Compact thermoelastic cooling system

Abstract

A compact cooling system based on thermoelastic effect is provided. In one embodiment, the system comprises a pair of rollers serving as a heat sink, stress applicator and belt drive, a cold reservoir and a solid refrigerant belt coupled to the cold reservoir and to the heat sinks to pump heat from the cold reservoir to the heat sink. The refrigerant belt comprises solid thermoelastic materials capable of thermoelastic effect. The refrigerant material is mechanically compressed when entering the gap of the roller and subsequently released after passing through. When compressed the refrigerant material transforms to martensite phase and releases heat to the roller and neighboring materials. After released by the rollers, the refrigerant material transforms back to austenite and absorbs heat from the ambient atmosphere.

Claims

1. A cooling system, comprising: a pair of rollers driven by a motor, the pair of rollers facing each other with a prescribed gap therebetween; a looped solid refrigerant belt that is sandwiched by the pair of rollers at the prescribed gap in such a stressed and compressed state that a portion of the solid refrigerant belt that comes out from the gap between the rollers transits to a colder thermodynamic state; and a cold reservoir containing a cooling medium, continuously receiving the portion of the solid refrigerant belt that comes out from the gap between the rollers so as to cool the cooling medium by said portion of the solid refrigerant belt, wherein the pair of rollers also receive heat from the solid refrigerant belt when the solid refrigerant belt is at the gap so as to act as a heat sink that is directly contacting the solid refrigerant belt, and wherein the solid refrigerant belt is made of a material capable of exhibiting thermoelastic effect.

2. The system according to claim 1, wherein the solid refrigerant belt releases heat to the pair of rollers as the heat sink when the solid refrigerant belt is at the gap and in thermal contact with the heat sink while the solid refrigerant is being stressed, and the solid refrigerant absorbs heat from the cooling medium in the cold reservoir when the solid refrigerant belt is in thermal contact with the cooling medium in the cold reservoir while said portion of the solid refrigerant belt is being relaxed from the stressed and compressed state.

3. The system according to claim 1, wherein the solid refrigerant belt is made of a unitary and continuous thermoelastic member.

4. The system according to claim 3, wherein the thermoelastic member is made of one of, or a composite of two or more of, Nickel Titanium alloys, Copper Aluminum Nickel, Copper Zinc Nickel, Iron Palladium, Gold Cadium, Nickel Manganese Gallium, or any derivative alloys thereof.

5. The system according to claim 1, wherein the solid refrigerant belt is made of a series of discrete blocks that are thermally disconnected from each other and connected through a connecting member that mechanically connects thermally disconnected individual blocks in a loop.

6. The system according to claim 1, wherein the refrigerant belt includes a composite of polymers that exhibit reversible transition that is associated with absorbing or releasing heat.

7. The system according to claim 1, wherein: the material of thermoelastic refrigerant requires stress to induce reversible a solid to solid phase transition; the heat associated with the transition is greater than 1 J/g; and the temperature at which the material completely transforms to a final high temperature phase without an aid of any external energy is equal or lower than a prescribed target temperature.

8. The system according to claim 3, wherein each of the roller has heat discharging fins on side surfaces thereof for heat exchange between the roller and an ambient environment.

9. The system according to claim 1, wherein the cold reservoir includes an inlet and an outlet for the cooling medium such that the cooling medium flows in a direction opposite to a direction in which the solid refrigerant belt generally moves inside the cold reservoir.

10. A cooling system, comprising: a pair of rollers driven by a motor, the pair of rollers facing each other with a prescribed gap therebetween; a looped solid refrigerant belt that is sandwiched by the pair of rollers at the prescribed gap in such a stressed and compressed state that a portion of the solid refrigerant belt that comes out from the gap between the rollers transits to a colder thermodynamic state; and a cold reservoir containing a cooling medium, continuously receiving the portion of the solid refrigerant belt that comes out from the gap between the rollers so as to cool the cooling medium by said portion of the solid refrigerant belt, wherein the pair of rollers also receive heat from the solid refrigerant belt when the solid refrigerant belt is at the gap so as to act as a heat sink that is directly contacting the solid refrigerant belt, wherein the solid refrigerant belt is made of a material capable of exhibiting thermoelastic effect, and wherein the gap that separates the pair of rollers has a gap dimension that is less than 97% of a thickness of the refrigerant belt so that as the solid refrigerant belt is fed into the gap, the belt is compressed at a strain of 3% or greater.

