U.S. patent application number 14/303335 was filed with the patent office on 2014-10-02 for electrochemical compressor and refrigeration system.
This patent application is currently assigned to XERGY INCORPORATED. The applicant listed for this patent is Bamdad Bahar. Invention is credited to Bamdad Bahar.
Application Number | 20140290295 14/303335 |
Document ID | / |
Family ID | 42221559 |
Filed Date | 2014-10-02 |
United States Patent
Application |
20140290295 |
Kind Code |
A1 |
Bahar; Bamdad |
October 2, 2014 |
ELECTROCHEMICAL COMPRESSOR AND REFRIGERATION SYSTEM
Abstract
A refrigeration system defines a dosed loop that contains a
working fluid, at least part or the working fluid being circulated
through the dosed loop. The refrigeration system includes a first
heat transfer device that transfers heat from the first heat
reservoir to the working fluid, a second heat transfer device that
transfers heat from the working fluid to the second heat reservoir,
and an electrochemical compressor between the first and second heat
transfer devices. The electrochemical compressor includes one or
more electrochemical Cells electrically connected to each other
through a power supply, each electrochemical cell including a gas
pervious anode, a gas pervious cathode, and an electrolytic
membrane disposed between and in intimate electrical contact with
the cathode and the anode. The working, fluid includes a
condensable refrigerant that bypasses the electrochemical process;
and an electrochemically active fluid that participates in die
electrochemical process within the electrochemical compressor.
Inventors: |
Bahar; Bamdad; (Chester,
MD) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bahar; Bamdad |
Chester |
MD |
US |
|
|
Assignee: |
XERGY INCORPORATED
Georgetown
MD
|
Family ID: |
42221559 |
Appl. No.: |
14/303335 |
Filed: |
June 12, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12626416 |
Nov 25, 2009 |
8769972 |
|
|
14303335 |
|
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61200714 |
Dec 2, 2008 |
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Current U.S.
Class: |
62/238.6 |
Current CPC
Class: |
C01B 2203/1241 20130101;
Y02E 60/50 20130101; C01B 2203/02 20130101; C01B 2203/066 20130101;
F25B 1/00 20130101 |
Class at
Publication: |
62/238.6 |
International
Class: |
F25B 1/00 20060101
F25B001/00 |
Claims
1. A refrigeration system that conveys heat from a first heat
reservoir at a relatively low temperature to a second heat
reservoir at relatively high temperature, the refrigeration system
defining a closed loop that contains a working fluid, at least part
of the working fluid being circulated through the closed loop, the
refrigeration system comprising: a first heat transfer device that
transfers heat from the first heat reservoir to the working fluid,
a second heat transfer device that transfers heat from the working
fluid to the second heat reservoir, an expansion valve between the
first and second heat transfer devices that reduces pressure of the
working fluid, a conduit system and an electrochemical compressor
between the first and second heat transfer devices; wherein the
electrochemical compressor comprises: one or more electrochemical
cells electrically connected to each other through a power supply,
each electrochemical cell comprising: a gas pervious anode, a gas
pervious cathode, an electrolyte disposed between and in intimate
electrical contact with the cathode and the anode; an
electrochemical compressor input, an electrochemical compressor
output, wherein at least one of said one or more electrochemical
cells comprises an electrochemical compressor bypass; wherein the
working fluid comprises: a condensable refrigerant that essentially
bypasses the electrochemical process and remains in the closed loop
; and an electrochemically active fluid that participates in the
electrochemical process within the electrochemical compressor;
wherein said conduit system receives at least one
electrochemically-active fluid of said working fluid from said
electrochemical compressor output and, other components of the
working fluid from said electrochemical compressor bypass, wherein
said conduit system has a geometry that enables at least a portion
of the received working fluid to be imparted with a gain in kinetic
energy as it moves through the conduit system.
2. The refrigeration system of claim 1, wherein the electrolyte
comprises a solid electrolyte.
3. The refrigeration system of claim 1, further comprising a
temperature sensor thermally coupled to one or more of the working
fluid, the first heat transfer device, and the second heat transfer
device.
4. The refrigeration system of claim 1, wherein the condensable
refrigerant does not participate in the electrochemical
process.
5. The refrigeration system of claim 1, wherein the electrochemical
compressor includes: a cathode gas space on a nonelectrolyte side
of the cathode: and an anode gas space on a nonelectrolyte side of
the anode.
6. The refrigeration system of claim 1, wherein the electrochemical
compressor includes: a first electrochemically active route that
traverses the anode and cathode: a second non-electrochemical route
that bypasses the anode and cathode: and a combiner that combines
the components that have traversed the first and second routes.
7. The refrigeration system of claim 1, wherein the first heat
transfer device comprises a condenser.
8. The refrigeration system of claim 1, wherein the second heat
transfer device comprises an evaporator.
9. The refrigeration system of claim 1, further comprising a
mechanical compressor in series with the electrochemical
compressor.
10. The refrigeration system of claim 9, wherein the mechanical
compressor is between the electrochemical compressor and the first
heat transfer device.
11. The refrigeration system of claim 9, wherein the mechanical
compressor is between the electrochemical compressor and second
heat transfer device.
12. The refrigeration system of claim 1, wherein the working fluid
includes carbon dioxide.
13. The refrigeration system of claim 1, wherein the working fluid
includes a fluorocarbon gas.
14. The refrigeration system of claim 1, wherein the condensable
refrigerant is not water.
15. The refrigeration system of claim 1, wherein the condensable
refrigerant consists essentially of water.
16. The refrigeration system of claim 1, wherein the working fluid
comprises water.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/626,416, filed on Nov. 25, 2009 and
entitled Electrochemical Compressor and Refrigeration System,
currently pending, which claims priority to U.S. Application No.
