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.
In some embodiments of this disclosure, a heat transfer system comprises a plurality of modules arranged in a stack. The stack modules comprise an electrocaloric element comprising an electrocaloric film. A first electrode is disposed on a first side of the electrocaloric film, and a second electrode is disposed on a second side of the electrocaloric film. A fluid flow path is disposed between two or more electrocaloric elements. A first electrical bus element in electrical contact with the first electrode, and a second electrical bus element in electrical contact with second electrode. The first electrical bus element is electrically connected to at least one other electrical bus of another electrocaloric element in the stack at the same polarity as said first electrical bus, or the second electrical bus element is electrically connected to at least one other electrical bus of another electrocaloric element in the stack at the same polarity as said second electrical bus.
The first electrical bus element is electrically connected to at least one other electrical bus of another electrocaloric element in the stack at the same polarity as said first electrical bus, and the second electrical bus element is electrically connected to at least one other electrical bus of another electrocaloric element in the stack at the same polarity as said second electrical bus.
In any of the foregoing embodiments, the first or second electrical bus is electrically connected to an electrical bus of an adjacent electrocaloric element in the stack at the same polarity as said first or second electrical bus.
In any of the foregoing embodiments, the first and second electrical bus elements are each electrically connected to electrical bus elements of an adjacent electrocaloric element in the stack at the same polarities as said first and second electrical bus elements, respectively.
In any of the foregoing embodiments, the first or second electrical bus element is in an interlocking configuration with an electrical bus of an adjacent electrocaloric element in the stack.
In any of the foregoing embodiments, the first and second electrical bus elements are each in an interlocking configuration to electrical bus elements of an adjacent electrocaloric element in the stack.
In any of the foregoing embodiments, the first electrical bus element is electrically connected to a live electrode and the second electrical bus element is electrically connected to a ground electrode.
In any of the foregoing embodiments, the first and second electrical bus elements are disposed along opposite edges of the electrocaloric element.
In any of the foregoing embodiments, the first electrode extends from the first electrical bus element along the first side of the electrocaloric film to a position physically separated from the second electrical bus element, and the second electrode extends from the second electrical bus element along the second side of the electrocaloric film to a position physically separated from the first electrical bus element.
In any of the foregoing embodiments, the first and second electrical bus elements are disposed along a common edge of the electrocaloric element.
In any of the foregoing embodiments, at least two adjacent electrocaloric elements that share an electrode are at least partially embedded between the electrocaloric films of the adjacent electrocaloric elements.
In any of the foregoing embodiments, the embedded electrode is a live electrode, and comprising ground electrodes adjacent to the fluid flow path.
In any of the foregoing embodiments, one or more spacer elements are disposed between electrocaloric elements.
In any of the foregoing embodiments, the one or more spacer elements extend axially along a direction of fluid flow along the fluid flow path.
In any of the foregoing embodiments, the one or more axially-extending spacer elements extend linearly along a direction of fluid flow along the fluid flow path.
In any of the foregoing embodiments, the one or more axially-extending spacer elements extend non-linearly along a direction of fluid flow along the fluid flow path.
In any of the foregoing embodiments, the one or more spacer elements are electrically non-conductive.
In any of the foregoing embodiments, the electrocaloric element thickness is 1 μm to 1000 μm.
In any of the foregoing embodiments, the physical separation between electrocaloric elements in adjacent modules is from 1 μm to 200 mm.
In any of the foregoing embodiments, the plurality of modules further comprise an electrically non-conductive support member connected to the electrocaloric element.
In any of the foregoing embodiments, the support includes header spaces at opposing ends of the electrocaloric elements in fluid communication with the fluid flow path.
In any of the foregoing embodiments, the supports of the plurality of modules together form an enclosure within which the electrocaloric elements and the spacer elements are disposed.
In any of the foregoing embodiments, the electrocaloric film comprises an electrocaloric polymer.
In any of the foregoing embodiments, the electrocaloric polymer comprises polyvinylidene fluoride (PVDF) or a liquid crystal polymer (LCP),
In any of the foregoing embodiments, the electrocaloric film comprises an inorganic electrocaloric material.
In any of the foregoing embodiments, the first and second electrodes each comprise a metalized layer deposited on the electrocaloric film.
In some embodiments, a heat transfer system comprises an electrocaloric element formed by the method of any of the above embodiments, a first thermal flow path between the electrocaloric element and a heat sink, a second thermal flow path between the electrocaloric element and a heat source, and a controller configured to control electrical current to the conductive layers and to selectively direct transfer of heat energy from the electrocaloric element to the heat sink along the first thermal flow path or from the heat source to the electrocaloric element along the second thermal flow path.
In another aspect, a method of fabricating the heat transfer system of any of the foregoing embodiments comprises assembling repeating units of the modules in a stack configuration.
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, a heat transfer system is disclosed that comprises a plurality of modules arranged in a stack. An example of an embodiment of a module is schematically depicted in
The electrocaloric film 12 can comprise any of a number of electrocaloric materials. In some embodiments, electrocaloric film thickness can be in a range from having a lower limit of 0.1 μm, more specifically 0.5 μm, and even more specifically 1 μm. In some embodiments, the film thickness range can and having an upper limit of 1000 μm, more specifically 100 μm, and even more specifically 10 μm. It is understood that these upper and lower range limits can be independently combined to disclose a number of different possible ranges. Examples of electrocaloric materials for the electrocaloric film can include but are not limited to inorganic materials (e.g., ceramics), electrocaloric polymers, and polymer/ceramic composites. Examples of inorganics include but are not limited to PbTiO3 (“PT”), Pb(Mg1/3Nb2/3)O3 (“PMN”), PMN-PT, LiTaO3, barium strontium titanate (BST) or PZT (lead, zirconium, titanium, oxygen). Examples of electrocaloric polymers include, but are not limited to ferroelectric polymers, liquid crystal polymers, and liquid crystal elastomers.
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
One or more support elements 22 can optionally be included for support and retention of the electrocaloric element. However, separate support elements are not required, as support and retention can also be provided by the bus elements as shown in
Spacer elements 28 can optionally be included to help maintain separation from adjacent electrocaloric elements for a fluid flow path for a working fluid (e.g., either a fluid to be heated or cooled directly such as air, or a heat transfer fluid such as a dielectric organic compound). Any configuration of spacer elements can be utilized, such as a set of discrete disk spacer elements. In some aspects, however, the spacer elements extend axially in a direction parallel to the direction of the fluid flow path 25. Such axial extension can be linear (i.e., in a straight line) as shown in
Turning now to
In some embodiments, adjacent electrical bus elements 18, 20 can have an interlocking configuration as shown 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.
Filing Document | Filing Date | Country | Kind |
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PCT/US15/67189 | 12/21/2015 | WO | 00 |