ELASTOCALORIC SYSTEM AND METHOD OF OPERATION

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 63/707,025, entitled ELASTOCALORIC SYSTEM AND METHOD OF OPERATION, filed on Oct. 14, 2024, U.S. Provisional Patent Application No. 63/707,031, entitled ELASTOCALORIC SYSTEM AND METHOD OF OPERATION, filed on Oct. 14, 2024, U.S. Provisional Patent Application No. 63/708,486, entitled ELASTOCALORIC SYSTEM AND METHOD OF OPERATION, filed on Oct. 17, 2024 and U.S. Provisional Patent Application No. 63/708,494, entitled ELASTOCALORIC SYSTEM AND METHOD OF OPERATION, filed on Oct. 17, 2024, the entire disclosures of which are incorporated by reference herein.

GOVERNMENT LICENSE RIGHTS

One or more of the inventions disclosed herein were made with government support under Contract No. W5170122C0101 awarded by the U.S. Army Research Laboratory. The government has certain rights in these invention. One or more of the inventions disclosed herein were made with government support under Prime Contract No. 80NSSC24K0280 awarded by the National Aeronautics and Space Administration. The government has certain rights in these inventions.

BACKGROUND

The development of elastocaloric cooling to date has primarily been focused on the use of either tension or compression to cause uniaxial stress and, accordingly, to cause the requisite phase changes. A key obstacle to the development of elastocaloric cooling has been the amount of force needed to produce this stress and, correspondingly, the need for bulky and expensive actuators to generate such force. A recent break-through by scientists at the Army Research Lab uses axisymmetric bending to reduce the actuation force by a factor of 7 while improving efficiency and producing sufficiently large temperature changes.

Follow-on studies demonstrated the ability to operate a continuous bending-mode elastocaloric cooling loop, but these suffered from difficulty of creating a loop joint with sufficient fatigue resistance, inadequate heat exchange to/from the SMA, and insufficient temperature lift. The entire disclosure of U.S. Pat. No. 11,204,189, entitled CONTINUOUS BENDING-MODE ELASTOCALORIC COOLING/HEATING FLOW LOOP, which issued on Dec. 21, 2021 is incorporated by reference herein. The inventions disclosed herein solve these three problems with, among other things, a reciprocating roller design, microchannel heat exchangers, and a novel form of active elastocaloric regeneration (AR).

SUMMARY

In one form, the invention comprises an elastocaloric cooling system comprising an elastocaloric material, a heat exchanger comprising a heat exchange surface, and a motor operable in forward and reverse to cyclically drive the elastocaloric material against the heat exchange surface to reciprocatingly cause strain within the elastocaloric material creating repeated first phase transformations in the elastocaloric material. The heat exchanger is configured to transfer exothermic latent heat emitted from the elastocaloric material due to the first phase transformations and the heat exchanger is configured to transfer endothermic latent heat from an ambient environment adjacent to the elastocaloric material when the motor is operated in reverse.

In one form, the invention comprises a method of cooling comprising providing an elastocaloric material, applying a force on the elastocaloric material in a reciprocating manner to cause mechanical deformation of the elastocaloric material, wherein the mechanical deformation creates a solid-to-solid phase transformation in the elastocaloric material, emitting exothermic latent heat from the elastocaloric material to increase a temperature of the elastocaloric material, removing the force from the elastocaloric material, and absorbing endothermic latent heat into the elastocaloric material to decrease the temperature of the elastocaloric material.

In one form, the invention comprises an article of clothing configured to be worn by a person comprising an elastocaloric material, a first heat exchanger comprising a first heat exchange surface configured to come into contact with the person, a second heat exchanger comprising a second heat exchange surface, wherein the first heat exchanger and the second heat exchanger are in fluid communication with one another, and a motor operable in forward and reverse to cyclically drive the elastocaloric material against the second heat exchange surface to reciprocatingly cause strain within the elastocaloric material creating repeated phase transformations in the elastocaloric material, wherein the second heat exchanger is configured to transfer exothermic latent heat emitted from the elastocaloric material due to the phase transformations, and wherein a temperature lift is created between the first heat exchanger and the second heat exchanger when the motor is operated in reverse that transfers endothermic latent heat from the person wearing the article of clothing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fluid path diagram of an elastocaloric heat exchange system including an elastocaloric material;

FIG. 2A illustrates a refrigeration cycle;

FIG. 2B depicts an elastocaloric cycle of an elastocaloric material used in the elastocaloric heat exchange system of FIG. 1;

FIG. 2C illustrates a refrigeration cycle with flow-reversing active regeneration using the elastocaloric material of FIG. 2B;

FIGS. 3A-3D illustrate the elastocaloric heat exchange system of FIG. 1 which comprises a roller including a fluid passage defined therein, a elastocaloric element mounted to the roller, and a heat exchanger ring, wherein the roller is rotated in a first direction to wind the elastocaloric element around the roller to transfer heat from the elastocaloric element to the roller (and the fluid flowing within the fluid passage defined in the roller), and wherein the roller is rotated in a second, or opposite, direction to unwind the elastocaloric element from the roller to transfer heat from the heat exchanger ring to the elastocaloric element;

FIGS. 4-6 illustrate another embodiment of an elastocaloric heat exchange system comprising four rollers—each roller including a fluid passage defined therethrough, first and second elastocaloric elements mounted to each roller, and a heat exchanger ring, wherein each roller is rotated in a first direction to wind the first elastocaloric element therearound and unwind the second elastocaloric element into contact with the heat exchanger ring, and wherein each roller is rotated in a second, or opposite, direction to unwind the first elastocaloric element into contact with the heat exchanger ring and wind the second elastocaloric element therearound;

FIG. 7 illustrates an interface between the elastocaloric element and the heat exchanger ring of FIGS. 3A-3D;

FIGS. 8A-8G illustrate another embodiment of an elastocaloric heat exchange system comprising a stacked configuration;

FIG. 9 is a schematic representation of the elastocaloric heat exchange system of FIGS. 8A-8E;

FIGS. 10A-10B depict thermodynamic properties of an elastocaloric heat exchange system;

FIG. 11 depicts the durability of various elastocaloric elements;

FIG. 12 is a diagram depicting the cooling capacity of an elastocaloric heat exchange system;

FIG. 13 is a schematic of a reciprocating drive mechanism;

FIG. 14 illustrates an active magnetic regenerator;

FIG. 15 illustrates an elastocaloric heat exchange system comprising a plurality of rollers, each roller including a fluid passage defined therein having an inlet and an outlet, elastocaloric elements mounted to the roller, a reciprocatable drive element meshingly engaged with the roller configured to reciprocatingly rotate the roller, a heat exchanger ring comprising slots defined therein within which the elastocaloric elements are positionable, an inlet manifold in fluid communication with the roller inlet and a cooling heat exchanger, and an outlet manifold in fluid communication with the roller outlet and a heat sink heat exchanger;

FIG. 16 is a cross-sectional perspective view of the roller and the heat exchanger ring of FIG. 15;

FIG. 17 is a perspective view of the roller of FIG. 15;

FIG. 18 is a cross-sectional view of the roller of FIG. 15 illustrating the fluid passage defined therein; and

FIG. 19 is another cross-sectional view of the roller of FIG. 15 highlighting the inlet and outlet of the fluid passage illustrated in FIG. 18.

