U.S. patent application number 14/142252 was filed with the patent office on 2014-07-03 for thermal energy storage for temperature regulation in electric vehicles.
The applicant listed for this patent is K. Russell Carrington, Arlon J. Hunt. Invention is credited to K. Russell Carrington, Arlon J. Hunt.
Application Number | 20140182319 14/142252 |
Document ID | / |
Family ID | 51015632 |
Filed Date | 2014-07-03 |
United States Patent
Application |
20140182319 |
Kind Code |
A1 |
Hunt; Arlon J. ; et
al. |
July 3, 2014 |
THERMAL ENERGY STORAGE FOR TEMPERATURE REGULATION IN ELECTRIC
VEHICLES
Abstract
A system to produce heated and refrigerated working fluids in an
electric vehicle comprises a storage material to store and release
thermal energy, an off-board energy source to provide thermal
energy to said storage material, and a refrigerator. The
refrigerator is powered by thermal energy from the storage material
to produce refrigeration. Thermal energy is transferred by at least
one working fluid. At least one heat exchanger element enables
thermal communication between the storage material, the off-board
energy source, the refrigerator, and the at least one working
fluid. At least one control element to control the flow of said at
least one working fluid.
Inventors: |
Hunt; Arlon J.; (El Cerrito,
CA) ; Carrington; K. Russell; (San Francisco,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hunt; Arlon J.
Carrington; K. Russell |
El Cerrito
San Francisco |
CA
CA |
US
US |
|
|
Family ID: |
51015632 |
Appl. No.: |
14/142252 |
Filed: |
December 27, 2013 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61746735 |
Dec 28, 2012 |
|
|
|
Current U.S.
Class: |
62/238.1 ;
165/10 |
Current CPC
Class: |
F25B 27/00 20130101;
B60H 1/00392 20130101; F25B 15/00 20130101; B60H 1/00257 20130101;
B60H 1/005 20130101; F25B 17/00 20130101; F25B 2400/24
20130101 |
Class at
Publication: |
62/238.1 ;
165/10 |
International
Class: |
F25B 17/02 20060101
F25B017/02 |
Claims
1. A system to produce heated and refrigerated working fluids in an
electric vehicle comprising: a storage material to store and
release thermal energy; a refrigerator, powered by thermal energy
from said storage material, to produce refrigeration; at least one
working fluid to transfer thermal energy released by said storage
material and refrigeration produced by said refrigerator; at least
one heat exchanger element to enable thermal communication between
said storage material, said refrigerator, and said at least one
working fluid; and at least one control element to control the flow
of said at least one working fluid.
2. The system of claim 1, including an off-board energy source to
provide thermal energy to said storage material.
3. The system of claim 1, wherein at least some of said heated and
refrigerated working fluids are used to heat and refrigerate the
cabin of said electric vehicle.
4. The system of claim 1, wherein at least some of said heated and
refrigerated working fluids are used to heat and refrigerate the
battery compartment of said electric vehicle.
5. The system of claim 1, wherein said storage material at least
partially melts to store thermal energy, and at least partially
solidifies to release the stored thermal energy.
6. The system of claim 5, wherein said storage material is a pure
metal or eutectic metal alloy that melts and solidifies at a single
temperature.
7. The system of claim 6, wherein said pure metal is one of
aluminum, magnesium, and zinc.
8. The system of claim 6, wherein said eutectic metal alloy has a
relative fraction of aluminum of at least 83 wt. % and a relative
fraction of silicon of 12 wt. %.
9. The system of claim 6, wherein said eutectic metal alloy has a
relative fraction of magnesium of at least 39 wt. % and a relative
fraction of silicon of 56 wt. %.
10. The system of claim 6, wherein said eutectic metal alloy has a
relative fraction of aluminum of at least 59 wt. % and a relative
fraction of magnesium of 36 wt. %.
11. The system of claim 5, wherein said storage material is a
hypoeutectic or hypoeutectic metal alloy that melts and solidifies
across a temperature range.
12. The system of claim 11, wherein said hypoeutectic or
hypoeutectic is composed of aluminum and silicon with relative
fractions of aluminum and silicon that sum to at least 90 wt. %,
but does not have a relative fraction of aluminum of at least 83
wt. % and a relative fraction of silicon of 12 wt. %.
