank 2015 inside the solid TES media 110. A copper fin 2020 extended down from each heat pipe 2040 toward the center of the TES media 110 (or to the stainless steel wall of the internal combustor chamber 2010). It was assumed that each of the heat pipes 2040 was an excellent conductor, and its temperature along the entire length of the TES media 110 was assumed to be 800 K. The phase change from a liquid to a solid releases stored thermal energy from the TES media 1 10.

When the TES media 1 10 was LiH, the geometry and combustor flow rates were the same as those used above in the LiF-NaF-MgF₂ eutectic analysis. It was assumed for a starting condition that the TES media 110 (i.e., LiH) was at a uniform temperature of 900 K. The energy release analysis proceeded as described above for the LiF-NaF-MgF₂ eutectic. While the energy storage on a volume basis is roughly equivalent for the two materials, it is noted that the thermal conductivity of the LiH is almost a factor of two lower than that used for the LiF-NaF-MgF₂ eutectic. This may make the fins 2020 attached to the heating pipes 2040 less effective conduits of energy out of the TES media 1 10, and will tend to reduce the rate of heat extraction from the TES media. This results in the lower rates of cooling.

Exemplary TES devices 10, 200, 400, 500, 800, 900, 1000, 1 100, 1200, 1500, 1700, 1800, and 2000 have been described as having various numbers and configurations of thermal energy heat transporting means for transporting thermal energy to and from the TES media 1 10. As discussed above, these heat transporting means may be implemented as hollow tubes, elongated cylinders, annular channels formed between a pair of sidewalls, radially outwardly extending channels, and the like. Further, the various heat transporting means may include conductive fins from increasing the amount of surface area forming the interface between the heat transporting means and the TES media 1 10.

As discussed above, the TES media 1 10 resides inside a relatively large vessel (e.g., the vessel 90). Thus, the heat transporting means, which traverse the inside of the vessel, help ensure that no portion of the TES media 1 10 is more than a predetermined distance (e.g., about one to two inches) away from a thermal energy heat transporting means. This arrangement helps ensure that thermal energy is (1 ) effectively distributed within the bulk TES media 1 10 and (2) effectively extracted from the bulk TES media 1 10. Those of ordinary skill in the art appreciate that alternate configuration of heat transporting means beyond those explicitly presented herein may be used to achieve this result and are therefore within the scope of the present teachings.

Further, in all of the exemplary embodiments, except the TES device 200, the thermal energy input portion and the thermal energy output portion have been depicted as being located at opposite ends of the TES device. Many of these TES devices have been depicted as having an elongated cylindrically shaped vessel. In such embodiments, the heat transporting means have been illustrated as extending substantially linearly between the opposite ends of the TES device to define a thermal energy flow direction along the longitudinal axis of the elongated cylindrically shaped vessel. As is appreciated by those of ordinary skill in the art, the heat transporting means can be configured such that thermal energy is not transferred axially along the longitudinal axis. For example, through application of ordinary skill in the art to the present teachings, a TES device may be configured for off-axial heat transfer into or out of the TES media. Such non-symmetrical configurations of heat transporting means can be placed, or oriented, as desired between the thermal energy input portion and the thermal energy output portion. Also, the overall shape of the vessel of the TES device can be altered depending upon system needs. While cylindrical configurations have been shown, other extruded shapes such as squares, rectangles, triangles, ovals, trapezoids, or any other closed perimeter could be used.

The exemplary TES devices 10, 200, 400, 500, 800, 900, 1000, 1 100, 1200, 1500, 1700, 1800, and 2000 have also been described as having a heat delivery assembly (e.g., the heat delivery assembly 150) at their thermal energy output portions. In particular embodiments, the heat delivery assembly includes a working fluid that may also circulate within the interior of at least a portion of the heat transporting means. The heat delivery assembly helps reduce hot spots and temperature gradients at the thermal energy output portion of the TES device by combining the individual thermal energy contributions of the individual heat transporting means transferring thermal energy to the heat delivery assembly before that thermal energy is transferred to an external device. Those of ordinary skill in the art appreciate that alternate configuration of heat delivery assembly beyond those explicitly presented herein may be used to achieve this result and are therefore within the scope of the present teachings.

