U.S. patent application number 14/097401 was filed with the patent office on 2014-06-12 for monolithically integrated bi-directional heat pump.
The applicant listed for this patent is Massachusetts Institute of Technology. Invention is credited to Carlos Hiller Hidrovo Chavez, Ian Salmon Mckay, Collier Miers, Shankar Narayanan, Evelyn N. Wang, Geoffrey Wehmeyer.
Application Number | 20140157815 14/097401 |
Document ID | / |
Family ID | 50879503 |
Filed Date | 2014-06-12 |
United States Patent
Application |
20140157815 |
Kind Code |
A1 |
Mckay; Ian Salmon ; et
al. |
June 12, 2014 |
Monolithically Integrated Bi-Directional Heat Pump
Abstract
Monolithically integrated heat pump. The heat pump includes as
adsorbent/absorbent condenser forming a hot terminal integrated
with a phase change heat exchanger forming a cold terminal. The
adsorbent/absorbent condenser and the phase change heat exchanger
are integrated into a single pressure vessel.
Inventors: |
Mckay; Ian Salmon; (Seattle,
WA) ; Miers; Collier; (Little Rock, AR) ;
Narayanan; Shankar; (Allston, MA) ; Wang; Evelyn
N.; (Cambridge, MA) ; Hidrovo Chavez; Carlos
Hiller; (Austin, TX) ; Wehmeyer; Geoffrey;
(Overland Park, KS) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Massachusetts Institute of Technology |
Cambridge |
MA |
US |
|
|
Family ID: |
50879503 |
Appl. No.: |
14/097401 |
Filed: |
December 5, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61733941 |
Dec 6, 2012 |
|
|
|
Current U.S.
Class: |
62/324.2 |
Current CPC
Class: |
Y02B 30/64 20130101;
F25B 17/08 20130101; F25B 17/00 20130101; Y02A 30/277 20180101;
F25B 39/00 20130101; F25B 37/00 20130101; F25B 35/04 20130101; F25B
30/04 20130101; Y02A 30/278 20180101; Y02B 30/00 20130101; Y02B
30/62 20130101 |
Class at
Publication: |
62/324.2 |
International
Class: |
F25B 30/04 20060101
F25B030/04 |
Goverment Interests
[0002] This invention was made with government support under grant
no. DE-AR0000185, awarded by the Department of Energy. The
government has certain rights in the invention.
Claims
1. Monolithically integrated heat pump comprising: an
adsorbent/absorbent condenser forming a hot terminal; a phase
change heat exchanger forming a cold terminal; and a pressure
vessel, wherein the adsorbent/absorbent condenser and the phase
change heat exchanger are integrated within the pressure
vessel.
2. The heat pump of claim 1 wherein the heat pump is liquid
cooled.
3. The heat pump of claim 1 wherein the heat pump is air
cooled.
4. Monolithically integrated heat pump comprising: a combined
evaporator-condenser unit for bi-directional heat pumping operation
including first tube structure for conveying a heat transfer fluid
therethrough; a second tube structure for conveying liquid
refrigerant into the combined evaporator-condenser unit; an
adsorbent bed in thermal contact with a third tube structure for
conveying heat transfer fluid be thermal contact with the adsorbent
bed; and a pressure vessel containing therewithin the combined
evaporator-condenser unit, the first, second, and third tube
structure, and the adsorbent bed.
5. The heat pump of claim 4 wherein the adsorbent bed includes
adsorbent-covered fins.
6. The heat pump of claim 5 wherein the fins have microchannels
engraved on their surface into which liquid water is dispensed from
the third tube structure.
7. The heat pump of claim 5 wherein the fins further include a wick
structure covering the fin surface.
Description
[0001] This application claims priority to provisional application
Ser. No. 61/733941, filed on Dec. 6, 2012, the contents of which
are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0003] This invention relates to heat pumps and more particularly
to a monolithically integrated bi-directional heat pump that
integrates evaporator, condenser and adsorption bed into a single
compact pressure vessel.
