WO2012151096A2

WO2012151096A2 - Vacuum insulated heat storage device

Info

Publication number: WO2012151096A2
Application number: PCT/US2012/035070
Authority: WO
Inventors: Andrey N. Soukhojak
Original assignee: Dow Global Technologies Llc
Priority date: 2011-05-04
Filing date: 2012-04-26
Publication date: 2012-11-08
Also published as: WO2012151096A3

Abstract

Thermal energy storage system using an insulated container and novel supporting for the insulated container within an evacuated chamber.

Description

VACUUM INSULATED HEAT STORAGE DEVICE

FIELD OF THE INVENTION

The present invention relates to thermal energy storage using an insulated container and supporting the insulated container within an evacuated chamber.

BACKGROUND OF THE INVENTION

Industry in general has been actively seeking a novel approach to capture and store waste heat efficiently such that it can be utilized at a more opportune time. Further, the desire to achieve energy storage in a compact space demands the development of novel materials that are capable of storing high energy content per unit weight and unit volume. Areas of potential application of breakthrough technology include transportation, solar energy, industrial manufacturing processes as well as municipal and/or commercial building heating.

Regarding the transportation industry, it is well known that internal combustion engines operate inefficiently. Sources of this inefficiency include heat lost via exhaust, cooling, radiant heat and mechanical losses from the system. It is estimated that more than 30% of the fuel energy supplied to an internal combustion engine (internal combustion engine) is lost to the environment via engine exhaust.

Devices, systems, and methods for storing and/or recovering heat are described in U.S. Patent Application Publication Nos. 2009/0211726 and 2009/0250189, and PCT Patent Application Publication No. WO 2011/037596, PCT Patent Application No. PCT/US 11/22662, filed on January 27, 2011 by Soukhojak et al., and PCT Patent Application No. PCT/US 12/32494, filed on April 6, 201 by Soukhojak et al. all incorporated herein by reference in their entirety.

Heat storage devices that are generally small and/or light weight are typically required in automotive applications. However, there is a continuing need to store heat for longer periods of time, for storing larger quantities of heat, or both. As such, there is a need for heat storage devices that lose less heat to the environment, and heat storage devices that are better insulated. In particular, in using a heat storage device having an insulated compartment (e.g., container) for storing heat, there is a need for reducing the thermal contact between the compartment and the external components of the device. SUMMARY OF THE INVENTION

One aspect of the invention is a heat storage device comprising a housing; a container for storing heat and transferring heat, wherein the container is inside the housing, wherein the container has a length and at least two opposing ends, including a first end and a second end; an insulating space between the housing and the container, wherein the insulated space is at least partially evacuated so that the heat conduction by the gas in the insulated space is reduced; one or more capsules inside the container, wherein the one or more capsules contains a thermal energy storage material; and a sufficient number of support members connecting the container to the housing so that movement (e.g., horizontal, lateral, vertical, rotational, or any combination thereof) of the container relative to the housing is substantially prevented; wherein the support members have one or more features that reduces the amount of heat loss from the container through the support members. The support members preferably include a plurality of support members connecting the first end of the container to the housing, and a plurality of support members connecting the second end of the container to the housing; wherein at least one of the support members has a projection onto a plane perpendicular to the length of the container which projection is greater than the distance from the center of the container to the housing, so that the thermal path for heat flow along support member is increased. The support members preferably reduce or substantially prevent translational movement between the container and the housing. More preferably, the support members reduce or substantially prevent both translational movement and rotational movement between the housing and the container. The support members preferably substantially prevent movement of the container with respect to the housing when the heat storage device is exposed to forces typically encountered under normal operations of a vehicle.

Another aspect of the invention is directed at heat storage systems comprising a heat storage device according to the teachings herein, and a fluid connection for transferring heat from the heat storage device.

Another aspect of the invention is directed at a method for storing heat and/or transferring heat using a heat storage device according to the teachings herein. For example, the heat storage device may be employed in a process that includes a step of maintaining a thermal energy storage material above 125 °C for about 24 hours or more (e.g., for about 48 hours or more), preferably without additional input of energy.

Advantageously, the heat storage devices according to the teachings herein may be light weight, have a high capacity for heat storage, have low heat losses to the environment, or any combination thereof. As such, the heat storage devices may be employed in applications requiring one or any combination of the following: storage of heat for extended periods of time; storage of large quantities of heat; storage of heat at temperatures of 100 °C or more above ambient; or storage of heat in a small space.

BRIEF DESCRIPTION OF THE FIGURES

The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:

FIG. 1 is a cross-section along the length of a heat storage device illustrating features of a heat storage device having a plurality of support members attached to a container.

FIG. 2 is an illustrative cross-section of a heat storage device in a direction perpendicular to the length of the heat storage device illustrating features of the end of a container and its arrangement with respect to a housing.

FIG. 3 illustrates an arrangement of the support members in a heat storage device.

FIG. 4 is an illustrative cross-section of a heat storage device in a direction perpendicular to the length of the heat storage device illustrating features of the end of a container and its arrangement with respect to a housing.

FIG. 5 is a schematic drawing illustrating features of a heat storage device.

FIG. 6 is an illustrative cross-section of a heat storage device in a direction perpendicular to the length of the heat storage device illustrating features of the end of a container and its arrangement with respect to a housing.

FIG. 7 illustrate a relationship between the thermal expansion and the arrangement of the support members. FIG. 8 is a schematic drawing showing illustrative features that may be included in a heat storage device.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In the following detailed description, the specific embodiments of the present invention are described in connection with its preferred embodiments. However, to the extent that the following description is specific to a particular embodiment or a particular use of the present techniques, it is intended to be illustrative only and merely provides a concise description of the exemplary embodiments. Accordingly, the invention is not limited to the specific embodiments described below, but rather; the invention includes all alternatives, modifications, and equivalents falling within the true scope of the appended claims.

As will be seen from the teachings herein, the present invention provides unique articles, devices, systems, and process for storing thermal energy and/or transferring stored thermal energy to a fluid. For example, the articles and devices for storing thermal energy of the present invention are more efficient at storing thermal energy, allow for reduced loss of heat via thermal conduction.