DETAILED DESCRIPTION

A conventional vapor compression refrigeration cycle 100 is illustrated in FIG. 2A. A compressor 110 of the vapor compression cycle 100 is operable to transfer heat Q from one environment, via an evaporator 120, to another environment, via a condenser 130. In many instances, the evaporator 120 is positioned in an environment, such as a house or an office building, for example, that is to be cooled. The efficiencies of such vapor compression refrigeration cycles, however, can be limited and many refrigerants used in such vapor compression refrigeration cycles can have various environmental issues. By way of comparison, an elastocaloric heat exchange system 1000 is illustrated in FIG. 1 and FIG. 2C. As discussed below, referring to FIG. 2C, the heat exchange system 1000 is configured to repeatedly bend and release one or more elastocaloric elements 1300 to transfer heat Q from one environment, via an evaporator 1500, to another environment, via a condenser 1600, for example. In at least one embodiment, as also discussed below, the heat exchange system 1000 is integrated into a wearable device, such as an article of clothing, for example.

Further to the above, the elastocaloric heat exchange system 1000 comprises a drive system 1400 and hot heat exchange (HHX) rollers 1100 that are rotated by the drive system 1400. FIG. 13 illustrates a reciprocating drive system 1400 that rotates the rollers 1100 in a back-and-forth manner. The elastocaloric heat exchange system 1000 further comprises elastocaloric elements 1300 mounted to the rollers 1100 that are wound around the rollers 1100 when the rollers 1100 are rotated in one direction, as illustrated in FIG. 3A, and unwound from the rollers 1100 when the rollers 1100 are rotated in an opposite direction, as illustrated in FIG. 3C. Owing to a solid-to-solid phase change of the elastocaloric elements 1300 when the elastocaloric elements 1300 are wound around the rollers 1100, referring to FIG. 3B, heat is released from the elastocaloric elements 1300 into the rollers 1100. The transformation of the elastocaloric material, or materials, in the elastocaloric elements in such instances is depicted in FIG. 2B. As discussed in greater detail below, each roller 1100 has a fluid passage 1140 defined therein and a fluid flowing through the fluid passages 1140 can absorb heat from the rollers 1100. When the rollers 1100 are rotated in the opposite direction and the elastocaloric elements 1300 unwind from the rollers 1100, referring to FIG. 3C, the solid-to-solid phase change in the elastocaloric elements 1300 is reversed and the elastocaloric elements 1300 absorb heat from a cold heat exchanger CHX 1200, as illustrated in FIG. 3D. The transformation of the elastocaloric material, or materials, in the elastocaloric elements in such instances is also depicted in FIG. 2B. The cold heat exchanger 1200 is in the shape of a ring 1210 having an annular fluid passage 1240 defined therein. That said, the cold heat exchanger 1200 can comprise any suitable shape. Further to the above, the elastocaloric elements 1300 contact the ring 1210 when the elastocaloric elements 1300 are unwound from the rollers 1100 and absorb heat from the fluid flowing in the fluid passage 1240 of the ring 1210. In this way, heat is transferred from the cold heat exchanger ring 1210 to the rollers 1100 via the elastocaloric elements 1300.

Further to the above, FIGS. 3A-3D depict the winding and unwinding of an elastocaloric element 1300. As can be seen in FIG. 3A, further to the above, the elastocaloric element 1300 is being wound around a roller 1100. The elastocaloric element 1300 has a first end pinned to the roller 1100 such that the roller 1100 pulls the elastocaloric element 1300 when the roller 1100 is rotated in its winding direction by the drive system 1400. The elastocaloric element 1300 also has a second end pinned to the ring 1210 and, to accommodate the winding of the elastocaloric element 1300 around the roller 1100, the drive mechanism 1400 also rotates the ring 1210 about a central axis to bring the pinned connection between the elastocaloric element 1300 and the ring 1210 closer to the roller 1100. As discussed above, such winding causes a solid-to-solid phase transition of the material comprising the elastocaloric element 1300 which releases heat from the elastocaloric element 1300 that is primarily absorbed by the roller 1100. As can be seen in FIG. 3B, the roller 1100 comprises internal microchannels 1140 defined therein which comprise a fluid inlet and a fluid outlet. In use, a coolant, such as water, for example, flows through the fluid inlet and into the microchannels 1140 defined in the roller 1100, absorbs heat from the roller 1100, and flows through the fluid outlet into a heat exchange circuit, as illustrated in FIG. 1. As can be seen in FIG. 3C, the rotation of the roller 1100 and the ring 1210 are reversed by the drive system 1400 to unwind the elastocaloric element 1300 from the roller 1100. In such instances, the elastocaloric element 1300 comes into contact with the ring 1210 and remains in a somewhat curved configuration as it unwinds. As the elastocaloric element 1300 unwinds, referring now to FIG. 3D, the solid-to-solid phase change in the material of the elastocaloric element 1300 is reversed which causes the elastocaloric material, or materials, of the elastocaloric element 1300 to absorb heat from its surrounding environment, but especially the ring 1210 of the cold heat exchanger 1200. Such a process is repeated to pump heat from the fluid in the cold heat exchanger 1200 to the hot heat exchanger rollers 1100.

Similar to the roller 1100, the ring 1210 comprises internal microchannels 1240 defined therein comprising a fluid inlet and a fluid outlet wherein a coolant, such as water, for example, flows through the fluid inlet and into the microchannels 1240 defined therein. Referring again to FIG. 1, the fluid passages through the roller 1100 and the ring 1210 are part of the same heat exchange circuit and the fluid flowing through the roller 1100 flows through the ring 1210 and then back into the roller 1100. That said, other embodiments are envisioned in which the roller 1100 and the ring 1210 are part of different discrete heat exchange systems that are not in fluid communication with other another.

