A wide variety of technologies exist for cooling applications, including but not limited to evaporative cooling, convective cooling, or solid state cooling such as electrothermic cooling. One of the most prevalent technologies in use for residential and commercial refrigeration and air conditioning is the vapor compression refrigerant heat transfer loop. These loops typically circulate a refrigerant having appropriate thermodynamic properties through a loop that comprises a compressor, a heat rejection heat exchanger (i.e., heat exchanger condenser), an expansion device and a heat absorption heat exchanger (i.e., heat exchanger evaporator). Vapor compression refrigerant loops effectively provide cooling and refrigeration in a variety of settings, and in some situations can be run in reverse as a heat pump. However, many of the refrigerants can present environmental hazards such as ozone depleting potential (ODP) or global warming potential (GWP), or can be toxic or flammable. Additionally, vapor compression refrigerant loops can be impractical or disadvantageous in environments lacking a ready source of power sufficient to drive the mechanical compressor in the refrigerant loop. For example, in an electric vehicle, the power demand of an air conditioning compressor can result in a significantly shortened vehicle battery life or driving range. Similarly, the weight and power requirements of the compressor can be problematic in various portable cooling applications.
Accordingly, there has been interest in developing cooling technologies as alternatives to vapor compression refrigerant loops. Various technologies have been proposed such as field-active heat or electric current-responsive heat transfer systems relying on materials such as electrocaloric materials, magnetocaloric materials, or thermoelectric materials. However, many proposals have been configured as bench-scale demonstrations with limited capabilities for scalability or mass production.
According to some embodiments of this disclosure, a heat transfer system comprises a plurality of electrocaloric elements comprising an electrocaloric film, a first electrode on a first side of the electrocaloric film, and a second electrode on a second side of the electrocaloric film. A fluid flow path is disposed along the plurality of electrocaloric elements, formed by corrugated fluid flow guide elements.
According to some embodiments of this disclosure, a heat transfer system comprises a continuous electrocaloric film comprising electrode layers on each side thereof, looped on a plurality of support elements to form a plurality of physically separated layers of the electrocaloric polymer film providing a fluid flow path between adjacent layers.
In any of the foregoing embodiments, the corrugated fluid flow guide elements comprise electrically non-conductive corrugated spacer elements disposed between adjacent electrocaloric elements.
In any of the foregoing embodiments, the corrugated fluid flow guide elements comprise electrically conductive corrugated spacers disposed between adjacent electrocaloric elements.
In any of the foregoing embodiments, the electrically conductive corrugated spacers comprise shaped electrically conductive structures in electrical contact with electrodes on adjacent electrocaloric elements.
In any of the foregoing embodiments, the electrically conductive corrugated spacers comprise an extension of conductive material electrodes on adjacent electrocaloric elements in a direction normal to a surface of the electrocaloric polymer film.
In any of the foregoing embodiments, the electrically conductive corrugated spacers are configured as a microchannel structure or an open-cell foam.
In any of the foregoing embodiments, the electrically conductive corrugated spacers comprise carbon nanotubes.
In any of the foregoing embodiments, the fluid flow guide elements comprise electrocaloric elements from said plurality of electrocaloric elements.
In any of the foregoing embodiments, the electrocaloric elements comprise alternating adjacent flat electrocaloric elements and corrugated electrocaloric elements.
In any of the foregoing embodiments, the electrocaloric elements comprise complementary corrugated electrocaloric elements that cooperate to form a honeycomb structure.
In any of the foregoing embodiments, adjacent electrocaloric elements comprise adhesive joints at intersecting junctions.
In any of the foregoing embodiments, the plurality of electrocaloric elements are arranged in an alternating order of polarity between adjacent electrocaloric elements.
In any of the foregoing embodiments, the electrocaloric film comprises an electrocaloric polymer, liquid crystal polymer (LCP), electrocaloric ceramic or an electrocaloric polymer/ceramic composite.
In any of the foregoing embodiments, a physical separation between adjacent electrocaloric elements is 1 μm to 100 mm.
In any of the foregoing embodiments, the electrocaloric elements have a thickness of 1 μm to 1000 μm.
In any of the foregoing embodiments, the electrocaloric film comprises an electrocaloric polymer.
