Patent Description:
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. <CIT> discloses a heat transfer system, comprising a plurality of modules arranged in a stack, each of the modules comprising an electrocaloric element 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 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; wherein 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.

In an aspect of the invention, a heat transfer system is provided according to claim <NUM>.

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 <NUM> to <NUM>.

In any of the foregoing embodiments, the physical separation between electrocaloric elements in adjacent modules is from <NUM> to <NUM>.

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 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 invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification.

As mentioned above, a heat transfer system is disclosed that comprises a plurality of modules arranged in a stack. An example of an of a module is schematically depicted in <FIG> and <FIG>. Although any directions described herein (e.g., "up", "down", "top", "bottom", "left", "right", "over", "under", etc.) are considered to be arbitrary and to not have any absolute meaning but only a meaning relative to other directions, <FIG> can be described as a "top" view of an example of a module and <FIG> can be described as a "side" cross-section view taken along the line A↔A shown in <FIG>. As shown in <FIG> and <FIG>, a module <NUM> comprises an electrocaloric element comprises an electrocaloric film <NUM>, a first electrode <NUM> on a first side of the film and a second electrode <NUM> on a second side of the film. It is noted that, for ease of illustration so that details of the electrocaloric film <NUM> and other components are not obscured, the electrodes <NUM>, <NUM> are omitted from <FIG> and are only illustrated in <FIG>.

The electrocaloric film <NUM> 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 <NUM>, more specifically <NUM>, and even more specifically <NUM>. In some embodiments, the film thickness range can and having an upper limit of <NUM>, more specifically <NUM>, and even more specifically <NUM>. 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 PbTiO<NUM> ("PT"), Pb(Mg<NUM>/<NUM>Nb<NUM>/<NUM>)O<NUM> ("PMN"), PMN-PT, LiTaO<NUM>, 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 <FIG> and <FIG>, first electrode <NUM> is electrically connected to a first electrical bus element <NUM>. Similarly, second electrode <NUM> is electrically connected to second electrical bus element <NUM>. The electrodes can be any type of conductive material, including but not limited to metallized layers of a conductive metal such as aluminum or copper, or other conductive materials such as carbon (e.g., carbon nanotubes, graphene, or other conductive carbon). Noble metals can also be used, but are not required. Other conductive materials such as a doped semiconductor, ceramic, or polymer, or conductive polymers can also be used. The electrical bus elements <NUM> and <NUM> of opposite polarity are disposed on opposite edges of the electrocaloric film <NUM> as shown in <FIG>, which can provide a physical separation that can reduce the risk of short circuits. As also shown in <FIG>, the electrodes <NUM> and <NUM> can extend from a position in contact with an electrical bus element on one edge of the film and extend across the film to a position that is not in contact with the electrical bus element of opposite polarity on the other edge of the film <NUM>. The electrical bus elements <NUM> and <NUM> can be disposed on the same side of the electrocaloric element as shown in <FIG> and <FIG>. <FIG> is a schematic depiction of a perspective exploded view of an electrocaloric film <NUM> having a top electrode <NUM> and a bottom electrode <NUM>. The top and bottom electrodes in <FIG> and <FIG> have lead portions 14y and 16y for an electrical connection to an electrical bus element <NUM>. The connection between the electrodes <NUM>, <NUM> and the bus element <NUM> is depicted in a top view in <FIG> where only a portion of electrocaloric film <NUM> and the bus element <NUM> are shown. As shown in <FIG>, bus element has a first polarity portion 19a connected to the lead portion 14y of top electrode <NUM> and a second polarity portion 19b connected to the lead portion 16y of bottom electrode <NUM>, and an electrically non-conductive portion 19c that electrically isolates the portions 19a and 19b of different polarities.

One or more support elements <NUM> 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 <FIG> described below. As shown in <FIG>, the support element(s) <NUM> can be configured to provide header spaces <NUM> and <NUM> for transport of working fluids to and from the electrocaloric element along fluid flow path <NUM>. Although not required in all design configurations, in some embodiments, the support elements can be made from an electrically non-conductive material.

Spacer elements <NUM> 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 <NUM>. Such axial extension can be linear (i.e., in a straight line) as shown in <FIG>, or can be non-linear (e.g., in a zig-zag or wavy pattern that extends generally in an axial direction. In some embodiments, the nonlinearity can promote good fluid mixing while the general extension in the axial direction can help avoid excessive back-pressure to the flowing fluid.

Turning now to <FIG> where like numbering is used as <FIG> and <FIG>, a number of modules <NUM> are shown assembled together in a stack <NUM>. As can be seen in <FIG>, the spacers promote maintaining a physical separation between adjacent electrocaloric elements to provide a fluid flow path <NUM> between the spacers and the adjacent electrocaloric elements. Although not required in all design configurations, in design configurations where the spacer elements are disposed adjacent to electrodes of opposite polarity as shown in <FIG>, the spacer elements can be made from an electrically non-conductive material. In some embodiments, spacing between adjacent electrocaloric elements can be in a range from having a lower limit of <NUM>, more specifically <NUM>, and even more specifically <NUM>. In some embodiments, the separation spacing range can have an upper limit of <NUM>, more specifically <NUM>, even more specifically <NUM>. It is understood that these upper and lower range limits can be independently combined to disclose a number of different possible ranges.