The heat storage device has a container that contains one or more thermal energy storage materials. When thermal energy is provided to the container, such as by a heat transfer fluid, the thermal energy storage material is heated and/or undergoes a solid to liquid phase transition. It may be desirable for the thermal energy storage material to retain some or all of the heat for an extended period of time. For example, in a vehicle application, it may be advantageous to be able to store heat for hours, or even days, so that the heat can be used during a cold start of an internal combustion engine in the vehicle.

It may be desirable to store the heat at a sufficiently high temperature so that the heat storage density of the container (i.e., the ratio of the amount of heat stored in the container to the volume of the container) is high and/or the volume of the heat storage device is low. This may be particularly advantageous in vehicle applications where the space available for a heat storage device is limited. As such, it may be desirable to store the heat (e.g., in the thermal energy storage material) at a temperature of about 100 °C or more, preferably about 150 °C or more, more preferably about 175 °C or more, and most preferably about 200 °C or more. As such, the components of the heat storage device may be exposed to temperatures of about 100°C or more, about 150°C or more, about 175 °C or more, about 200 °C or more, or about 250 °C or more.

In order to store heat at a high temperature, it may be desirable to place the container inside a housing and at least partially evacuating a space between the container and the housing, thus creating an insulating space. The container may be supported within the housing by one or more support members (e.g., one or more spokes) connecting the container to the housing and preventing the generally preventing movement of the container relative to the housing in one or more directions. For example, the heat storage device may include a sufficient number of support members so that the container does not move relative to the housing in one or more horizontal directions, in a vertical direction, or any combination thereof. With respect to an automotive application, the support members may prevent the motion of the container with respect to the housing in a forward or reverse direction of travel (e.g., during acceleration and/or deceleration), in a lateral direction, in a vertical direction (e.g., due to uneven road surface, such as a pothole), rotation around one or more axis (e.g., an X, Y or Z axis, or any combination thereof) or any combination thereof. As such, the support members preferably have sufficient load bearing capacity (e.g., the product of tensile strength and cross- sectional area) to support the container within the housing during some or all anticipated forces. The need for support members having high strength may result in support members having high cross- sectional areas and the selection of materials that have generally high thermal conductivity, such as low carbon steel.

It will be appreciated that the support members will contribute to the thermal losses from the heat storage devices due to thermal conduction from the container through the support members. Such heat losses may not be significant in devices having large volumes or in devices operating at generally low temperatures (e.g., when the temperature of the thermal energy storage material minus an ambient temperature of about -20 °C is less than about 150 °C). The thermal conduction through the support members will generally increase with the cross-sectional area of the support members and with the difference between the temperature of the container and the temperature of the housing.

As such it may be desirable to employ one or more features in the support members so that the heat flow through the support members is reduced. Such a feature (e.g., a means of reducing the heat losses through the support members) may be particularly desirable when the difference between the temperature of the container (or the temperature of a material inside the container, such as the thermal energy storage material) and an ambient temperature of -20°C is about 150°C or more, about 175 °C or more, about 200 °C or more, about 225 °C or more, about 250 °C or more, or about 270 °C or more. According to the teachings herein, one or more of the support members (e.g., a plurality of the support members or even all of the support members) may include one or any combination of the following features that may reduce the heat losses from the container: an increased path length of the support member, a reduced cross sectional area of the support member in the direction perpendicular to the length of the support member, the support member includes a material having a high tensile strength at elevated temperature (e.g., at about 250 °C, at about 350 °C, or both), the support member has a low thermal conductivity, or the support member has a ratio of tensile strength at 250 °C to thermal conductivity that is high. The support member preferably has a tensile strength at 250 °C of about 100 MPa or more, more preferably about 200 MPa or more, and more preferably about 300 MPa or more. The support member preferably has a tensile strength at 350 °C of about 100 MPa or more, more preferably about 200 MPa or more, and most preferably about 300 MPa or more. Preferred support members have a thermal conductivity of about 25 W/m-K or less, more preferably about 14 W/m- K or less, and most preferably about 10 W/m- K or less. Preferred support members have a ratio of tensile strength at 250 °C to thermal conductivity of about 8 MPa/(W/m- K) or more, more preferably about 20 MPa/(W/m-K) or more, even more preferably about 50 MPa/(W/m- K) or more, and most preferably about 80 MPa/(W/m- K) or more.

A cross-section of an illustrative heat storage device according to the teachings herein is shown in FIG. 1. With reference to FIG. 1, the heat storage device 10 may include a housing 12 and a container 14 located within the housing 12. Preferably, the housing 12 and the container 14 are not in direct contact. The device preferably includes an insulating space 18 between the housing 12 and the container 14. The housing 12 may have one or more side walls 25 and opposing end walls 23. The insulating space 18 preferably is at least partially evacuated so that the thermal conductivity of the insulating space is reduced (e.g., relative to the conductivity of air at standard temperature and pressure). The container 14 may be partially or entirely supported inside the housing 12 by a plurality of support members 22. The support members 22 connect the container 14 and the housing 12. The support members 22 preferably prevent the container 14 from moving relative to the housing 12. Preferably the support members 22 are in tension. The support members 22 may be connected directly to the container 14 or the support members 22 may be connected to the container 14 by way of one or more attachments 24. The attachment 24 may be a separate component or may be a part of another component. For example, an attachment may be part of the container 14, an attachment may be part of support member 22, or both. The container 14 preferably has two opposing end walls 20, 20' at either end of the length of the container 54. The container has an inside 16 that includes a thermal energy storage material 19. The thermal storage material 19 may be in any arrangment. Preferably, the thermal energy storage material is encapsulated in one or more capsular packages 17. Preferably, the capsular packages 17 or otherwise arranged so that a heat transfer fluid can flow between two adjacent capsular packages 17 for transferring heat into and out of the thermal energy storage material 19. The length 50 of the projection of the support member 22 on a plane perpendicular to the length of the container 14 preferably is greater than the distance 52 between the center of the container 14 and the side wall 25 of the housing 12 (e.g., so that the flow path for thermal conduction in the support member is increased). Thus, the length of the support member 22 may be greater than if the support member is attached to the housing at the nearest location on the housing (e.g., at least with respect to the radial component or the projection of the support member on a plane perpendicular to the length of the container). The device 10 preferably includes a plurality of support members (e.g., about 2 or more, about 4 or more, or about 6 or more) that are connected to the first end wall of the container 20. The device 10 preferably includes a plurality of support members (e.g., about 2 or more, about 4 or more, or about 6 or more) that are connected to the second end wall of the container 20'.