In any of the foregoing embodiments comprising a continuous looped electrocaloric film, the heat transfer system further comprises one or more spacer elements disposed between adjacent layers of the electrocaloric film. In some embodiments, the one or more spacer elements are electrically conductive. In some embodiments, the one or more spacer elements are electrically non-conductive.
In any of the foregoing embodiments comprising a continuous looped electrocaloric film, the support elements further comprise electrical bus elements in electrical contact with the conductive material electrode layers.
In any of the foregoing embodiments comprising a continuous looped electrocaloric film, the loops of the continuous electrocaloric polymer film are in a back and forth configuration.
In any of the foregoing embodiments, the heat transfer system comprises at least two adjacent electrocaloric elements that share an electrode at least partially embedded between the electrocaloric films of the adjacent electrocaloric elements. In some embodiments, the embedded electrode is a live electrode, and comprising ground electrodes adjacent to the fluid flow path.
In any of the foregoing embodiments, the electrocaloric film comprises an electrocaloric polymer film under tensile stress.
In any of the foregoing embodiments, the heat transfer system further comprises a first thermal flow path between the fluid flow path and a heat sink, a second thermal flow path between the fluid flow path and a heat source, and a controller configured to control electrical current to the electrodes and to selectively direct transfer of heat energy from the fluid flow path in thermal communication with electrocaloric element to the heat sink along the first thermal flow path or from the heat source to the fluid flow path in thermal communication with the electrocaloric element along the second thermal flow path.
Subject matter of this disclosure is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the present disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
As mentioned above, the heat transfer systems disclosed herein comprise a fluid flow along a plurality of electrocaloric elements, formed by corrugated fluid flow guide elements. In some embodiments, the corrugated fluid flow guide elements can mean fluid flow guide elements configured with ridges and/or grooves. Corrugated configurations are not limited to any particular configuration or design, and can include any configuration comprising grooves and/or ridges, including without limitation alternating grooves and ridges, regular patterns of grooves, ridges, wings, projections, and/or extensions, or irregular patterns with any of the above features. Examples of corrugated configurations include without limitation ziz-zag patterns, triangular, sinusoidal, regular or irregular waves, triangular, trapezoidal, rhomboidal, notched, square or rectangular notched, fluted, louvered with openings through the spacer element adjacent to or in between grooves, microchannel louvered, ridges, wings, or extensions, or any sort of irregular rough pattern such as an open-cell foam.
With reference now to
Ferroelectric polymers are crystalline polymers, or polymers with a high degree of crystallinity, where the crystalline alignment of polymer chains into lamellae and/or spherulite structures can be modified by application of an electric field. Such characteristics can be provided by polar structures integrated into the polymer backbone or appended to the polymer backbone with a fixed orientation to the backbone. Examples of ferroelectric polymers include polyvinylidene fluoride (PVDF), polytriethylene fluoride, odd-numbered nylon, copolymers containing repeat units derived from vinylidene fluoride, and copolymers containing repeat units derived from triethylene fluoride. Polyvinylidene fluoride and copolymers containing repeat units derived from vinylidene fluoride have been widely studied for their ferroelectric and electrocaloric properties. Examples of vinylidene fluoride-containing copolymers include copolymers with methyl methacrylate, and copolymers with one or more halogenated co-monomers including but not limited to trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, trichloroethylene, vinylidene chloride, vinyl chloride, and other halogenated unsaturated monomers.
Liquid crystal polymers, or polymer liquid crystals comprise polymer molecules that include mesogenic groups. Mesogenic molecular structures are well-known, and are often described as rod-like or disk-like molecular structures having electron density orientations that produce a dipole moment in response to an external field such as an external electric field. Liquid crystal polymers typically comprise numerous mesogenic groups connected by non-mesogenic molecular structures. The non-mesogenic connecting structures and their connection, placement and spacing in the polymer molecule along with mesogenic structures are important in providing the fluid deformable response to the external field. Typically, the connecting structures provide stiffness low enough so that molecular realignment is induced by application of the external field, and high enough to provide the characteristics of a polymer when the external field is not applied.
