U.S. patent application number 16/064827 was filed with the patent office on 2019-01-03 for electrocaloric heat transfer system.
The applicant listed for this patent is UNITED TECHNOLOGIES CORPORATION. Invention is credited to Subramanyaravi Annapragada, Mikhail B. Gorbounov, Neal R. Herring, Ulf J. Jonsson, Andrzej E. Kuczek, Matthew E. Lynch, Thomas D. Radcliff, Andrew Smeltz, Parmesh Verma.
Application Number | 20190003748 16/064827 |
Document ID | / |
Family ID | 55168428 |
Filed Date | 2019-01-03 |
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United States Patent
Application |
20190003748 |
Kind Code |
A1 |
Gorbounov; Mikhail B. ; et
al. |
January 3, 2019 |
ELECTROCALORIC HEAT TRANSFER SYSTEM
Abstract
A heat transfer system is disclosed that includes a plurality of
electrocaloric elements (12) including an electrocaloric film (14),
a first electrode (16) on a first side of the electrocaloric film,
and a second electrode (18) on a second side of the electrocaloric
film. A fluid flow path (20) is disposed along the plurality of
electrocaloric elements, formed by corrugated fluid flow guide
elements (19).
Inventors: |
Gorbounov; Mikhail B.;
(South Windsor, CT) ; Verma; Parmesh; (South
Windsor, CT) ; Annapragada; Subramanyaravi;
(Shrewsbury, MA) ; Kuczek; Andrzej E.; (Bristol,
CT) ; Lynch; Matthew E.; (Cantoon, CT) ;
Smeltz; Andrew; (Glastonbury, CT) ; Herring; Neal
R.; (East Hampton, CT) ; Jonsson; Ulf J.;
(South Windsor, CT) ; Radcliff; Thomas D.;
(Vernon, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UNITED TECHNOLOGIES CORPORATION |
Hartford |
CT |
US |
|
|
Family ID: |
55168428 |
Appl. No.: |
16/064827 |
Filed: |
December 21, 2015 |
PCT Filed: |
December 21, 2015 |
PCT NO: |
PCT/US2015/067182 |
371 Date: |
June 21, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25B 2321/001 20130101;
Y02B 30/66 20130101; F25B 21/00 20130101; Y02B 30/00 20130101 |
International
Class: |
F25B 21/00 20060101
F25B021/00 |
Claims
1. A heat transfer system, comprising 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; and a fluid flow path along
the plurality of electrocaloric elements, formed by corrugated
fluid flow guide elements.
2. The heat transfer system of claim 1, wherein the corrugated
fluid flow guide elements comprise electrically non-conductive
corrugated spacer elements disposed between adjacent electrocaloric
elements.
3. The heat transfer system of claim 1, wherein the corrugated
fluid flow guide elements comprise electrically conductive
corrugated spacers disposed between adjacent electrocaloric
elements.
4. The heat transfer system of claim 3, wherein the electrically
conductive corrugated spacers comprise shaped electrically
conductive structures in electrical contact with electrodes on
adjacent electrocaloric elements.
5. The heat transfer system of claim 3, wherein 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.
6. The heat transfer system of claim 5, wherein the electrically
conductive corrugated spacers are configured as a microchannel
structure or an open-cell foam.
7. The heat transfer system of claim 3, wherein the electrically
conductive corrugated spacers comprise carbon nanotubes.
8. The heat transfer system of claim 1, wherein the fluid flow
guide elements comprise electrocaloric elements from said plurality
of electrocaloric elements.
9. The heat transfer system of claim 8, wherein the electrocaloric
elements comprise alternating adjacent flat electrocaloric elements
and corrugated electrocaloric elements.
10. The heat transfer system of claim 8, wherein the electrocaloric
elements comprise complementary corrugated electrocaloric elements
that cooperate to form a honeycomb structure.
11. (canceled)
12. The heat transfer system of claim 3, wherein the plurality of
electrocaloric elements are arranged in an alternating order of
polarity between adjacent electrocaloric elements.