13. The system of claim 11, wherein said hypoeutectic or
hypoeutectic is composed of magnesium and silicon with relative
fractions of magnesium and silicon that sum to at least 90 wt. %,
but does not have a relative fraction of magnesium of at least 39
wt. % and a relative fraction of silicon of 56 wt. %.
14. The system of claim 11, wherein said hypoeutectic or
hypoeutectic is composed of aluminum and magnesium with relative
fractions of aluminum and magnesium that sum to at least 90 wt. %,
but does not have a relative fraction of aluminum of at least 59
wt. % and a relative fraction of magnesium of 36 wt. %.
15. The system of claim 1, including an off-board energy source
that is an electrical source.
16. The system of claim 15, wherein said electrical source is the
same electrical source as that used to charge the electrochemical
battery of said electric vehicle.
17. The system of claim 15, wherein said at least one heat
exchanger element is an electrical resistance heating wire that
converts electrical energy from said electrical source to thermal
energy to store in said storage material.
18. The system of claim 1, including an off-board energy source
that is a high-temperature heat source.
19. The system of claim 18, wherein said high-temperature heat
source is a natural gas combustor.
20. The system of claim 1, wherein said refrigerator is an
absorption refrigerator.
21. The system of claim 20, wherein said absorption refrigerator
uses water as the absorbent and ammonia as the absorbate.
22. The system of claim 1, wherein said refrigerator is an
adsorption refrigerator.
23. The system of claim 22, wherein said adsorption refrigerator
uses zeolites, silicas, aluminas, active carbons, or graphites as
the adsorbent.
24. The system of claim 1, wherein said at least one working fluid
is air.
25. The system of claim 1, wherein said at least one working fluid
is not air.
Description
CLAIM OF PRIORITY
[0001] This application claims priority to U.S. patent application
Ser. No. 61/746,735, filed Dec. 28, 2012, entitled "THERMAL ENERGY
STORAGE FOR TEMPERATURE REGULATION IN ELECTRIC VEHICLES" which is
incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] Embodiments of the present invention relate to systems and
methods for using on-board thermal energy storage to supply heated
or refrigerated working fluid to the cabin and electrochemical
battery compartment of an electric vehicle.
BACKGROUND OF THE INVENTION
[0003] Driving range and upfront cost are considerations in a
consumer's decision to purchase an electric vehicle (EV). Both are
related to the on-board electrochemical battery: driving range is
related to capacity and other performance characteristics of the
battery, and the cost of the battery affects vehicle upfront
cost.
[0004] In some EVs, the battery supplies energy to the vehicle's
powertrain, heating, ventilation, and air-conditioning (HVAC)
system, battery compartment, and other power systems (e.g., those
responsible for steering, windows, locks, etc.). The HVAC system
can require a significant amount of energy; in some cases,
operating the powertrain and HVAC systems simultaneously can reduce
driving range up to 35%. Furthermore, the cost of the battery
required to supply energy to the HVAC system can account for up to
20% of vehicle upfront cost. The battery compartment requires
energy to regulate battery temperature, which influences
performance characteristics (as a general rule, temperatures that
are too low decrease battery performance while temperatures that
are too high destabilize battery chemistry). Therefore achieving
and maintaining an appropriate battery temperature decreases the
energy supplied by the battery to the powertrain and reduces
driving range.
[0005] The powertrain requires electrical energy, but batteries are
expensive for storing energy for the HVAC system and battery
compartment. High-temperature thermal energy storage systems are
less expensive than batteries and can provide thermal energy of
sufficient quality for an HVAC system using direct heating and a
thermally-powered refrigerator, and for a battery compartment to
regulate battery temperature.
INCORPORATION BY REFERENCE
[0006] The following references are incorporated herein by
reference in their entireties:
[0007] Deloitte LLP. "Unplugged: Electric vehicle realities versus
consumer expectations." 2011.
[0008] Barnitt, R., Brooker, A., Ramroth, L., Rugh, J., Smith, K.