[0004] Resistance to mass transfer fundamentally limits the
performance of most heat pumps that rely on chemical driving forces
for passive operation. In the case of adsorption or absorption
chillers, for example, a vapor passage constriction between the
evaporator and adsorber or adsorber can significantly reduce the
maximum power of the heat pump. As shown in FIGS. 1A and B, the
mass transfer impedance severely limits the performance of some
emergent heat-pump technologies, such as thermo-adsorptive
batteries for electric vehicle climate control that could otherwise
enable significant enhancement in electric vehicle driving range
[1].
[0005] Mass transfer impedance limits the performance of some heat
pump systems that use working fluids at low pressure, because of
the high volumetric flow rates involved. For an adsorption system
using low pressure water vapor as a working fluid [1], FIG. 1A
shows the maximum heat delivery as a function of the length
cross-sectional area of the connection between the evaporator and
adsorber. This calculation is based on purely diffusive transport.
FIG. 1B shows the connection geometry required to achieve 2500 W
heat pumping at a variety of adsorption site temperatures. While
the mass transfer improves if advective transport is also
considered, this improvement conies at fee cost of a pressure drop
that reduces the useful temperature range of the heat pump.
[0006] An object of the invention is a new heat pump design which
increases the effective evaporator-bed connection area and
minimizes the connection length by integrating fee evaporator,
condenser, and adsorption bed into a single compact pressure
vessel.
SUMMARY OF THE INVENTION
[0007] In one aspect the invention is a monolithically integrated
bi-directional heat pump having as adsorbent/absorbent condenser
forming a hot terminal and a phase change heat exchanger forming a
cold terminal. Both the adsorbent/absorbent condenser and the phase
change heat exchanger are integrated within a single pressure
vessel. The monolithically integrated bi-directional heat pump is
also referred to herein as a thermal battery and other similar
designations.
[0008] The hot terminal of the thermal battery may comprise a
packed granular or continuous material that reversibly or
irreversibly physisorbs or chemisorbs the refrigerant to release
heat. The hot terminal of the battery could also consist of a
liquid material that reversibly or irreversibly absorbs the
refrigerant to release heat.
[0009] In all cases the choice of active hot-terminal material
depends on the operating pressure and adsorbate. Examples of
potential physisorptive materials include silica gel, zeolites, and
microporous metal-organic frameworks. Examples of potential
reversible chemisorptive materials include activated alumina and
magnesium oxides. Examples of potential irreversible chemisorptive
materials include any compound that reacts exothermically with the
refrigerant in the vapor phase. Examples of liquid absorbents
include ammonia, lithium bromide, or hydrophilic ionic liquids.
[0010] In preferred embodiments of this aspect of the invention,
the heat pump is liquid cooled or air cooled.
[0011] In another aspect the monolithically-integrated heat pump
according to the invention includes a combined evaporator-condenser
unit for bidirectional heat pumping operation, including a first
tube structure for conveying a heat transfer fluid therethrough and
a second tube structure for conveying liquid refrigerant into the
combined evaporator-condenser unit. An adsorbent bed is in thermal
contact with a third tube structure for conveying heat transfer
fluid for thermal contact with the adsorbent bed. A pressure vessel
is provided to contain therewithin the combined
evaporator-condenser unit, the first, second, and third tube
structures, and the absorbent bed.
[0012] In a preferred embodiment of this aspect of the invention
the adsorbent bed includes adsorbent-covered fins that have
microchannels engraved on their surface into which heat transfer
fluid is dispensed from the third tube structure. The fins further
include a structure covering the fin surface.
BRIEF DESCRIPTION OF THE DRAWING
[0013] FIG. 1(A) is a graph of heat pump capacity versus diffusion
gap for various evaporator areas.
[0014] FIG. 1(B) is a graph of required diffusion area versus
diffusion length at a variety of adsorption site temperatures.
[0015] FIG. 2(A) and 2(B) are perspective views of an integrated
design in a T-shape adapted for electric vehicle integration.