13. (canceled)
14. A heat transfer system, comprising 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.
15. The heat transfer system of claim 14, wherein the
electrocaloric film comprises an electrocaloric polymer.
16. (canceled)
17. The heat transfer system of claim 14, further comprising one or
more electrically conductive spacer elements disposed between
adjacent layers of the electrocaloric film.
18. The heat transfer system of claim 14, further comprising one or
more electrically non-conductive spacer elements disposed between
adjacent layers of the electrocaloric film.
19. The heat transfer system of claim 14, wherein the support
elements further comprise electrical bus elements in electrical
contact with the conductive material electrode layers.
20. The heat transfer system of claim 14, wherein the loops of the
continuous electrocaloric polymer film are in a back and forth
configuration.
21. (canceled)
22. (canceled)
23. The heat transfer system of claim 1, comprising at least two
adjacent electrocaloric elements that share an electrode at least
partially embedded between the electrocaloric films of the adjacent
electrocaloric elements.
24. The heat transfer system of claim 23, wherein the embedded
electrode is a live electrode, and comprising ground electrodes
adjacent to the fluid flow path.
25. The heat transfer system of claim 1, wherein the electrocaloric
film comprises an electrocaloric polymer film under tensile stress.
Description
BACKGROUND
[0001] 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.
[0002] 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.
BRIEF DESCRIPTION
[0003] 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.
[0004] 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.
[0005] In any of the foregoing embodiments, the corrugated fluid
flow guide elements comprise electrically non-conductive corrugated
spacer elements disposed between adjacent electrocaloric
elements.
[0006] In any of the foregoing embodiments, the corrugated fluid
flow guide elements comprise electrically conductive corrugated
spacers disposed between adjacent electrocaloric elements.
[0007] 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.
[0008] 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.
[0009] In any of the foregoing embodiments, the electrically
conductive corrugated spacers are configured as a microchannel
structure or an open-cell foam.
[0010] In any of the foregoing embodiments, the electrically
conductive corrugated spacers comprise carbon nanotubes.
[0011] In any of the foregoing embodiments, the fluid flow guide
elements comprise electrocaloric elements from said plurality of
electrocaloric elements.
[0012] In any of the foregoing embodiments, the electrocaloric
elements comprise alternating adjacent flat electrocaloric elements
and corrugated electrocaloric elements.
[0013] In any of the foregoing embodiments, the electrocaloric
elements comprise complementary corrugated electrocaloric elements
that cooperate to form a honeycomb structure.
[0014] In any of the foregoing embodiments, adjacent electrocaloric
elements comprise adhesive joints at intersecting junctions.
[0015] In any of the foregoing embodiments, the plurality of
electrocaloric elements are arranged in an alternating order of
polarity between adjacent electrocaloric elements.
[0016] 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.
[0017] In any of the foregoing embodiments, a physical separation
between adjacent electrocaloric elements is 1 .mu.m to 100 mm.
[0018] In any of the foregoing embodiments, the electrocaloric
elements have a thickness of 1 .mu.m to 1000 .mu.m.
[0019] In any of the foregoing embodiments, the electrocaloric film
comprises an electrocaloric polymer.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] In any of the foregoing embodiments, the electrocaloric film
comprises an electrocaloric polymer film under tensile stress.