The foregoing described embodiments depict different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being "operably connected," or "operably coupled," to each other to achieve the desired functionality.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from this invention and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of this invention. Furthermore, it is to be understood that the invention is solely defined by the appended claims. It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should typically be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations, or two or more recitations).

Accordingly, the invention is not limited except as by the appended claims.

Claims

CLAIMSThe invention claimed is:

1. A thermal energy storage device comprising: a thermal energy input portion; a thermal energy output portion; a thermal energy storage media; a first interior chamber connecting the thermal energy input portion and the thermal energy output portion, and housing the thermal energy storage media in a continuous volume between the thermal energy input portion and the thermal energy output portion; at least one first thermal energy transport member extending from the thermal energy output portion into the thermal energy storage media housed inside the first interior chamber, the at least one first thermal energy transport member being configured to transport thermal energy from the thermal energy output portion into the thermal energy storage media; and at least one second thermal energy transport member extending between the thermal energy input portion and the thermal energy output portion, and being ccoonnffiigguurreedd ttoo ttrraannssppoorrtt tthheerrmmaall eenneerrggyy from the thermal energy input portion directly to the thermal energy output portion.

2. The thermal energy storage device of claim 1 , wherein at least one second thermal energy transport member is insulated from the thermal energy storage media to limit thermal energy transfer from the at least one second thermal energy transport member to the thermal energy storage media.

3. The thermal energy storage device of claim 2, further comprising: a second interior chamber adjacent the first interior chamber and isolated from the thermal energy storage media, the at least one second thermal energy transport member being inside the second interior chamber and insulated from the thermal energy storage media thereby.

4. The thermal energy storage device of claim 3, further comprising insulation disposed inside the second interior chamber.

5. The thermal energy storage device of claim 2, wherein the at least one first thermal energy transport member comprises a first plurality of heat pipes each housing a working fluid, the working fluid housed in each of the first plurality of heat pipes being isolated from the working fluid housed in the others of the first plurality of heat pipes, the at least one second thermal energy transport member comprises a second plurality of heat pipes each housing a working fluid, the working fluid housed in each of the second plurality of heat pipes being isolated from the working fluid housed in the others of the second plurality of heat pipes, the thermal energy output portion comprises an output heat pipe housing a working fluid, the working fluid of the output heat pipe being isolated from the working fluid housed in the first plurality of heat pipes and the working fluid housed in the second plurality of heat pipes, and the thermal energy input portion comprises an input heat pipe housing a working fluid, the working fluid of the input heat pipe being isolated from the working fluid housed in the second plurality of heat pipes.

6. The thermal energy storage device of claim 5, wherein a first end portion of each of the second plurality of heat pipes extends into the input heat pipe, a second end portion of each of the second plurality of heat pipes extends into the output heat pipe, and a first end portion of each of the first plurality of heat pipes extends into the output heat pipe.

7. The thermal energy storage device of claim 1 , wherein the thermal energy output portion comprises a first heat pipe having an end portion, the at least one second thermal energy transport member being configured to transport thermal energy to the end portion of the first heat pipe and the at least one second thermal energy transport member being configured to transport thermal energy away from the end portion of the first heat pipe.

8. The thermal energy storage device of claim 7, wherein the thermal energy input portion comprises a second heat pipe having an end portion, and the at least one first thermal energy transport member is configured to transport thermal energy away from the end portion of the second heat pipe.

9. The thermal energy storage device of claim 8, wherein: the end portion of the first heat pipe has a first temperature; the end portion of the second heat pipe has a second temperature; the at least one first thermal energy transport member is configured to transport thermal energy from the end portion of the first heat pipe into portions of the thermal energy storage media having temperatures less than the first temperature, the at least one first thermal energy transport member is further configured to transport thermal energy to the end portion of the first heat pipe from portions of the thermal energy storage media having temperatures greater than the first temperature; and the at least one second thermal energy transport member is configured to transport thermal energy from the end portion of the second heat pipe directly to the end portion of the first heat pipe when the second temperature is greater than the first temperature.