[0016] FIG. 3(A) is a perspective, schematic view of an evaporator
fin having a porous mesh covering.
[0017] FIG. 3(B) is a cross-sectional view of a single channel in
an embodiment of the invention.
[0018] FIG. 4(A) is a graph of required evaporator are versus
temperature for different meshes.
[0019] FIG. 4(B) is a graph of fin height versus fin
temperatures.
[0020] FIG. 5 is a graph of required mass fraction uptake versus
adsorbent density in a design with four 0.6 cm adsorbent coolant
tubes mounted with 0.7 mm fins and with an adsorption site
temperature of 80.degree. C.
[0021] FIG. 6(A) is a schematic illustration showing heat flow and
coolant/antifreeze routing for automotive cooling.
[0022] FIG. 6(B) is a schematic illustration showing heat flow and
coolant/antifreeze routing for automotive heating.
[0023] FIG. 7 is a schematic illustration showing coolant routing
for a monolithically-integrated thermo-adsorptive battery during
recharge.
[0024] FIG. 8 is a schematic illustration showing coolant routing
for a monolithically-integrated thermo-adsorptive battery mounted
thermally in parallel with a solid state heat pump bank.
[0025] FIG. 9 shows predicted adsorption site temperature on each
adsorbent fin for radially-symmetric fins. This figure shows
simulations for different adsorbent thermal conductivities and
determines the resulting adsorbent layer thickness required to keep
the maximum temperature below 80.degree. C.
[0026] FIG. 10 is a schematic illustration of a combined advective
and diffusive heat and mass transfer model of the adsorption bed of
an embodiment of the invention disclosed herein.
[0027] FIG. 11 are graphs of temperature or concentration against
vapor gap for an embodiment delivering 2,500 W of cooling.
[0028] FIG. 12 is a graph of interfacial area versus vapor
diffusivity of an embodiment delivering 2,500 W of cooling.
[0029] FIG. 13 is a schematic illustration of a monolithically
integrated thermo-adsorptive battery with a simplified
geometry.
[0030] FIG. 14 is a schematic illustration of the shape of a
monolithically-integrated thermal battery designed for integration
into a battery electric vehicle according to an embodiment of the
invention.
[0031] FIG. 15 is a perspective view of an embodiment of the
advanced thermal battery according to the invention showing a
monolithic integration of an adsorption bed with an
evaporator/condenser unit.
[0032] FIG. 16a is a perspective view of an embodiment of a liquid
cooled adsorption bed that can be accommodated within an electric
vehicle.
[0033] FIG. 16b is a perspective view of a simpler rectangular
geometry of an embodiment of the invention.
[0034] FIG. 16c is a cross-sectional view of the adsorbent bed
showing a centrally located evaporator/condenser (PHEX) interfaced
with adsorbent on both sides.
[0035] FIG. 16d are views of a detailed design of an embodiment of
the ATB showing characteristic dimensions of sub-components. The
front view shows characteristic dimensions and arrangement of
coolant types, adsorption bed and phase-change heat exchange. The
top view shows the characteristic thickness and arrangement of the
adsorption stacks on both sides of the phase change heat
exchanger.
[0036] FIG. 17 is a graph of adsorption capacity versus density of
adsorbent for a fixed overall volume of the advanced thermal
battery disclosed herein.
[0037] FIG. 18a is a graph of net vapor adsorption versus time
showing temporal variation in net vapor adsorption.
[0038] FIG. 18b is a graph of average temperature versus time
showing average adsorbent temperature during the first 60 minutes
of operation of an adsorbent delivering 30 weight percent vapor
adsorption capacity at 760 Pa and 80 degrees C. The overall average
rate of adsorption was approximately 0.0011 kg/s.
[0039] FIG. 19a is a graph of average adsorbent temperature versus
antifreeze/coolant HTC showing the average temperature distribution
of adsorption as a function of its thermal conductivity and heat
transfer coefficient of the coolant.