[0025] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] 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:
[0027] FIG. 1 is a schematic depiction of an example embodiment of
an electrocaloric heat transfer system and stack and spacer
configuration;
[0028] FIGS. 2A, 2B, 2C, 2D, 2E, and 2F each is a schematic
depiction of example embodiments of different corrugated spacer
configurations;
[0029] FIG. 3 is a schematic depiction of an example embodiment of
a corrugated spacer configuration with an electrically conductive
spacer;
[0030] FIG. 4 is a schematic depiction of an example embodiment of
a spacer that is integrated with an electrocaloric element
electrode;
[0031] FIG. 5 is a schematic depiction of another example
embodiment of a spacer that is integrated with an electrocaloric
element electrode;
[0032] FIG. 6 is a schematic depiction of an example embodiment of
a corrugated spacer configuration with an electrically
non-conductive spacer;
[0033] FIG. 7 is a schematic depiction of an example embodiment
where an electrocaloric element serves as a corrugated spacer;
[0034] FIG. 8 is a schematic depiction of another example
embodiment where an electrocaloric element serves as a corrugated
spacer;
[0035] FIG. 9 is a schematic depiction of another example
embodiment where an electrocaloric element serves as a corrugated
spacer;
[0036] FIG. 10 is a schematic depiction of an alternate embodiment
of an electrocaloric heat transfer system and stack and spacer
configuration;
[0037] FIG. 11 is a schematic depiction of an alternate embodiment
of an electrocaloric heat transfer system and stack and spacer
configuration; and
[0038] FIG. 12 is a schematic depiction of an example embodiment of
heat transfer system comprising an electrocaloric stack and other
components.
DETAILED DESCRIPTION
[0039] 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.
[0040] With reference now to FIG. 1, an example of a stack 10 of
electrocaloric elements 12 is shown in a perspective view and in an
exploded front cross-sectional view. As shown in FIG. 1, the
electrocaloric elements 12 comprise an electrocaloric film 14, a
first electrode 16, and a second electrode 18. In some embodiments,
electrocaloric film thickness can be in a range from having a lower
limit of 0.1 .mu.m, more specifically 0.5 .mu.m, and even more
specifically 1 .mu.m. In some embodiments, the film thickness range
can and having an upper limit of 1000 .mu.m, more specifically 100
.mu.m, and even more specifically 10 .mu.m. 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.sub.3 ("PT"),
Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3 ("PMN"), PMN-PT, LiTaO.sub.3,
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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] With continued reference to FIG. 1, corrugated spacer
elements 19 are disposed between the electrocaloric elements 12,
and form a fluid flow path 20 along the electrocaloric elements 12
for a working fluid such as a fluid to be thermally conditioned
(e.g., air) or a heat transfer fluid (e.g., a dielectric organic
compound) for thermal communication with an external heat source or
heat sink. In some aspects, the corrugation pattern is on a plane
generally perpendicular to the fluid flow path 20, and extends in a
direction generally parallel to the fluid flow path 20. The
extension along the fluid flow path can be linear (i.e., in a
straight line) or non-linear. In some embodiments, spacing between
adjacent electrocaloric elements can be in a range from having a
lower limit of 1 .mu.m, more specifically 10 .mu.m, and even more
specifically 50 .mu.m. In some embodiments, the separation spacing
range can have an upper limit of 200 mm, more specifically 10 mm,
even more specifically 2 mm. It is understood that these upper and
lower range limits can be independently combined to disclose a
number of different possible ranges.
[0045] 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 FIGS. 2A-2F. FIG. 2A
depicts a triangular corrugated spacer configuration that extends
linearly along the fluid flow path. FIG. 2B depicts a triangular
corrugated spacer configuration that extends non-linearly along the
fluid flow path (a waveform extension in this case, but other
non-linear extension patterns are contemplated as well). FIG. 2C
depicts a sinusoidal corrugated configuration that extends linearly
along the fluid flow path. FIG. 2D depicts a trapezoidal corrugated
configuration that extends non-linearly along the fluid flow path.
FIG. 2E depicts a rectangular strip corrugated configuration that
extends non-linearly along the fluid flow path. FIG. 2F depicts a
cylindrical corrugated configuration that extends linearly along
the fluid flow path. These examples are of course only
representative of many possible configurations of corrugated spacer
elements, and should not be considered as limiting. It should also
be noted that although FIG. 1 depicts a single continuous spacer
element between each electrocaloric element, multiple discrete
corrugated spacer elements between electrocaloric elements can be
used as well.
[0046] 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.