In some exemplary embodiments, a liquid crystal polymer can have rod-like mesogenic structures in the polymer backbone separated by non-mesogenic spacer groups having flexibility to allow for re-ordering of the mesogenic groups in response to an external field. Such polymers are also known as main-chain liquid crystal polymers. In some exemplary embodiments, a liquid crystal polymer can have rod-like mesogenic structures attached as side groups attached to the polymer backbone. Such polymers are also known as side-chain liquid crystal polymers.
With continued reference to
The corrugated spacer elements can have a variety of different configurations. A few representative examples of different configurations of spacer 19 disposed between electrocaloric elements 12 are shown in
In some aspects of the disclosure, the corrugated spacer elements can contribute to maintaining a physical separation between electrocaloric elements for a fluid flow path. In some aspects of the disclosure, the corrugated spacer elements can contribute to structural integrity of a stack structure of electrocaloric elements. In some aspects the corrugated spacer elements can contribute to electrical continuity between electrodes of the same polarity, and in some aspects the corrugated spacer elements can contribute to maintaining electrical isolation between electrodes of different or opposite polarity. In this regard, the corrugated spacer elements can be electrically conductive or electrically non-conductive.
An example of an embodiment of electrically conductive spacer elements is depicted in
In some aspects, an electrically conductive spacer can be partially or fully integrated with one or more electrodes so that one element serves both as a spacer between electrocaloric elements and electrode as part of one or more electrocaloric elements. Examples of such embodiments are shown in
An example of an embodiment of electrically non-conductive spacer elements is depicted in
In some embodiments, the corrugated spacer element can be formed from the electrocaloric element itself so that both the electrocaloric element and the corrugated spacer element are provided by the same structure. Examples of such embodiments are shown in
Another example of an embodiment is depicted in
Another type of corrugated pattern can be provided by a continuous electrocaloric film comprising electrode layers on each side thereof, looped on a plurality of support elements. An example of such an embodiment is schematically depicted in
An example embodiment of a heat transfer system and its operation are further described with respect to
In operation, the system 310 can be operated by the controller 324 applying an electric field as a voltage differential across the electrocaloric elements in the stack 311 to cause a decrease in entropy and a release of heat energy by the electrocaloric elements. The controller 324 opens the control valve 326 to transfer at least a portion of the released heat energy along flow path 318 to heat sink 317. This transfer of heat can occur after the temperature of the electrocaloric elements has risen to a threshold temperature. In some embodiments, heat transfer to the heat sink 317 is begun as soon as the temperature of the electrocaloric elements increases to be about equal to the temperature of the heat sink 317. After application of the electric field for a time to induce a desired release and transfer of heat energy from the electrocaloric elements to the heat sink 317, the electric field can be removed. Removal of the electric field causes an increase in entropy and a decrease in heat energy of the electrocaloric elements. This decrease in heat energy manifests as a reduction in temperature of the electrocaloric elements to a temperature below that of the heat source 320. The controller 324 closes control valve 326 to terminate flow along flow path 318, and opens control device 328 to transfer heat energy from the heat source 320 to the colder electrocaloric elements.
In some embodiments, for example where a heat transfer system is utilized to maintain a temperature in a conditioned space or thermal target, the electric field can be applied to the electrocaloric elements to increase its temperature until the temperature of the electrocaloric element reaches a first threshold. After the first temperature threshold, the controller 324 opens control valve 326 to transfer heat from the electrocaloric elements to the heat sink 317 until a second temperature threshold is reached. The electric field can continue to be applied during all or a portion of the time period between the first and second temperature thresholds, and is then removed to reduce the temperature of the electrocaloric elements until a third temperature threshold is reached. The controller 324 then closes control valve 326 to terminate heat flow transfer along heat flow path 318, and opens control valve 328 to transfer heat from the heat source 320 to the electrocaloric elements. The above steps can be optionally repeated until a target temperature of the conditioned space or thermal target (which can be either the heat source or the heat sink) is reached.
While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the present disclosure. Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments. Accordingly, the present disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
This application is a divisional of U.S. patent application Ser. No. 16/064,827, filed Jun. 21, 2018, which claims priority to International Application No. PCT/US2015/067182, filed Dec. 21, 2015, both of which are incorporated by reference in their entirety herein.
Number | Date | Country | |
---|---|---|---|
Parent | 16064827 | Jun 2018 | US |
Child | 17406620 | US |