61/200,714, filed on Dec. 2, 2008 and entitled "Electrochemical
Compressor and Heat Pump System,"; both of which are incorporated
herein by reference.
TECHNICAL FIELD
[0002] The disclosed subject matter relates to a refrigeration
system that includes a vapor-compression refrigeration cycle that
includes an electrochemical compressor configured to transfer a
refrigerant.
BACKGROUND
[0003] The function of both refrigeration cycles and heat pumps is
to remove heat from a heat source or reservoir at low temperature
and to reject the heat to a heat sink or reservoir at high
temperature. While many thermodynamic effects have been exploited
in the development of heat pumps and refrigeration cycles, the most
popular today is the vapor compression approach. This approach is
sometimes called mechanical refrigeration because a mechanical
compressor is used in the cycle.
[0004] Mechanical compressors account for approximately 30% of a
household's energy requirements and thus consume a substantial
portion of most utilities' base load power. Any improvement in
efficiency related to compressor performance can have significant
benefits in terms of energy savings and thus have significant
positive environmental impact. In addition, there are increasing
thermal management problems in electronic circuits, which require
smaller heat pumping devices with greater thermal management
capabilities.
[0005] Vapor compression refrigeration cycles generally contain
five important components. The first is a mechanical compressor
that is used to pressurize a gaseous working fluid. After
proceeding through the compressor, the hot pressurized working
fluid is condensed in a condenser. The latent heat of vaporization
of the working fluid is given up to a high temperature reservoir
often called the sink. The liquefied working fluid is then expanded
at substantially constant enthalpy in a thermal expansion valve or
orifice. The cooled liquid working fluid is then passed through an
evaporator. In the evaporator, the working fluid absorbs its latent
heat of vaporization from a low temperature reservoir often called
a source. The last element in the vapor compression refrigeration
cycle is the working fluid itself.
[0006] In conventional vapor compression cycles, the working fluid
selection is based on the properties of the fluid and the
temperatures of the heat source and sink. The factors in the
selection include the specific heat of the working fluid, its
latent heat of vaporization, its specific volume and its safety.
The selection of the working fluid affects the coefficient of
performance of the cycle.
[0007] For a refrigeration cycle operating between a lower limit,
or source temperature, and an upper limit, or sink temperature, the
maximum efficiency of the cycle is limited to the Carnot
efficiency. The efficiency of a refrigeration cycle is generally
defined by its coefficient of performance, which is the quotient of
the heat absorbed from the sink divided by the net work input
required by the cycle.
SUMMARY
[0008] In one general aspect, a refrigeration system conveys heat
from a first heat reservoir at a relatively low temperature to a
second heat reservoir at relatively high temperature. The
refrigeration system defines a closed loop that contains a working
fluid, at least part of the working fluid being circulated through
the closed loop. The refrigeration system includes a first heat
transfer device that transfers heat from the first heat reservoir
to the working fluid, a second heat transfer device that transfers
heat from the working fluid to the second heat reservoir, an
expansion valve between the first and second heat transfer devices
that reduces pressure of the working fluid, and an electrochemical
compressor between the first and second heat transfer devices. The
electrochemical compressor includes one or more electrochemical
cells electrically connected to each other through a power supply,
each electrochemical cell including a gas pervious anode, a gas
pervious cathode, and an electrolytic membrane disposed between and
in intimate electrical contact with the cathode and the anode.
[0009] Implementations can include one or more of the following
features. For example, the working fluid can include a condensable
refrigerant that bypasses the electrochemical process; and an
electrochemically active fluid that participates in the
electrochemical process within the electrochemical compressor.
[0010] In other implementations, the working fluid can include a
condensable refrigerant; water; and an electrochemically active
fluid. In other implementations, the working fluid includes a
condensable refrigerant that is not water; and an electrochemically
active fluid. In some implementations, the condensable refrigerant
does not participate in the electrochemical process.
[0011] The working fluid can include carbon dioxide. The working
fluid can include a fluorocarbon gas. The electrolytic membrane can
include a solid electrolyte, for example, a gel.
[0012] The refrigeration system can include a temperature sensor
thermally coupled to one or more of the working fluid, the first
heat transfer device, and the second heat transfer device. The
first heat transfer device can include a condenser. The second heat
transfer device can include an evaporator.
[0013] The electrochemical compressor can include a cathode gas
space on a nonelectrolyte side of the cathode; and an anode gas
space on a nonelectrolyte side of the anode. The electrochemical
compressor can include a first electrochemically active route that
traverses the anode and cathode; a second non-electrochemical route
that bypasses the anode and cathode; and a combiner that combines
the components that have traversed the first and second routes.
[0014] The refrigeration system can also include a mechanical
compressor. The mechanical compressor can be in series with the
electrochemical compressor. The mechanical compressor can be
between the electrochemical compressor and the first heat transfer
device. The mechanical compressor can be between the
electrochemical compressor and second heat transfer device.
[0015] In another general aspect, an electrochemical compressor
includes an inlet fluidly coupled to an evaporator to receive a
working fluid that comprises a condensable refrigerant and an
electrochemically active fluid; an outlet fluidly coupled to a
condenser; and one or more electrochemical cells electrically
connected to each other through a power supply. Each
electrochemical cell includes a gas pervious anode, a gas pervious
cathode, and an electrolytic membrane disposed between and in
intimate electrical contact with the cathode and the anode. The
anode, the cathode, and the electrolytic membrane are configured to
pass the electrochemically active fluid. The electrochemical cell
is configured to disassociate the condensable refrigerant from the
electrochemically active fluid to prevent the condensable
refrigerant from passing through the anode, the cathode, and the
electrolytic membrane. The electrolytic membrane includes a
membrane having a porous microstructure and an ion exchange
material impregnated throughout the membrane.
