WO2022123208A1

WO2022123208A1 - Heat storage device

Info

Publication number: WO2022123208A1
Application number: PCT/GB2021/053042
Authority: WO
Inventors: Matthew LEGG; Robert Kyle; Matthew JENNINGS; Matthew MUNDY
Original assignee: Dyson Technology Limited
Priority date: 2020-12-08
Filing date: 2021-11-24
Publication date: 2022-06-16
Also published as: CN116568985A; GB2601995B; GB2601995A; GB202019285D0

Abstract

A heat storage device (100, 300, 600) for an air conditioning apparatus comprises: a phase change material, PCM (102, 302, 602); a plurality of thermally conductive elements (104, 304, 604); and a heat spreader (106, 306, 606) in thermal contact with the thermally conductive elements, the heat spreader for transferring heat from a heat exchanger of the air conditioning apparatus to the thermally conductive elements, wherein the thermally conductive elements are embedded within the PCM.

Description

Heat Storage Device

Technical Field

The present disclosure relates to a heat storage device for an air conditioning apparatus. The present disclosure also relates to an air conditioning apparatus and a kit, both comprising the heat storage device.

Background

Thermal energy storage by means of the solid to liquid phase transition in a phase change material (PCM) is known. A key challenge when storing heat energy in a PCM is how to efficiently transfer heat to the PCM. This is especially important in refrigeration circuits of air conditioning systems, because the magnitude of the thermal gradient between the PCM and the condenser directly impacts the efficiency of the refrigeration cycle. However, efficient transfer of heat into the PCM whilst maintaining a minimal thermal gradient is very challenging. This is because PCMs typically have thermal conductivities which are more comparable to those of thermally insulating materials, such as rubber or softwoods.

Known systems employing PCMs for heat storage typically employ additional components, such as mechanical stirring devices, to promote the transfer of heat into the PCM. However, such additional components introduce additional system complexity and cost. Also, the mechanical stirring devices themselves consume power, which is undesirable. Furthermore, with additional complexity comes the potential for system unreliability, thereby shortening the lifetime of the device or requiring servicing at regular intervals.

It is an object of the present disclosure to provide an improved heat storage device for an air conditioning apparatus.

Summary

According to a first aspect of the present disclosure, there is provided a heat storage device for an air conditioning apparatus, the heat storage device comprising: a phase change material, PCM; a plurality of thermally conductive elements; and a heat spreader in thermal contact with the thermally conductive elements, the heat spreader for transferring heat from a heat exchanger of the air conditioning apparatus to the thermally conductive elements, wherein the thermally conductive elements are embedded within the PCM.

The thermally conductive elements transfer heat from the heat spreader into the PCM. By embedding the thermally conductive elements in the PCM, the thermal resistance of heat transfer into the PCM can be reduced, thereby enabling a more efficient transfer of heat from the heat exchanger of the air conditioning apparatus into the PCM. This is because the thermally conductive elements can be arranged to reduce the thickness of PCM through which heat is transferred via conduction. This allows the thermal gradient to be reduced, which in turn reduces the impact on the efficiency of the refrigeration cycle. Heat storage devices according to the first aspect can be considered as a form of ‘thermal battery’ which can be removable in use. This assists in providing a portable air conditioning device that does not require specialist installation or external ducting.

In embodiments, the plurality of thermally conductive elements comprise an array of fins extending from the heat spreader. In this manner, the fin structure provides a thermally conductive path throughout the comparatively insulating PCM, thereby improving the ability of the PCM to absorb heat efficiently.

In embodiments, the array of fins comprises fins having a regular polygonal cross section, such as a honeycomb structure. In embodiments, the honeycomb structure is filled with the PCM. In this manner, the fin structure forms part or all of a mechanical encapsulation for the PCM, which is desirable when the heat storage device is intended to be a removable component of an air conditioning apparatus.

In embodiments, the array of fins comprises a plurality of parallel plate fins. In embodiments, at least some of the parallel plate fins comprise laterally extending projections. The laterally extending projections further reduce the thermal resistance of heat transfer into the PCM.

In embodiments, the heat spreader comprises a planar disc or plate. In embodiments, the array of fins extends from a first face of the heat spreader. In embodiments, a second face of the heat spreader opposite the first face is arranged in use to be in thermal contact with the heat exchanger of the air conditioning apparatus.