[0047] An example of an embodiment of electrically conductive
spacer elements is depicted in FIG. 3. As shown in FIG. 3,
electrocaloric elements 12 are disposed in a stack in an
alternating order of polarity between adjacent electrocaloric
elements, with the electrocaloric element 12 shown at the top of
the stack having a positive polarity electrode on top and a
negative polarity electrode on the bottom. Alternatively, instead
of positive and negative electrodes in the stack, the electrodes
can be categorized as either live electrodes (either positive or
negative polarity) or ground electrodes. The electrocaloric element
12 adjacent to the top electrode has a reverse order of polarity
with a negative electrode on top and a positive electrode on the
bottom. This alternating order of polarity can then be repeated
throughout the stack. Such a configuration allows the corrugated
spacer elements 19a to be electrically conducting, which can help
promote uniform charge across the electrodes and avoid parasitic or
non-uniform electrical current that could adversely affect
electrocaloric performance. Electrically conductive spacer elements
can be formed by various techniques including but not limited to
depositing a layer of conductive material like metal or carbon
nanotubes and lithographically etching a corrugated pattern into
the layer (e.g., through a lithographic mask), or depositing a
conductive material or growing carbon nanotubes in a corrugated
pattern, microchannel extrusion, open-cell foam, or by laminating a
corrugated layer of conductive material to the electrocaloric
element.
[0048] 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 FIGS. 4 and 5. As shown
in FIG. 4, a partial integration is achieved by forming spacer
element 19a as an extension of electrode 18a, which is then
electrically connected to electrode 18b. This can be accomplished
for example by depositing a conductive layer for electrode 18a
(e.g., depositing carbon nanotubes by chemical vapor deposition or
depositing metal by sputtering or other deposition techniques). The
conductive layer can then be masked in areas other than where
spacer 19a is desired, and continued deposition of conductive
material continued to form the conductive spacer 19a. The resulting
structure than then be connected to an adjacent electrocaloric
element with an electrical connection between conductive spacer 19a
and adjacent electrode 18b, with electrodes of different polarity
disposed on the opposite sides of the electrocaloric films 14 from
the electrodes 18a and 18b. An example of a full integration of a
conductive spacer with electrodes on adjacent electrocaloric
elements is shown in FIG. 5. In FIG. 5, an electrically conductive
combination electrode 18a and spacer 19a can be formed by
microchannel extrusion techniques and disposed between adjacent
electrocaloric elements 14.
[0049] An example of an embodiment of electrically non-conductive
spacer elements is depicted in FIG. 6. As shown in FIG. 6,
electrocaloric elements 12 are disposed in a stack in a uniform
order of polarity, with each electrocaloric element 12 having a
negative polarity electrode on top and a positive polarity
electrode on the bottom. Alternatively, instead of positive and
negative electrodes in the stack, the electrodes can be categorized
as either live electrodes (either positive or negative polarity) or
ground electrodes. In this configuration, electrically
non-conductive spacer elements 19b can contribute to electrical
isolation between electrodes of different polarities by maintaining
physical separation between the electrocaloric elements without
providing a conductive path. Similar fabrication techniques as
described above for conductive spacer elements can be used for
non-conductive spacer elements, but with non-conductive materials,
e.g., plastics or ceramics.
[0050] 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 FIGS. 7 and 8. As shown in FIG. 7, a honeycomb structure
of electrocaloric elements 14a is disposed in a stack 10a, retained
at the edges by electric bus/support elements 22. The honeycomb
structure of the electrocaloric elements 14a also provides a
corrugated flow guide structure 19c. As used herein, "honeycomb"
includes any cellular structure that extends generally parallel to
the direction of fluid flow, and is not limited to hexagonal
cellular structures. For example, the cellular structure depicted
in FIG. 7 has a rhomboid cellular structure. In some aspects, the
honeycomb structure of electrocaloric elements can utilize the
above-described alternating order of polarity configuration to
avoid shorting across adjoining electrocaloric elements in the
structure, although this is not required, as insulators such as
insulating adhesive could also be used to prevent short circuits.