10. The thermal energy storage device of claim 1 , wherein the thermal energy storage media comprises a low energy state, a saturated state, and a high energy state, the thermal energy storage media being in a solid phase when in the low energy state, a combination solid phase and liquid phase when in the saturated state, and a liquid phase when in the high energy state.

1 1. The thermal energy storage device of claim 1 , wherein the at least one first thermal energy transport member comprises a plurality of heat pipes arranged within the first interior chamber.

12. The thermal energy storage device of claim 1 for use with a solar energy concentrator, wherein the thermal energy input portion is configured to receive thermal energy from the solar energy concentrator and transfer the received thermal energy to the at least one second thermal energy transport member.

13. The thermal energy storage device of claim 1 for use with a combustion chamber, wherein the thermal energy input portion is configured to receive thermal energy from the combustion chamber and transfer the received thermal energy to the at least one second thermal energy transport member.

14. The thermal energy storage device of claim 1 for use with a Stirling engine comprising a thermal energy receiving portion, wherein the thermal energy output portion is configured to transfer thermal energy to the thermal energy receiving portion of the Stirling engine.

15. A thermal energy storage device for use with an external device, the thermal energy storage device comprising: a first working fluid; a heat receiving assembly comprising a heat input portion, a heat output portion, and a first portion of the first working fluid, the heat input portion being configured to receive thermal energy and transfer it to the first portion of the first working fluid; a second working fluid; a heat delivery assembly comprising a heat input portion, a heat output portion, and a first portion of the second working fluid, the heat delivery assembly being spaced apart from the heat receiving assembly; a thermal energy storage media positioned between the heat receiving assembly and the heat delivery assembly; a first plurality of thermal energy transport members extending from the heat output portion of the heat receiving assembly into the thermal energy storage media, the heat output portion of the heat receiving assembly being configured to receive thermal energy from the first portion of the first working fluid and transfer it to the first plurality of thermal energy transport members, the first plurality of thermal energy transport members being configured to transport thermal energy from the heat output portion of the heat receiving assembly to the thermal energy storage media; and a second plurality of thermal energy transport members extending from the heat input portion of the heat delivery assembly into the thermal energy storage media, the second plurality of thermal energy transport members being configured to transport thermal energy from the thermal energy storage media to the heat input portion of the heat delivery assembly, the heat input portion of the heat delivery assembly being configured to receive thermal energy and transfer it to the first portion of the second working fluid, the heat output portion of the heat delivery assembly being configured to receive thermal energy from the first portion of the second working fluid and transfer the received thermal energy to the external device.

16. The thermal energy storage device of claim 15, wherein the thermal energy storage media comprises a low energy state, a saturated state, and a high energy state, the thermal energy storage media being in a solid phase when in the low energy state, a combination solid phase and liquid phase when in the saturated state, and a liquid phase when in the high energy state.

17. The thermal energy storage device of claim 15, wherein the first plurality of thermal energy transport members each comprise an internal channel housing a second portion of the first working fluid and having an open end portion in communication with the first portion of the first working fluid of the heat receiving assembly, the open end portion being configured to allow the first working fluid to flow between the internal channel and the heat receiving assembly, and the first plurality of thermal energy transport members are configured to transport thermal energy from the heat output portion of the heat receiving assembly to the thermal energy storage media at least in part by allowing the first working fluid to flow between the heat receiving assembly and the internal channels of the first plurality of thermal energy transport members.

18. The thermal energy storage device of claim 15, wherein the second plurality of thermal energy transport members each comprise an internal channel housing a second portion of the second working fluid and having an open end portion in communication with the first portion of the second working fluid of the heat delivery assembly, the open end portion being configured to allow the second working fluid to flow between the internal channel and the heat delivery assembly, and the second plurality of thermal energy transport members is configured to transport thermal energy from the thermal energy storage media to the heat input portion of the heat delivery assembly at least in part by allowing the second working fluid to flow between the internal channels of the second plurality of thermal energy transport members and the heat delivery assembly.