[0040] FIG. 19b is a graph of pumping power versus antifreeze HTC
showing pumping power required for circulation as a function of the
beat transfer coefficient.
[0041] FIG. 20 is a graph of relative pressure versus
antifreeze/coolant temperature between 303 K (30 degrees C.) and
333 K (60 degrees C.), which represent typical conditions that can
be expected during mild summer and winter.
[0042] FIG. 21 is a view of a single cell or "button cell"
embodiment of the present invention.
[0043] FIG. 22 are perspective views of a button cell embodiment
showing a hot terminal of Zt 13.times. compressed in an aluminum
honeycomb and a cold terminal including a porous media evaporator
and bare condenser plate connected to a reservoir.
[0044] FIGS. 23 and 24 are perspective views of an adsorbent test
station showing Zt 13.times. thermo-compressed in aluminum
honeycomb.
[0045] FIG. 25 comprises views of the evaporator side of the ATB
showing 10.times. compressed 95% porosity copper foam having
approximately 110 .mu.m pores and also showing the liquid directed
to minichannels beneath the porous copper.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0046] An embodiment of the invention is shown in FIGS. 2(A) and
(B). FIG. 2(A) shows the integrated design in a T-shape
particularly adapted for battery electric vehicle integration. The
integrated design 10 includes a combined evaporator-condenser unit
12 along with adsorbent-covered fins 14. In the explored view of
FIG. 2(B), showing the adsorbent material mounted on liquid-cooled
fin tubes, arrow 1 indicates the flow of heat transfer fluid to the
evaporator-condesner 12. The arrow 2 indicated the flow of liquid
refrigerant into the evaporator-condesner unit during battery
discharge. Arrow 3 indicates the flow of heat transfer fluid to the
adsorbent fins. The pressure vessel containing these elements is
not, itself, shown for the sake of clarity.
[0047] The monolithically-integrated design disclosed herein
combines three separate subsystems from traditional adsorption heat
pumps--the evaporator, condenser, and adsorbent bed, into a single
pressure vessel. This consolidation increases the planned
connection area by nearly 200.times., from 0.0008 m.sup.2 in a
traditional duct-based system to 0.136 m.sup.2, and decreases the
mean connection length from approximately 0.2 m to 0.076 m, thereby
addressing the mass transfer impedance challenges that have
hampered previous efforts to develop compact, energy dense
adsorption heat pumps. Additionally, the consolidation to a single
pressure vessel comes at an estimated system volume savings of 4.5
L form a conventional design by eliminating the evaporator and
condenser subunits, as well as associated brackets and tubing.
[0048] Any thermal leak is mitigated by ensuring minimal contact
between the adsorption bed and the combined evaporator/condenser in
this design (as shown in FIG. 2). Thermal leakage can take place
due to heat conduction through the vapor phase separating the
adsorption-bed and the evaporator, and conduction through the
coolant pipes that connect the adsorption bed and the pressure
vessel. This thermal leak through the vapor is estimated to be less
than 1 W during bed operation, based on the low thermal
conductivity of 0.01 W/mK of steam at 710 Pa. The thermal leak
through the endwalls is estimated to be 6 W based on 0.001 m thick
stainless steel walls and thermally insulated, 0.01 m diameter
KF-type (vacuum) pipe fittings.
[0049] The combination of the evaporator and condenser units into a
single fin structure requires the development of a surface that is
conducive to both thin-film evaporation and either filmwise or
dropwise condensation. A design is shown in FIG. 3. In the cooling
mode, wherein the evaporator is utilized, liquid water is dispensed
into microchannels engraved on the surface of the fin from
refrigerant lines running through the evaporator fins. Water
spreads through the microchannels, and fills a which structure
covering the fin. This wick structure serves to enhance thin-film
evaporation [2] and provide the pressure gradient necessary for
evaporation that would otherwise be provided by an expansion valve
or capillary. Filmwise or dropwise condensation also occurs on this
wick structure, which will consist of a multi-layered sintered
copper or aluminum wick. The condensation is collected in a trough
at the bottom of the fin and is routed out of the bottom of the
integrated pressure vessel.