A partial cross-sectional view of the ring 1210 of the cold heat exchanger 1200 is illustrated in FIG. 7. The ring 1210 comprises an inner surface, an outer surface, and a radial thickness defined between the inner surface and the outer surface. The inner surface of the ring 1210 is defined by a copper ring 1230 positioned within an annular recess 1220 defined in the inner surface of the ring 1210 and, when the elastocaloric element 1300 comes into contact with the ring 1210, the elastocaloric element 1300 predominantly, if not exclusively, contacts the ring 1210 by way of the copper ring 1230. As illustrated in FIG. 7, the copper ring 1230 comprises an inner surface that is directly contacted by the elastocaloric element 1300 and an outer surface that forms at least one sidewall of the channels 1240 defined in the ring 1210 such that the fluid flowing within the channels 1240 directly contacts the copper ring 1230. Owing to the direct contact between the copper ring 1230 and both the elastocaloric element 1300 and the fluid, the heat transfer between the elastocaloric element 1300 and the fluid can be highly efficient. That said, embodiments are envisioned in which the ring 1210 comprises a structural support positioned intermediate the copper ring 1230 and the fluid, for example. Moreover, the copper ring 1230 can be comprised of pure copper, brass, and/or bronze, for example. In various embodiments, the copper ring 1210 comprises an alloy of copper, silver, aluminum, zinc, and/or tin, for example. In at least one embodiment, the copper ring 1210 is electroplated with silver and/or a silver alloy, for example. In other embodiments, a ring comprised of silver and/or a silver alloy can be used in addition to or in lieu of the copper ring 1210, for example. In various embodiments, a ring comprised of aluminum and/or an aluminum alloy can be used in addition to or in lieu of the copper ring 1210, for example.

An elastocaloric heat exchange system 2000 is illustrated in FIGS. 4-6 and is similar to the elastocaloric heat exchange system 1000 in many respects. The elastocaloric heat exchange system 2000 comprises a reciprocating drive system and hot heat exchange rollers 2100 that are rotated by the drive system in a back-and-forth manner. The elastocaloric heat exchange system 2000 further comprises elastocaloric elements 2300 mounted to the rollers 2100 that are, in such instances, wound around, and unwound from, the rollers 2100. Notably, each roller 2100 of the elastocaloric heat exchange system 2000 has a body including fluid channels defined therein and two elastocaloric elements 2300 mounted thereto. Similar to the elastocaloric elements 1300, each elastocaloric element 2300 comprises an end that is pinned to a roller 2100 at a pin joint 2135. Moreover, the elastocaloric heat exchange system 2000 further comprises a cold heat exchanger 2200. Similar to the cold heat exchanger 1200, the cold heat exchanger 2200 is in the shape of a ring 2210 having one or more annular fluid passages defined therein. That said, the cold heat exchanger 2200 can comprise any suitable shape. Further to the above, the elastocaloric elements 2300 contact the ring 2210 when the elastocaloric elements 2300 are unwound from the rollers 2100 and absorb heat from the fluid flowing in the fluid passages of the ring 2210. In this way, heat is transferred from the cold heat exchanger ring 2210 to the rollers 2100 via the elastocaloric elements 2300. Similar to the elastocaloric elements 1300, each elastocaloric element 2300 comprises an end that is pinned to the ring 2210 at a pin joint 2235.

As discussed above, referring again to FIGS. 4-6, two elastocaloric elements 2300 are mounted to each roller 2100. When a roller 2100 is rotated in one direction, i.e., STATE A, one of elastocaloric elements 2300 mounted thereto is wound around the roller 2100 while the other elastocaloric element 2300 mounted thereto is unwound from the roller 2100. In such instances, as a result, one of the elastocaloric elements 2300 is moved out of contact with the ring 2210 and the other elastocaloric element 2300 is moved into contact with the ring 2210. Moreover, in such instances, the elastocaloric 2300 element being wound around the roller 2100 transfers heat to the roller 2100 while the elastocaloric element 2300 being unwound from the roller 2100 absorbs heat from the ring 2210. When the rotation of the rollers 2100 is reversed, i.e., STATE B, the function of each elastocaloric element 2300 is reversed. For instance, the elastocaloric element 2300 that was being wound around the roller 2100 and transferring heat to the roller 2100 is unwound from the roller 2100 and absorbs heat from the ring 2210 and, correspondingly, the elastocaloric element 2300 that was in contact with and absorbing heat from the ring 2210 is would around the roller 2100 and transfers heat to the roller 2100. Such a process is repeated in a reciprocating manner as the elastocaloric heat exchange system 2000 is cycled between STATE A and STATE B.

Further to the above, referring again to FIGS. 4-6, the elastocaloric heat exchange system 2000 is depicted in two stages-STATE A which represents full rotation in a first direction and STATE B which represents full rotation in a second, or opposite, direction. In use, the elastocaloric heat exchange system 2000 is reciprocated back and forth between STATE A and STATE B by a reciprocating drive mechanism to pump heat from the fluid flowing through the cold heat exchanger 2200 to the fluid flowing through the rollers 2100. In various embodiments, a stepper motor, for example, can be used to rotate the rollers 2100 in a reciprocating manner between STATE A and STATE B; however, any suitable mechanism could be used. See, for instance, the mechanism depicted in FIG. 13. In various instances, a full cycle of the elastocaloric heat exchange system 2000 can comprise going from STATE A to STATE B and then back to STATE A again. Such a cycle can comprise one period and the elastocaloric heat exchange system 2000 can be cycled at a constant frequency, for example, and/or at different frequencies depending on the amount of heat transfer that is desired. For instance, the elastocaloric heat exchange system 2000 can be cycled at a faster frequency to pump more heat and/or at a lower frequency to pump less heat.

An elastocaloric heat exchange system 3000 is illustrated in FIGS. 8A-8G and 9 and is similar to the elastocaloric heat exchange systems 1000 and 2000, discussed above, in many respects. Referring primarily to FIGS. 8A, 8C, and 8D, the elastocaloric heat exchange system 3000 comprises hot heat exchange rollers 3100 and cold heat exchangers 3200 that are arranged in layers. Each layer comprises a cold heat exchanger 3200 which, similar to the cold heat exchangers 1200 and 2200, is in the shape of a ring. That said, the cold heat exchanger 3200 can comprise any suitable shape. Each layer also comprises eight hot heat exchange rollers 3100, each having an elastocaloric element 3300 (FIG. 9) mounted thereto. That said, each layer can comprise any suitable number of hot heat exchange rollers 3100 and any suitable number of elastocaloric elements 3300 mounted thereto in various other embodiments. Referring to FIGS. 8C and 8D, the layers of the elastocaloric heat exchange system 3000 are stacked intermediate adjacent manifolds 3700. For instance, five layers of the elastocaloric heat exchange system 3000 are positioned intermediate adjacent manifolds 3700 to create sub-stacks. That said, any suitable number layers can be present in a sub-stack. Referring primarily to FIG. 8D, the manifolds 3700 are in fluid communication with the evaporator 1500 and the condenser 1600 of a refrigeration circuit, via conduits, or pipes, 3800.

