GB2621968A

GB2621968A - Improvements to heat pumps

Info

Publication number: GB2621968A
Application number: GB2202146.3A
Authority: GB
Inventors: James Wyllie Nicholas; Singh Chana Kamaljit
Original assignee: Botanic Energy Ltd
Current assignee: Botanic Energy Ltd
Priority date: 2022-02-17
Filing date: 2022-02-17
Publication date: 2024-03-06
Also published as: GB202202146D0

Abstract

A heat pump comprises a first thermoelectric module 1 connected to a controllable source of electrical power, and a first heat pipe 2 containing a phase change fluid in thermal communication at a first end with a first side of the thermoelectric module. The heat pump may comprise a second thermoelectric module (5, fig 2 or 12, fig 3), and the first heat pipe disposed between the first and second thermoelectric modules and in thermal communication at its second end with a second side of the second thermoelectric module (fig 3). The first heat pipe may comprise a plurality of heat pipes with first ends in fluid communication with each other by a first passageway (4) defining a first reservoir, and second ends in fluid communication by a bridging section (8) defining a second reservoir. Also claimed is a thermoelectric module coupled to a first face of a first solid thermally conductive block 3 of aluminium, which can also be a sealed reservoir containing a phase change fluid (e.g. ammonia). The heat pump may comprise a closed loop thermosyphon (fig 5). The thermoelectric module(s) may be disconnected and connected to an electrical load for power storage (e.g. a battery).

Description

Improvements to heat pumps Field of the invention

[001] The invention relates to a heat pump and methods of operating a heat pump. In particular, the invention relates to a solid state heat pump and methods of operating the same. In some embodiments, the invention relates to a solid state heat pump without compression or expansion chambers, using instead direct heating and cooling by thermoelectric modules to cause evaporation and condensation of the working fluid.

Background of the invention

[002] Heat pumps are devices which spend energy transferring heat from a cooler place to a warmer place. They are a very efficient means of heating or cooling. The most familiar example of a heat pump is found in refrigerators, such as domestic refrigerators.

[3] A refrigerator circulates a fluid called a refrigerant around a closed system. 15 Heat is absorbed into the fluid at a first part of the system, and is expelled from the fluid at a second part of the system. Thus, the first part is cooled by the refrigerant and the second part is heated.

[4] The first part is called an evaporator. Prior to entering the evaporator, the refrigerant in a saturated liquid state passes through an expander which causes its pressure to drop, causing partial evaporation of the fluid and thus a temperature to drop to below the ambient temperature around the evaporator. As the fluid passes through the evaporator, it absorbs heat from the warmer environment of the evaporator, and thus cools the environment of the evaporator. Absorbing the heat causes further evaporation of the remaining liquid component of the refrigerant, until it reaches a saturated vapour state.

[005] The second part is called a condenser. Prior to entering the condenser, the refrigerant, still in a saturated vapour state, passes through a compressor which causes an increase in pressure and thus in temperature. Now in a superheated vapour state, the fluid passes into the condenser, around which the ambient temperature is lower than that of the superheated vapour. Consequently, heat escapes from the refrigerant, warning the environment of the condenser and cooling the refrigerant, until it returns to a saturated liquid state, ready to return to the expander and repeat the cycle.

10061 Compressors are typically mechanical devices driven by either internal or external motors, containing a variety of moving parts. The maintenance of so many working parts is one of the design and engineering challenges associated with 10 typical heat pumps of this kind.

10071 It is common for the heat absorption by the environment of the condenser and heat extraction from the environment of the evaporator to be aided by air-flow generators, such as fans, directing a flow of air towards each of the condenser and the evaporator.

10081 A heat pipe is a heat transfer device which employs some similar principles to those described above for a refrigeration cycle, relying on the evaporation and condensation of a working fluid to absorb and expel heat. Rather than spending energy transferring heat from a lower temperature place to a higher temperature place, a heat pipe is a very efficient conductor of heat from a higher temperature place to a lower temperature place.

10091 A heat pipe is typically a closed fluid conduit partly filled with a saturated liquid, and otherwise filled with the gas phase of the same fluid. When the heat pipe is placed across a temperature differential, that is, when a first end of the heat pipe is placed in a higher temperature environment and the second end is placed in a lower temperature environment, the first end absorbs heat from the higher temperature environment, causing the working fluid at the first end to evaporate. The vapour at the first end travels to the second end. The cooler environment at the second end absorbs heat from the working fluid, causing it to condense. The liquid is then returned to the first end, either by gravity, by a wick structure, or by some other means known to persons skilled in the art.