19. The thermal energy storage device of claim 15, wherein the first plurality of thermal energy transport members comprise a first plurality of concentrically arranged cylindrically shaped members, the second plurality of thermal energy transport members comprise a second plurality of concentrically arranged cylindrically shaped members, the first plurality of concentrically arranged cylindrically shaped members are concentric with the second plurality of concentrically arranged cylindrically shaped members, and the first plurality of concentrically arranged cylindrically shaped members are arranged in an alternating pattern with the second plurality of concentrically arranged cylindrically shaped members inside the thermal energy storage media.

20. The thermal energy storage device of claim 15 for use with an external device comprising a Stirling engine having a heater head portion, wherein the heat output portion of the heat delivery assembly comprises the heater head portion of the Stirling engine.

21. An electrothermal system comprising: a thermal energy storage device comprising a vessel storing a continuous volume of thermal energy storage media, a thermal energy input portion, a thermal energy output portion spaced apart from the thermal energy input portion, and a plurality of thermal energy transport members each extending from at least one of the thermal energy input portion and the thermal energy output portion into the thermal energy storage media; a solar energy collection assembly configured to collect thermal energy generated by the sun and transfer the thermal energy collected to the thermal energy input portion of the thermal energy storage device; and a thermal energy driven electric power generation device connected to the thermal energy output portion of the thermal energy storage device, and configured to receive thermal energy from the thermal energy output portion of the thermal energy storage device, and generate electric power from the received thermal energy, a first portion of the plurality of thermal energy transport members being configured to transfer thermal energy from the thermal energy input portion to the thermal energy storage media for storage thereby and a second portion of the plurality of thermal energy transport members being configured to transfer thermal energy stored by the thermal energy storage media from the thermal energy storage media to the thermal energy output portion of the thermal energy storage device.

22. The electrothermal system of claim 21 , wherein the thermal energy storage media comprises a low energy state, a saturated state, and a high energy state, the thermal energy storage media being in a solid phase when in the low energy state, a combination solid phase and liquid phase when in the saturated state, and a liquid phase when in the high energy state.

23. The electrothermal system of claim 21 , wherein the first portion of the plurality of thermal energy transport members is different from the second portion of the plurality of thermal energy transport members.

24. The electrothermal system of claim 21 , wherein a third portion of the plurality of thermal energy transport members are configured to transfer thermal energy directly from the thermal energy input portion to the thermal energy output portion.

25. A thermal energy generation and storage device for use with a fuel and an external device, the device comprising: a continuous volume of a thermal storage media configured to store thermal energy, the thermal storage media having a first portion and a second portion different from the first portion; a vessel housing the second portion of the thermal storage media; a combustion assembly coupled to the vessel and housing the first portion of the thermal storage media, the combustion assembly comprising a combustion chamber positioned inside the first portion of the thermal storage media, the combustion chamber being configured to burn the fuel to produce thermal energy and heated combustion products; a plurality of thermal energy transport members each having a first transport portion and a second transport portion, the first transport portion extending alongside the combustion chamber in the first portion of the thermal storage media, the first transport portion being configured to receive a portion of the thermal energy produced by the combustion chamber and transport that thermal energy to the second transport portion, the second transport portion extending into the second portion of the thermal storage media and being configured to transport a portion of the thermal energy received by the second transport portion to the second portion of the thermal storage media for storage thereby; and a thermal energy output portion coupled to the vessel and configured to extract thermal energy stored by the second portion of the thermal storage media and output that extracted thermal energy to the external device.

26. The thermal energy generation and storage device of claim 25, wherein the thermal energy storage media comprises a low energy state, a saturated state, and a high energy state, the thermal energy storage media being in a solid phase when in the low energy state, a combination solid phase and liquid phase when in the saturated state, and a liquid phase when in the high energy state.

27. The thermal energy generation and storage device of claim 25, wherein the combustion assembly further comprises a plurality of exhaust channels configured to direct the heated combustion products produced by the combustion chamber outside the combustion assembly, the plurality of exhaust channels being further configured to conduct thermal energy from the heated combustion products to the first portion of the thermal storage media.