FIG. 2 illustrates a heat storage device 10 in the direction perpendicular to the length of the container 14, showing a view of the first end 20 of the container 14. The first end of the container 14 is connected to the housing 12 using six support members 22. It will be appreciated according to the teachings herein that the number of support members may also be less than 6 or may be greater than 6. The center 32 of the container 14 is illustrated in FIG. 2 by a point so that it can be clearly observed that some or all of the support members 22 have a length (in this projection perpendicular to the length of the container 14) that is greater than the distance between the center 32 of the container 14 and the housing 12. As illustrated in FIG. 2, a pair of support members 22(A) and 22(B) may have a point of nearest contact 30 that is located between the location where each of the pair of support members contact the container 14 and where each of the support members contact the housing 12. For example, the point of nearest contact between a first support member and a second support member, such as adjacent support members, may be at a position that is not at either end of the first support member, not at either end of the second support member, or both.

The device preferably includes an insulating material between the container and the housing. If employed, the insulating material may have a thermal conductivity less than the thermal conductivity of the container, less than the thermal conductivity of the housing, or both. For example, the insulating material may be a coating over a portion or over the entire outer surface of the container; a coating over a portion of or over the entire inner surface of the housing, or both. An insulating material between the housing and the container may be particularly useful for preventing a direct contact between the housing and the container during the use of the device, for preventing a direct contact between a support member and a tube (e.g., an inlet tube or an outlet tube), or both. As such, the insulating material, if employed, may prevent a short circuiting (with respect to conduction of heat) between the container and the housing. The insulting material, if employed may be a nonwoven material. The insulating material, if employed, may be a fibrous material. The insulating material, if employed, may be a material having a generally low bulk density (e.g., about 0.9 g/cm or less, about 0.7 g/cm 3 or less, about 0.5 g/cm 3 or less, about 0.3 g/cm 3 or less or about 0.1 g/cm or less). A preferred insulating material that may be used is glass fiber insulation.

The heat storage device preferably has a sufficient number of support members so that movement (e.g., translational movement, rotational movement, or preferably both) of the container relative to the housing is minimized or eliminated in one or any combination of (e.g., all of) the six motional degrees of freedom (i.e. the three translational axes and three rotational axes). When used in a vehicle, the support members preferably minimize or eliminate the movement of the container relative to the housing in the direction of travel, in a direction lateral to the direction of travel, in a vertical direction, or any combination thereof. More preferably, the support members minimize or eliminate the movement of the container relative to the housing in the direction of travel, in a direction lateral to the direction of travel, and in a vertical direction. In the absence of forces due to acceleration, some or preferably all of the support members are in tension. The total number of support members in the heat storage device (e.g., the number of support members that are in tension when the heat storage device is at rest) may be about 6 or more, preferably about 8 or more, more preferably about 10 or more and most preferably about 12 or more. The heat storage device preferably includes support members attached to a first end of the container and a plurality of support members attached to a second end of the container. The number of support members attached to the first end of the container preferably is about 3 or more, more preferably about 4 or more, even more preferably about 5 or more, and most preferably about 6 or more. The number of support members attached to the second end of the container preferably is about 3 or more, more preferably about 4 or more, even more preferably about 5 or more, and most preferably about 6 or more.

The support members preferably are long and have a small cross-sectional area in the direction perpendicular to their length so that the flow of heat through the support member is generally low. For example, the support members may each have a low cross- sectional area. The cross- sectional area of the support member in the direction perpendicular to the length of the support member preferably is about 100 mm² or less, more preferably about 20 mm² or less, even more preferably about 8 mm² or less, even more preferably about 4 mm² or less, and most preferably about 2 mm² or less. The cross- sectional area of the support members preferably are sufficiently high so that the support members can minimize the movement or eliminate the movement of the container relative to the housing during one or more (e.g., all) expected forces. The cross-sectional area of a support member in the direction perpendicular to the length of the support member preferably is about 0.5 mm² or more, more preferably about 1 mm² or more. The total cross- sectional area of all of the support member (in the direction perpendicular to the length of the support member) preferably is about 600 mm² or less, more preferably about 100 mm² or less, even more preferably about 25 mm² or less, even more preferably about 15 mm² or less, and most preferably about 10 mm² or less. The total cross- sectional area of all of the support members is preferably about 3 mm² or more.

The support members may have any shape or size that is capable of supporting a tensile load. Without limitation, examples of support members that may be employed for a support member include a wire, a spoke, a chain, a rope, a cable, a braid, a spring, or any combination thereof. It will be appreciated that a plurality of support members may be formed from a single support material. For example, a support material, such as a wire, chain, rope, cable, or braid, may be laced so that it attaches to the container in a plurality of locations, so that it attaches to the housing in a plurality of locations, or both. A support member that is a spring (e.g., a spring having a curvilinear heat flow path, such as a spiral heat flow path) or a chain may advantageously increase the heat flow path length between the container and the housing. A support member having two or more chain links may advantageously be used to reduce the heat flow through the support member due to the generally small contact area between two adjacent links.

The support members may be the same or different. For example, the heat storage device may include support members having the same cross- sectional area or support members having different cross-sectional areas (in the direction perpendicular to the length of the support member). By way of example, the heat storage device may include a first support member that partially supports the weight of the container (and the materials inside the container) and has a larger cross- sectional area than the cross-sectional area of a second support member that does not support the weight of the container. The cross-section of the support member may have any shape. For example the cross-section of the support member may have a generally arcuate shape (e.g., a circular shape, or an oval shape), a generally polygonal shape (e.g., polygonal shape, such as a square shape, a rectangular shape, a triangular shape, or a hexagonal shape), or any combination thereof.