[0050] Based on a conservative filmwise condensation model [3] as
shown in FIG. 4A, a 4 cm tall condenser fin that spans the length
of the bed could facilitate recharge within 2 hours with a
40.degree. C. condenser temperature. Based on the heat fluxes
observed in [2] and a 1 mm copper mesh which structure, the
evaporator should be sized as shown in FIG. 4B.
[0051] The design disclosed herein allows more volume for adsorbent
material than traditional systems, as a result of the consolidation
of the evaporator and condenser to a single structure, and the
elimination of bulky ducting and local air heat exchangers. As a
result, the mass percent uptake required to reach a 4500 W heating
benchmark for automotive integration varies with the adsorbent
density and acceptable adsorbent site temperature as shown in FIG.
5. For comparison, the required uptake for an identical chiller
using a conventional modular design ranges from 50-80%. In the
figure, four 0.6 cm adsorbent coolant tubes were mounted with 0.7
mm fns and with an adsorption site temperature of 80.degree. C.
[0052] As shown in FIGS. 6 and 7, the combination of all system
components into a single pressure vessel is conducive to
integration with pre-existing automotive heat exchange structures
via simple valve structures.
[0053] FIG. 6A shows heat flow and coolant/antifreeze routing for
automotive cooling. FIG. 6B shows heat flow and coolant/antifreeze
routing for automotive heating.
[0054] The monolithically-integrated design disclosed herein is
also conducive to integration with a secondary heat pump system, as
shown in FIG. 8. This type of integration could be of interest in
mobile applications, in which the system may occasionally be
required to supply more heating or cooling than the adsorption
system can store.
[0055] Based on the energy density of a typical electric vehicle
primary battery bank (0.234 MJ/L) and the heat pump COP of
commercially-available Peltier units (1.8 heating, 0.6 cooling), a
vehicle climate-control system based on solid-state heat pumps
would be approximately 40-60% as energy-dense as the
adsorption-based system in [1] (9 MJ heating or cooling in 30 L).
However, due to the small size of the Peltier units themselves (0.1
L), they may represent a space-efficient means to increase the
maximum power and endurance of the ATB system. Because the Peltier
units draw power from the primary battery, the units effectively
only displace volume electric vehicle only when they are in use,
unlike an adsorption system. In all, integration with a secondary
solid-state heat pump could allow the system more flexibility for
occasional overloads that the adsorption system alone could not
handle.
[0056] While many details of heat and mass transfer for this design
remain the be established, the adsorbent temperature can be
estimated based on assumed radiator and heater core heat exchanger
efficiencies. Assuming .eta..sub.Radiator=.eta..sub.Heater Core=0.9
and four 1 cm diameter adsorbent coolant pipes as depicted in FIG.
2, the average coolant temperature in the adsorbent cooling tubes
could be kept at approximately 70.degree. C. with an adsorbent
temperature profile on each fin as shown below. This configuration
would require an estimated 40 W of pumping power for the
circulation of a coolant or antifreeze. FIG. 8 shows the expected
temperature distribution across the adsorbent based on these
assumptions for fins mounted with adsorbents with different thermal
conductivities ranging between 0.3 to 5 W/mK. For these
computational simulations, the volumetric heat generation is
assumed to be a constant 126 kW/m.sup.3, corresponding to an
overall heat delivery of 2500 W. Because the heat of adsorption is
higher than the heat of evaporation, the adsorbent temperature will
likely be higher than that shown in FIG. 8, during a 2500 W cooling
operation.
[0057] FIG. 9, shows predicted adsorption site temperature on each
adsorbent fin as drawn in FIG. 1 for radially symmetric fins. The
maximum temperature is held to 80.degree. C., the coolant flow is
at the system average of 70.degree. C. through 0.6 cm pipes and the
fin thickness is 0.7 mm. The figure shows simulations for different
adsorbent thermal conductivities .epsilon., and determines the
resulting adsorbent layer thickness t.sub.ad required to keep the
maximum temperature below 80.degree. C. Note that the vertical axis
of each figure is in millimeters, while the horizontal axis is in
meters.