In embodiments, the array of fins comprises a plurality of fins extending radially outward from the heat spreader. In embodiments, at least some of the fins comprise laterally extending projections. In embodiments, the heat spreader comprises a curved portion comprising an outer face from which the array of fins extend. In embodiments, the curved portion comprises an inner face arranged in use to be in thermal contact with the heat exchanger of the air conditioning apparatus, which is received concentrically within the heat spreader.

In embodiments, the thermally conductive elements are attached to the heat spreader with brazed joints. In embodiments, the thermally conductive elements are adhered to the heat spreader with thermal adhesive. In embodiments, the fins and the heat spreader are formed as a single extrusion. This allows for a simpler manufacturing process and a more resilient construction of the heat storage device.

In embodiments, the fins are formed of at least one piece of folded material. Forming the fins 304 from a piece of folded material eases the manufacturing process. The folded fins 304 also have a reduced weight and cost. Further, the fins 304 can be manufactured with lower thickness thus improving the overall volumetric efficiency of the heat storage device.

In embodiments, the heat storage device further comprises a casing portion, wherein the casing portion and the heat spreader together form at least part, or all, of a mechanical encapsulation for the PCM.

In embodiments, the casing portion, the heat spreader and the thermally conductive elements together form the mechanical encapsulation for the PCM.

In embodiments, the heat spreader and the thermally conductive elements are formed of metal, such as aluminium.

According to a second aspect of the present disclosure, there is provided an air conditioning apparatus, comprising: the heat storage device of any preceding claim; and a refrigeration circuit comprising a condenser and/or an evaporator heat exchanger, wherein the PCM of the heat storage device is arranged to store heat rejected by the condenser and/or the evaporator.

In embodiments, the air conditioning apparatus further comprises a mechanism arranged to releasably engage with the heat storage device so as to allow the heat storage device to be removed from the air conditioning apparatus. In this manner, when the heat storage device is near or at its maximum heat storage capacity, it can be easily removed from the air conditioning apparatus and replaced with a second heat storage device which has been ‘recharged’, i.e. one in which the PCM is in the solid phase.

According to a third aspect of the present disclosure, there is provided a kit comprising the air conditioning apparatus according to the second aspect and one or more further heat storage devices according to the first aspect.

It should be appreciated that features described in relation to one aspect of the present disclosure may be incorporated into other aspects of the present disclosure.

Description of the Drawings

Embodiments of the present disclosure will now be described by way of example only with reference to the accompanying schematic drawings of which: Figure 1 illustrates a heat storage device for an air conditioning apparatus according to embodiments of the present disclosure;

Figure 2 illustrates a plurality of thermally conductive elements according to the embodiments of Figure 1;

Figure 3 illustrates a heat storage device for an air conditioning apparatus according to embodiments of the present disclosure;

Figure 4 illustrates a plurality of thermally conductive elements according to the embodiments of Figure 3;

Figure 5 illustrates a plurality of thermally conductive elements according to embodiments of the present disclosure;

Figure 6 illustrates a plurality of thermally conductive elements according to embodiments of the present disclosure;

Figure 7 illustrates a heat storage device for an air conditioning apparatus according to embodiments of the present disclosure; and

Figure 8 illustrates a plurality of thermally conductive elements according to the embodiments of Figure 7.

Detailed Description

Figure 1 illustrates a heat storage device 100 for an air conditioning apparatus according to embodiments of the present disclosure. The heat storage device 100 comprises a phase change material (PCM) 102, a plurality of thermally conductive elements 104, and a heat spreader 106 which is in thermal contact with the thermally conductive elements 104. The heat spreader is suitable for transferring heat from a heat exchanger of the air conditioning apparatus, such as a condenser or evaporator coil 108, to the thermally conductive elements 104. Figure 1 is an exploded view, and the thermally conductive elements 104 are embedded within the PCM 102 in use. In use, heat is expelled by the heat exchanger 108 of the air conditioning apparatus which is in thermal contact with the heat spreader 106 of the heat storage device 100, via an interface 110 of the air conditioning apparatus. The expelled heat is then transferred from the heat spreader 106 to the PCM 102 via the thermally conductive elements 104. The structure of the thermally conductive elements 104, and the fact that they are embedded within the PCM 102, provides for efficient transfer of heat into the comparatively thermally insulating PCM 102. This is because the thickness of PCM 102 through which heat is transferred via conduction is minimized, whilst still providing adequate volume for occupation by the PCM 102. In general, air conditioning apparatus (which perform heating and cooling operations) in which heat storage devices 100 according to embodiments of the present disclosure may be used have an interface 110 which is arranged to mate with the heat spreader 106 of the heat storage device 100. For example, the interface 110 may include a mechanism arranged to releasably engage with the heat storage device 100 so as to allow the heat storage device to be removed from the air conditioning apparatus when its heat storage capacity has been reached, and for a further heat storage device to be attached to the air conditioning apparatus for continued cooling operation. The same applies in respect of the heat storage devices according to the embodiments of Figures 3 and 6.