11. The system according to claim 10, wherein the solid refrigerant belt releases heat to the pair of rollers as the heat sink when the solid refrigerant belt is at the gap and in thermal contact with the heat sink while the solid refrigerant is being stressed, and the solid refrigerant absorbs heat from the cooling medium in the cold reservoir when the solid refrigerant belt is in thermal contact with the cooling medium in the cold reservoir while said portion of the solid refrigerant belt is being relaxed from the stressed and compressed state.

12. The system according to claim 10, wherein the solid refrigerant belt is made of a unitary and continuous thermoelastic member.

13. The system according to claim 12, wherein the thermoelastic member is made of one of, or a composite of two or more of, Nickel Titanium alloys, Copper Aluminum Nickel, Copper Zinc Nickel, Iron Palladium, Gold Cadium, Nickel Manganese Gallium, or any derivative alloys thereof.

14. The system according to claim 10, wherein the solid refrigerant belt is made of a series of discrete blocks that are thermally disconnected from each other and connected through a connecting member that mechanically connects thermally disconnected individual blocks in a loop.

15. The system according to claim 10, wherein the cold reservoir includes an inlet and an outlet for the cooling medium such that the cooling medium flows in a direction opposite to a direction in which the solid refrigerant belt generally moves inside the cold reservoir.

16. A cooling system, comprising: a pair of rollers driven by a motor, the pair of rollers facing each other with a prescribed gap therebetween; a looped solid refrigerant belt that is sandwiched by the pair of rollers at the prescribed gap in such a stressed and compressed state that a portion of the solid refrigerant belt that comes out from the gap between the rollers transits to a colder thermodynamic state; and a cold reservoir containing a cooling medium, continuously receiving the portion of the solid refrigerant belt that comes out from the gap between the rollers so as to cool the cooling medium by said portion of the solid refrigerant belt, wherein the pair of rollers also receive heat from the solid refrigerant belt when the solid refrigerant belt is at the gap so as to act as a heat sink that is directly contacting the solid refrigerant belt, wherein the solid refrigerant belt is made of a material capable of exhibiting thermoelastic effect, wherein the solid refrigerant belt is made of a unitary and continuous thermoelastic member, and wherein each of the roller has a groove to guide and accommodate the solid refrigerant belt so as to create a bigger contact area with the solid refrigerant belt.

17. The system according to claim 16, wherein the solid refrigerant belt releases heat to the pair of rollers as the heat sink when the solid refrigerant belt is at the gap and in thermal contact with the heat sink while the solid refrigerant is being stressed, and the solid refrigerant absorbs heat from the cooling medium in the cold reservoir when the solid refrigerant belt is in thermal contact with the cooling medium in the cold reservoir while said portion of the solid refrigerant belt is being relaxed from the stressed and compressed state.

18. The system according to claim 16, wherein the thermoelastic member is made of one of, or a composite of two or more of, Nickel Titanium alloys, Copper Aluminum Nickel, Copper Zinc Nickel, Iron Palladium, Gold Cadium, Nickel Manganese Gallium, or any derivative alloys thereof.

19. The system according to claim 16 wherein each of the roller has heat discharging fins on side surfaces thereof for heat exchange between the roller and an ambient environment.

20. The system according to claim 16, wherein the cold reservoir includes an inlet and an outlet for the cooling medium such that the cooling medium flows in a direction opposite to a direction in which the solid refrigerant belt generally moves inside the cold reservoir.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a graphical representation of stress-strain relations in a CuAlNi alloy.

(2) FIG. 2 is a graphical representation of the DSC curves of a NiTi alloy.

(3) FIG. 3 is a schematic of a compact thermoelastic cooling system according to an embodiment of the present invention.

(4) FIG. 4 schematically illustrates the process and heat flows when a refrigerant belt passes through the gap between a pair of the rollers of the embodiment depicted in FIG. 3.