An example of such an alternating polarity configuration is
illustrated in FIG. 8 for a hexagonal honeycomb structure, where
electrocaloric elements 14 (comprising an electrocaloric film
sandwiched between conductive electrodes as described herein) are
configured in a honeycomb pattern to serve as both electrocaloric
elements and as corrugated spacer structure 19c. A conductive
adhesive (e.g., a polymer resin adhesive) joint 24 can optionally
be disposed at the interfaces between adjacent electrocaloric
elements to promote electrical and structural integrity for the
structure. A non-conductive adhesive can also be used if an
electrical connection at the interfaces is not needed or desired.
In another embodiment, flat or planar electrocaloric elements 12
alternate with corrugated electrocaloric elements 19 to form a
honeycomb structure (with the electrocaloric elements comprising an
electrocaloric film sandwiched between conductive electrodes as
described herein). An example of such a structure is shown in FIG.
9.
[0051] Another example of an embodiment is depicted in FIG. 10.
With reference now to FIG. 10, a stack is shown where bus elements
electrodes 16a and 18a are connected to bus bars 22. As shown in
FIG. 10 the electrodes 18a are at least partially embedded between
the electrocaloric films 14 of adjacent electrocaloric elements. In
this embodiment, the electrode 18a serves as an electrode for two
adjacent electrocaloric elements or, put another way, the two
adjacent electrocaloric elements share a single electrode. The
electrodes 16a of opposite polarity are disposed on the outside of
the electrocaloric element `sandwich` and are not shared. Spacer
elements 19 are disposed between adjacent electrocaloric elements
on the side of electrodes 16a. The configuration of FIG. 10 can
provide technical benefits by protecting the embedded electrode 18a
from potential short circuits. In some embodiments, the at least
partially embedded electrode is a live electrode, and the electrode
exposed to the fluid flow path is a ground electrode. In some
embodiments, embedded electrodes of different shapes or
configurations can be printed to provide various properties (e.g.,
stress management) to the electrocaloric elements. It should be
noted that although FIG. 10 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.
[0052] 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 FIG. 11 where a
continuous electrocaloric element 14a is looped in a back and forth
configuration around supporting electrical bus elements 22a and
22b. In this configuration, the positive polarity bus elements 22b
and negative polarity bus elements 22a and the back-and-forth loop
configuration cooperate to provide a stack configuration with an
alternating order of polarity, so that spacer elements 26 can be
electrically conductive without causing a short circuit. Of course,
the spacer elements 26 can also be non-conductive. In other
alternative embodiments, the bus elements can be live and ground
instead of positive and negative polarity. Alternatively, the bus
elements could be live elements and ground elements. In some
embodiments, the electrocaloric film is an electrocaloric polymer
film under tensile stress. The level of tensile stress can be
adjusted by the skilled person to achieve design parameters such as
to influence crystal structure ordering in an electrocaloric
polymer material. In some embodiments, the tensile stress is
sufficient to maintain an electrocaloric film taut or stretched,
which can in some cases provide promote maintaining physical
separation between film layers in a stack configuration. Although
any of the embodiments described herein can be configured with
electrocaloric elements under tensile stress, the loop
configuration of FIG. 11 can in some embodiments promote a secure
connection to the support elements when tensile stress is
applied.
[0053] An example embodiment of a heat transfer system and its
operation are further described with respect to FIG. 12. As shown
in FIG. 12, a heat transfer system 310 comprises an electrocaloric
stack 311 has one or more electrically conductive liquids in
thermal communication with a heat sink 317 through a first thermal
flow path 318, and in thermal communication with a heat source 320
through a second thermal flow path 322. A controller 324 is
configured to control electrical current to through a power source
(not shown) to selectively activate electrocaloric elements (not
shown) in the stack 311. The controller 324 is also configured to
open and close control valves 326 and 328 to selectively direct the
electrically conductive liquid along the first and second flow
paths 318 and 322.
[0054] 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.
[0055] 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.
[0056] 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.
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