"Analysis of Off-Board Powered Thermal Preconditioning in Electric
Drive Vehicles," Presented at the 25.sup.th World Battery, Hybrid
and Fuel Cell Electric Vehicle Symposium & Exhibition.
Shenzhen, China November 5-9, 2010, NREL/CP-5400-49252, December
2010.
[0009] The Wall Street Journal. "Nissan Says Leaf Electric Will Be
Profitable With U.S. Plant." Published May 13, 2010; retrieved Oct.
25, 2012.
[0010] Birchenall, C. E., Reichman, A. F. "Heat Storage in Eutectic
Alloys." Metallurgical Transactions A, Volume 11A, August
1980-1415.
SUMMARY OF THE INVENTION
[0011] Embodiments of the system and method of the invention
include a system and a method for using on-board thermal energy
storage to supply heated or refrigerated working fluid to the cabin
and battery compartment of an electric vehicle. The system
comprises one or more of the following: a storage material to store
thermal energy; an off-board energy source to provide thermal
energy to the storage material during charging; a refrigerator
powered by thermal energy stored by the storage material; piping
and one or more working fluids to transfer thermal energy or
refrigeration through the system; heat exchanger elements to enable
thermal communication between the storage material, off-board
energy source, refrigerator, battery compartment, and working
fluids; and control elements to control the flow of the working
fluids.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 shows an embodiment of the invention that uses air as
the working fluid.
[0013] FIG. 2 shows an embodiment of the invention that uses a
working fluid other than air.
[0014] FIG. 3 shows an embodiment of the invention that uses air as
the working fluid during charging.
[0015] FIG. 4 shows an embodiment of the invention that uses air as
the working fluid during heating only.
[0016] FIG. 5 shows an embodiment of the invention that uses air as
the working fluid during refrigeration only.
[0017] FIG. 6 shows an embodiment of the invention that uses a
working fluid other than air during heating only with additional
detail on the piping, variable-speed fans/pumps, and valves.
[0018] FIG. 7 shows an embodiment of the invention that uses a
working fluid other than air during refrigeration only with
additional detail on the piping, variable-speed fans/pumps, and
valves that supply heated or refrigerated air to the cabin and
batter compartment.
[0019] FIG. 8 shows an embodiment of the invention that uses a
working fluid other than air during heating only with additional
detail on the piping, variable-speed fans/pumps, and valves that
supply heated or refrigerated air to the cabin, and heated or
refrigerated non-air working fluid to the battery compartment.
[0020] FIG. 9 shows an embodiment of the invention that uses a
working fluid other than air during refrigeration only with
additional detail on the piping, variable-speed fans/pumps and
valves that supply heated or refrigerated air to the cabin, and
heated or refrigerated non-air working fluid to the battery
compartment.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0021] The invention is illustrated, by way of example and not by
way of limitation, in the figures of the accompanying drawings in
which like references indicate similar elements. References to
embodiments in this disclosure are not necessarily to the same
embodiment, and such references mean at least one. While specific
implementations are discussed, it is understood that this is done
for illustrative purposes only. A person skilled in the relevant
art will recognize that other components and configurations may be
used without departing from the scope and spirit of the
invention.
[0022] In the following description, numerous specific details will
be set forth to provide a thorough description of the invention.
However, it will be apparent to those skilled in the art that the
invention and embodiments thereof may be practiced without these
specific details. In other instances, well-known features have not
been described in detail so as not to obscure the invention.
[0023] Embodiments of the invention relate to the use of on-board
thermal energy storage to supply heated or refrigerated working
fluid to the cabin and battery compartment of an electric vehicle.
In a preferred embodiment, a system in accordance with the present
invention comprises: a storage material to store thermal energy; an
off-board energy source to provide thermal energy to the storage
material during charging; a refrigerator powered by thermal energy
stored by the storage material; piping and one or more working
fluids to transfer thermal energy or refrigeration through the
system; heat exchanger elements to enable thermal communication
between the storage material, off-board energy source,
refrigerator, battery compartment, and working fluids; and control
elements such as variable-speed fans/pumps and valves to control
the flow of the working fluids. In the following figures, dotted
pipes indicate no working fluid is flowing through them, and black
heat exchanger elements, variable-speed fans/pumps, and valves
indicate they are not active or closed.