[0016] Implementations can include one or more of the following
features. For example, the impregnated membrane can have a Gurley
number of greater than 10,000 seconds.
[0017] The ion exchange membrane can be able to withstand a
pressure gradient between a side adjacent the anode and a side
adjacent the cathode. The ion exchange membrane can be able to
withstand a pressure gradient of at least 30 psi between a side
adjacent the anode and a side adjacent the cathode.
[0018] The ion exchange membrane can include a synthetic
fluoropolymer of tetrafluoroethylene. The synthetic fluoropolymer
can be an expanded polytetrafiuoroethylene having a porous
microstructure of polymeric fibrils. The ion exchange material can
substantially impregnate the membrane so as to render an interior
volume of the membrane substantially occlusive. The ion exchange
material can be impermeable to gas. The ion exchange material can
be permeable to gas. The ion exchange material can be selected from
a group consisting of perfluorinated sulfonic acid resin,
perfluorinated carboxylic acid resin, polyvinyl alcohol, divinyl
benzene, styrene-based polymers, and metal salts with or without a
polymer.
[0019] The anode, the cathode, and the electrolytic membrane can be
configured to pass the electrochemically active fluid if the
working fluid includes less than 50% of water.
[0020] The one or more electrochemical cells can be connected in
parallel with each other.
[0021] A first electrochemically active route can be defined by the
anode, the electrolytic membrane, and the cathode; and a second
non-electrochemical route bypasses the anode, the electrolytic
membrane, and the cathode.
[0022] The compressor can include a combiner that combines the
components of the working fluid that have traversed the first,
route, the second route, or both the first and second routes.
[0023] The ion exchange material can include a liquid electrolyte
embedded in a matrix. The ion exchange material can include an
anionic exchange membrane and the anode gas space operates at a
higher pressure than the cathode gas space.
[0024] The porous membrane can have a total thickness of less than
0.025 mm.
[0025] In another general aspect, a method of refrigeration
includes conveying heat from a first heat reservoir at a relatively
low temperature to a second heat reservoir at relatively high
temperature by circulating a working fluid through a closed loop
that is thermally coupled to the first heat reservoir at a first
portion and is thermally coupled to the second heat reservoir at a
second portion. The conveying includes transferring heat from the
working fluid at the second loop portion to the second heat
reservoir including liquefying at least some of the working fluid;
reducing a pressure of the at least partially liquefied working
fluid by expanding the working fluid at a substantially constant
enthalpy; and transferring heat from the first heat reservoir to
the working fluid at the first loop portion including vaporizing at
least some of the working fluid. The conveying also includes
increasing a pressure of the working fluid by dissociating an
electrochemically active fluid from a condensable refrigerant
within the working fluid to enable the condensable refrigerant to
separate from the electrochemically active fluid, electrochemically
ionizing the electrochemically active fluid by stripping charged
particles from the electrochemically active fluid, enabling the
ionized electrochemically active fluid to pass through an
electrolytic membrane, pumping the charged particles to create an
electric potential gradient across the electrolytic membrane,
pumping the ionized electrochemically active fluid across the
electrolytic membrane using the electric potential gradient,
electrochemically de-ionizing the electrochemically active fluid by
combining the pumped charged particles with the ionized
electrochemically active fluid, and pressuring the de-ionized
electrochemically active fluid. The conveying further includes
re-associating the pressurized de-ionized electrochemically active
fluid with the condensable refrigerant to form a pressurized
working fluid that flows to the second loop portion.
[0026] Implementations can include one or more of the following
features. For example, dissociating the electrochemically active
fluid from the condensable refrigerant can include passing the
working fluid through an anode gas space to thereby dissociate the
electrochemically active fluid from the condensable refrigerant
within the working fluid. Electrochemically ionizing the
electrochemically active fluid by stripping charged particles from
the electrochemically active fluid can include electrochemically
ionizing the electrochemically active fluid within a gas pervious
anode adjacent the anode gas space. Enabling the ionized
electrochemically active fluid to pass through the electrolytic
membrane can include enabling the ionized electrochemically active
fluid to enter the electrolytic membrane that is disposed between
the gas pervious anode and a gas pervious cathode.
[0027] Pumping the charged particles to create the electric
potential gradient across the electrolytic membrane can include
pumping electrons from the gas pervious anode to the gas pervious
cathode to create the electric potential gradient between the gas
pervious anode and the gas pervious cathode, and pumping the
ionized electrochemically active fluid across the electrolytic
membrane using the electric potential gradient can include pumping
the ionized electrochemically active fluid to the gas pervious
cathode.
[0028] Electrochemically de-ionizing the electrochemically active
fluid can include combining the pumped charged particles in the gas
pervious cathode with the ionized electrochemically active fluid,
and pressuring the de-ionized electrochemically active fluid can
include pressuring the de-ionized electrochemically active fluid
within a cathode gas space that is adjacent the gas pervious
cathode and is maintained at a higher pressure than the anode gas
space.
[0029] The method can also include controlling the amount of heat
conveyed by varying one or more of a current and a voltage applied
to pump the charged particles to create the electric potential
gradient across the electrolytic membrane.
[0030] There are several benefits to using carbon dioxide as a
refrigerant in a refrigeration system. If carbon dioxide manages to
leak out of the system, and make its way up to the ozone layer, the
ultraviolet radiation does not break up the molecule to release
highly active chlorine radicals that help to deplete the ozone
layer. Therefore, carbon dioxide does not deplete the ozone
layer.