Similar to the cold heat exchangers 1200 and 2200, referring again to FIGS. 8C and 8D, each cold heat exchanger 3200 comprises a fluid inlet, a fluid outlet, and channels fluidically connecting the fluid inlet and the fluid outlet. For each sub-stack of layers, the cold heat exchangers 3200 of the sub-stack are concentrically aligned and arranged along a longitudinal axis such that the channels in the cold heat exchangers 3200, via their respective fluid inlets and outlets, define a continuous fluid path between adjacent manifolds 3700. Moreover, the hot heat exchange rollers 3100 of each sub-stack are positioned and arranged such that they are stacked on top of one another. For instance, each sub-stack of the elastocaloric heat exchange system 3000 comprises eight columns of roller stacks, each roller stack having five hot heat exchange rollers 3100 included therein. By way of example, a roller stack including two hot heat exchange rollers 3100 is illustrated in FIGS. 8B and 8E. As discussed in greater detail below, each roller stack of a sub-stack defines a fluid path between adjacent manifolds 3700. Moreover, the fluid paths of each roller stack in a sub-stack are in fluid communication with one other via the manifolds 3700 that define the sub-stack; however, the fluid paths through the roller stacks are not in fluid communication with the fluid path extending through the cold heat exchangers 3200 in the layers of the sub-stack and/or in the manifolds 3700 that define the sub-stack. Rather, the fluid paths through the roller stacks are separately defined from the fluid path through the cold heat exchangers 3200 in the layers of the sub-stack and in the manifolds 3700 that define the sub-stack.

Further to the above, referring again to FIGS. 8A-8E, the elastocaloric heat exchange system 3000 comprises a reciprocating drive system 1400 that rotates the hot heat exchange rollers 3100 and the cold heat exchangers 3200 in a back-and-forth manner. The rotation of the rollers 3100 and the cold heat exchangers 3200 is synchronized such that rollers 3100 and the cold heat exchangers 3200 rotate a predetermined ratio. In at least one such instance, the rollers 3100 turn at 4 times the rate as the cold heat exchangers 3200, for example. Referring primarily to FIGS. 8B and 8E, each roller 3100 comprises a conduit body 3110 and a gear body 3120 mounted thereto such that the conduit body 3110 and the gear body 3120 rotate together. In at least one embodiment, the conduit body 3110 and the gear body 3120 are fastened together by one or more fasteners, for example. The gear body 3120 comprises an annular array of teeth 3125 extending therearound that is intermeshed with an annular array of teeth defined on a cold heat exchanger 3200. As a result of this arrangement, the drive mechanism 1400 can rotate the rollers 3100 and the rotation of the rollers 3100 can drive the cold heat exchangers 3200. In other embodiments, the drive mechanism 1400 can rotate the cold heat exchangers 3200 and the rotation of the cold heat exchangers 3200 can drive the rollers 3100.

As discussed above, each layer of the elastocaloric heat exchange system 3000 comprises a cold heat exchanger ring 3200 and eight hot heat exchange rollers 3100. When the elastocaloric heat exchange system 3000 is rotated in a first direction, four of the heat exchange rollers 3100 wind their elastocaloric elements 3300 attached thereto while the other four heat exchange rollers 3100 unwind their elastocaloric elements 3300. When the elastocaloric heat exchange system 3000 is rotated in a second, or opposite, direction, further to the above, the rotation of the rollers 3100, and the winding and unwinding of the elastocaloric elements 3300, is reversed. In various embodiments, all of the layers of the elastocaloric heat exchange system 3000 are driven by a common drive system 1400, for example. That said, other embodiments are envisioned in which one or more sub-stacks of the elastocaloric heat exchange system 3000 are driven by a first drive system and one or more sub-stacks of the elastocaloric heat exchange system 3000 are driven by a second drive system, for example.

Further to the above, each roller 3100 has an aperture 3130 defined therein that is configured to receive the conduit body 3110 of an adjacent roller 3100 stacked thereunder. Positioned intermediate the stacked rollers 3100 is a bushing 3135 configured to permit relative rotation between the stacked rollers 3100. In various instances, the bushing 3135 is comprised of copper, brass, and/or bronze, for example, and/or any other suitable material. In other embodiments, the stacked rollers 3100 can be locked together such that they rotate together. In any event, a mounting pad 3115 is positioned intermediate the stacked rollers 3100 that is configured to support and space the stacked rollers 3100.

Further to the above, each roller 3100 comprises a bearing 3170 defined thereon that is configured to contact and support an elastocaloric element 3300, as described above, such that heat can be efficiently transferred from the elastocaloric element 3300 to the roller 3100. The bearing 3170 can be comprised of pure copper, brass, and/or bronze, for example. In various embodiments, the bearing 3170 comprises an alloy of copper, silver, aluminum, zinc, and/or tin, for example. In at least one embodiment, the bearing 3170 is electroplated with silver and/or a silver alloy, for example. In other embodiments, a bearing comprised of silver and/or a silver alloy can be used in addition to or in lieu of the bearing 3170, for example. In various embodiments, a bearing comprised of aluminum and/or an aluminum alloy can be used in addition to or in lieu of the bearing 3170, for example.

Further to the above, a fluid path extends through the conduit body 3110 of each roller 3100. The fluid path comprises a fluid inlet 3180 in communication with the aperture 3130 and a fluid outlet 3190 at the top of the conduit body 3110. Interconnecting the fluid inlet 3180 and the fluid outlet 3190 is a fluid channel 3185 defined between the bearing 3170 and the conduit body 3110. To enclose the fluid channel 3185, the roller 3100 further comprises a seal cap 3160 engaged with the conduit body 3110 and one or more sealants, for example, that can be used to seal the seams between the conduit body 3110, the seal cap 3160, and the bearing 3170. Moreover, each roller 3100 further comprises a seal 3140, such as an o-ring, for example, mounted on the conduit body 3110 that is configured to sealingly engage the sidewalls of an aperture 3130 of a roller 3100 stacked thereon. As a result of this sealed arrangement, fluid can flow through the stacked rollers 3100 as described above.

As discussed above, the reciprocating drive of the elastocaloric heat exchange system 1000, 2000, and/or 3000 is configured to reverse the rotation of the hot heat exchange rollers and the cold heat exchanger rings. In use, the reciprocating drive rotates the rollers and the rings in one direction, stops the rotation of the rollers and the rings, and then reverses the rotation of the rollers and the rings in an opposite direction. Thereafter, the reciprocating drive stops the rotation of the rollers and the rings and repeats the process. In various embodiments, the reciprocating drive system holds the rollers and the rings in their stopped positions. In such embodiments, the rollers and the rings are held in a dwell for a sufficient period of time such that the above-discussed heat transfer between the elastocaloric elements, the rollers, and the rings has time to occur before reversing the rotation of the rollers and the rings. In other embodiments, the reciprocating drive does not hold the rollers and the rings in a dwell.