Preferably, the support member is a metal or metal alloy that is partially or entirely coated with one or more insulating materials so that the support member does not short circuit (with respect to the flow of heat) when the support member contacts another component (such as the housing, the container, a fluid pipe, or another support member) or another portion of the support member (e.g., an adjoining winding of a spring). If an insulating material is employed to coat the support member, the ratio of the thermal conductivity of the insulting material to the thermal conductivity of the metal or metal alloy of the support member is preferably about 0.1 or less, more preferably about 0.01 or less, and most preferably about 0.001 or less. Preferred insulating materials for coating a support member have a conductivity of about 0.5 W/m-K or less.

The support member preferably includes a metal or metal alloy having high tensile strength so that the cross-section of the support member can be reduced or minimized (e.g., so that the heat losses are reduce). The support member preferably includes, consists essentially of, or consists entirely of a metal or metal alloy having a tensile strength of about 50 MPa or more, preferably about 100 MPa or more, more preferably about 200 MPa or more, even more preferably about 300 MPa or more, even more preferably about 400 MPa or more, even more preferably about 600 MPa or more, and most preferably about 700 MPa or more, wherein the tensile strength (i.e., tensile yield strength) is measured at room temperature and/or one or more elevated temperatures (e.g., about 150 °C, about 200 °C, about 250 °C, about 300 °C, or about 350 °C, or any combination thereof).

The support member preferably includes a metal or metal alloy having a low thermal conductivity so that the heat losses through the support member are reduced and/or minimized. The support member preferably includes, consists essentially of, or consists entirely of a metal or metal alloy having a thermal conductivity (e.g., measured at about 25 °C) of about 60 W/m-K or less, more preferably about 35 W/m-K or less, even more preferably about 20 W/m-K or less, even more preferably about 15 W/m-K or less, and most preferably about 10 W/m-K or less.

The support member may include a metal or metal alloy having a generally high ratio of tensile strength to thermal conductivity. The support member preferably includes, consists essentially of, or consists entirely of a metal or metal alloy having a ratio of tensile strength to thermal conductivity of about 5 MPa/(W/m- K) or more, more preferably about 10 MPa/(W/m- K) or more, even more preferably about 20 MPa/(W/m- K) or more, even more preferably about 40 MPa/(W/m-K) or more, and most preferably about 80 MPa/(W/m- K) or more wherein the tensile strength is measured at about 25 °C and/or one or more elevated temperatures (e.g., about 150 °C, about 200 °C, about 250 °C, about 300 °C, or about 350 °C, or any combination thereof), and the thermal conductivity is measured at about 25 °C.

A particularly preferred metal that may be used in the support member is a titanium alloy. The titanium alloy may be any alloy that includes titanium and one or more additional elements. The concentration of titanium atoms in the titanium alloy may be about 10% or more, about 20% or more, about 30% or more, about 40% or more, or about 50% or more, based on the total number of atoms in the alloy. Preferred titanium alloys include about 70 atomic % or more titanium atoms. The titanium alloy may include one or more elements selected from the group consisting of aluminum, titanium, oxygen, iron, tin, palladium, cobalt, silicon, nickel, molybdenum, niobium, zirconium, chromium, and any combination thereof. For example, the support member may include, consist essentially of, or consist entirely of a titanium aluminum vanadium alloy (such as Ti6A14V alloy, also known as grade 5). Ti6A14V alloy has a tensile yield strength of about 800 MPa at a temperature of about 250 °C, and a thermal conductivity of about 8 W/m-K.

The support member may include a metal or metal alloy having a generally low coefficient of thermal expansion so that the size of the heat storage device may be generally small (as described herein). Preferably the support member includes, consists essentially of, or consists entirely of a metal or metal alloy having a linear coefficient of thermal expansion of about 24 xlO^"6 K^"1 or less, more preferably about 16 xlO^"6 K^"1 or less, even more preferably about 12 xlO^"6 K^"1 or less, and most preferably about 10 xlO^"6 K^"1 or less. The support member preferably includes, consists essentially of, or consists entirely of one or more metal alloys having a linear coefficient of thermal expansion of about 1 xlO^"6 K^"1 or less. The support member preferably has a coefficient of linear thermal expansion that is less than the coefficient of linear thermal expansion of the container. The ratio of the coefficient of linear thermal expansion of the support member to the coefficient of linear thermal expansion of the container preferably is about 0.98 or less, more preferably about 0.9 or less, even more preferably about 0.8 or less, and most preferably about 0.7 or less.

The insulating space preferably is at least partially evacuated so that heat loss through the insulating space is minimized. The pressure in the insulating space is preferably about 0.8 atmospheres or less, more preferably about 0.5 atmospheres or less, even more preferably about 0.1 atmospheres or less, and most preferably about 0.01 atmospheres or less.

The volume of the insulating space, the distance between the container than the housing, or both, preferably is sufficiently large so that contact between the container and the housing is substantially, or entirely prevented. The volume of the insulating space, the distance between the container than the housing, or both, preferably is sufficiently small so that the heat storage device is capable of being installed in the limited space of a vehicle. The ratio of the volume of the insulating space to the volume of the heat storage device is preferably about 0.4 or less, more preferably about 0.2 or less, and most preferably about 0.1 or less. The container holds the thermal energy storage material. During a charging step, a heat transfer fluid having a temperature greater than the temperature of the thermal energy storage material flows into the container, through the container, and exits the container, causing an increases in the temperature of the thermal energy storage material and/or causes some or all of the thermal energy storage material to undergo a solid to liquid phase transition. During a discharging step, a heat transfer fluid having a temperature less than the temperature of the thermal energy storage material flows into the container, through the container, and exits the container, causing the temperature of the thermal energy storage material to decrease and/or some or all of the thermal energy storage material to undergo a liquid to solid phase transition. During a step of storing heat, the flow of the heat transfer fluid through the container is substantially or entirely eliminated, so that convective heat flow is minimized.