[0031] Moreover, while many have noted a few problems associated
with the use of carbon dioxide in refrigeration systems, for
example, requiring operating at higher pressure and higher
compressor temperature, these operating requirements are found to
be more advantageous in automotive applications. The very high
cycle pressure results in a high fluid density throughout the
cycle, allowing miniaturization of the systems for the same heat
pumping power requirements. Furthermore, the high outlet
temperature of the compressor can permit faster defrosting of
automobile windshields and can even be used for combined space
heating and hot water heating in home usage. In fuel cell
applications involving the production of hydrogen from hydrocarbon
sources such as natural gas, hydrogen gas is fed to the electrode
assembly as a mixed gas stream with carbon dioxide present
(typically referred to as reformate). Thus, electrodes have been
developed and are commercially available (such as W. L. Gore &
Associates Inc. series 56 PRIMEA assembly) with suitable
electrochemical performance with mixed hydrogen and carbon dioxide
gas streams.
[0032] The vapor compression refrigeration system uses an
electrochemical compressor and therefore is modular (that is, it
can be of different sizes without limitation). The vapor
compression refrigeration system is electrically driven and thus
fully electronically controlled. The vapor compression
refrigeration system can be considered essentially noiseless, and
thus is less noisy than conventional mechanical refrigeration
systems. The vapor compression refrigeration system is more
efficient than conventional mechanical refrigeration systems.
DRAWING DESCRIPTION
[0033] FIG. 1 is block diagram of an exemplary refrigeration system
that defines a closed loop that contains a working fluid and
includes an electrochemical compressor.
[0034] FIG. 2 is block diagram of an electrochemical compressor and
components of a working fluid that can be used in the refrigeration
system of FIG. 1.
[0035] FIGS. 3A-3C are block diagrams of electrochemical
compressors that include a plurality of electrochemical cells and
can be used in the refrigeration system of FIG. 1.
[0036] FIG. 4A is a flow chart of a procedure performed by the
refrigeration system of FIG. 1.
[0037] FIG. 4B is a flow chart of a procedure performed by a
control system within the refrigeration system of FIG. 1.
[0038] FIG. 5 is a block diagram of an exemplary refrigeration
system that defines a closed loop that contains a working fluid and
includes an electrochemical compressor and a mechanical compressor
in parallel with each other.
[0039] FIG. 6 is a block diagram of an exemplary refrigeration
system that defines a closed loop that contains a working fluid and
includes an electrochemical compressor and a mechanical compressor
in series with each other.
DESCRIPTION
[0040] Referring to FIG. 1, an exemplary refrigeration system 100
defines a closed loop that contains a working fluid. The system 100
includes an electrochemical compressor 105 that lacks moving parts,
a first heat transfer device 110 that transfers heat from a first
heat reservoir (a heat source or object to be cooled) to the
working fluid, a second heat transfer device 115 that transfers
heat from the working fluid to a second heat reservoir (a heat
sink), and a thermostatic expansion valve 120 between the first and
second heat transfer devices. The system 100 also includes one or
more sensors (for example, temperature sensors) 125, 130 placed
along flow paths between components of the system 100 to provide
feedback to a control system 135 that is also coupled to the
compressor 105, the first heat transfer device 110, and the second
heat transfer device 115.
[0041] The working fluid contained within the closed loop of the
system 100 includes at least a first component that is
electrochemically active and therefore takes part in the
electrochemical process within the compressor 105. The working
fluid includes at least a second component that is a condensable
refrigerant that can be used for the heat pump application under
consideration. The condensable refrigerant is any suitable
condensable composition that does not include water. As discussed
below, the condensable refrigerant bypasses the electrochemical
process within the compressor 105.
[0042] Additionally, the working fluid includes a third component
that is water to hydrate an ion exchange membrane within the
compressor 105 (as discussed below). Water can be considered a
contaminant of some standard refrigerants, and it can negatively
impact heat exchange performance of the refrigerant. Thus water as
the third component of the working fluid can be reduced for
example, to a minimal amount that is needed to provide enough
hydration to one or more components of the compressor 105.
[0043] In some implementations, the first component (which is
electrochemically active) includes hydrogen (H.sub.2) and the
second component (which is a condensable refrigerant) includes
carbon dioxide (CO.sub.2). In this implementation, the components
are present in the proportion of approximately one part hydrogen
and four parts of carbon dioxide by volume. The relative
proportions of hydrogen and carbon dioxide are governed by the
desired relative efficiency of the electrochemical compressor 105
and the system 100. The quantity of water maintained in the working
fluid is governed by the thickness of membranes employed in the
compressor 105, the equivalent weight (acidity) of the ion exchange
media employed in the compressor 105, and the amount of hydrogen in
the system 100. Thinner membranes of higher equivalent weight (that
is, lower acidity) employed in systems with lower proton capability
require less water. In general, the working fluid includes less
than 50% of water, but can include less than 20%, less than 10%, or
less than 1% water, depending on the application.
[0044] It should be noted that while hydrogen is being used
primarily as the electrochemically active component of the working
fluid, hydrogen also possesses useful heat transfer properties.
Hydrogen's low density, high specific heat, and thermal
conductivity make it a superior coolant. Hydrogen gas can be used
as the heat transfer medium industrially in, for example, turbine
generators. The presence of hydrogen gas within the working fluid
thus enhances the performance of the condensable refrigerant; and
provides thermal exchange opportunities at points away from
thermally conductive surfaces of the fluid conduits and the heat
transfer devices.