In various embodiments, further to the above, the elastocaloric heat exchange system 1000, and/or any of the elastocaloric heat exchange systems disclosed herein, such as the elastocaloric heat exchange systems 2000 and/or 3000, for example, are embedded into a wearable article. In at least one embodiment, the wearable article comprises a wristband, for example. In at least one such embodiment, the evaporator 1500 of the heat exchange system 1000, for example, comprises a heat exchange surface configured to contact the volar side, or palm side, of a person's wrist which places the evaporator 1500 adjacent their radial and ulnar arteries. In use, as a result, the wristband can quickly cool the person. Moreover, in at least one embodiment, the wearable article comprises an article of clothing, such as a shirt, for example. In at least one such embodiment, the shirt comprises an inner surface and an outer surface and a heat exchange surface of the evaporator 1500 is positioned on, or is otherwise formed with, the inner surface of the inner surface of the shirt. In at least one such embodiment, the evaporator 1500 is positioned in the collar of a shirt which places the evaporator 1500 adjacent the carotid and vertebral arteries of the person wearing the shirt, for example.

Further to the above, elastocaloric heat pumps rely on Shape Memory Alloys (SMA) undergoing a phase change (i.e., a change in their internal molecular structure) based on a change in stress. In at least one example, FIG. 2B illustrates the interplay between stress and heat during the operation of a single stage elastocaloric heat pump and the vapor compression cycle analogue illustrated in FIG. 2A.

Further to the above, a metric that has emerged in elastocaloric system design is fatigue life. The number of loading cycles the SMA can endure is proportional to the useful product life of an elastocaloric air conditioner according to Equation 1, reproduced below, where N_f is cycles to failure, f is cycle frequency (cycles/second), and K is operational lifetime in hours. It is believed that commercially-available high-purity Nitinol (NiTi) is capable of surviving over ten million loading cycles under certain loading conditions. By way of example, FIG. 11 shows cycles to failure as a function of strain amplitude for NiTi under a cyclic bending load. In this example, all high-purity grade NiTi samples survived ten million cycles with a 3% mean strain and 2% strain amplitude. To reproduce these strains in another device, we use Equation 2 to determine radius of curvature p for a given NiTi sample thickness/to achieve strain Emax.

L = N f 3600 ⁢ f Equation ⁢ 1 ϵ max = t 2 ⁢ ρ Equation ⁢ 2

With continued reference to FIG. 11, a comparison of typical vs. high purity nitinol is depicted. Specimens were Z-shaped 0.5 mm diameter wire electropolished after shape setting. The fatigue test was conducted at a 20 Hz cycle rate in a 37° C. water bath. None of the five high-purity grade specimens fractured at 2.0% alternating strain. Filled symbols represent test samples that fractured, whereas open symbols represent those samples which survived the corresponding number of fatigue cycles.

By bending commercially-available Nitinol (NiTi) SMA instead of stretching or compressing it, scientists at the Army Research Lab demonstrated a temperature reduction up to 11.3° C. (20° F.), material coefficients of performance up to 50% Carnot (2.31-21.71 depending on temperature lift), and a 6.09- to 7.75-fold reduction in required actuation force compared to uniaxial tension, in at least one instance. The reduction in required actuation force allows the technology to scale to much smaller applications than would be possible with uniaxial tension or compression, such as personal cooling devices, window-sized AC units, and IECUs.

With reference to FIGS. 10A-10B and the example provided above, a 4% max strain corresponds to a 2% alternating strain with 2% mean strain (i.e., 0% to 4% range). Under these conditions, in one instance, the SMA evaluated changed temperature by about 7.5° C., corresponding to a latent heat of 3.23 J/g. The experiment, in this instance, also found that the hysteresis work from bending the samples to 4% and unbending to 0% was about 0.5 J/g.

Further to the embodiments provided herein, we achieve superior heat exchange with the SMA by building microchannel heat exchangers into the surface of the reels. Water flowing through the channels is in the laminar regime, characterized by relatively low flow rates and minimal mixing. In laminar flow, the convection heat transfer coefficient, h, becomes inversely proportional to the hydraulic diameter of the channel, D_H. These relationships are described in Equation 3, provided below, where A_C is the area of the channel cross-section perpendicular to flow and P is the perimeter of that cross section, and Equation 4, provided below, where k is the thermal conductivity of the channel wall. A benefit of microchannels is that reducing the diameter of the channel improves both heat transfer as well as compactness of the unit. Whereas channels with truly micro-scale dimensions can be difficult to manufacture, our feasibility study showed that 0.25 mm (0.01″) deep channels are small enough to achieve excellent heat transfer.

D H = 4 ⁢ A c P Equation ⁢ 3 h ∝ k D H Equation ⁢ 4

We imagine a method of arranging the cycles in a compact enough manner to meet a 0.54 W/in³ cooling capacity per unit volume requirement.

First, in one embodiment, we roll up the microchannel heat exchangers into a cylindrical shape and choose the roller radius based on Equation 2, so that forcing a 0.04″ thick NiTi element against the roller surface will produce the required 2% strain amplitude. We affix the ends of each NiTi element to the rollers and arrange the rollers so that the SMA is unable to fully relax when being transferred from roller to roller. For instance, setting the “hot” roller diameter to 0.85″ and the “cold” roller diameter to 5.46″ produces a strain of 4.7% and 0.7%, respectively, providing a mean strain of 2.7% in our 0.04″ thick SMA samples. In this way, we approximate loading conditions that we believe can achieve ten million fatigue cycles. An elastocaloric refrigeration cycle is achieved as shown in FIGS. 3A-3D.

The concept shown in FIGS. 8A-8E packs four parallel AR cycles into a 6.27″ diameter ring, for example. In this example, each roller carries a 2.62″ NiTi element, so to obtain 13.1″ total NiTi length we stack 5 rings, each at 0.64″ thickness. This five-ring stack, in this example, has a volume of 98.8 in³ and a cooling capacity of 57.2 W. Moreover, in this example, the resulting cooling capacity per unit volume of 0.58 W/in³ exceeds a target cooling capacity density requirement.

In various instances, producing a 20° C. temperature drop requires amplifying the 7.5° C. SMA temperature change. Active regeneration (AR) is a method that has been used successfully to scale the temperature drop and cooling capacity of elastocaloric refrigeration. We employ microchannel heat exchanger technology to minimize thermal resistance between our working fluid (water) and the SMA, as shown in FIG. 7. Copper or aluminum serves as a thermally conductive interface between the SMA and the fluid in the microchannels.

CFD modelling using SolidWorks Flow Simulation shows that our novel implementation of AR combined with microchannel heat exchangers can produce, in this embodiment, a 24.4° C. temperature drop and 14.3 W cooling capacity per AR cycle, with a COP efficiency of 5.0. Each AR cycle uses 13.1″ L×0.4″ W×0.04″ D NiTi SMA elements.