10101 Heat pipes are typically used in situations where the rapid conduction of heat is desirable. For example, they are often used in cooling systems in which it is desirable to rapidly remove heat from a heat source and draw it to a second location from which it might more easily dissipate. While they are extremely efficient, each heat pipe is only efficient within a limited range of temperatures, and so each one must be carefully designed for a particular purpose. The working fluid and other parameters must be selected according to the intended operating temperature range.

10111 Thermoelectric modules and assemblies are semiconductor devices which can be used as heat pumps to provide cooling or heating in domestic, commercial and industrial applications.

10121 The use of thermoelectric modules and assemblies to transfer heat by the Peltier method and nerate power by the Seebeck method is well known for many applications. Theimoelectric modules and assemblies are incorporated into systems to transfer heat and/or to generate or reclaim electrical ene 10131 Throughout the specification, the follow te, should be understood as defined here: :lucrors, -are individual chaps, nareriat, such as may)c a. lectric semiconductors, stacks or pieces of thermoelectric scmicom incorporated into a module as. defined below; b. thennoelect c modules (TEIVIs) are electronic circuit components comprising one or more thermoelectric semiconductors, typically in a casing with electrical contact points or terminals suallv for use either in. heat pumping or power generation; c. thermoelectric assemblies (TKAs) are devices or constructions -which incorporate one or more TEMs and other components to achieve a purpose, such as heat pumping or electric d. thermoelectric coolers ( C5) are lI1Ms or IfiAs particularly conlipured, through the selection of materials, components and so on, for efficient use as heat.

pumps; C. lectric generators (MGs) are TEMs or TEAs particularly con figured, through the selection of materials, components and so on, for efficient use in electrical power generation, [014] It will be appreciated that li±Cs and TILGs are essentially ngeable, since an.y thernoelectric module will demonstrate the Peltier effect when a current is applied across it, and the Seebeck effect when a temperature difference is applied across it. Nevertheless, it is common for TKGs and TE,Xis to be formed differently, for example being optimized for operation in different environments or for different efficiency priorities, [015] ig a current through a thermoelectric di tor create flux, drawing heat from one side and radiating heat on.ther. Electrical energy is converted into heat energy with the semiconductors acting as resisters. This is known as the Peltier effect.

[016] A. temperature differential exist 0. across a thermoelectric semiconductor causes electrical energy to be generate it the greater the temperature difference between the hot and cold sides, the greater the electrical energy generation. This is called the Seebeck effect, [017] Thermoelectric assemblies often comprise hermoelec r c semiconductors or 25 modules, thermally conducting plates, arid optionally heat sinks and/or fans. A typical thcnuoeiecrrme assembly arrangement t consists ot semiconductors placed between thermally conductive plates with the beat sinks mounted onto the plates, optionally with fans to increase the movement of the surrounding fluid (such as air) across or \vnnm the heat sinks.

[18] '1 hermoelectric semiconductors or modules can operate ndiyidually, can be grouped together in stacks, or can form part of a system. number of semiconductors or modules in a system, the application and variation of electrical current (both in terms of magnitude and direction), and the temperature differential across modules can he controlled to provide flexible operation.

[19] Typically, a controllable Dower source connected to the temniinais of a 10 thermoelectric module will pass an electrical current through the sc mconckctors then no-ed (leen:kit:11viti s s thermoelectric module, resulting in a hot side and a cold side. Reversing the polarity of the electric: current changes the direction of the heat transfer and reverses the hot side and the cold side.

[020] TECs are solid state i-u at pumps Laving thermally conductive plates or heat sinks exposed to the hot and cold sides. Electrical energy is applied, to transfer heat from the cold side to the hot side. When the plied current is switched off, the heat will return from the hot side to the cold side by thermal conduction within the module or assembly, until thermal equilibrium is achieved across the device.

[021] Furthermore, as the temperature difference increases across a.

TEM/TEA, it becomes less efficient as a heat purnp and the heat transfer slows until the device itself heats up and transfers heat back to the cold side.

[22] Because the hot and cold sides are.4) 4-her, and thermally coupled, it is difficult to thermally insulate them n order to stop or reduce the reverse heat transfer.