[0045] The first heat transfer device 110 includes an evaporator
that acts as a heat exchanger that places the working fluid in a
heat exchange relationship with the first heat reservoir or source
of heat (for example, a source fluid). The first heat transfer
device 110 includes inlet and outlet ports coupled to respective
conduits 111, 112 that contain the working fluid of the system 100.
The second heat transfer device 115 includes a condenser that acts
as a heat exchanger that places the working fluid in a heat
exchange relationship with the second heat reservoir or heat sink
(for example, a sink fluid). The second heat transfer device 115
includes inlet and outlet ports coupled to respective conduits 116,
117 that contain the working fluid of the system 100.
[0046] The expansion valve 120 is an orifice that is able controls
the amount of working fluid flow. The valve 120 can include a
temperature sensing bulb filled with a similar gas as in the
working fluid that causes the valve to open against the spring
pressure in the valve body as the temperature on the bulb
increases. As temperatures in the evaporator 110 decrease, so does
the pressure in the bulb and therefore on the spring causing the
valve to close.
[0047] Referring also to FIG. 2, the electrochemical compressor 105
is a device that raises the pressure of a component of the working
fluid 200 by an electrochemical process. Accordingly, at least one
component of the working fluid must be electrochemically active. In
particular, the electrochemically active component (the first
component) must be ionizable. For example, the electrochemically
active component is oxidizable at a gas pervious anode 205 of the
compressor 105 and is reducible at a gas pervious cathode 210 of
the compressor 105.
[0048] The design in which the compressor 105 includes only one
exemplary cell 202 is shown in FIG. 2. However, the electrochemical
compressor 105 can include a plurality of electrochemical cells
302, as shown in FIGS. 3A-C. In some implementations, the
electrochemical compressor 105 is an annular stack of
electrochemical cells electrically connected in series such as, for
example, the cells generally described in U.S. Pat. No. 2,913,511
(Grubb); in U.S. Pat. No. 3,432,355 (Neidrach); and in U.S. Pat.
No. 3,489,670.
[0049] Each cell 202 includes the anode 205, where the
electrochemically active component (EC) of the working fluid is
oxidized; the cathode 210, where the electrochemically active
component EC of the working fluid is reduced; and an electrolyte
215 that serves to conduct the ionic species (EC.sup.+) from the
anode 205 to the cathode 210. The electrolyte 215 can be an
impermeable solid ion exchange membrane having a porous
microstructure and an ion exchange material impregnated through the
membrane such that the electrolyte 215 can withstand an appreciable
pressure gradient between its anode and cathode sides. The examples
provided here employ impermeable ion exchange membranes, and the
electrochemically active component of the working fluid is remixed
with the working fluid after compression and thus the pressure of
the working fluid 200 is elevated prior to the condensation phase
of the refrigeration process. However, a permeable ion exchange
membrane is also feasible with the working fluid traversing in a
unidirectional and sequential path through electrode assemblies
with increasing pressure. The active components of the working
fluid dissolve into the ion exchange media of the ion exchange
membrane and the gas in the working fluid traverses through the ion
exchange membrane.
[0050] As another example, the electrolyte 215 can be made of a
solid electrolyte, for example, a gel, that is, any solid,
jelly-like material that can have properties ranging from soft and
weak to hard and tough and being defined as a substantially dilute
crosslinked system that exhibits no flow when in the steady-state.
The solid electrolyte can be made very thin, for example, it can
have a thickness of less than 0.2 mm, to provide additional
strength to the gel. Alternatively, the solid electrolyte can have
a thickness of less than 0.2 mm if it is reinforced with one or
more reinforcing layers like a polytetrafluoroethylene (PTFE)
membrane (having a thickness of about 0.04 mm or less) depending on
the application and the ion exchange media of the electrolyte.
[0051] Each of the anode 205 and the cathode 210 can be an
electrocatalyst such as platinum or palladium or any other suitable
candidate catalyst. The electrolyte 215 can be a solid polymer
electrolyte such as Nafion (trademark for an ion exchange membrane
manufactured by the I. E. DuPont DeNemours Company) or GoreSelect
(trademark for a composite ion exchange membrane manufactured by W.
L. Gore & Associates Inc.). The catalysts (that is, the anode
205 and the cathode 210) are intimately bonded to each side of the
electrolyte 215. The anode 205 includes an anode gas space (a gas
diffusion media) 207 and the cathode 210 includes a cathode gas
space (a gas diffusion media) 212. The electrodes (the anode 205
and the cathode 210) of the cell 202 can be considered as the
electrocatalytic structure that is bonded to the solid electrolyte
215. The combination of the electrolyte 215 (which can be an ion
exchange membrane) and the electrodes (the anode 205 and the
cathode 210) is referred to as a membrane electrode assembly or
MEA.
[0052] Adjacent the anode gas space 207 is an anode current
collector 209 and adjacent the cathode gas space 212 is a cathode
current collector 214. The anode collector 209 and the cathode
collector 214 are electrically driven by the power supply 250. The
anode collector 209 and the cathode collector 214 are porous,
electronically conductive structures that can be woven metal
screens (also available from Tech Etch) or woven carbon cloth or
pressed carbon fiber or variations thereof. The pores in the
current collectors 209, 214 serve to facilitate the flow of gases
within the gas spaces 207, 212 adjacent to the respective
electrodes 205, 210.
[0053] Outer surfaces of the collectors 209, 214 are connected to
respective bipolar plates 221, 226 that provide fluid barriers that
retain the gases within the cell 202. Additionally, if the cell 202
is provided in a stack of cells, then the bipolar plates 221, 226
separate the anode and cathode gases within each of the adjacent
cells in the cell stack from each other and facilitate the
conduction of electricity from one cell to the next cell in the
cell stack of the compressor. The bipolar plate 221, 226 can be
obtained from a number of suppliers including Tech Etch
(Massachusetts).