[0058] The monolithically-integrated adsorption heat pump system
was analyzed using a 1-D model incorporating both advective and
diffusive heat and mass transfer between the system hot and cold
sides. A schematic view of this model is shown in FIG. 10. Based on
a 2500 W cooling deliver benchmark, the design will operate as
shown in FIGS. 11 and 12, with a net thermal leak of .about.15 W
including conduction, diffusion, convention, and radiation, based
on a stainless steel vessel and emissivity .epsilon. of 0.2 for the
adsorbent material.
[0059] Possible risks of the monolithically integrated design
include a thermal leak between the evaporator and adsorption bed
during bed discharge, additional entropy generation associate with
the intermediate antifreeze air het exchangers, and the possibility
of boiling the antifreeze during the high temperature system
recharge.
[0060] The evaporator/condenser and adsorption bed will be
thermally isolated form one another by non-conductive KF-type
vacuum fittings between the coolant pipes and the pressure vessel
enwalls. These fittings represent the only thermal contact between
the two subsystems. If this thermal resistance is found to be
insufficient, additional isolation can be achieved by fabricating
the pressure vessel from a relatively thermally insulating
material, such as stainless steel.
[0061] While some additional temperature drop between the ATB
system and the passenger cabin is inevitable with the intermediate
heat exchange step in the heater core, the temperature drop is
estimated between 2 and 6.degree. C. based on the efficiency of
typical automotive heater cores. This temperature drop is offset by
the additional adsorption capacity afforded by the liquid cooling
strategy.
[0062] Since typical zeolite desorption temperatures exceed the
boiling temperature of most liquid coolants, coolant boiling in the
antifreeze line is possible during system recharge. Boiling within
the coolant lines can be minimized either by draining the coolant
line prior to recharge, or by allowing for some volume expansion
using a venting mechanism within the coolant reservoir.
[0063] Another risk associated with all heat pump systems that use
water as a working fluid is refrigerant freezing in very cold
temperatures. This risk might be avoided by using a mixture of an
alcohol (such as methanol) and water as the working fluid. In this
way, freezing can be avoided without significantly impacting heat
delivery capacity, as many alcohols are also useful as adsorbates.
Moreover, if the liquid mixture is near the azeotropic point, the
evaporator temperature can be made lower during system discharge,
increasing the effectiveness of the heat pump system.
[0064] A planned prototype with a simplified `button cell` heat
transfer geometry is shown in FIG. 13. The button cell design will
be discussed further below.
[0065] While further modeling is required to validate the
monolithically-integrated bi-directional heat pump structure
presented in the document design, these preliminary calculations
indicate that the revised design can greatly enhance the energy
density of a thermo-adsorptive battery system by 1) reducing the
system volume by combining three different system components, 2)
eliminate mass transfer resistance between the evaporator/condenser
units, and the adsorption bed, and 3) streamlining vehicle
integration by utilizing pre-existing heat exchange infrastructure
(radiator and heater core) and incorporating smaller and more
flexible liquid coolant lines in place of air ducts.
[0066] A T-shaped embodiment of the invention is shown in FIG. 14
and is suited for automotive use.