[23] The m seeks to improve the efficiency of pumps, which can operate across a wider range of temperatures before reaching their efficiency limits. The invention seeks to achieve this goal by slowing the increatie in We temperature difference across a TEA /TF,N1 Of the invention, by at least on a. More rapidly extracting heat from the hot side of a TI APFI M of the invention being operated as a heater or cooler, by employing

improved heat sinks compared with the prior art.

b More rapidly providing heat to the cold side of a TRA/TFAI of the invention being operated as a heater or cooler, by employing improved heat sinks to the external environment, compared with the prior art, in thermal communication with the cold side, or by employing a heat source in thermal communication with the cold side.

c. Providing stepped heat pumping with a plurality of TEAs/iEMs, stacked with interposing thermal conductors and heat storage reservoirs which are improved compared with those of the prior art.

10241 A typical prior art heat sink associated with a ILA/TEM comprises a plate formed of a thermally conductive material, such as a metal. Fins typically protrude from their external faces, in order to increase their surface area in contact with the surrounding fluid, such as air. They may be provided with fans to further increase the contact between the surrounding air and the heat sink fins. The invention seeks to improve on this design.

10251 Many useful embodiments of the invenon will become apparent to the skilled reader progressing through this specification. One particularly useful set of embodiments relates to solid state heat pumps for use in refrigeration systems, making use of heat pipes and refrigerant cycles. There are many advantages to such embodiments, not least the removal of the need for moving parts, such as those required by prior art compressors. These, and all embodiments described below, provide IT,As/TFAls with conditions in which they are able to operate over a much wider range of temperatures than in prior art conditions.

Summary of the invention

[026] A first aspect of the invention provides a heat pump comprising a first thermoelectric module connected to a controllable source of electrical power, and a first heat pipe containing a phase change fluid in thermal communication at a first end with a first side of the first thermoelectric module.

[027] A heat pipe is a much more effective heat sink than the heat sinks associated with thermoelectric assemblies of the prior art. If the heat pipe is coupled to the hot side, in use, of the thermoelectric module, the phase change fluid at the first end will evaporate, rapidly cooling the thermoelectric module's hot side, and transporting the heat energy extracted to the second end of the heat pipe, where the fluid will condense and rapidly release the heat energy.

[028] If the heat pipe is coupled to the cold side, in use, of the thermoelectric module, the phase change fluid at the first end will condense, rapidly releasing heat to the cold side of the thermoelectric module, and causing evaporation due to pressure change at the second end, rapidly drawing heat from the external environment around the second end. Thus, the heat pipe draws heat from the external environment to the cold side of a thermoelectric module much more rapidly than a conventional heat sink.

[29] It will be clear that the principles of both of the options described above can be combined to form a particularly effective heat pump using two heat pipes. Thus, some embodiments further comprise a second heat pipe, having a first end 25 in thermal communication with the second side of the first thermoelectric module.

[30] If a heat pipe is positioned so that its condensing end is above its evaporating end, the condensed fluid will return to the evaporating end under gravity. Wicks or similar provisions can be made for the return of the fluid otherwise.

[0311 Some embodiments of the invention further comprise a second thermoelectric module connected to a controllable source of electrical power, wherein the first heat pipe is disposed between the first and second thermoelectric modules, in thermal communication at its second end with a second side of the second thermoelectric module.

[0321 Such an assembly is extremely versatile. In one possible mode of operation, both the first and second thermoelectric modules can be powered simultaneously, with the same polarity, providing a particularly efficient heat pump in which the range of temperatures across which the two thermoelectric modules are able to operate effectively is considerably increased. For example, when the thermoelectric modules are powered so that their first sides are their hot sides and their second sides are their cold sides, the first thermoelectric module heats the first end of the heat pipe, causing rapid extraction of the heat from the first thermoelectric module's hot side, and rapid heating of the second thermoelectric module's cold side. Because the first hot side is being rapidly cooled and the second cold side is being rapidly heated, a great deal more heat is transferred by the heat pump before either thermoelectric module experiences a heat differential sufficient to significantly impair its effectiveness.

[033] In another mode of operation, only one of the thermoelectric modules might be powered at any one time. For example, the second thermoelectric module could be powered Sc) that its first side is its cold side, thus extracting heat from the environment around the heat pipe. This might lend itself to an efficient refrigeration system, in which the heat pipe and first thermoelectric module protrude from the roof of a refrigeration chamber, while the second thermoelectric module's hot side is positioned outside of the chamber to allow the extracted heat to escape. Although the first thermoelectric module is not being powered in this mode, since it would not be desirable to activate a heat source within a cooling chamber, the provision of both thermoelectric modules in this embodiment provides a very efficient general purpose heat pump that can easily be used to meet a variety of needs.