In the embodiments of Figure 1, the plurality of thermally conductive elements 104 comprise an array of fins 104 extending away from the heat spreader 106. The array of fins 104 has a regular polygonal cross section. An example of this is illustrated in cross section in Figure 2, which shows an array of fins 104 comprising a honeycomb structure. The honeycomb structure is filled with the PCM 102. Therefore, with such a fin structure 104, in addition to providing efficient transfer of heat from the heat spreader 106 to the PCM 102, the fins 104 also form at least part of a mechanical encapsulation for the PCM 102, which prevents leakage of the PCM 102 when in a liquid state. In embodiments, the height of the fins 104 (i.e. the extent of the fins in the direction generally perpendicular to the plane of the heat spreader 106) is in the range 150 mm to 250 mm. In embodiments, the wall thickness of the fins 104 is in the range 0.05 mm to 0.20 mm. In embodiments, the effective diameter, or lateral extent, of each honeycomb fin 104 is in the range 5 mm to 20 mm. In embodiments, the overall diameter of the heat storage device 100 is in the range 200 mm to 300 mm.

Figure 3 illustrates alternative embodiments of a heat storage device 300 for an air conditioning apparatus. In these embodiments, the plurality of thermally conductive elements 304 comprise an array of fins 304 extending radially outward from the heat spreader 306. As above, the fins 304 are embedded within the PCM 302. The heat spreader 306 comprises a curved portion comprising an outer face 307, from which the array of fins 304 extend, and an inner face 309 arranged to be in thermal contact with the heat exchanger 308 of the air conditioning apparatus. Specifically, the inner face 309 is arranged to engage with the interface 310 of the air conditioning apparatus heat exchanger. In this manner, the heat exchanger 308 is received concentrically within the heat spreader 306. Figure 4 is a cross section through the heat storage device 300, showing the heat spreader 306 and radially outward extending fins 304. Although not shown, in an alternative embodiment, the heat spreader 306 comprises a curved portion comprising an inner face, from which the array of fins 304 extend, and an outer face arranged to be in thermal contact with the heat exchanger 308 of the air conditioning apparatus.

Figure 5 shows an alternative embodiment of a cross section through the heat storage device 300, showing fins 304 that extend radially outward from the heat spreader 306, the fins 304 are embedded within the PCM 302. The fins 304 are formed of at least one piece of folded material. In embodiments, the fins 304 are formed as a series of folded material returns. In embodiments, the fins 304 are formed of a single piece of folded material. Forming the fins 304 from a piece of folded material eases the manufacturing process. The folded fins 304 also have a reduced weight and cost. Further, the fins 304 can be manufactured with lower thickness thus improving the overall volumetric efficiency of the heat storage device.

With reference to Figure 6, in embodiments at least some of the fins 304 comprise laterally extending projections 314. Such laterally extending projections 314 have been found to further reduce the thermal resistance of heat transfer from the fins 304 to the PCM 302. It should be appreciated that in general there is an optimal density of fins 304 and/or laterally extending projections 314 for a given geometry of the heat storage device 300. This is because although adding more fins 304 and projections 314 per unit volume of the heat storage device 300 may decrease the overall thermal resistance per unit volume, it may come at the expense of reducing the total volume of PCM 302 which the heat storage device 300 can accommodate, thereby affecting its total heat storage capacity.

Figure 7 illustrates alternative embodiments of a heat storage device 600 for an air conditioning apparatus. In this embodiment, the plurality of thermally conductive elements 604 comprise an array of parallel plate fins 604 extending from the heat spreader 606. As above, the fins 604 are embedded within the PCM 602. At least some of the parallel plate fins 604 may comprise laterally extending projections (not illustrated in Figure 6), in a manner similar to that illustrated in Figure 6. In this embodiment, the heat spreader 606 consists of a generally planar disc or plate, whereby the fins 604 extend from a first face 607 of the heat spreader 606. A second face 609 of the heat spreader 606, opposite the first face 607, is arranged in use to be in thermal contact with the heat exchanger 608 of the air conditioning apparatus via an interface 610 of the air conditioning apparatus. Figure 8 is a cross section through the heat storage device 600 of Figure 7, showing the arrangement of the heat spreader 606 and the parallel plate fins 604.