With reference to FIG. 12, temperature drop and cooling capacity increase linearly with NiTi element length. COP was reduced, but the effect lessened as length increased.

Preliminary results from our CFD simulation are extremely promising and form the basis of our feasibility justification by dramatically increasing our temperature drop while maintaining ultra-high efficiency. A benefit of our proposed system over typical AR systems is continuous fluid flow. Typical AR systems use reversing fluid flow, and the energy required to reverse the momentum of all working fluid twice per thermodynamic cycle results in pumping power that can consume, for instance, 18% of total input power. The simulation of our continuous flow system's pumping power shows that pumping losses represent only 0.05% of total input power, for instance. This is an enormous savings that contributes to our high predicted COP efficiency. This AR scheme represents an elastocaloric implementation of the magnetocaloric AR concept in FIG. 14. In the elastocaloric implementation, the function of the thermal diodes is achieved by mechanically removing the elastocaloric element from contact with one heat exchanger, thereby preventing heat flow to that heat exchanger, and mechanically bringing it into contact with another heat exchanger, thereby enabling heat flow into that heat exchanger.

To minimize the required actuator size, in various embodiments, a mechanism for actuating SMA elements sequentially rather than simultaneously could be implemented. Referring to FIG. 13, the drive system 1400 also enables automatic direction reversal halfway through each cycle so that the drive input can operate continuously in one direction. Based on the single-element torque measured in an early prototype, the peak torque when actuating rings sequentially is 100 in-lbf, and to actuate 50 rings required to reach 9K cooling capacity in each 8 s cycle period requires a speed of 300 rpm (one actuation requires about ⅘ of a revolution), for example. A 0.5 hp motor, for instance, could easily drive this system. To actuate the 50 rings simultaneously at the same strain rate would require a 24 hp motor, or more realistically, an altogether different actuator technology, for instance.

In various embodiments, an air conditioner can utilize one or more elastocaloric elements to transfer heat from a room and/or building, for example. In at least one embodiment, the air conditioner comprises an elastocaloric material, a heat exchanger, an actuator operable in forward and reverse to cyclically bend the elastocaloric material to reciprocatingly cause strain within the elastocaloric material creating repeated solid-to-solid phase transformations in the elastocaloric material, and a fluid circuit comprising a working fluid configured to transfer heat from the heat exchanger to the elastocaloric material due to the solid-to-solid phase transformations. The fluid circuit can comprise a pump to push the working fluid through the fluid circuit. In various embodiments, the working fluid can comprise water, for example.

In various embodiments, a heat pump can utilize one or more elastocaloric elements to transfer heat to a person via a wearable device, for example, and/or to transfer heat to a room and/or a building, for example. In at least one embodiment, the heat pump comprises an elastocaloric material, a heat exchanger, an actuator operable in forward and reverse to cyclically bend the elastocaloric material to reciprocatingly cause strain within the elastocaloric material creating repeated solid-to-solid phase transformations in the elastocaloric material, and a fluid circuit comprising a working fluid configured to transfer heat emitted from the elastocaloric material due to the solid-to-solid phase transformations to the heat exchanger. The fluid circuit can comprise a pump to push the working fluid through the fluid circuit. In various embodiments, the working fluid can comprise water, for example.

The entire disclosures of Tušek, J., Engelbrecht, K., Mikkelsen, L. P., & Pryds, N. (2015). Elastocaloric effect of Ni—Ti wire for application in a cooling device. Journal of Applied Physics, 117(12); M Launey, M., Robertson, S. W., Vien, L., Senthilnathan, K., Chintapalli, P., & Pelton, A. R. (2014). Influence of microstructural purity on the bending fatigue behavior of VAR-melted superelastic Nitinol. Journal of the mechanical behavior of biomedical materials, 34, 181-186; Sharar, D. J., Radice, J., Warzoha, R., Hanrahan, B., & Smith, A. (2021). Low-force elastocaloric refrigeration via bending. Applied Physics Letters, 118(18); Y. A. Cengel, “8-5 Laminar Flow in Tubes,” in Heat and Mass Transfer: A Practical Approach, New York, McGraw-Hill, 2007, pp. 463-469; J Tušek, J., Žerovnik, A., Čebron, M., Brojan, M., Žužek, B., Engelbrecht, K., & Cadelli, A. (2018). Elastocaloric effect vs fatigue life: Exploring the durability limits of Ni—Ti plates under pre-strain conditions for elastocaloric cooling. Acta Materialia, 150, 295-307; Eriksen, D., Engelbrecht, K., Haffenden Bahl, C. R., & Bjørk, R. (2016). Exploring the efficiency potential for an active magnetic regenerator. Science and Technology for the Built Environment, 22(5), 527-533; Tušek, J., & Kitanovski, A. (2015). Magnetocaloric energy conversion: From theory to applications. Heidelberg ua: Springer; and Robertson, S. W., Pelton, A. R., & Ritchie, R. O. (2012). Mechanical fatigue and fracture of Nitinol. International Materials Reviews, 57(1), 1-37 are incorporated herein by reference.

An elastocaloric heat exchange system 5000 is illustrated in FIGS. 15-19 and is similar to the elastocaloric heat exchange systems 1000, 2000, and 3000, discussed above, in many respects. Referring primarily to FIGS. 15 and 16, the elastocaloric heat exchange system 5000 comprises a plurality of hot heat exchange rollers 5100 (although only one is depicted) and a cold heat exchanger 5200 in the shape of a cylinder, or ring, 5210. That said, the cold heat exchanger 5200 can comprise any suitable shape. The ring 5210 comprises an internal ring gear 5220 that is meshingly engaged with spur gear portions 5120 defined on the rollers 5100 (see FIG. 17) such that the rotation of the rollers 5100 by a drive mechanism, such as the drive mechanism 1400, for example, drives the rotation of the ring 5210. Referring primarily to FIGS. 17 and 18, each roller 5100 comprises a body 5110 having bearing supports 5115 on opposite ends thereof that rotatably support the roller 5100 in, referring to FIG. 15, a fluid inlet manifold 5800 and a fluid outlet manifold 5700. As described in greater detail below, each roller 5100 comprises a fluid path extending therethrough that is in fluid communication with the fluid inlet manifold 5800 and the fluid outlet manifold 5700.