28. The thermal energy generation and storage device of claim 27, wherein each of the plurality of exhaust channels comprises a branched portion.

29. The thermal energy generation and storage device of claim 27, wherein the combustion assembly comprises a peripheral portion disposed about the first portion of the thermal storage media and the plurality of exhaust channels is configured to conduct more thermal energy to regions of the first portion of the thermal storage media adjacent the peripheral portion of the combustion assembly than to regions of the first portion of the thermal storage media adjacent the combustion chamber.

30. The thermal energy generation and storage device of claim 27, wherein the first transport portions of the plurality of thermal energy transport members extend between adjacent sections of the plurality of exhaust channels, receive a portion of the thermal energy conducted by the plurality of exhaust channels to the first portion of the thermal storage media, and transport the thermal energy received to the second transport portions, which transport the thermal energy to the second portion of the thermal storage media for storage thereby.

31. The thermal energy generation and storage device of claim 25, wherein the combustion chamber further comprises at least one outlet through which the heated combustion products exit the combustion chamber, the combustion assembly further comprises an outside surface, and a plurality of branched exhaust channels extending inwardly from the outside surface into the first portion of the thermal storage media, each of the branched exhaust channels comprise a first segment connected to a plurality of branch segments, the first segment is adjacent the at least one outlet of the combustion chamber, and configured to receive the heated combustion products therefrom, the first segment is further configured to direct at least a portion of the received heated combustion products into the plurality of branch segments, the first segment and the plurality of branch segments each comprise an exit aperture formed in the outside surface through which the heated combustion products exit the branched exhaust channels, and the plurality of branched exhaust channels are further configured to conduct thermal energy from the heated combustion products to the first portion of the thermal storage media.

32. The thermal energy generation and storage device of claim 31 , wherein each of the plurality of branch segments of the branched exhaust channels are configured to conduct substantially identical amounts of thermal energy from the combustion products to the first portion of the thermal storage media.

33. The thermal energy generation and storage device of claim 31 , wherein each of the first segments of the branched exhaust channels configured to direct substantially equal amounts of the received heated combustion products into the plurality of branch segments.

34. The thermal energy generation and storage device of claim 25, wherein the combustion chamber further comprises at least one outlet through which heated combustion products exit the combustion chamber, and the combustion assembly further comprises an outside surface, and a plurality of branched exhaust channels extending inwardly from the outside surface into the first portion of the thermal storage media, each of the plurality of branched exhaust channels further extending radially outwardly from the combustion chamber, each of the plurality of branched exhaust channels comprises a first segment connected to a plurality of branch segments, and a grooved member extending from the outside surface into the first segment and the plurality of branch segments, the first segment is adjacent the at least one outlet of the combustion chamber and configured to receive the heated combustion products therefrom, the first segment is further configured to direct the received heated combustion products radially into the plurality of branch segments, the first segment and the plurality of branch segments each comprise a plurality of exit apertures formed in the outside surface through which the heated combustion products exit the branched exhaust channels, inside the first segment and the plurality of branch segments, the grooved member comprises a groove aligned with each of the exit apertures, the grooves are configured to limit the flow of the heated combustion products through the first segment and the plurality of branch segments and out the exit apertures, and the plurality of branched exhaust channels are further configured to conduct thermal energy from the heated combustion products to the first portion of the thermal storage media.

35. The thermal energy generation and storage device of claim 25, wherein the vessel comprises an inside surface, each of the plurality of thermal energy transport members is coupled to the inside surface and configured to conduct thermal energy thereto, the thermal energy output portion further comprises a vapor chamber adjacent the inside surface of the vessel, the vapor chamber comprises a working fluid and an outside surface, the working fluid is configured to collect thermal energy conducted to the inside surface by the plurality of conductors, and substantially uniformly distribute the collected thermal energy to the outside surface of the vapor chamber.