The container seals the inside of the container from the insulating space. The container may prevent loss of vacuum of the insulating space. The container may be sufficiently strong so that it allows for the flow of the heat transfer fluid through the container.

The container may have a generally elongated shape with two spaced apart ends. According to the teachings herein, the container preferably is attached to the a plurality of support members on each of the two ends. The container may have protrusions and or hubs capable of attaching to the support members. The protrusions and or hubs, if employed, may be integrated into the container, or may be attached to the container.

As illustrated in FIG. 1, the support members may have an angle of incline relative to the plane perpendicular to the length of the container. This angle of incline 44 is illustrated in FIG. 3. The right triangle in FIG. 3 has an angle of incline 44 of the support member 22. The support member 22 is the hypotenuse of the triangle, the adjacent side 40 of the angle 44 is the direction perpendicular to the length of the container 14, and the opposing side 42 of the angle 44 is the direction parallel to the length of the container 14.

The incident angle is preferably selected so that the thermal stresses in the support members, the housing and the container are reduced or minimized when the heat storage devices is thermally cycled. The optimized value of the incident angle 44 may be calculated from the equation: Optimized angle = ½ arcsin[(2D_{s s})/(Li i)] where D_s is the distance of the support member in the projection on the plane parallel to the length of the container, a_s is the coefficient of linear thermal expansion of the support member, Li is the initial length of the container (including any protrusion and/or hub extending to the point of connection with the support member), and ¾ is the coefficient of linear thermal expansion of the container. For example, the initial length of the container may be measured when the thermal energy storage material has a low temperature, such as a temperature of about 20 °C.

Preferably the incident angle is the optimized angle ± 5°.

A low incident angle is desirable for minimizing the distance between an end of the container and the housing, so that the volume of the heat storage device is minimized. The optimized angle, the incident angle, or both preferably is about 35° or less, more preferably about 25° or less, even more preferably about 20° or less, and most preferably about 15° or less. The incident angle should be sufficiently high so that the support members prevent motion of the container in the direction parallel to the length of the container. The incident angle preferably is about 5° or more, more preferably about 7° or more, and most preferably about 9° or more.

The container of the heat storage device may have a means of providing a fluid (e.g., a heat transfer fluid) into the container so that heat can be transferred into the container, so that heat can be removed from the container, or both. For example, the container of the heat storage device may include one or more inlets, one or more outlets, or both. An inlet and an outlet may be in fluid communication with each other (e.g., through the inside of the container). The heat storage device may include one or more tubes for flowing a fluid into and/or out of the container. For example the device may include one or more inlet tubes for flowing a fluid through an inlet of the container and into the inside of the container. The device may include one or more outlet tubes for flowing a fluid from the inside of the container through an outlet of the container and out of the heat storage device. The portion of the an inlet tube, an outlet tube, or both inside an insulating space may be longer than required for connecting the tube to the container, so that heat losses from the tube is reduced during a time of heat storage. As such, a fluid transfer tube (e.g., an inlet tube or an outlet tube) may have a circuitous path within the insulating pace. For example, an inlet tube, an outlet tube or both may have one or more windings within the insulating space between the housing and container. FIG. 4 illustrates features of an end of a heat storage device 10. With reference to FIG. 4, the heat storage device 10 may include an inlet tube 34, an outlet tube 36, or both. As illustrated in FIG. 4, an inlet tube and an outlet tube may be on the same end wall 20 of a container 14. An end wall 20 of the container may include a hub 38. The hub 38 may be integrated into the container 14 or attached to the container 14. The inlet tube 34, the outlet tube 36, or both, may connect to the hub 38. The inlet tube and the outlet tube may be arranged so that heat trasfer fluid flows into the container 14 through an inlet tube 34 and exits through an outlet tube 36. An inlet tube and an outlet tube may be connected to opposing ends 20 of a container. Preferably, the inlet tube 34 and the outlet tube 36 do not contact the support members 22. As illustrated in FIG. 4, the hub 38 may have a generally rectangular (e.g., square shape). However hubs having other shapes may be employed. If the container 14 includes and/or is attached to) a hub 38, the hub may be used for attaching the support members 22 to the container 14. As such, the shape of the hub 38 preferably is selected so that a support member 22 can have a long length (e.g., a long length that is free of contact, such as with the container or the hub, except at or near the ends of the support member). The hub may have a polyogonal shape (e.g., triangular, rectangular, pentagonal, hexagonal, or a polygon having 7 or more sides), an arcuate shape (e.g., a circular shape, an oval shape, a half-circle, and the like). As illustrated in Figure 6. the hub may have a triangular shape, such as an isosceles or equillateral triangular shape. The hub may be a single structure or may consist of a plurality of separate projections that combined form a hub structure. The heat storage device may include a plurality of hubs. For example, the heat storage device may include two or more hubs. Preferably, the heat storage device includes two hubs located on opposing ends of the container. The device may include a container attachment feature 35 suitable for attaching a support member 22 to the container 14, such as via a hub 38. The device may include a housing attachment feature 37 suitable for attaching a support member 22 to the housing.

FIG. 5 illustrates a side view of a portion of heat storage device showing components and features that may be between one end wall 25 of the container 12 and one end 20 of the housing 14. As illustrated in FIG. 5, the inlet tube, the outlet tube, or both preferably pass through the housing of the heat storage device. It will be appreciated that a fluid transfer tube that passes through the housing forms a good seal with the housing so that air or other fluid cannot enter the insulated space through a gap between the fluid transfer tube and the housing. Such seal between the housing and the tubes passing through it should be sufficient so that the insulated space may be a vacuum. Instead of passing though the housing, a tube connecting element may be employed on the inside and/or outside of the housing sufficient for providing a fluid connection between a fluid transfer tube and the outside of the housing.