Further to the above, the roller 5100 comprises a fluid inlet 5150, a fluid outlet 5160, and a fluid path 5140 extending between the fluid inlet 5150 and the fluid outlet 5160. Moreover, the roller 5100 further comprises seals, such as o-ring seals, for example, at opposite ends thereof that are seated in seal grooves 5155 defined in the body 5110 that sealingly engage the fluid inlet manifold 5800 and the fluid outlet manifold 5700 such that fluid does not leak from the interfaces between the roller 5100 and the manifolds 5700 and 5800. The roller 5100 further comprises an internal chamber 5170 defined in the fluid path 5140 and a flow insert 5180 positioned in the internal chamber 5170. The flow insert 5180 is sized and configured to restrict the flow of fluid through the fluid path 5140 to narrow channels 5145 that are adjacent the exterior surfaces of the roller 5100. More specifically, the channels 5145 extend closely behind a spool section 5130 of the roller 5100, discussed further below, to improve the transfer of heat from elastocaloric elements that are bent around the spool sections 5130 and the fluid flowing through the fluid path 5140. The flow insert 5180 is substantially cylindrical, but can comprise any suitable shape. Moreover, the flow insert 5180 also comprises conical-shaped ends 5185, for example, that assist in directing the flow of fluid into the channels 5145. In various instances, the exterior surface of the flow insert 5180 is smooth so as to maintain the laminar flow of the fluid flowing through the fluid path 5140; however, the exterior surface of the flow insert 5180 can comprise features that, for instance, assist in directing the fluid into the channels 5145.

Further to the above, each roller 5100 comprises at least one elastocaloric element mounted thereto. In at least one embodiment, four elastocaloric elements, for example, are mounted to each roller 5100. In various embodiments, each elastocaloric element comprises a round cross-section, for example, but can comprise any suitable cross-section, such as a rectangular cross-section, for example. Each roller 5100 comprises one or more attachment points 5135 for mounting one of the ends of the elastocaloric elements to the roller 5100. In at least one embodiment, the roller 5100 comprises one or more tensioning elements, such as spring elements, for example, that can apply a biasing force to the elastocaloric elements. Further to the above, referring primarily to FIG. 17, the spool section 5130 of the roller 5100 including grooves 5131 defined therein which are configured to receive the elastocaloric elements when the elastocaloric elements are wound around the roller 5100 and release the elastocaloric elements when the elastocaloric elements are unwound from the roller 5100. The spool section 5130 is cylindrical, but could comprise any suitable configuration. The diameter of the spool section 5130 is selected such that the elastocaloric elements are sufficiently strained, or bent, to undergo a solid-to-solid phase transformation discussed herein without yielding the material of the elastocaloric elements. In various embodiments, the grooves 5131 extending around the spool section 5130 are circular and are separated by ribs that are configured to position the elastocaloric elements in the grooves 5131. In other embodiments, the grooves 5131 are helical and the ribs separate the windings of the helical grooves 5131, for example. The grooves 5131 are smooth, for example, which can facilitate the release of the elastocaloric elements from the roller 5100.

As the elastocaloric elements are released from the roller 5100, the elastocaloric elements begin to relax and bear against the ring 5210 of the cold heat exchanger 5200. In such instances, as discussed herein, the elastocaloric elements undergo a second, or reverse, phase transformation that absorbs heat from the environment surrounding the elastocaloric elements, such as the ring 5210, for example. That said, the elastocaloric elements are still maintained in a curved state when the elastocaloric elements are relaxed into engagement with the ring 5210. Moreover, it has been discussed herein that the elastocaloric elements undergo phase changes as they are strained and relaxed. While it is possible that an entire elastocaloric element can undergo a phase change all at once, it is more likely that portions of the elastocaloric element will undergo the phase change sequentially and perhaps some portions of the elastocaloric element may not undergo a phase change at all. For instance, the portions of the elastocaloric elements immediately attached to the rollers 5100 are in a highly-strained state when the elastocaloric elements are wound around the rollers 5100 and remain so even when the elastocaloric elements have been unwound from the rollers 5100. Such portions of the elastocaloric elements may not undergo the cyclic solid-to-solid phase transitions discussed herein. Also, for instance, the portions of the elastocaloric elements immediately attached to the ring 5210 may never be sufficiently strained to cause such portions to undergo the cyclic solid-to-solid phase transitions discussed herein. The above notwithstanding, it is desirable to keep as much of the elastocaloric elements in a strain range that causes a maximum length of the elastocaloric elements to undergo the cyclic solid-to-solid phase transitions discussed herein to improve the efficiency of the elastocaloric heat exchange system 5000. That said, keeping the portions of the elastocaloric elements immediately attached to the rollers 5100 in a constant, or near-constant, strained state can reduce the fatigue of the elastocaloric elements at their attachment points 5135.

Further to the above, referring again to FIGS. 15 and 16, the ring 5210 also comprises grooves 5230 defined in a spool section thereof that are configured to receive the elastocaloric elements as they are unwound from the rollers 5100. Similar to the spool section 5130 of the rollers 5100, the grooves 5230 can be circular and/or helical, for example. In either case, the grooves 5230 are separated by ribs that are configured to position the elastocaloric elements in the grooves 5230 and control the release of the elastocaloric elements from the grooves 5230. Further to the above, the ring 5210 comprises attachment points that attach the elastocaloric elements to the ring 5210 and align the elastocaloric elements with the grooves 5230. As discussed above, the ends of the elastocaloric elements attached to the ring 5210 can remain in a low-stress state during the operation of the elastocaloric heat exchange system 5000 which can reduce the fatigue of the elastocaloric elements at the attachment points. In various embodiments, the ring 5210 can comprise one or more tensioning elements, such as spring elements, for example, that can apply a biasing force to the elastocaloric elements.

Further to the above, the elastocaloric elements can comprise any suitable shape and/or configuration. In various embodiments, the elastocaloric elements comprise elongate cables, for example. In various instances, each elastocaloric element has a round, or an at least substantially circular, cross-section that nests within a groove 5230, for example. In some instances, each elastocaloric element, such as elements 3300, for example, has a polygonal cross-section, such as a rectangular cross-section, for example, having one or more flat surfaces. Such elastocaloric elements can also be considered cables.

In various instances, the efficiency of the elastocaloric heat exchange system 5000 is improved by maximizing the contact area between the elastocaloric elements and the rollers 5100 and the contact area between the elastocaloric elements and the ring 5210. Also, in various instances, the efficiency of the elastocaloric heat exchange system 5000 is improved by minimizing, or even eliminating, sliding friction between the elastocaloric elements and both the rollers 5100 and the ring 5210. In various instances, one or more thermal greases can be used at the interfaces between the elastocaloric elements and the rollers 5100 and the ring 5210. Such thermal greases can improve the heat transfer between the elastocaloric elements and the rollers 5100 and the ring 5210 as well as reduce sliding friction therebetween.

Further to the above, the ring 5210 comprises a fluid path defined therein comprising a fluid inlet 5250, a fluid outlet 5260, and a fluid channel 5240 that fluidically couples the fluid inlet 5250 and the fluid outlet 5260. A fluid flowing through the fluid channel 5240 can deliver heat to the cold heat exchanger 5200 which is transferred to the rollers 5100 via the elastocaloric elements as discussed herein. In various embodiments, the fluid channel 5240 comprises one or more inserts positioned therein which can direct flow adjacent the grooves 5230 to improve the heat transfer between the fluid and the elastocaloric elements.