36. The thermal energy generation and storage device of claim 36, wherein the outside surface of the vapor chamber comprises a heater head portion of a Stirling engine.

37. A method for use with an external device and a thermal energy storage device, the external device comprising an input portion and a temperature control operable to control an operating temperature of the input portion, the thermal energy storage device comprising a thermal energy storage media, and a first thermal energy transport assembly connected to the input portion of the external device and extending into a portion of the thermal energy storage media having a media temperature, the first thermal energy transport assembly being configured to transport thermal energy from a higher temperature region to a lower temperature region, the method comprising: at a first time, adjusting the temperature control of the external device to set the operating temperature of the input portion of the external device to a first temperature that is less than the media temperature of the portion of the thermal energy storage media into which the first thermal energy transport assembly extends, thereby causing the first thermal energy transport assembly to transport thermal energy from the portion of the thermal energy storage media to the input portion of the external device; and at a second time different from the first time, adjusting the temperature control of the external device to set the operating temperature of the input portion of the external device to a second temperature that is greater than the media temperature of the portion of the thermal energy storage media into which the first thermal energy transport assembly extends, thereby causing the first thermal energy transport assembly to transport thermal energy from the input portion of the external device to the portion of the thermal energy storage media for storage thereby.

38. A method for use with an external device and a thermal energy storage device, the external device comprising an input portion and a temperature control operable to control an operating temperature of the input portion, the thermal energy storage device comprising a thermal energy output portion conductively coupled to the input portion of the external device, a thermal energy storage media, and a first thermal energy transport assembly connected to the thermal energy output portion and extending into a portion of the thermal energy storage media having a media temperature, the first thermal energy transport assembly being configured to transport thermal energy from a higher temperature region to a lower temperature region, the method comprising: at a first time, adjusting the temperature control of the external device to set the operating temperature of the input portion of the external device to a first temperature that is less than the media temperature of the portion of the thermal energy storage media into which the first thermal energy transport assembly extends, thereby conductively adjusting a second temperature of the thermal energy output portion to be less than the media temperature and causing the first thermal energy transport assembly to transport thermal energy from the portion of the thermal energy storage media to the thermal energy output portion which conducts the thermal energy to the external device; and at a second time different from the first time, adjusting the temperature control of the external device to set the operating temperature of the input portion of the external device to a third temperature that is greater than the media temperature of the portion of the thermal energy storage media into which the first thermal energy transport assembly extends, thereby conductively adjusting a fourth temperature of the thermal energy output portion to be greater than the media temperature and causing the first thermal energy transport assembly to transport thermal energy from the thermal energy output portion to the portion of the thermal energy storage media for storage thereby.

39. A method for use with an external device and a thermal energy storage device, the external device comprising an input portion and a temperature control operable to control an operating temperature of the input portion, the thermal energy storage device comprising a thermal energy output portion conductively coupled to the input portion of the external device, a thermal energy storage media, and a first thermal energy transport assembly connected to the thermal energy output portion and extending into a portion of the thermal energy storage media having a media temperature, the first thermal energy transport assembly being configured to transport thermal energy from a higher temperature region to a lower temperature region, the method comprising: monitoring a quantity of thermal energy stored in the thermal energy storage media; comparing the quantity of thermal energy stored in the thermal energy storage media to a predetermined threshold amount; when the quantity of thermal energy stored in the thermal energy storage media is greater than the predetermined threshold amount, adjusting the temperature control of the external device to set the operating temperature of the input portion of the external device to a first temperature that is less than the media temperature of the portion of the thermal energy storage media into which the first thermal energy transport assembly extends, thereby causing the first thermal energy transport assembly to transport thermal energy from the portion of the thermal energy storage media to the input portion of the external device; and when the quantity of thermal energy stored in the thermal energy storage media is less than the predetermined threshold amount, adjusting the temperature control of the external device to set the operating temperature of the input portion of the external device to a second temperature that is greater than the media temperature of the portion of the thermal energy storage media into which the first thermal energy transport assembly extends, thereby causing the first thermal energy transport assembly to transport thermal energy from the input portion of the external device to the portion of the thermal energy storage media for storage thereby.