[0024] Some embodiments, referred to as air embodiments, use air as
the only working fluid. An air embodiment, shown in FIG. 1,
comprises: a storage material 100; an off-board energy source 160;
a connector 170; a refrigerator 110; heat exchanger elements 120a
to 120e; variable-speed fans/pumps 130a to 130c; valves 140a to
140d; and pipes 150a to 150k. Pipes 150a to 150d, termed the heat
pipe system, contain air that transfers thermal energy from the
storage material 100 that is used to heat the cabin and battery
compartment. Pipes 150e to 150i, termed the storage-refrigerator
pipe system, contain air that transfers thermal energy from the
storage material 100 to the refrigerator 110. Pipes 150j to 150k,
termed the refrigeration pipe system, contain air that transfers
refrigeration from the refrigerator 110 that is used to refrigerate
the cabin and battery compartment. All of the pipe systems in this
air embodiment are open so that air can be continuously taken in
from, and exhausted to, the environment.
[0025] Other embodiments, referred to as hybrid embodiments, use
non-air working fluid (e.g., oil) in at least one pipe system. In a
hybrid embodiment shown in FIG. 2, the storage material 100,
off-board energy source 160, connector 170, refrigerator 110, heat
exchanger elements 120a to 120e, variable-speed fans/pumps 130a to
130c, valves 140a to 140d, and pipes 150a to 150k are the same as
the air embodiment shown in FIG. 1. However, the heat,
storage-refrigerator, and refrigeration pipe systems contain the
same or different non-air working fluids, and are closed so the
non-air working fluids are not lost to the environment. The heat
piping system, pipes 150a to 150d and 150m, transfers thermal
energy from the storage material 100 to heat exchanger element 120f
where it may be used to heat air to heat the cabin and battery
compartment, heat another non-air working fluid to heat the battery
compartment, or heat the battery compartment directly. The
refrigeration piping system, pipes 150j to 150l, transfers
refrigeration from the refrigerator 110 to heat exchanger element
120g where it may be used to refrigerate air to refrigerate the
cabin and battery compartment, refrigerate another non-air working
fluid to refrigerate the battery compartment, or refrigerate the
battery compartment directly. It is noted that any of the heat,
storage-refrigerator, or refrigeration pipe systems in a preferred
hybrid embodiment may contain air as the working fluid, and
therefore be open as in FIG. 1, as long as non-air working fluid is
used in at least one pipe system of the hybrid embodiment.
[0026] The requirements of an embodiment depend on EV
considerations such as the temperature range of the environment
around the EV (e.g., -80.degree. C. to 60.degree. C.), the heating
and cooling loads of the EV (e.g., 10 kW), and the target upfront
cost of the EV. The degree to which an embodiment meets these
requirements in turn depends on the choice of working fluid(s),
which can be influenced by many factors including, by way of
example: the temperature range at which the working fluid is
physically and chemically stable (i.e., it does not undergo phase
change or chemical decomposition); the specific heat, thermal
conductivity, and density of the working fluid; the chemical
reactivity of the working fluid with the materials of the pipes,
heat exchangers, variable-speed fans/pumps, valves; and the current
and future prices, and availability, of the working fluid.
Therefore an air embodiment may be best suited for one set of EV
considerations, and a hybrid embodiment with at least one non-air
working fluid may be best suited for another set of
considerations.
[0027] FIG. 3 shows a schematic of the air embodiment shown in FIG.
1 during charging; however, a person of ordinary skill in the
relevant art will recognize that the following discussion on
charging is relevant to all embodiments, regardless of the choice
of working fluid(s). The off-board energy source 160 connects to
the storage material 100 through the connector 170. Thermal energy
from the off-board energy source 160 transfers through the heat
exchanger element 120a and is stored in the storage material
100.
[0028] In an embodiment, the off-board energy source 160 can be an
electrical source, and can be the same electrical source used to
charge the batteries that supply energy to the powertrain. In this
case, the connector 170 establishes an electrical connection
between the off-board electrical source 160 and the heat exchanger
element 120a. The heat exchanger element 120a can be an electrical
resistance heating wire that simultaneously converts electrical
energy from the off-board electrical source 160 into thermal
energy, and transfers thermal energy to the storage material
100.