[0067] The overall design of an embodiment of the advanced
thermo-adsorptive battery is illustrative in FIG. 15 (not drawn to
scale). The ATB consists of an adsorption bed monolithically
integrated with a phase-change heat exchanger (PHEX) serving as an
evaporator as well as a condenser. During the ATB discharging
process the PHEX is used as an evaporator, while it is used as a
condenser during ATB recharge process. The adsorption bed and the
PHEX are thermally interfaced with coolant lines for supplying or
rejecting heat from the ATB. The adsorption bed is composed of
several rows of adsorbent stacks with minimal spacing to allow
vapor transport. Each stack consists of thin adsorbent layers
attached to metallic substrates that are in contact with the
coolant lines. This arrangement minimizes the net thermal
resistance for heat dissipation from the adsorption bed to the
coolant. The evaporator/condenser is constructed using a porous
media to provide a large surface area for evaporation and
condensation of water during ATB discharge and recharge process,
respectively. A refrigerant line supplies liquid water, while
multiple coolant lines allow exchange of heat with the
evaporator/condenser unit. During ATB discharging process, water is
pumped from a reservoir to the evaporator. The vapor generated due
to evaporation diffuses into the bed, where it is adsorbed. During
summer, the evaporator provides cooling and during winter the
adsorption bed delivers heating. The adsorption bed is regenerated
by providing heat which causes vapor desorption. The desorbed vapor
diffuses back into the PHEX, which functions as a condenser for the
regeneration mode. The condensate collected in the ATB is
transported back into the reservoir for subsequent use. Note that
the reservoir is externally located and not shown for clarity.
[0068] An embodiment of the invention, particularly adapted for
electric vehicle integration, is shown in FIGS. 16a, b, c and d.
The characteristic dimensions and arrangement of various
sub-components within the ATB including the coolant tubes, the
adsorption bed and the PHEX are shown in this figure. A total of 8
coolant lines are interfaced with each half of the adsorption bed
to dissipate the heat released during adsorption for vapor. The
adsorption bed consists of multiple rows of stacks, with each stack
representing a metallic fin attached with thin layers of
mechanically-compressed adsorbent. The gap between the rows of
stacks facilitates efficient transport of vapor between the
evaporator and the adsorption bed, and allows maximum utilization
of the adsorbent in the desired operational duration. The heat
generated during adsorption is conducted across the thin adsorbent
layers to the thermally conductive metallic fin which dissipates
heat to the coolant line. Consequently, the design allows efficient
heat and mass transfer to deliver high energy and power density for
climate control in electric vehicles. It should be noted that FIG.
16 is an optimized design for the use of ATB in the electric
vehicles. However, with minor modifications in the dimensional and
form factor, a similar arrangement of sub-components can be
utilized for various applications desiring temperature control,
e.g. heating and cooling in buildings, storage and transport of
heat sensitive materials such as medical supplies, organs,
biological specimens etc.
[0069] In order to deliver a net heating and cooling capacity
exceeding 2.5 kW, FIG. 17 shows the required adsorption capacity as
a function of the average packing density of the adsorbent for the
design illustrated in FIG. 16 using water as a refrigerant. For
instance, with an average packing density of 850 kg/m.sup.3, a net
vapor uptake of .about.0.3 kg.sub.vapor/kg.sub.adsorbent or 30 wt.
% is required to deliver .about.2.5 kW of heating and cooling. The
average packing density also determines the total mass of adsorbent
inside the ATB. For instance, with a packing density of 850
kg/m.sup.3, the ATB utilizes close to 19 kg of adsorbent.
[0070] With a detailed computational analysis of adsorption
dynamics, the performance variation of ATB over time can be
predicted. Using an adsorbent that delivers a 30 wt. % vapor
adsorption capacity at lower vapor pressures (.about.760 Pa) the
ATB performance variation over 60 minutes of operation is shown in
FIGS. 18a and b. Starting with dry conditions, the initial rate of
adsorption of vapor is quite high when ATB is exposed to a constant
vapor pressure of 760 Pa. However, due to saturation, the rate of
vapor adsorption is gradually diminished, as shown in FIG. 18(a).
This variation in the rate of vapor adsorption results in an
initial spike in the temperature of the adsorbent followed by a
gradual decrease, as shown in FIG. 18(b). In the actual
implementation of the ATB, the refrigerant supply to the evaporator
will be controlled using a flow control valve. This will regulate
the pressure inside the ATB to provide a steady operating
condition. The detailed computational analysis also shows that an
adsorbent with 30 wt. % adsorption capacity at 760 Pa will provide
an average heating and cooling rate exceeding 2.5 kW for a duration
of 1 hour when it is incorporated into the design illustrated in
FIG. 16(d).