In all of the above described embodiments, the thermally conductive elements (fins) 104, 304, 604 can be attached to the heat spreader 106, 306, 606 with brazed joints or adhered to the heat spreader with thermal adhesive. Alternatively, in the embodiments of Figures 3 and 6, the fins 304, 604 and the heat spreader 306, 606 can be formed as a single extrusion (optionally additionally with the laterally extending projections 314). Certain embodiments include a casing portion 112, 312, 612, which, together with the heat spreader 106, 306, 606, forms at least part of a mechanical encapsulation for the PCM. In embodiments, the heat spreader and the thermally conductive elements are formed of metal, such as aluminium, for example, or any other material having a generally good thermal conductivity compared that of the PCM. Suitable PCMs typically have low thermal conductivity in the order of 0.2 to 0.6 W/mK, such as, for example, RUBITHERM® RT manufactured by Rubitherm Technologies GmbH. Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present disclosure, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the present disclosure that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the present disclosure, may not be desirable, and may therefore be absent, in other embodiments.

Claims

- 8 - Claims

1. A heat storage device for an air conditioning apparatus, the heat storage device comprising: a phase change material, PCM; a plurality of thermally conductive elements; and a heat spreader in thermal contact with the thermally conductive elements, the heat spreader for transferring heat from a heat exchanger of the air conditioning apparatus to the thermally conductive elements, wherein the thermally conductive elements are embedded within the PCM.

2. The heat storage device of claim 1, wherein the plurality of thermally conductive elements comprise an array of fins extending from the heat spreader.

3. The heat storage device of claim 2, wherein the array of fins comprises fins having a regular polygonal cross section.

4. The heat storage device of claim 2 or 3, wherein the array of fins comprises a honeycomb structure.

5. The heat storage device of claim 4, wherein the honeycomb structure is filled with the PCM.

6. The heat storage device of claim 2, wherein the array of fins comprises a plurality of parallel plate fins.

7. The heat storage device of claim 6, wherein at least some of the parallel plate fins comprise laterally extending projections.

8. The heat storage device of any one of claims 2 to 7, wherein the heat spreader comprises a planar disc or plate.

9. The heat storage device of claim 8, wherein the array of fins extends from a first face of the heat spreader. - 9 -

10. The heat storage device of claim 9, wherein a second face of the heat spreader opposite the first face is arranged in use to be in thermal contact with the heat exchanger of the air conditioning apparatus.

11. The heat storage device of claim 2, wherein the array of fins comprises a plurality of fins extending radially outward from the heat spreader.

12. The heat storage device of claim 11, wherein at least some of the fins comprise laterally extending projections.

13. The heat storage device of claim 11 or 12, wherein the heat spreader comprises a curved portion comprising an outer face from which the array of fins extend.

14. The heat storage device of claim 13, wherein the curved portion comprises an inner face arranged in use to be in thermal contact with the heat exchanger of the air conditioning apparatus, which is received concentrically within the heat spreader.

15. The heat storage device of any preceding claim, wherein the thermally conductive elements are attached to the heat spreader with brazed joints.

16. The heat storage device of any preceding claim, wherein the thermally conductive elements are adhered to the heat spreader with thermal adhesive.

17. The heat storage device of claim 6 or 11, wherein the fins and the heat spreader are formed as a single extrusion.

18. The heat storage device of claim 11, wherein the fins are formed of at least one piece of folded material.

19. The heat storage device of any preceding claim, further comprising a casing portion, wherein the casing portion and the heat spreader together form at least part of a mechanical encapsulation for the PCM. - 10 -

20. The heat storage device of claim 19, wherein the casing portion, the heat spreader and the thermally conductive elements together form the mechanical encapsulation for the PCM.

21. The heat storage device of any preceding claim, wherein the heat spreader and the thermally conductive elements are formed of metal.

22. An air conditioning apparatus, comprising: the heat storage device of any preceding claim; and a refrigeration circuit comprising a condenser and/or an evaporator heat exchanger, wherein the PCM of the heat storage device is arranged to store heat rejected by the condenser and/or the evaporator.

23. The air conditioning apparatus of claim 22, further comprising a mechanism arranged to releasably engage with the heat storage device so as to allow the heat storage device to be removed from the air conditioning apparatus.

24. A kit comprising the air conditioning apparatus of claim 22 or 23 and one or more further heat storage devices according to any one of claims 1 to 21.