[0029] In another embodiment, the off-board energy source 160 can
be a high-temperature heat source such as a natural gas combustor.
In this case, the connector 170 can establish a connection capable
of transferring thermal energy in a working fluid between the
off-board high-temperature heat source 160 and the heat exchanger
element 120a, and the heat exchanger element 120a transfers thermal
energy to the storage material 100.
[0030] FIG. 4 shows a schematic of an air embodiment during heating
only with additional detail on the piping, variable-speed
fans/pumps, and valves that supply heated or refrigerated air to
the cabin and battery compartment. Variable-speed fan/pump 130a
forces ambient air through heat exchanger element 120b, which
causes heat exchange between the storage material 100 and air.
During heat exchange, the storage material 100 releases thermal
energy stored during charging, and the air absorbs thermal energy
and increases in temperature. The temperature of the heated air
depends on the air mass flow rate as specified by variable-speed
fan/pump 130a, the geometry of heat exchanger element 120b, and the
temperature difference between the storage material 100 and air.
Therefore the temperature of the heated air can be reasonably
controlled below the temperature of the storage material 100 by
specifying the air mass flow rate with variable-speed fan/pump
130a. A thermometer such as a k type thermocouple (not shown)
located in pipe 150d can measure the temperature of the heated air
and provide feedback to variable-speed fan/pump 130a.
[0031] The heated air is split at valve 140e, with the fraction
used to heat the cabin directed to valve 140f through pipe 150n,
and the other fraction used to heat the battery compartment
directed to valve 140g through pipe 150o. At valve 140f, the heated
air from pipe 150n mixes with ambient air from pipe 150p, and the
heated air mixture flows to the cabin through 150r. The mass flow
rate and temperature of the heated air mixture flowing to the cabin
depends on the mass flow rates and temperatures of the heated air
from pipe 150n and ambient air from pipe 150p. The mass flow rate
of the heated air from pipe 150n can be specified by variable-speed
fan/pump 130a and the fraction split at valve 140e; the mass flow
rate of ambient air from pipe 150p can be specified by
variable-speed fan/pump 130d; and the temperatures of the heated
air from pipe 150n and ambient air from pipe 150p are measured by
thermometers (not shown) located in pipe 150d and in the
environment, respectively. Therefore the mass flow rate and
temperature of the heated air mixture flowing to the cabin can be
reasonably controlled by specifying the mass flow rates of the
heated air and ambient air with variable-speed fans/pump 130a and
130d, and valve 140e.
[0032] At valve 140g, the heated air from pipe 150o mixes with
ambient air from pipe 150q, and the heated air mixture flows to the
battery compartment through 150s. Using the same logic as that in
the above paragraph, the mass flow rate and temperature of the
heated air mixture flowing to the battery compartment can be
reasonably controlled by specifying the mass flow rates of the
heated air and ambient air with variable-speed fans 130a and 130d,
and valve 140e. Thermometers (not shown) located in pipes 150r and
150s can measure the temperatures of the heated air mixtures
flowing to the cabin and battery compartment, respectively, and
provide feedback to variable-speed fans/pumps 130a and 130d, and
valve 140e.
[0033] FIG. 5 shows a schematic of the air embodiment shown in FIG.
4 during refrigeration only. Variable-speed fan 130b forces ambient
air through heat exchanger element 120c to heat the air. Using a
similar analysis to that described above, the mass flow rate and
temperature of the heated air flowing to the refrigerator can be
reasonably controlled by specifying the air mass flow rate with
variable-speed fan/pump 130b. The heated air flows through pipes
150g and 150h to heat exchanger element 120d. Thermal energy from
the heated air transfers through heat exchanger element 120d to a
refrigerator 110 that is powered by thermal energy and the air can
be exhausted to the environment through pipe 150i. The refrigerator
110 uses the heat transferred through heat exchanger element 120d
to power a thermodynamic cycle and produce refrigeration at heat
exchanger element 120e.