[034] In some embodiments, the first heat pipe may comprise a first plurality of heat pipes, each heat pipe of the first plurality of heat pipes having a respective first end and second end, wherein all of the first ends are in fluid communication with each other by means of a first fluid passageway section of pipe.

[35] Such embodiments lend themselves particularly well to heating or cooling an 10 external environment, since the plurality of heat pipes in mutual fluid communication increases the surface area of the heat pipe system, thus providing more rapid transfer of heat.

[36] In some such embodiments, it may be advantageous to provide a plurality of first thermoelectric modules in thermal communication at their respective first sides with the first end of the first heat pipe. In this case, the plurality of first thermoelectric modules may be in direct thermal communication with the first fluid passageway section of pipe.

[37] At least one adjacent pair of heat pipes of the first plurality of heat pipes may additionally be in fluid communication with each other at their second ends by 20 means of a fluid bridging section of pipe.

10381 The inventor has found, that by bridging the heat pipes of the first plurality of heat pipes at their second ends, the incidence of unwanted hot spots within the heat pipe system is considerably reduced.

10391 Furthermore, by bridging two or more of the heat pipes of the first plurality 25 of heat pipes at their respective second ends, a second fluid passageway section of pipe is formed In embodiments with a second thermoelectric module, or a plurality of second thermoelectric modules, at the second end of the first heat pipe arrangement, such a second fluid passageway section of pipe provides a suitable interface with the second thermoelectric module(s).

[40] Alternatively or additionally, the first heat pipe may comprise a first reservoir section, in fluid communication with and having a greater cross section than other sections of the first heat pipe, wherein the first reservoir section is the section of heat pipe closest to and in most direct thermal communication with the first thermoelectric module.

[41] The inventor has found, surprisingly, that providing a first reservoir of phase change material at the interface between the first thermoelectric module(s) and the first heat pipe, still greater efficiencies of heat transfer can be achieved.

The reservoir acts as both an effective heat sink and an effective heat store.

[42] In some such embodiments, in which the first heat pipe comprises a first plurality of heat pipes, the first reservoir may provide the first fluid passageway section.

[043] Tn other such embodiments, a second reservoir may be provided at the second end of the first heat pipe. This may be particularly advantageous in embodiments having a second thermoelectric module or a plurality of second thermoelectric modules, which can interface with the second reservoir.

[44] In such embodiments in which the first heat pipe comprises a first plurality 20 of heat pipes, the second reservoir may form the second fluid passageway section.

[45] In some alternative embodiments, the first heat pipe may form a closed loop.

[46] A looped heat pipe, also called a thcsmosyphon, provides a conduit around which the phase change fluid can circulate, driven by pressure changes and, in 25 some orientations, gravity. Powering the first thermoelectric module to heat or cool the first end of the first heat pipe in a loop configuration causes the circulation of fluid around the thermosyphon, providing for rapid heat transfer from the first end to the second end of the thermosyphon.

[047] Some such embodiments comprise a second thermoelectric module at the second end of the thermosyphon.

10481 Since closed loops do not have 'ends' in the sense of extreme opposing vertices, references to the first and second ends of a thermosiphon in the context of this specification should be taken to mean any two points around the loop which are separated from and substantially opposed to one another. This may take different meanings depending on the shape of the loop.

l0491 In such embodiments, having two thermoelectric modules, the system operates in a similar way to a refrigeration cycle described earlier in this specification. The first thermoelectric module may be operated to heat the thermosyphon, and thus perform the function of the evaporator. Similarly, the second thermoelectric module may be operated to cool the thermosyphon, and thus perform the function of the condenser.

10501 In some thermosyphon embodiments having only a first thermoelectric module, said first thermoelectric module may be arranged so that its second side is in thermal communication with the second end of the thermosyphon. In this way, one side can operate as an evaporator while the other side operates as a condenser.

In such embodiments it may be advantageous to position the condenser offset with the evaporator so that the condenser is positioned higher than the evaporator.