The heat storage device may include one or more rims or other reinforcing structure along the housing (e.g., along the inside of the housing, along the outside of the housing or both inside and outside the housing). A rim may run a portion of the circumference of the housing or may run the entire circumference of the housing. Preferred rims run along the entire circumference of the housing on the inside of the housing. A rim may be attached to the housing or may be formed from the housing. For example, a rim may be integrated into the housing. The rim may be employed for attaching one or more support members to the housing. The heat storage device preferably includes two or more rims. The rims preferably are located along the side walls of the container. For example, the heat storage device may include a first rim near one end of the housing for attaching support members that are attached to a first end of the container and a second rim near the other end of the housing for attaching support members that are attached to an opposing end of the container. As illustrated in FIG. 5, a support member 22 may be attached to a rim 46. A rim 46 may be positioned along a side wall 25 of the housing 12. The rim 46 may be positioned near an end wall 23 of the housing. The angle of incline of the support member 22 may be defined by the location of the rim 46. For example, the rim 46 may be located so that thermal stresses translated by the support member 22 are reduced or minimized during thermal cycling of the device 10. In FIG. 5, the support members 22 are attached near the center of the hub 38. However, as discussed hereinbefore, the support members 22 are preferably attached at other locations so that the length of the support members 22 can be longer. As illustrated in FIG. 5, the support members 22 preferably are free of contact with any tubes or other components within the insulated space 18, except for the attachments to the container 14 and the housing 12. As illustrated in FIGs. 7 and 8, the length of the heat storage device may change when the temperature difference between the housing and the container changes. As such, it may be desirable to balance the thermal expansion of the support member with the relative expansion of the container (to the housing) so that changes to the tensile force (due to heating or cooling) on the support member are reduced, minimized, or eliminated. For example, the housing 12 may be exposed to generally small temperature variations, such as the temperature variations of the ambient conditions. In comparison, the container 14 may be exposed to much greater temperature variations as the thermal energy storage material is heated and cooled. As the temperature of the container cycles, the length of the container may increase. As illustrated in FIGs. 7 and 8, the support member 22 may be positioned to form an angle theta, Θ, with the normal line 29 to the side wall 25 of the housing 12. Upon heating, the positioning of the support member 22' may be at a different angle, as illustrated in FIG. 7.

The heat storage device may include one, two, or more mounting harnesses. A mounting harness may be employed for positioning and/or attaching the heat storage device to another component (such as in a vehicle). The mounting harness preferably is attached directly or indirectly to the housing. For example, one or more mounting harness may be attached to or integrated into a rim that is along the housing, such as a rim that is along a circumference of the outside of the housing.

So that the heat losses from the support member are reduced, a support member may be arranged so that it does not contact any component of the heat storage device (e.g., an inlet tube, an outlet tube, a hub, a portion of the container, a portion of the housing) from the point the support member connects with the container to the point where the support member connects with the housing. Although two support members may contact each other without affecting the heat storage capabilities of the device, it may be preferable that support members do not contact each other so that they do not damage each other during use.

Support members may each be individual structures (e.g., monolithic structures). However, two or more support members may be formed by a single structure, such as by bending the single structure at one or more attachment points. For example, a support member (such as a spoke, a chain, or wire), may be bent at a point of attachment to a container (e.g. a hub), at a point of attachment to a housing (e.g., a rim) or both.

Heat loss from the support members when the thermal energy storage material has a temperature about 200 °C greater than the temperature of the housing, is about 8 W or less, preferably about 2 W or less, more preferably about 1.0 W or less, even more preferably about 0.5 W or less, and most preferably about 0.3 W or less.

Without limitation, suitable thermal energy storage materials for the heat storage device include materials that are capable of exhibiting a relatively high density of thermal energy as sensible heat, latent heat, or preferably both. The thermal energy storage material is preferably compatible with the operating temperature range of the heat storage device. For example the thermal energy storage material is preferably a solid at the lower operating temperature of the heat storage device, is at least partially a liquid (e.g., entirely a liquid) at the maximum operating temperature of the heat storage device, does not significantly degrade or decompose at the maximum operating temperature of the device, or any combination thereof. The thermal energy storage material preferably does not significantly degrade or decompose when heated to the maximum operating temperature of the device for about 1,000 hours or more, or even for about 10,000 hours or more.

The thermal energy storage material may be a phase change material having a solid to liquid transition temperature. The solid to liquid transition temperature of the thermal energy storage material may be a liquidus temperature, a melting temperature, or a eutectic temperature. The solid to liquid transition temperature should be sufficiently high so that when the thermal energy storage material is at least partially or even substantially entirely in a liquid state enough energy is stored to heat the one or more objects to be heated to a desired temperature. The solid to liquid transition temperature should be sufficiently low so that the heat transfer fluid, the one or more objects to be heated, or both, are not heated to a temperature at which it may degrade. As such the desired temperature of the solid to liquid transition temperature may depend on the object to be heated and the method of transferring the heat. For example, in an application that transfers the stored heat to an engine (e.g., an internal combustion engine) using a glycol/water heat transfer fluid, the maximum solid to liquid transition temperature may be the temperature at which the heat transfer fluid degrades. As another example, the stored heat may be transferred to an electrochemical cell of a battery using a heat transfer fluid where the heat transfer fluid has a high degradation temperature, and the maximum solid to liquid temperature may be determined by the temperature at which the electrochemical cell degrades or otherwise fail. The solid to liquid transition temperature may be greater than about 30 °C, preferably greater than about 35 °C, more preferably greater than about 40 °C, even more preferably greater than about 45 °C, and most preferably greater than about 50 °C. The thermal energy storage material may have a solid to liquid transition temperature less than about 400°C, preferably less than about 350°C, more preferably less than about 290°C, even more preferably less than about 250°C, and most preferably less than about 200°C. It will be appreciated that depending on the application, the solid to liquid transition temperature may be from about 30°C to about 100°C, from about 50°C to about 150°C. from about 100°C to about 200°C, from about 150°C to about 250°C, from about 175°C to about 400°C, from about 200°C to about 375°C, from about 225°C to about 400°C, or from about 200°C to about 300°C.