[0034] Variable-speed fan 130c forces ambient air through heat
exchanger element 120e to refrigerate the air. Using a similar
analysis to that described above, the mass flow rate and
temperature of the refrigerated air can be reasonably controlled by
specifying the air mass flow rate with variable-speed fan/pump
130c. The refrigerated air is split at valve 140e, with the
fraction used to refrigerate the cabin directed to valve 140i
through pipe 150t, and the other fraction used to refrigerate the
compartment directed to valve 140j through pipe 150u. At valve
140i, the refrigerated air from pipe 150t mixes with ambient air
from pipe 150v, and the refrigerated air mixture flows to the cabin
through 150x. At valve 140j, the refrigerated air from pipe 150u
mixes with ambient air from pipe 150w, and the refrigerated air
mixture flows to the battery compartment through 150y. Using a
similar analysis to that described above, the mass flow rates and
temperatures of the refrigerated air mixtures flowing to the cabin
and battery compartment can be reasonably controlled by specifying
the mass flow rates of the heated air and ambient air with
variable-speed fans/pump 130a and 130d, and valve 140e.
[0035] FIGS. 4 and 5 show schematics of an air embodiment during
heating and refrigeration only, respectively. However, a person of
ordinary skill in the relevant art will recognize from FIGS. 4 and
5, and indeed from any of the above figures, that charging,
heating, and refrigeration can be accomplished simultaneously.
Simultaneous charging, heating, and refrigerating can be
advantageous for heating and refrigerating the cabin and battery
compartment of an EV before disconnecting the EV from the off-board
energy source because initial heating and cooling loads tend to be
much higher than steady-state loads. Furthermore, a person of
ordinary skill in the relevant art will recognize that other
arrangements of piping, variable-speed fans/pumps, and valves that
supplies heated and refrigerated air to the cabin and battery
compartment in an air embodiment may be used without departing from
the scope and spirit of the invention.
[0036] FIGS. 6 and 7 show schematics of a hybrid embodiment during
heating and refrigeration only, respectively, with additional
detail on the piping, variable-speed fans/pumps, and valves that
supply heated or refrigerated air to the cabin and battery
compartment. The operation of this hybrid embodiment is similar to
that of the air embodiment in FIGS. 4 and 5, except that the heat,
storage-refrigerator, and refrigeration pipe systems are closed,
and additional heat exchanger elements 120f to 120i are required to
transfer thermal energy and refrigeration to air that flows to the
cabin and battery compartment.
[0037] FIGS. 8 and 9 show schematics of a hybrid embodiment during
heating and refrigeration only, respectively, with additional
detail on the piping, variable-speed fans/pumps, and valves that
supply heated or refrigerated air to the cabin, and heated or
refrigerated non-air working fluid to the battery compartment. The
operation of this other hybrid embodiment is similar to that of the
hybrid embodiment in FIGS. 6 and 7, except that a closed pipe
system is used to heat and refrigerate the battery compartment with
a non-air working fluid. Using similar analyses to those described
above, the mass flow rate and temperature of the heated or
refrigerated air flowing to the cabin, and the heated or
refrigerated air or non-air working fluid flowing to the battery
compartment, can be reasonably controlled by specifying mass flow
rates with variable-speed fans/pumps 130a to 130e, and valves 140a
to 140l. A person of ordinary skill in the relevant art will
recognize that other arrangements of piping, variable-speed
fans/pumps, and valves that supplies heated or refrigerated air to
the cabin, and heated or refrigerated air or non-air working fluid
to the battery compartment, in a hybrid embodiment may be used
without departing from the scope and spirit of the invention.
[0038] There are a number of storage materials that store thermal
energy, and a person of ordinary skill in the relevant art will
recognize that any material that stores thermal energy may be used
in an embodiment without departing from the scope and spirit of the
invention. However, a storage material that at least partially
melts to store thermal energy, and that at least partially
solidifies to release thermal energy, is usable in an embodiment
because it uses latent heat storage. The choice of a storage
material in an embodiment can be influenced by many factors
including, by way of example: the temperatures at which at least
part of the storage material melts or solidifies; the latent heat
associated with melting and solidification; the densities of the
solid and liquid phases; the kinetics of melting and
solidification; the thermal conductivities in the solid,
solid-liquid, and liquid phases; the stability during cycling; the
chemical reactivity with containment materials and heat exchanger
elements; the effects of contaminants on the above factors; and the
current and future prices, and availability, of the storage
material. A preferred storage material has: a single temperature at
which it melts and solidifies, to better predict the temperature
difference between it and the working fluid; high latent heat and
density so less mass and volume are required; comparable solid and
liquid densities to reduce stresses associated with thermal
expansion; fast kinetics and high thermal conductivities (in all
phases) to decrease the duration of charging; a high degree of
chemical stability; and low-priced and readily-available
precursors.