10511 In some embodiments, the first thermoelectric module comprises a first stack of thermoelectric modules, each successive one of the thermoelectric modules of the first stack being rated for optimal operation across a different successive temperature range. Alternatively or additionally, the second thermoelectric module may comprise a second stack of thermoelectric modules, each successive one of the thermoelectric modules fo the second stack beinc, rated for optimal operation across a different successive temperature range.

[052] A second aspect of the invention provides a heat pump comprising a first thermoelectric module, connected to a controllable source of electrical power, thermally coupled at a first side to a first face of a first Hock of a thermally conducting solid.

[053] The word 'block' should be understood in this context to refer to any suitable three dimensional shape. In some embodiments, for example, the block may be a non-planar shape, that is, a three dimensional shape with a thickness which is not significantly smaller than its height and width. In some embodiments, portions of the block my be hollow or may define recesses, fins, or cavities, depending on the particular purpose.

[54] The inventor has found that a block of thermally conducting material is a more effective heat sink than the prior art heat sinks which are typically finned plates of thermally conducting material. Unlike the heat sinks of the prior art, it can also act as a store of thermal energy, which may be useful in some instances.

Different choices of material and dimensions will determine whether the block is better suited to retain heat, or release it, for example when coupled to the cold side of a thermoelectric module.

[55] In some embodiments, a second block of thermally conducting solid is thermally coupled to the second side of the first thermoelectric modules, providing 20 an improved heat sink to both sides of the thermoelectric module.

[56] Additionally or alternatively, a second thermoelectric module, connected to a controllable source of electrical power, may be thermally coupled, by a second side, to a second face of the first block of thermally conducting solid.

[57] If the characteristics of the block are selected appropriately, for improved heat extraction and release, and if successive thermoelectric modules are powered with the same polarity, such an arrangement provides an improved stack of thermoelectric modules over prior art stacks which typically interpose thin thermally conducting plates between each layer of thermoelectric semiconductors. I3

The improvement is due at least to more rapid heat extraction from a thermoelectric module's hot side thermally coupled to the first block, which allows more heat to be transferred by the stack before said thermoelectric module reaches its efficiency limits as described above, when compared with a prior art stack containing thermoelectric modules with the same configuration.

10581 A third aspect of the invention provides a heat pump comprising a first thermoelectric module thermally coupled at a first side to a first face of a first reservoir of a phase change fluid.

[059] The inventor has found that a reservoir of phase change fluid is a more effective heat sink than the prior art heat sinks which are typically finned plates of thermally conducting material. This is because the phase change fluid evaporates in thermal communication with a hot side of a thermoelectric module, leading to a very rapid extraction of heat. Unlike the heat sinks of the prior art, it can also act as a store of thermal energy, which may be useful in some instances.

[060] In some embodiments, a second reservoir of phase change fluid is thermally coupled to the second side of the first thermoelectric modules, providing an improved heat sink to both sides of the thermoelectric module.

[61] Additionally or alternatively, a second thermoelectric module may be thermally coupled, by a second side, to a second face of the first reservoir of phase 20 change fluid.

[62] Such an arrangement provides a significantly improved stack of thermoelectric modules over prior art stacks which typically interpose thin thermally conducting plates between each layer of thermoelectric semiconductors. The improvement is due at least to more rapid heat extraction from a thermoelectric module's hot side thermally coupled to the first block, and faster release of heat to another thermoelectric modules cold side. These effects allow more heat to be transferred by the stack before said thermoelectric modules reach their efficiency limits as described above, when compared with a prior art stack containing thermoelectric modules with the same configuration.

[063] in any one of the aspects defined above, some or all of the thermoelectric modules may be additionally switch-ably connected to an electrical load, such that when the thermoelectric modules so connected are situated with an existing heat differential across them, they can be disconnected from the controllable source of electrical power and connected to the electrical load. In this way, the electrical energy generated by the Seebeck effect can power the electrical load. The electrical load may be an electrical energy storage system, such as a battery.

[064] Various elements of the improved heat pumps defined above may be combined in various ways to useful effect in various circumstances.

Brief description of the drawings

[065] I ',mbodiments of the invention will now be described, by way of example only, with reference to the following drawings.

[066] Figure 1 depicts an embodiment of various aspects of the invention comprising a reservoir or block and a heat pipe coupled to respective sides of a thermoelectric module.

[67] Figure 2 depicts an embodiment of various aspects of the invention comprising a reservoir or block and two heat pipe arrangements arranged around 20 two thermoelectric modules.