(5) FIG. 5 is a thermal image of the refrigerant belt coming out of the compression by a pair of rollers according to the embodiment depicted in FIG. 3.

(6) FIG. 6 is a schematic of a compact thermoeleastic cooling system with details of the refrigerant belt according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENTS

(7) Achieving efficient heat exchange is the key challenge for commercializing the thermoelastic cooling technology because of the following constraints: 1) heat exchange coefficient between the refrigerant and the heat-exchange medium is low, 2) solid refrigerant is mechanically compressed and released periodically, and the heat exchange must be in synchronization with the periodical application of stress, 3) compressive stress is preferred over tensile and torsional stress due to fatigue life concern, 4) solid refrigerant must maintain certain geometric aspect ratio to avoid buckling under compression, 5) higher system operation frequency is preferred for higher system power density. An innovative system design that can balance the above-mentioned constraints is needed to achieve a compact, efficient, and cost-effective thermoelastic cooling system.

(8) The present invention, in one aspect, discloses a compact thermoelastic cooling system that includes a set of rollers, a refrigerant belt made of thermoelastic material, and a cold reservoir containing a heat exchange medium. An embodiment of this system is depicted in FIG. 3.

(9) A pair of rollers 2 is driven by a motor through the shaft 5. The rollers 2 catch and compress a portion of a solid refrigerant belt 1. A belt 1 is inserted into a cold reservoir 6, which is an enclosure for a cooling medium that has an inlet 7 and an outlet 8 for the cooling medium. A system frame 9 is provided to support the shafts 5 and the cold reservoir 6. Each roller 2 has a groove 4 to grab and guide the solid refrigerant belt 1, and is equipped with fin blades 3 on die surfaces of the roller for heat discharge.

(10) With the rotating motion of the rollers, the compressed portion of the refrigerant belt is then released and moved forward. The gap between the rollers is less than the thickness of the refrigerant belt (<97%, for example) so that the belt is compressed when it passes through the rollers such that the refrigerant materials can undergo stress induced phase transformation.

(11) The rollers 2 of the present embodiment have three functions: applying compressive stress to the refrigerant, driving the refrigerant belt forward, and serving as heat sink by absorbing heat generated by the refrigerant belt 1 under compression and dumping the heat to the ambient atmosphere. Because of the large compressive stress, the roller 2 and the refrigerant belt 1 are in intimate contact. The heat transfer between these two intimately contacted metal surfaces is fast enough for the majority of the generated heat to be transferred to the roller if the rolling speed is adequately controlled and not too fast. The roller has high hardness for applying stress and high thermal conductivity for transferring heat.

(12) In this embodiment, the roller has curved fin feature 3 on the side surface to maximize its heat exchange with the ambient atmosphere. The roller surface is grooved (the groove 4) to ensure the refrigerant belt is properly aligned with the roller and to increase the thermal contact area between the rollers 2 and the refrigerant belt 1.

(13) Lubricant coating such Boron Nitride can be applied to the roller to minimize the friction force and to improve heat exchange efficient.

(14) The cold reservoir 6 of the present embodiment contains heat an exchange medium (a cooling medium) such as air or water, and engulfs the cold part of the refrigerant. The cooling medium flows into the cold reservoir 6 through the inlet 7 and flows out to a target space (i.e., the target to be cooled) through the outlet 8, countering against the belt moving direction. The cold reservoir 6 has sufficiently small opening or similar mechanism to limit or prevent water from running out. The various parts of the embodiment of the present invention, as described above, can be constructed from any suitable materials having adequate physical properties/characteristics, such as materials having sufficiently large mechanical strengths and adequate thermal conductivities, etc.

(15) FIG. 4 schematically illustrates the process and heat flows when the refrigerant belt 1 passes through the gap between a pair of the rollers 2 of the embodiment depicted in FIG. 3. When the refrigerant belt 1 passes through the rollers 2, a portion of the refrigerant belt 1 is compressed and transformed to martensite. Latent heat is generated and subsequently dissipated into the neighboring objects. A part of the generated heat Q.sub.1 transfers to the two rollers that are in contact with the transformed materials. As shown in FIG. 4, the rest of the heat transfers within the refrigerant belt: one part Q.sub.2 travels along the belt moving direction, and one part Q.sub.3 travels against the belt moving direction.