In some embodiments, adjacent electrical bus elements <NUM>, <NUM> can have an interlocking configuration as shown in <FIG>. As used herein, interlocking means that adjacent elements have complementary contour of projections and recesses where a projection of one bus element projects is adjacent or projects into to a complementary recess of an adjacent bus element. Such an arrangement can in some embodiments facilitate assembly and promote structural integrity and electrical continuity of the assembled bus elements in the stack.

<FIG> depicts a stack with alternating electrocaloric elements and fluid flow passages; however, <FIG> represents only one example of a stack and is not limiting. An embodiment in accordance with the claimed invention is depicted in <FIG>. With reference now to <FIG>, a stack 30a is shown where bus elements 18b are connected to a bus bar 18a and bus elements 20b are connected to a bus bar 20a. As shown in <FIG> the electrodes 16a electrically connected to bus elements 20b are embedded between the electrocaloric films <NUM> of adjacent electrocaloric elements. In accordance with the claimed invention, the electrode 16a serves as an electrode for two adjacent electrocaloric elements or, put another way, the two adjacent electrocaloric elements share a single electrode. The electrodes 14a of opposite polarity are disposed on the outside of the electrocaloric element 'sandwich' and are not shared. This configuration can provide technical benefits by protecting the embedded electrode 16a from potential short circuits. In some embodiments, the embedded electrode is a live electrode, and the electrode exposed to the fluid flow path <NUM> is a ground electrode. It should be noted that although <FIG> depicts a sandwich of two films surrounding the embedded electrode, sandwiches of more than two films with embedded electrodes of alternating polarities are also contemplated.

An example embodiment of a heat transfer system and its operation are further described with respect to <FIG>. As shown in <FIG>, a heat transfer system <NUM> comprises an electrocaloric stack <NUM> has one or more electrically conductive liquids in thermal communication with a heat sink <NUM> through a first thermal flow path <NUM>, and in thermal communication with a heat source <NUM> through a second thermal flow path <NUM>. A controller <NUM> is configured to control electrical current to through a power source (not shown) to selectively activate electrocaloric elements (not shown) in the stack <NUM>. The controller <NUM> is also configured to open and close control valves <NUM> and <NUM> to selectively direct the electrically conductive liquid along the first and second flow paths <NUM> and <NUM>.

In operation, the system <NUM> can be operated by the controller <NUM> applying an electric field as a voltage differential across the electrocaloric elements in the stack <NUM> to cause a decrease in entropy and a release of heat energy by the electrocaloric elements. The controller <NUM> opens the control valve <NUM> to transfer at least a portion of the released heat energy along flow path <NUM> to heat sink <NUM>. 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 <NUM> is begun as soon as the temperature of the electrocaloric elements increases to be about equal to the temperature of the heat sink <NUM>. 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 <NUM>, 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 <NUM>. The controller <NUM> closes control valve <NUM> to terminate flow along flow path <NUM>, and opens control device <NUM> to transfer heat energy from the heat source <NUM> 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 <NUM> opens control valve <NUM> to transfer heat from the electrocaloric elements to the heat sink <NUM> 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 <NUM> then closes control valve <NUM> to terminate heat flow transfer along heat flow path <NUM>, and opens control valve <NUM> to transfer heat from the heat source <NUM> 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.

Claim 1:
A heat transfer system, comprising:
a fluid flow path (<NUM>) between two or more electrocaloric elements;
a plurality of modules arranged in a stack (30a), each of the modules comprising at least two adjacent electrocaloric elements, each electrocaloric element comprising an electrocaloric film (<NUM>), a respective first electrode (14a) on a first side of the electrocaloric film (<NUM>), and a second electrode (14a) on a second side of the electrocaloric film (<NUM>), wherein the first electrode (14a) is exposed to the fluid flow path (<NUM>), wherein the at least two adjacent electrocaloric elements share a single second electrode (16a), and the second electrode (16a) is embedded between the electrocaloric films (<NUM>) of the adjacent electrocaloric elements;
a first electrical bus element (18b) in electrical contact with the first electrodes (14a); and
a second electrical bus element (20b) in electrical contact with the second electrode (16a);
wherein the first electrical bus element (18b) is electrically connected to at least one other electrical bus (18b) of another electrocaloric element in the stack (<NUM>) at the same polarity as said first electrical bus (18b), or the second electrical bus element (20b) is electrically connected to at least one other electrical bus (20b) of another electrocaloric element in the stack (30a) at the same polarity as said second electrical bus.