[68] Figure 3 depicts an embodiment of the first aspect of the invention comprising a heat pipe arrangement with two integral reservoirs interfacing with a first and a second plurality of thermoelectric modules.

[69] Figure 4 depicts an embodiment of the first aspect of the invention 25 comprising a heat pipe arrangement with a single integral reservoir interfacing with first plurality of thermoelectric modules.

[70] Figure 5 depicts an embodiment of the first aspect of the invention comprising a thermosyphon and two thermoelectric assemblies.

Detailed description

[71] Figure 1 depicts a basic embodiment of the first aspect of the invention, and a basic embodiment of either the second or third aspects of the invention. A first thermoelectric module 1 is thermally coupled on its first side to a first end of a heat pipe 2. The thermoelectric module is thermally coupled on its second side to a first face of a reset Nroir block 3.

[72] The thermoelectric module 1 is a conventional stack of semiconductors sandwiched between electrically conductive plates as is well known to the skilled person. It is connected to a controllable source of electrical power, in-particular to a source of direct current (not shown). The power source is controllable to apply current across the thermoelectric module in either a first direction or a second direction, so as to pump heat across the module in either a first direction or a second direction by the Peltier effect. The power source should also be controllable to apply no current at all in some modes of operation.

1073] The thermoelectric module 1 may also be switch-ably connectable to an electrical load (not shown). Thus, if the thermoelectric module has an existing heat differential across it, it can supply power to the load by the Seebeck effect. The control circuitry is preferably arranged so that the controllable source of electrical power cannot be controlled to supply current to the thermoelectric module while the module is also connected to the electrical load. The electrical load may be an electrical energy storage system, such as a battery. It may alternatively be a water heating system, a domestic appliance, or a metered feed to a utility grid.

Appropriate conversion circuitry should be provided according to the particular case.

[074] The heat pipe 2 is a closed, elongate fluid conduit containing a phase change fluid, such as water. It is partly filled with the fluid in the liquid state, and otherwise filled with the same fluid in a gaseous state. Tt is common to fill heat pipes of this kind by adding the fluid in liquid form and boiling it so as to evacuate any air in the tube, replacing it with the fluid in gaseous form, and then sealing the pipe. The pipe is made of a thermally conductive material, such as copper. The dimensions of the pipe, as well as the material from which it is formed and the fluid with which it is filled, all determine the particular heat transfer characteristics of the heat pipe, and these should be selected carefully according to the particular intended purpose.

10751 In this embodiment, the heat pipe 2 comprises an interface region 4 at its first end. This has a greater cross section than the rest of the pipe 2, but a shorter length than the rest of the pipe 2. It is to the first end of the interface region 4 that the thermoelectric module is coupled. Since the width of the heat pipe 2 is a significant contributing factor to its heat transfer characteristics, and since the area of the thermoelectric module 1 is a significant contributing factor to its heat transfer characteristics, an interface region may well be advantageous in many configurations in which the cross section of the heat pipe 2 is smaller than the area of the thermoelectric module 1.

10761 The reservoir block 3 may be a solid block of thermally conducting material, such as aluminium. The material and dimensions should be selected according to 20 the particular purpose.

10771 Alternatively, the reservoir block 3 may be a reservoir of phase change fluid, preferably comprising a chamber defined by a thermally conductive casing, such as a copper casing, filled with a suitable fluid, such as ammonia. The ammonia will partially fill the reservoir in liquid form, and fill the rest of the reservoir in gaseous form The chamber is typically sealed.

10781 The assembly depicted in Figure 1 can be operated in a variety of modes. In one exemplary mode, power is applied to the thermoelectric module 1 while all elements are at room temperature, such that the hot side is coupled to the heat pipe 2 and the cold side is coupled to the reservoir block 3. Tn this mode, heat is extracted quickly from the hot side of the thermoelectric module 1 by the evaporation of fluid in the heat pipe 2. This heat is then dissipated to the surrounding environment when the fluid condenses at the second end of the heat pipe 2. At the same time, heat is extracted from the reservoir Hock 3 by the cold side of the thermoelectric module. Because heat is extracted so quickly from the hot side by the heat pipe 2, more heat is transferred by the assembly, compared with the prior art, before the temperature difference between the hot side and the cold side of the thermoelectric module reaches the point at which it can no longer operate effectively.