For some applications, such as transportation related applications, it may desirable for the thermal energy material to efficiently store energy in a small space. As such, the thermal energy storage material may have a high heat of fusion density (expressed in units of megajoules per liter), defined by the product of the heat of fusion (expressed in megajoules per kilogram) and the density (measured at about 25°C and expressed in units of kilograms per liter). The thermal energy storage material may have a heat of fusion density greater than about 0.1 M iter, preferably greater than about 0.2 MJ/liter, more preferably greater than about 0.4 MJ/liter, and most preferably greater than about 0.6 MJ/liter. Typically, the thermal energy storage material has a heat of fusion density less than about 5 MJ/liter. However, thermal energy storage materials having a higher heat of fusion density may also be employed.

For some applications, such as transportation related applications, it may be desirable for the thermal energy storage material to be light weight. For example, the thermal energy storage material may have a density (measured at about 25°C) less than about 5 g/cm 3 , preferably less than about 4 g/cm 3 , more preferably less than about 3.5 g/cm 3 , and most preferably less than about 3 g/cm . The lower limit on density is practicality. The thermal energy storage material may have a density (measured at about 25 °C) greater than about 0.6 g/cm 3 , preferably greater than about 1.2 g/cm 3 , and more preferably greater than about 1.7 g/cm .

The sealed spaces may contain any art known thermal energy storage material.

Examples of thermal energy storage materials that may be employed in the thermal energy storage material compartments include the materials described in Atul Sharma, V.V. Tyagi,

C.R. Chen, D. Buddhi, "Review on thermal energy storage with phase change materials and applications," Renewable and Sustainable Energy Reviews 13 (2009) 318-345, and in Belen Zalba, Jose Ma Mann, Luisa F. Cabeza, Harald Mehling, "Review on thermal energy storage with phase change: materials, heat transfer analysis and applications," Applied Thermal Engineering 23 (2003) 251-283, both incorporated herein by reference in their entirety. Other examples of suitable thermal energy storage materials that may be employed in the heat transfer device include the thermal energy storage materials described in U.S. Patent Application No. 12/389,416 entitled "Thermal Energy Storage Materials" and filed on February 20, 2009; and U.S. Patent Application No. 12/389,598 entitled "Heat Storage Devices" and filed on February 20, 2009.

The thermal energy storage material may include an organic material, an inorganic material or a mixture of an organic and an inorganic material that exhibits the solid to liquid transition temperature, the heat of fusion density, or both, described hereinbefore. Organic compounds that may be employed include paraffins and non-paraffinic organic materials, such as a fatty acid. Inorganic materials that may be employed include salt hydrates and metallics. The thermal energy storage material may be a compound or a mixture (e.g., a eutectic mixture) having a solid to liquid transition at generally a single temperature. The thermal energy storage material may be a compound or a mixture having a solid to liquid transition over a range of temperatures (e.g., a range of greater than about 3°C, or greater than about 5°C).

Without limitation, suitable non-paraffinic organic materials for use as a thermal energy storage material include acids, alcohols, aldehydes, amides, organic salts, mixtures thereof and combinations thereof. By way of example, the non-paraffinic organic materials that may be used alone or as a mixture include polyethylene glycol, capric acid, eladic acid, lauric acid, pentadecanoic acid, tristearin, myristic acid, palmatic acid, stearic acid, acetamide, methyl fumarate, formic acid, caprilic acid, glycerin, D-lactic acid, methyl palmitate, camphenilone, docasyl bromide, caprylone, phenol, heptadecanone, 1-cyclo- hexylooctadecane, 4-heptadacanone, p-joluidine, cyanamide, methyl eicosanate, 3-hepta- decanone, 2-heptadecanone, hydrocinnamic, cetyl alcohol, nepthylamine, camphene, o-nitroaniline, 9-heptadecanone, thymol, methyl behenate, diphenyl amine, p-dichlorobenzene, oxolate, hypophosphoric, o-xylene dichloride, chloroacetic, nitro naphthalene, trimyristin, heptaudecanoic, bees wax, glyolic acid, glycolic acid, p-bromophenol, azobenzene, acrylic acid, dinto toluent, phenylacetic acid, thiosinamine, bromcamphor, durene, benzylamine, methyl brombrenzoate, alpha napthol, glautaric acid, p-xylene dichloride, catechol, quinone, acetanilide, succinic anhydride, benzoic acid, stibene, benzamide, or any combination thereof.

Without limitation, the thermal energy storage material may include one or more inorganic salts selected from the group consisting of nitrates, nitrites, bromides, chlorides, other halides, sulfates, sulfides, phophates, phosphites, hydroxides, carboxides, bromates, mixtures thereof, and combinations thereof. By way of example, the thermal energy storage material may include, or consist substantially of K₂HP0₄-6 H₂0, FeBr₃-6H₂0, Μη(Ν0₃)₂· 6 Η₂0, FeBr₃-6 H₂0, CaCl₂- 12 H₂0, LiN0₃-2 H₂0, LiN0₃-3 H₂0, Na₂C0₃- 10 H₂0, Na₂SO₄ 10 H₂0, KFe(S0₃)₂- 12 H₂0, CaBr₂-6 H₂0, LiBr₂-2 H₂0, Ζη(Ν0₃)₂· 6 H₂0, FeCl₃-6 H₂0, Μη(Ν0₃)₂·4 H₂0, Na₂HP0₄ 12 H₂0, CoS0₄-7 H₂0, KF-2 H₂0, MgI₂- 8 H₂0, CaI₂- 6 H₂0, Κ₂ΗΡ0₄·7 H₂0, Ζη(Ν0₃)₂·4 H₂0, Mg(N0₃)-4 H₂0, Ca(N0₃)-4 H₂0, Fe(N0₃)₂- 9 H₂0, Na₂Si0₃-4 H₂0, Κ₂ΗΡ0₄·3 H₂0, Na₂S₂0₃-5 H₂0, MgS0₄-7 H₂0, Ca(N0₃)₂- 3 H₂0, Ζη(Ν0₃)₂·2 H₂0, FeCl₃-2 H₂0, Ni(N0₃)₂- 6 H₂0, MnCl₂-4 H₂0, MgCl₂-4 H₂0, CH₃COONa-3 H₂0, Fe(N0₃)₂-6 H₂0, NaAl(S0₄)₂- 10 H₂0, NaOH- H₂0, Na₃P0₄- 12 H₂0, LiCH₃C0O2 H₂0, Α1(Ν0₃)₂·9 H₂0, Ba(OH)₂- 8 H₂0, Mg(N0₃)₂- 6 H₂0, KA1 (S0₄)₂- 12 H₂0, MgCl₂- 6 H₂0, or any combination thereof. It will be appreciated that inorganic salts having higher or lower concentrations of water may be used.