(16) As the refrigerant belt 1 moving forward, the portion of the belt that was under compression is now released from compression. It starts to transforms back to austenite and absorbs latent heat from the surrounding atmosphere Q.sub.4 and from neighboring materials Q.sub.2 and Q.sub.5. Since only a part of the previously generated heat Q.sub.2 transfers in the forward direction, the net heat absorbed Q.sub.4+Q.sub.5 is equivalent to Q.sub.1+Q.sub.3. As shown in FIG. 4, because of the net heat absorption, the part of the refrigerant belt immediately coming out of the roller is cold. Similarly, because the net heat accumulation, the part of the refrigerant belt that is about to be fed into the roller is hot. FIG. 5 shows the result of a confirming experiment; that is, a thermal image of a refrigerant belt coming out of the compression by a pair of rollers. It shows a spot on the roller (Sp#1) is colder than roller or the other spot (Sp#2) that is farther away from the roller. This confirm the above-mentioned principle of the operation.

(17) Although the refrigerant belt 1 is physically connected, the thermal conductivity of the belt 1 varies. The part that is under compression by the two rollers is in martensite state. For NiTi, the thermal conductivity of martensite is 86 W/m-K; the parts of the belt that are coming in and coming out of the roller are both stress-free and are in austenite state. The thermal conductivity of austenite NiTi is 180 W/m-K. Because of the lower thermal conductivity of the section that separates the hot and the cold sections of the refrigerant belt, the temperature gradient is sufficiently maintained.

(18) A refrigerant belt made of a continuous thermoelastic material, as described above, has the advantage of being capable of constructing simple systems, but its maximum temperature lift (T) is somewhat limited because of the heat dissipation from the transforming neighbor materials. In another embodiment, a refrigerant belt made of discrete thermoelastic materials may be used. This allows pulse operation, which may maximize heat exchange between the rollers and the refrigerant by prolonging the duration of the compression. Once the heat generated by compressing the refrigerant into martensite is mostly transferred to the rollers, the refrigerant reaches the lowest temperature when in martensite state. This lowest temperature enables the refrigerant to exhibit maximum temperature lift. However, a discrete refrigerant belt implies engineering complexity, lower system reliability, and higher cost. Thus, a design choice can be made by balancing the cons and pros of both types of the belt.

(19) Embodiments of the present invention, as described above, address the need of new cooling technology that is affordable, highly efficient, and environmental friendly. For example, in one aspect, the present invention can be applied to construct a relatively compact thermoelastic cooling system using a set of rollers to continuously apply compressive stress to the solid refrigerant belt and extract heat from the solid refrigerant belt, as shown in FIG. 3.

(20) The refrigerant belt 1 may have rectangular, circular, or elliptical cross-section. Further, the refrigerant belt may loop around the roller more than one turn in some embodiments.

(21) In the embodiments, as described above, the part of the refrigerant belt just released from the compression of the rollers is cold while the part that is about to be compressed by the rollers is hot. The hot part of the refrigerant belt and the rollers exchange heat with ambient air; while the cold part of the refrigerant belt exchange heat with the medium in the cold reservoir. The medium may be water or other environmental friendly heat exchange medium.

(22) In the present embodiment, as shown in FIG. 6, the refrigerant belt 1 may be constructed of a series of blocks 11 of thermoelastic materials. The blocks 11 are linked through a certain mechanical member, such as a connecting member 10, allowing forward driving motion of the whole belt, but maintaining individual thermal characteristics during the phase transformation.

(23) Another embodiment of the invention is a thermoelastic cooling system for dehumidification (i.e., a dehumidifier). The cold part of the refrigerant belt has a temperature below dew point and its cold surface is in contact with ambient air. Water condenses on the cold surface and collected by the rollers during compression.

(24) It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations that come within the scope of the appended claims and their equivalents. In particular, it is explicitly contemplated that any part or whole of any two or more of the embodiments and their modifications described above can be combined and regarded within the scope of the present invention.