[0054] Additionally, subassemblies of components of the
electrochemical cell can be commercially obtained from
manufacturers such as W. L. Gore & Associates Inc. under the
PRIMEA trademark or Ion Power Inc. Commercially available
assemblies are designed for oxygen reduction on one electrode and
therefore the electrodes (the anode 205 and cathode 210) may need
to be modified for hydrogen reduction.
[0055] Hydrogen reduction at the cathode 210 actually requires
lower loadings of precious metal catalysts and also is feasible
with alternative lower cost catalysts such as palladium. Thus, the
eventual production costs of assemblies employed in the system 100
are substantially lower than typical fuel cell components.
[0056] As mentioned above, the control system 135 is coupled to the
compressor 105, the first heat transfer device 110, and the second
heat transfer device 115. The control system 135 is also coupled to
one or more temperature sensors 125, 130, 140, 145 placed within
the system 100 to monitor or measure the temperature of various
features of the system 100. For example, the temperature sensor 125
can be configured to measure the temperature of the working fluid
within the conduit 111 and the temperature sensor 130 can be
configured to measure the temperature of the working fluid within
the conduit 117. As another example, temperature sensors 140, 145
can be placed near respective heat transfer devices 110, 115 to
measure the temperature at which the heat transfer device operates,
to measure the temperature of the working fluid within the
respective heat transfer device, or to measure the heat source
fluid temperature or heat sink fluid temperature.
[0057] The control system 135 can be a general system including
sub-components that perform distinct steps. For example, the
control system 135 includes the power supply 250 (such as, for
example, a battery, a rectifier, or other electric source) that
supplies a direct current electric power to the compressor 105.
[0058] Moreover, the control system 135 can include one or more of
digital electronic circuitry, computer hardware, firmware, and
software. The control system 135 can also include appropriate input
and output devices, a computer processor, and a computer program
product tangibly embodied in a machine-readable storage device for
execution by a programmable processor. The procedure embodying
these techniques (discussed below) may be performed by a
programmable processor executing a program of instructions to
perform desired functions by operating on input data and generating
appropriate output. Generally, a processor receives instructions
and data from a read-only memory and/or a random access memory.
Storage devices suitable for tangibly embodying computer program
instructions and data include all forms of non-volatile memory,
including, by way of example, semiconductor memory devices, such as
EPROM, EEPROM, and flash memory devices; magnetic disks such as
internal hard disks and removable disks; magneto-optical disks; and
CD-ROM disks. Any of the foregoing may be supplemented by, or
incorporated in, specially-designed ASICs (application-specific
integrated circuits).
[0059] The controller 135 receives information from components
(such as the temperature sensors and the compressor 105) of the
system 100 and controls operation of a procedure (as discussed
below) that can either maintain the heat source or the heat sink at
a relatively constant temperature condition. Additionally,
controlling the operation of an electrochemical compressor 105
consists of turning its current on or off through the power supply.
Alternatively, the voltage applied to the electrochemical
compressor 105 can be set to be in proportion to the heat source
fluid temperature or the heat sink fluid temperature. In some
applications, such as electric cars without internal combustion
engines, there may be an advantage in operating the vehicle air
conditioning system electrically and driving each wheel
independently without a central motor (required to drive the air
conditioning system).
[0060] The refrigeration system 100 can also include one-way valves
150, 155 at the output of the compressor 105. The one-way valve
150, 155 can be any mechanical device, such as a check valve, that
normally allows fluid (liquid or gas) to flow through it in only
one direction (the direction of the arrows). The valves 150, 155
ensure proper delivery of the components of the working fluid that
exit the compressor 105 into the rest of the refrigeration system
100 by reducing or avoiding back-pressure into the last cell in the
compressor 105, and therefore ensure unidirectional flow of the
fluids (which include gases). For example, the valve 150 is placed
within a conduit 152 that transports the high pressure
electrochemically active component plus the small amount of water
that is involved in the electrochemical process and the valve 155
is placed within a conduit 157 that transports the condensable
refrigerant that bypasses the electrochemical process.
[0061] The refrigeration system 100 can also include a dryer 160
that is configured to remove water from the working fluid prior to
reaching the expansion valve 120 to reduce the chance of water
freezing within the valve 120 and potentially clogging the valve
120, and to increase the efficiency of the expansion process within
the valve 120.
[0062] Referring also to FIG. 3A, in another implementation, the
electrochemical compressor 105 includes a plurality of cells 300,
301, 302, 303 arranged in series with each other, with the first
cell 300 receiving the low pressure working fluid 200 from the
conduit 112 and diverting the low pressure refrigerant along
conduit 305. In this implementation, only the first cell 300
diverts the low pressure refrigerant along the conduit 305. An
output 310 from the first cell 300 is a higher pressure mixture of
the electrochemically active component and water; the output 310 is
fed into an input 311 of the second cell 301. Likewise, an output
312 from the second cell 301 is fed into an input 313 of the third
cell 302, and an output 314 of the third cell 302 is fed into an
input 315 of the fourth cell 303. An output 316 from the fourth
cell 303 carries the high pressure mixture of the electrochemically
active component and water, and this output is mixed with the
diverted refrigerant in conduit 305, as discussed above, and
directed along conduit 116 toward the second heat transfer device
115.
[0063] As shown in FIG. 3A, the power supply is connected to the
anode and cathode collector of each of the cells 300, 301, 302,
303. In other implementations, the anode collector of the cell 300
and the cathode collector of the cell 303 are the only collectors
connected to the power supply. In this case, the end plates of each
cell receive all the current and the current is then "conveyed"
across the cells.