[0071] In order to determine the operating conditions to deliver
the required uptake shown in FIG. 18, it is necessary to determine
the temperature distribution within the bed during operation. FIGS.
19a and b show the average bed temperature as a function of the
thermal conductivity of the adsorbent and the heat transfer
coefficient (HTC) provided by circulating the coolant in the
coolant lines (see FIGS. 15 and 16 illustrating the coolant flow
arrangement). This corresponds to a uniform rate of heat generated
(0.23 MW/m.sup.3) in the adsorption bed. Clearly, the bed
temperature can be lowered if the thermal conductivity and the HTC
are both increased. While the HTC can be increased at the expense
of higher pumping power (FIG. 19(b)), a higher thermal conductivity
can be obtained using high-k binding materials. In order to
minimize the overall thermal resistance between the bed and the
coolant, a thermal conductivity >1 W/mK is desirable.
[0072] A higher thermal conductivity resulting in a lower
operational temperature is essential to maximize adsorption during
ATB operation. FIG. 20, shows the relative pressure as a function
of thermal conductivity and the coolant temperature. The
temperature of the coolant depends on the ambient weather
conditions. In this regard, the most challenging operating
conditions for adsorption correspond to the winter, wherein tire
coolant providing heating to the EV cabin has to be maintained at a
temperature of 60.degree. C. This operating condition corresponds
to a relative pressure of .about.2%, if the average thermal
conductivity of the adsorbent is 1 W/mK. In summary, an adsorbent
packing density of 850 kg/m.sup.3, thermal conductivity of 1 W/mK,
and an adsorption capacity of 30 wt. % at a relative pressure of
2%, will deliver heating and cooling in excess of 2.5 kW using the
ATB design illustrated in FIG. 16.
[0073] While water is the preferred refrigerant due to superior
thermophysical properties, it is also environmentally benign and
safe for applications. however, freezing of water is detrimental to
the overall performance of the device. Consequently, in the actual
ATB application, water is added with methanol to avoid freezing.
Apart from reducing the freezing point of the refrigerant methanol
is also adsorbed by the adsorption bed.
[0074] A single cell or "button cell" embodiment of the invention
will now be discussed in conjunction with FIGS. 21-25.
[0075] FIG. 21 shows the overall integrated design for this
embodiment. As shown in FIG. 22, one side is a hot terminal
comprising Zt 13.times. compressed in an aluminum honeycomb and a
cold terminal including a porous medium evaporator and bare
condenser plate connected to a reservoir, in this case a 120 ml
reservoir.
[0076] FIGS. 23 and 24 show more detail of the compressed aluminum
honeycomb.
[0077] FIG. 25 shows the evaporator side including 10.times.
compressed 95% porosity copper foam having approximately 110 .mu.m
pore size. Minichannels serve to direct liquid beneath the porous
copper. As shown in FIG. 13, the ATB is a heat pump that can be
charged and discharged like a battery. The unit is charged up by
applying a temperature difference to the terminals. The temperature
difference can be recovered at a later time by opening a valve
connecting a reservoir to the adsorbent bed.
[0078] The numbers in square brackets refer to the references
listed herein. The contents of all of these references are
incorporated herein by reference in their entirety.
[0079] It is recognized that modifications and variations of the
present invention will occur to those of skill in the art, and it
is intended that all such modifications and variations be included
within the scope of the appended claims.
REFERENCES
[0080] [1] See original technology disclosure for MIT Case
15230
[0081] [2] Chen Li et al., Evaporation/Boiling in Thin Capillary
Wicks--Wick Thickness Effects, Transactions of ASME 2006,
128(1).
[0082] [3] Frank Incropera, Fundamentals of Heat and Mass Transfer,
Wiley 2002.
[0083] [4] Ernst-Jan Bakker and Robert de Boer, Development of a
2.5 kW Adsorption Chiller for Heat-Driven Cooling, Energy research
Centre of the Netherlands 2008.
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