The thermal energy storage material may include (or may even consist essentially of or consist of) at least one first metal containing material, and more preferably a combination of the at least one first metal containing material and at least one second metal containing material. The first metal containing material, the second metal containing material, or both, may be a substantially pure metal, an alloy such as one including a substantially pure metal and one or more additional alloying ingredients (e.g., one or more other metals), an intermetallic, a metal compound (e.g., a salt, an oxide or otherwise), or any combination thereof. One preferred approach is to employ one or more metal containing materials as part of a metal compound; a more preferred approach is to employ a mixture of at least two metal compounds. By way of example, a suitable metal compound may be selected from oxides, hydroxides, compounds including nitrogen and oxygen (e.g., nitrates, nitrites or both), halides, or any combination thereof. It is possible that ternary, quaternary or other multiple component material systems may be employed also. The thermal energy storage materials herein may be mixtures of two or more materials that exhibit a eutectic. The ratio of the total volume of thermal energy storage material (e.g., measured at about 25 °C) contained in the inside of the container to the total interior volume of the container (e.g., at a temperature of about 25°C) may be greater than about 0.3, preferably greater than about 0.5, more preferably greater than about 0.6, even more preferably greater than about 0.7, and most preferably greater than about 0.8. The upper limit on the volume of thermal energy storage material in the container is the need for space for a heat transfer fluid that contacts the articles for transferring thermal energy. The ratio of the total volume of thermal energy storage material (e.g., measured at about 25°C) contained in the container to the total interior volume of the container (e.g., at a temperature of about 25°C) may be less than about 0.99, preferably less than about 0.95.

Claims

1. A heat storage device comprising

i) a housing;

ii) a container for storing heat and transferring heat, wherein the container is inside the housing, wherein the container has a length and at least two opposing ends, including a first end and a second end;

iii) an insulating space between the housing and the container, wherein the insulating space is at least partially evacuated so that the heat conduction by gas molecules in the insulating space is reduced;

iv) a thermal energy storage material contained inside the container; and

v) a sufficient number of support members connecting the container to the housing so that translational movement of the container relative to the housing is substantially prevented;

wherein the support members have one or more features that reduces the amount of heat loss from the container through the support members.

2. The heat storage device of claim 1, wherein the support members include a plurality of support members connecting the first end of the container to the housing, and a plurality of support members connecting the second end of the container to the housing;

wherein at least one of the support members has a projection onto the plane perpendicular to the length of the compartment that is greater than the distance from the center of the container to the housing, so that the thermal path for heat flow along support member is increased.

3. The heat storage device of claim 1 or 2, wherein the support member is formed of a material having thermal conductivity less than steel so that the heat loss due to thermal conduction along the length of the support member is low.

4. The heat storage device of any of claims 1 through 3, wherein the support member has a tensile strength at a temperature of about 350 °C that is sufficiently high so that the support members are capable of supporting the container at elevated temperatures.

5. The heat storage device of any of claims 1 through 4, wherein the support members are spokes having a length and a generally uniform cross-section in the direction perpendicular to the length.

6. The heat storage device of any of claims 1 through 5, wherein one or more of the support members are attached directly to the container.

7. The heat storage device of any of claims 1 through 6, wherein one or more of the support members are attached to a hub or a projection extending from an end of the container.

8. The heat storage device of any of claims 1 through 7, wherein the support members have a path for flowing heat that is longer than the length of the support member.

9. The heat storage device of claim 8, wherein the support member includes a spring or a chain.

10. The heat storage device of any of claims 1 through 9, wherein the support member is formed of a material having a sufficiently low coefficient of linear thermal expansion so that the angle of incline of the support member towards the direction of the length of the container is 35°, or less (preferably 20° or less) so that the space between the container and the housing can be reduced.

11. The heat storage device of any of claims 1 through 10, wherein the container includes a first hub and a second hub located on the separate spaced apart ends of the container.

12. The heat storage device of any of claims 1 through 11, wherein the device includes at least 8 support members, and wherein the support members substantially prevent both translational and rotational movement of the container relative to the housing.

13. The heat storage device of any of claims 1 through 12, wherein the device includes at least 4 pairs of support members, wherein each pair of support members has a point of closest approach to each other that is between their attachments to the container and the housing wall.

14. The heat storage device of any of claims 1 through 13, wherein at least some of the support members are in tension.

15. The heat storage device of any of claims 1 through 14, wherein the heat storage device has an inlet, an outlet, or both.

16. The heat storage device of any of claims 1 through 15, wherein the heat storage device has a high heat storage density greater than about 0.5 MJ/L, as measured from the heat removed when cooling the heat storage device from 300°C to 80°C.

17. The heat storage device of any of claims 1 through 16, wherein the support member includes a metal having ratio of tensile strength at 250 °C to thermal conductivity greater than about 8 MPa/(W/m-K).

18. The heat storage device of any of claims 1 through 17, wherein the thermal energy storage material has a solid to liquid phase transition greater than 175 °C and the device includes a plurality of capsules containing the thermal energy storage material.

19. A system for storing heat including a heat storage device of any of claims 1 through 16, and a means for transferring heat into the heat storage device.

20. A method of storing heat including a step of increasing the temperature of the thermal energy storage material in the heat storage device of any of claims 1 through 15.