10791 In another exemplary mode of operation, the reservoir block 3 has been pre-conditioned by another heat source, so that it is warmer than room temperature. Power is then applied to the thermoelectric module 1 so that the hot side is coupled to the heat pipe 2 and the cold side is coupled to the reservoir block 3. Because the cold side is warmer than the hot side to begin with, and the warmed reservoir block 3 acts as a source of heat as it releases its stored heat to the cold side of the thermoelectric module 1, more heat is transferred by the assembly, compared with the prior art, before the temperature difference between the hot side and the cold side of the thermoelectric module reaches the point at which it can no longer operate effectively.

10801 Figure 2 depicts another assembly combining a more complicated embodiment of the first aspect of the invention with a more complicated embodiment of the second or third aspects of the invention.

10811 A first thermoelectric module 1 is coupled, on its first side, to a first end of a first heat pipe arrangement 2, and to a first face of a reservoir block 3 on its second side. A second thermoelectric module 5 is coupled, on its first side, to a second face of the reservoir block 3, and to a first end of a second heat pipe arrangement 6 on its second side.

[82] Both of the thermoelectric modules 1, 5 are controllably connected to power circuitry and load circuity, as in the first embodiment described above.

[83] The first heat pipe assembly 2 comprises a first plurality of heat pipes, all protruding from the first interface region 4, which is similar to that described in 5 the first embodiment above.

[84] The second heat pipe assembly 6 similarly comprises a second plurality of heat pipes, all protruding from a second interface region 7.

[85] The second ends of all of the heat pipes of the first plurality of heat pipes are joined in fluid communication with each other by means of a first bridging conduit 8. The second ends of two pairs of adjacent heat pipes of the second plurality of heat pipes are similarly joined to each other in fluid communication by means of second 9 and third 10 bridging conduits. The skilled reader will appreciate that, more generally, all of the heat pipes, or any set or sets of heat pipes, or no heat pipes, may be joined at their second ends in this way. The inventor has found that joining at least some of the heat pipes at their second ends in this way prevents the formation of unwanted hot spots within the heat pipe arrangements.

[86] In some embodiments, it will be appreciated that these fluid conduits 8-10 may form additional interface regions for additional thermoelectric modules 20 coupled to the second ends of the heat pipes.

[87] As is indicated by apparent relative depth in Figure 2, the interface regions 4, 7 each have a greater volume than the fluid conduits 8-10. This optional characteristic is selected to form reservoirs 4, 7 of phase change fluid which are integral to the heat pipe arrangements 2, 6, and which are directly coupled to the thermoelectric modules 1, 5. The inventor has found, surprisingly, that the heat extraction characteristics of the heat pipe arrangements are improved by the provision of an integral reservoir of phase change fluid. For the purposes of this specification, an integral reservoir should be understood to be any portion of a heat pipe arrangement with a greater volume per unit distance in any direction, than the rest of the heat pipe arrangement.

[088] Figure 3 shows an embodiment of the first aspect of the invention, comprising a single heat pipe arrangement 2, with an integral reservoir 4 at the first end and an integral reservoir 11 at the second end. The usefulness of the integral reservoirs as interface regions can be seen in the connection of a first plurality of thermoelectric modules 1 to the first integral reservoir 4, across more than one face of the reservoir 4. A second plurality of thermoelectric modules 12 is provided at the second integral reservoir 11, on only a single face.

[089] The skilled reader will appreciate that the heat pipe and integral reservoir arrangements can take a vast array of forms, such as that depicted in Figure 4, which shows a first plurality of heat pipes 2 protruding in a first direction from an integral reservoir 4, and a second plurality of heat pipes 13, protruding in a second direction from the same integral reservoir 4. All of the heat pipes in the two pluralities of heat pipes 2, 13 are in fluid communication with each other via the integral reservoir. A plurality of thermoelectric modules 1 is coupled to at least one face of the integral reservoir 4.

[090] Figure 5 depicts a loop thermosyphon system according to the invention. A heat pipe arrangement 2 is fbrmed into a closed loop conduit of a suitable phase change fluid. A first section of the heat pipe 2 passes though an evaporator 14. The evaporator may be an integral reservoir, or it may simply be a length of pipe similar in cross section to the rest of the pipe 2. It may be a heat transfer block which encases or surrounds the first section of pipe. The skilled reader will appreciate that many heat transfer mechanisms will be suitable for this purpose.