40. The method of claim 39, further comprising: determining a quantity of thermal energy required to operate the external device for a predetermined period of time; and determining the predetermined threshold amount based on the predetermined period of time.

41. A thermal energy storage device for use with a thermal energy source and a thermal energy recipient device, the thermal energy storage device comprising: a thermal energy storage media; a thermal energy input portion configured to receive thermal energy from the thermal energy source; a thermal energy output portion configured to transport thermal energy to the thermal energy recipient device; mmeeaannss ffoorr ttrraannssppoorrttiinngg tthheerrmmaall eenneerrggyy ffrroomm aatt lleeaasstt oonnee ooff tthhee tthheerrmmal energy input portion and the thermal energy output portion to the thermal energy storage media for storage thereby; means for extracting stored thermal energy from the thermal energy storage media; and a vessel configured to house the thermal energy storage media as a continuous volume, the means for transporting thermal energy and the means for extracting stored thermal energy both being housed inside the vessel and positioned in ddiirreecctt ccoonnttaacctt with the thermal energy storage media.

42. The thermal energy storage device of claim 41 , wherein during operation of the thermal energy storage device, the thermal energy storage media undergoes freeze and melt cycles, the thermal energy storage device further comprising: one or more first temperature sensors positioned at locations in the thermal energy storage media whereat the thermal energy storage media melts last; and one or more second temperature sensors positioned at locations in the thermal energy storage media whereat the thermal energy storage media freezes last.

43. The thermal energy storage device of claim 42, further comprising: means for determining a state of the thermal energy storage media based on information received from the one or more first and second temperature sensors.

44. The thermal energy storage device of claim 41 , further comprising: means for determining an amount of thermal energy stored in the thermal energy storage media.

45. The thermal energy storage device of claim 44, wherein the means for determining an amount of thermal energy stored in the thermal energy storage media comprise: one or more first temperature sensors adjacent the thermal energy input portion; and one or more second temperature sensors adjacent the thermal energy output portion.

46. The thermal energy storage device of claim 41 , further comprising: means for transporting thermal energy from the thermal energy input portion to the thermal energy output portion.

47. The thermal energy storage device of claim 46, wherein the means for transporting thermal energy from the thermal energy input portion to the thermal energy output portion is insulated from the thermal energy storage media to limit conduction of thermal energy to the thermal energy storage media.

48. The thermal energy storage device of claim 46, wherein the means for transporting thermal energy from the thermal energy input portion to the thermal energy output portion conducts thermal energy to the thermal energy storage media.

49. The thermal energy storage device of claim 41 for use with a second thermal energy source, the thermal energy storage device further comprising: a second thermal energy input portion configured to receive thermal ee enni ieeerriggyyyy f irioumi n t uhiee s ώeecuouni idu t uhieeri mi i iadli e eni ieeri gyyy s suouuirucee;, a dni idu means for transporting thermal energy from the second thermal energy input portion to at least one of the thermal energy output portion and the thermal energy storage media for storage thereby.

50. A method for use with a thermal energy storage device configured to receive thermal energy at an input rate, store thermal energy in a thermal storage media at a storage rate, and output thermal energy at an output rate, the method comprising: monitoring an amount of thermal energy received by the thermal energy storage device over a time period; monitoring an amount of thermal energy output by the thermal energy storage device over the same time period; determining a quantity of thermal energy stored in the thermal energy storage media over the time period based on the amount of thermal energy received by the thermal energy storage device over the time period and the amount of thermal energy output by the thermal energy storage device over the time period; comparing the quantity of thermal energy stored in the thermal energy storage media over the time period to a predetermined threshold amount; when the quantity of thermal energy stored in the thermal energy storage media over the time period is greater than the predetermined threshold amount, increasing the output rate of the thermal energy storage device and reducing the storage rate of the thermal energy storage device; and when the quantity of thermal energy stored in the thermal energy storage media is less than the predetermined threshold amount, reducing the output rate of the thermal energy storage device and increasing the storage rate of the thermal energy storage device