Further to the above, the elastocaloric elements, such as elements 1300, 2300, and/or 3300, for example, disclosed herein can be comprised of a shape memory alloy (SMA), for example. In various embodiments, the elastocaloric elements are comprised of any of nitinol-based, copper-based, polymer-based, and/or magnetic shape memory materials, for example. In various embodiments, a shape memory alloy is comprised of elastocaloric crystals that undergo a first solid-to-solid phase transformation when the shape memory alloy is strained and a second, or reverse, solid-to-solid phase transformation when the shape memory alloy is relaxed. In such instances, the shape memory alloy undergoes an austenite crystal to martensite crystal transformation during the first phase transformation and a martensite crystal to austenite crystal transformation during the second, or reverse, phase transformation.

The elastocaloric elements described herein can have any suitable shape. In various embodiments, an elastocaloric element has a rectangular cross-section, for example. In at least one embodiment, an elastocaloric element has a round cross-section, for example. In certain embodiments, an elastocaloric element has a rope configuration, for example.

The elastocaloric elements described herein can have any suitable pre-set configuration. For instance, an elastocaloric element can have a straight pre-set configuration. In at least one such embodiment, the elastocaloric element comprises a first end, a second end, and an intermediate section extending between the first end and the second end where the first end, the second end, and the intermediate section are positioned along a line, or axis when the elastocaloric element is in an unflexed state. In other embodiments, an elastocaloric element has a curved pre-set configuration. In at least one such embodiment, the elastocaloric element has a first end, a second end, and a curved intermediate portion extending between the first end and the second end, for example. Such a curved intermediate portion can be defined by a single radius of curvature or multiple radiuses of curvature, for example. In at least one embodiment, the elastocaloric element is comprised of a shape memory alloy, such as nitinol, for example, that is heated, bent into a curved shape while heated, and then held in its curved shape while it cools which leaves the elastocaloric element in a curved pre-set configuration. In various embodiments, an elastocaloric element, such as the one used in connection with the elastocaloric heat exchange system 5000, for example, has a helical pre-set configuration, for example. In such an arrangement, less torque may be required to wind the elastocaloric element which means that a smaller motor can be used which requires less energy to run. Such a system may weigh less and may be more efficient.

Further to the above, referring again to FIG. 13, the reciprocating drive 1400 comprises, in various embodiments, an electric motor comprising a rotatable output and a cam 1470 fixedly mounted to the rotatable output. The electric motor can comprise any suitable motor, such as an AC motor and/or a DC motor, for example. Moreover, the reciprocating drive 1400 can comprise any suitable rotatable input, such as a fluid-driven impeller, for example. In at least one embodiment, the cam 1470 comprises a perimeter, or outer circumference, comprising one or more lobes, for example; however, the cam 1470 can comprise any suitable configuration. In at least one embodiment, the cam 1470 comprises a barrel cam, for example, comprising one or more grooves defined in the outer perimeter thereof. The reciprocating drive 1400 further comprises a cam follower 1480 engaged with the perimeter of the cam 1470 that is driven by the cam 1470 as the cam 1470 is rotated by the electric motor. In various embodiments, the reciprocating drive 1400 further comprises a biasing element 1485, such as a spring, for example, configured to keep the cam follower 1480 in contact with the cam 1470. As a result of this arrangement, the continuous rotational motion of the cam 1470 in one direction can create a cyclical reciprocating motion of the cam follower 1480. Such reciprocating motion of the cam follower 1480 can be transmitted to one or more heat exchangers, as described above, in any suitable manner. For instance, the reciprocating drive 1400 can further comprise a translatable drive element 1460 that is slid back and forth along a drive shaft 1450 by a linkage system 1490 operably connecting the cam follower 1480 and the drive element 1460. The drive shaft 1450 is driven by an electric motor, such as an AC motor and/or a DC motor, for example, but could be driven by any suitable rotatable input, such as a fluid-driven impeller, for example. In use, the drive element 1460 is driven by the cam 1470 and the cam follower 1480 between a first position in which the drive element 1460 operably connects the drive shaft 1450 with a first, or forward, bevel output gear 1430 and a second position in which the drive element 1460 operably connects the drive shaft 1450 with a second, or reverse, bevel output gear 1440 positioned opposite the first bevel output gear 1430. In at least one embodiment, the drive element 1460 and the drive shaft 1450 are connected by a slot/key or tongue-and-groove arrangement which permits the drive element 1460 to slide longitudinally along the drive shaft 1450 but not rotate relative to the drive shaft 1450, for example. Notably, a first end of the drive element 1460 has a first gear face, or clutch interface, configured to engage an opposing gear face defined on the first bevel output gear 1430 and, correspondingly, a second gear face, or clutch interface, configured to engage an opposing gear face defined on the second bevel output gear 1440. Moreover, notably, when the drive element 1460 is engaged with the first bevel output gear 1430, the drive element 1460 is not engaged with the second bevel output gear 1440. Likewise, the drive element 1460 is not engaged with the first bevel output gear 1430 when the drive element 1460 is engaged with the second bevel output gear 1440. As a result of this arrangement, the second bevel output gear 1440 can rotate freely with respect to, or about, the drive shaft 1450 when the drive shaft 1450 is coupled to the first bevel output gear 1430 via the drive element 1460 and, correspondingly, the first bevel output gear 1430 can rotate freely with respect to, or about, the drive shaft 1450 when the drive shaft 1450 is coupled to the second bevel output gear 1440 via the drive element 1460. The first bevel output gear 1430 and the second bevel output gear 1440 are both meshingly engaged with a main output gear 1420 such that the main output gear 1420 is rotated in a first direction when the first bevel output gear 1430 is driven by the drive shaft 1450 and in a second, or opposite, direction when the second bevel output gear 1440 is driven by the output shaft 1450. Stated another way, the reciprocating drive mechanism 1400 operates in a manner which causes the main bevel gear 1420 to be rotated back and forth—in a forward and reverse manner—about a central drive axis, the rotation of which can be transmitted to the heat exchangers via a drive shaft 1410 and/or a transmission system comprising a plurality of gears and/or shafts, for example. In various embodiments, the reciprocating drive 1400 can be used to drive the hot rollers 5100, as described above, as well as the cold heat exchanger ring 5200, for example. Such an arrangement can maintain the rotational timing between the hot rollers 5100 and the heat exchanger ring 5200, for example, as they are both driven by the same drive shaft. That said, other embodiments are envisioned in which the hot rollers 5100 and the heat exchanger ring 5200 are driven by separate drive systems.