[0064] Referring to FIG. 3B, in another implementation, the
electrochemical compressor 105 includes a plurality of cells 320,
321, 322 arranged in series with each other, with the first cell
320 receiving the low pressure working fluid 200 from the conduit
112 and diverting the low pressure refrigerant along conduit 325.
In this implementation, the low pressure refrigerant is mixed with
the higher pressure mixture of the electrochemically active
component and water directed through an output after each of the
cells 320, 321, 322 and each of the cells 320, 321, 322 diverts the
low pressure refrigerant. Thus, output 330 from the first cell 320
is a higher pressure mixture of the electrochemically active
component and water and this mixture is mixed with the diverted low
pressure refrigerant traveling in the conduit 325 to form a mixture
of the higher pressure electrochemically active component, the
water, and the refrigerant that is directed to an input 331 of the
second cell 321. An output 333 from the second cell 321 is a higher
pressure mixture of the electrochemically active component and
water and this mixture is mixed with the diverted low pressure
refrigerant traveling in conduit 332 to form a mixture of the
higher pressure electrochemically active component, the water, and
the refrigerant that is directed to an input 334 of the third cell
322. Lastly, an output 336 from the third cell 322 is a higher
pressure mixture of the electrochemically active component and
water and this mixture is mixed with the diverted low pressure
refrigerant traveling in conduit 335 to form a mixture of the
higher pressure electrochemically active component, the water, and
the refrigerant that is directed along conduit 116 toward the
second heat transfer device 115.
[0065] As shown in FIG. 3B, the power supply is connected to the
anode collector of the first cell 320 and to the cathode collector
of the third cell 322. In this case, the end plates of each cell
receive all the current and the current is then "conveyed" across
the cells. In other implementations, the anode collector and
cathode collector of each of the cells 320, 321, 322 are connected
to the power supply.
[0066] Referring to FIG. 3C, in another implementation, the
electrochemical compressor 105 includes a plurality of cells 350,
351, 352, 353 arranged in parallel with each other, with each of
the cells 350, 351, 352, 353 receiving the low pressure working
fluid 200 from the conduit 112 and each of the cells 350, 351, 352,
353 diverting the low pressure refrigerant along respective
conduits 360, 361, 362, 363. In this implementation, the low
pressure refrigerant from each of the cells 350, 351, 352, 353 is
mixed together and passed through conduit 364, and the high
pressure mixture of the electrochemically active component and
water directed through respective outputs 370, 371, 372, 373 of
each of the cells 350, 351, 352, 353 is mixed together and passed
through conduit 374. These two mixtures in the conduits 364 and 374
are combined with each other and directed along the conduit 116
toward the second heat transfer device 115.
[0067] The power supply can be connected to the anode collector and
to the cathode connector of each of the cells 350, 351, 352,
353.
[0068] While three or four cells are shown in these drawings, it is
noted that any number of cells can be used in the compressor 105,
and the number of cells can be selected depending on the cooling
application of the system 100.
[0069] Referring also to FIG. 4A, the system 100 performs a
procedure 400 for transferring heat from the heat source at the
first heat transfer device 110 to the heat sink at the second heat
transfer device 115.
[0070] Low pressure working fluid 200 (which is typically a gas
mixture of hydrogen, condensable refrigerant, and water) enters
compressor 105 (step 405). A mixture of hydrogen and water is
dissociated from the condensable refrigerant (step 410). In
particular, the hydrogen (in the form of a proton) and water
dissolve into the ion exchange media while the condensable
refrigerant does not. The condensable refrigerant is diverted along
a path separate from the electrochemical path through the membrane
electrode assembly (step 415). The dissociated mixture is then
pumped across the membrane electrode assembly of each cell in the
compressor 105 (step 420). In particular, electrons are stripped
from the hydrogen in the hydrogen/water mixture at the anode
collector of the cell, and the hydrogen ions are transported across
the anode, electrolyte, and toward the cathode due to the
electrical potential applied across the collectors from the power
supply. Additionally, the hydrogen ion gas is pressurized across
the membrane electrode assembly. Next, the hydrogen ions are
recombined with the electrons at the cathode collector to reform
hydrogen gas at a higher pressure, and this higher pressure
hydrogen gas is recombined with the diverted condensable
refrigerant to thereby raise the pressure of the working fluid
(step 430).
[0071] Thus, the electrochemical compressor 105 raises the pressure
of the working fluid 200 and delivers the higher pressure working
fluid 200 to the second heat transfer device (the condenser) 115
where the condensable refrigerant is precipitated by heat exchange
with the sink fluid (step 435). The working fluid is then reduced
in pressure in the expansion valve 120 (step 440). Subsequently,
the low pressure working fluid is delivered to the first heat
transfer device (the evaporator) 110 where the condensed phase of
the working fluid is boiled by heat exchange with the source fluid
(step 445). The evaporator effluent working fluid may be partially
in the gas phase and partially in the liquid phase when it is
returned from the evaporator to the electrochemical compressor 105.
In the process, heat energy is transported from the evaporator to
the condenser and consequently, from the heat source at a
relatively lower temperature to the heat sink at relatively higher
temperature.