[091] A first plurality of thermoelectric modules 1 is thermally coupled to the evaporator 14. The hot sides of the first plurality of thermoelectric modules are coupled to the evaporator. Tn this embodiment, the cold sides of the First plurality of thermoelectric modules are coupled to a first face of a reservoir block 3, similar to those in previous embodiments. The hot sides of a second plurality of thermoelectric modules 5 are coupled to a second face of the reservoir block 3. The cold sides of the second plurality of thermoelectric modules 5 are coupled to another heat sink 15, in this case a conventional finned heat sink but the skilled person will readily be able to apply the principles of this invention to select an improved heat sink if required.

[92] A second section of heat pipe 2 is thermally coupled to a condenser. The condenser is arranged similarly to the evaporator, with a combination of thermoelectric modules, a reservoir block, and a heat sink, but with the hot sides 10 and cold sides of the thermoelectric modules reversed.

[93] In a preferred mode of operation, the evaporator is heated and the condenser is cooled, causing the circulation of the working fluid as described above in relation to a refrigeration cycle. Preferably, the condenser is arranged above the evaporator so that gravity will aid the return of the condensed liquid to the evaporator.

[94] The phase change fluid rapidly extracts heat from the evaporator, and rapidly expels heat to the condenser, thus transferring heat very efficiently from the evaporator to the condenser. Because of the principles of the invention applied to the thermoelectric modules of the condenser and the evaporator, considerably more heat will be transferred before they reach the limits of their usefulness, when compared with identically rated thermoelectric modules in prior art assemblies.

[95] Specific embodiments of the invention have been described in detail above. These embodiments have been selected so as to facilitate a clear explanation of the principles behind the invention. The skilled reader will appreciate that there are an untold number of applications for the invention. The invention itself is not limited to the embodiments described above, but rather is defined by the claims that follow.

Claims

Claims 1. A heat pump comprising a first thermoelectric module connected to a controllable source of electrical power, and a first heat pipe containing a phase change fluid in thermal communication at a first end with a first side of the first 5 thermoelectric module.
2. A heat pump according to claim 1 comprising a second thermoelectric module connected to a controllable source of electrical power, wherein the first heat pipe is disposed between the first and second thermoelectric modules, in thermal communication at its second end with a second side of the second thermoelectric module.
3 A heat pump according to claim 1 or claim 2, wherein the first heat pipe comprises a first plurality of heat pipes, each heat pipe of the first plurality of heat pipes having a respective first end and second end, wherein all of the first ends are in fluid communication with each other by means of a first fluid passageway section of pipe.
4. A heat pump according to claim 3, wherein at least one pair of adjacent heat pipes of the first plurality of heat pipes are also in fluid communication with each other at their second ends by means of a fluid bridging section of pipe.
5. A heat pump according to any preceding claim, wherein the first heat pipe comprises a first reservoir section, in fluid communication with and having a greater cross section than other sections of the first heat pipe, and wherein the first reservoir section is the section of heat pipe closest to and in most direct thermal communication with the first thermoelectric module.
6. A heat pump according to claim 5, further comprising a second reservoir at 25 the second end of the first heat pipe.
7. A heat pump according to any preceding claim, wherein the first heat pipe forms a closed loop.
8. A heat pump comprising a first thermoelectric module, connected to a controllable source of electrical power, thermally coupled at a first side to a first face of a first block of a thermally conducting solid.
9. A heat pump according to claim 8, wherein a second Hock of thermally conducting solid is thermally coupled to the second side of the first thermoelectric modules.
10. A heat pump according to claim 8 or claim 9, further comprising a second 10 thermoelectric module, connected to a controllable source of electrical power, thermally coupled by a second side, to a second face of the first block of thermally conducting solid.
11. A heat pump comprising a first thermoelectric module, connected to a controllable source of electrical power, thermally coupled at a first side to a first 15 face of a first reservoir of a phase change fluid.
12. A heat pump according to claim 11, further comprising a second reservoir of phase change fluid, thermally coupled to the second side of the first thermoelectric modules.
13. A heat pump according to claim 11 or claim 12, comprising a second thermoelectric module, connected to a controllable source of electrical power, thermally coupled by a second side, to a second face of the first reservoir of phase change fluid.
14. A heat pump according to any preceding claim in which the first thermoelectric module is switch-ably connected to an electrical load.
15. A heat pump according to claim 14, in which the electrical load is a battery.