[0039] Pure metals and eutectic metal alloys are useable in
embodiments because they melt and solidify at a single temperature
and have high latent heats and densities, fast kinetics, very high
thermal conductivities, high chemical stability, and relatively
cheap and available precursors. By way of example, aluminum-silicon
alloy with 12 wt. % silicon melts and solidifies at a single
temperature of approximately 577.degree. C. and has a latent heat
of fusion of approximately 515 kJ/kg, thermal conductivities in the
solid and liquid phases of approximately 180 W/m-.degree. C. and 70
W/m-.degree. C. respectively, known and stable chemistry, and low
historic precursor prices. Other examples of preferred pure metal
and eutectic metal alloys include pure aluminum, pure magnesium,
pure zinc, magnesium-silicon alloy with 56 wt. % silicon, and
aluminum-magnesium alloy with 36 wt. % magnesium.
[0040] Hypoeutectic and hypereutectic metal alloys are also useable
in embodiments. Hypoeutectic and hypereutectic metal alloys form a
system with two distinct phase changes from solid to liquid. The
first phase change from solid to mushy (i.e., partially solid,
partially liquid) occurs at the solidus temperature, and the second
phase change from mushy to liquid occurs at the liquidus
temperature. Both phase changes depend on the relative fractions of
elements, and type and quantity of trace elements present. When the
liquidus temperature is equal to the solidus temperature,
solid-to-mushy and mushy-to-liquid phase changes occur at a single
temperature; the metal alloy with these relative fractions is
termed the eutectic metal alloy. Metal alloys with a lower relative
fraction of an element than the eutectic metal alloy are termed
hypoeutectics, and those with a higher relative fraction are termed
hypereutectics. For example, aluminum-silicon alloy with 12 wt. %
silicon is the eutectic metal alloy of the aluminum-silicon system;
any aluminum-silicon alloy with less than 12 wt. % silicon is a
hypoeutectic of that system, while on with greater than 12 wt. %
silicon is hypereutectic.
[0041] A person of ordinary skill in the art will recognize that
any refrigerator that is powered by thermal energy may be used in
an embodiment without departing from the scope and spirit of the
invention. Two of the most common such refrigerators are absorption
and adsorption refrigerators. Absorption and adsorption
refrigerators both use thermal energy to drive a
sorption/desorption chemical reaction in a generator, which
compresses a working fluid and is analogous to the compressor in a
compression refrigerator. Absorption refrigerators are based on
liquid absorbent, with lithium bromide-water and water-ammonia the
most common absorbent-working fluid pairs. Adsorption
refrigerators, in contrast, are based on solid absorbent; there are
many adsorbent-working fluid pairs, but zeolites, silicas,
aluminas, active carbons, are graphites are common adsorbents for
water working fluid. The compressed working fluid eventually
evaporates in an evaporator, which absorbs thermal energy from its
surroundings. In any of the above figures, the generator is in
thermal communication with heat exchanger element 120d and the
evaporator is in thermal communication with heat exchanger element
120e. In embodiments, the refrigerator is a water-ammonia
absorption refrigerator, or an adsorption refrigerator that uses
zeolites, silicas, aluminas, active carbons, and/or graphites as
the adsorbent and water as the adsorbate.
[0042] The previous description of the preferred embodiments is
provided to enable any person skilled in the art to make or use the
embodiments of the present invention. While the invention has been
particularly shown and described with reference to preferred
embodiments thereof, it will be understood by those skilled in the
art that various changes in form and details may be made therein
without departing from the spirit and scope of the invention.
* * * * *