[0072] Referring also to FIG. 4B, concurrently with the procedure
400, the control system 135 performs a procedure 450 for
controlling the amount of electrical potential applies to the
current collectors of the compressor 105, and therefore also
controls the amount of heat energy transported from the evaporator
to the condenser. The control system 135 receives information from
the one or more sensors (for example, temperature or pressure
sensors) in the system 100 indicating physical characteristics
(such as temperature or pressure) at key locations of the system
100 (step 455). The control system 135 analyzes the information
(step 460) and determines whether physical properties of the system
100 need to be adjusted based on the analyzed information (step
465). For example, the control system 135 can determine that a
current applied to the compressor 105 (and therefore the current
applied to the electrode collectors) needs to be adjusted. As
another example, the control system 135 can determine that a flow
rate of one or more of the heat sink fluid and the heat source
fluid that transport heat from and to the devices 115, 110 needs to
be adjusted. If the control system 135 determines that a physical
property of the system 100 should be adjusted, then the control
system 135 sends a signal to the component that is affected to
adjust the particular property (step 470). For example, the control
system 135 can send a signal to the power supply to adjust the
amount of current applied to the current collectors in the
compressor 105. Otherwise, the control system 135 continues to
receive information from the one or more sensors (step 455).
[0073] In summary, the system 100 includes an electrochemical cell
of the compressor 105 that compresses an electrochemically active
component of the working fluid, and remixes the compressed (at high
pressure) electrochemically active component (the first component)
with the condensable refrigerant (the second component) to elevate
the pressure of the mixed gas working fluid in a vapor compression
refrigeration cycle. In this way, the electrochemical compressor
105 is capable of producing high pressure hydrogen gas from a mixed
component working fluid having an electrochemically active
component such as, hydrogen and at least one condensable
refrigerant. In this arrangement, hydrogen is compressed to a much
higher pressure than the final working fluid pressure (that is, the
pressure of the remixed working fluid), and because of this, the
hydrogen when mixed with the lower pressure condensable refrigerant
is at the required higher pressure. The exact pressure requirements
for the hydrogen stream depends on the volume of condensable
refrigerant being pressurized in relation to the volume of
hydrogen, the desired final pressure requirements of the remixed
working fluid, and the targeted energy efficiency. The check valves
150, 155 are employed to make sure the gas flows are maintained in
the intended directions and that no back flow is allowed towards
the cells of the compressor 105.
[0074] The energy efficiency of the system 100 depends on the
available surface area of the anode 205 and the cathode 210, and
the current density and operating voltage applied to the cells from
the power supply. Higher current densities result in greater the
resistive losses for the system 100.
[0075] The size reduction of the compressor 105 is feasible because
of its cellular design, and because it is operating using an
electrochemical process. If an application requires significant
size reductions, the electrode (the anode and the cathode) surfaces
can be reduced, the applied current densities and voltages can be
increased, and as a result a smaller mass of cells can be employed
in the compressor 105. This would result in an almost order of
magnitude reduction in size and weight for the system 100 compared
to conventional mechanical systems.
[0076] Since cooling capacity is linked to applied current and
voltage, one advantage of this system is that it can more easily
modulate from low capacity (that is, low current density at a
specific voltage) to a high capacity. A system 100 designed to
operate at high capacities actually becomes more efficient at lower
utilizations, while, the opposite is true for mechanical
systems.
[0077] Referring also to FIGS. 5 and 6, exemplary hybrid
refrigeration systems 500, 600 define a closed loop that contains a
working fluid and include the same components (for example, the
electrochemical compressor, the heat transfer devices, and the
thermostatic expansion valve) of the system 100. These systems 500,
600 also include mechanical compressors 580, 680 operating in
conjunction with the electrochemical compressors 505, 605 in a
hybrid fashion. Such a design is useful for use in electric
vehicles, for example. The design of the systems 500, 600 provides
high efficiency service at low refrigeration requirements and
allows the mechanical segment of the system 500, 600 to take over
at constant and higher refrigeration demands. The mechanical
segment of the system 500, 600 is the segment that bypasses the
electrochemical compressor 505, 605.
[0078] As shown in FIG. 5, the mechanical compressor 580 is in
parallel with the electrochemical compressor 505. For simplicity,
the one way valves (such as the valves 150, 155) and the separate
conduits for the high pressure electrochemically active component
and the condensable refrigerant (such as the conduits 152, 157)
that are found at the output of the compressor 505 are omitted from
this drawing. As shown in FIG. 6, the mechanical compressor 680 is
in series with the electrochemical compressor 605.
[0079] The refrigeration system 100, 500, 600 can work with a wide
range of condensable refrigerants. However the choice of
refrigerant depends on the exact application under consideration
and other external regulatory factors. Care should be taken in the
selection of the refrigerant to ensure that the refrigerant does
not degrade the electrochemical performance of the system 100, 500,
600 or poison the electrocatalyst employed.
[0080] An ideal refrigerant has good thermodynamic properties, is
noncorrosive, stable, and safe. The desired thermodynamic
properties are at a boiling point somewhat below the target
temperature, a high heat of vaporization, a moderate density in
liquid form, a relatively high density in gaseous form, and a high
critical temperature. Since boiling point and gas density are
affected by pressure, refrigerants may be made more suitable for a
particular application by choice of operating pressure.
[0081] While we have described an electrochemical compressor that
uses a multiple component working fluid utilizing hydrogen and that
is based on a cationic exchange membrane, it is also possible to
use a working fluid including chlorine as a component; such a
working fluid could be used advantageously in an anionic exchange
membrane cell. In an electrochemical compressor using an anionic
exchange membrane, the electrochemically active component of the
working fluid is first reduced at a cathode. The anions formed at
the cathode migrate to the anode where they are oxidized. The gas
evolved at the anode is at a higher pressure than the fluid
entering the cathode. The process is the reverse of the cationic
electrochemical compressor previously described above with
reference to FIGS. 1-4B.
[0082] Other implementations are within the scope of the following
claims.
* * * * *