U.S. patent application number 13/058182 was filed with the patent office on 2011-07-28 for microscale heat or heat and mass transfer system.
This patent application is currently assigned to Georgia Tech Research Corporation. Invention is credited to Matthew Delos Determan, Srinivas Garimella.
Application Number | 20110180235 13/058182 |
Document ID | / |
Family ID | 41610741 |
Filed Date | 2011-07-28 |
United States Patent
Application |
20110180235 |
Kind Code |
A1 |
Garimella; Srinivas ; et
al. |
July 28, 2011 |
MICROSCALE HEAT OR HEAT AND MASS TRANSFER SYSTEM
Abstract
Microscale, monolithic heat or heat and mass transfer systems: a
plurality of shims (102, 104) assembled between two outer plates
(110, 111) that, when combined, form discrete but integrated heat
and mass transfer system components that make up a microscale,
monolithic absorption cooling and/or heating system, or other heat
or heat and mass transfer system. The shims generally include a
plurality of microchannels (702), voids, fluid passages, and other
features for transferring fluids between defined components
throughout the system, and into and out of the system to and from
heating and cooling sources and sinks as needed. Generally, two
distinct shim types are used and combined together as a plurality
of shim pairs to enable thermal contact between the fluids flowing
within the microchannels in each shim pair, each shim in each shim
pair comprising slightly different microchannel and fluid passage
arrangements as compared to each other.
Inventors: |
Garimella; Srinivas;
(Smyrna, GA) ; Determan; Matthew Delos; (Atlanta,
GA) |
Assignee: |
Georgia Tech Research
Corporation
Atlanta
GA
|
Family ID: |
41610741 |
Appl. No.: |
13/058182 |
Filed: |
July 31, 2009 |
PCT Filed: |
July 31, 2009 |
PCT NO: |
PCT/US2009/052362 |
371 Date: |
February 8, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61085192 |
Jul 31, 2008 |
|
|
|
Current U.S.
Class: |
165/104.11 |
Current CPC
Class: |
F28F 3/12 20130101; F28F
2260/02 20130101; F25B 15/00 20130101; F25B 2400/15 20130101; Y02A
30/277 20180101; Y02B 30/62 20130101; F25B 2500/01 20130101; F28D
21/0015 20130101; F28D 9/0093 20130101; F28D 9/005 20130101; Y02A
30/27 20180101; F25B 37/00 20130101 |
Class at
Publication: |
165/104.11 |
International
Class: |
F28D 15/00 20060101
F28D015/00 |
Claims
1-214. (canceled)
215. An integrated heat and mass transfer apparatus comprising: a
heat and mass transfer system having at least one heat exchange
region for affecting a heat transfer function of a particular
component; a fluid coupling means for coupling a thermally modified
flow of a coupling fluid through the at least one heat exchange
region; and a pair of cover plates that include ports for
introducing a working fluid and the coupling fluid into functional
components and for transporting the working fluid and the coupling
fluid out of the functional components; wherein the at least one
heat exchange region defined by a plurality of rows of
microchannels of a plurality of shims, the shims being stacked,
planar, and heat conducting shims, each shim comprising: openings
that define a plurality of fluid voids for containing: the working
fluid; and the coupling fluid for conveying thermal energy into or
out of the heat and mass transfer system; the plurality of rows of
microchannels being formed by microscale indentations on the
plurality of shims; wherein the plurality of rows of microchannels
comprise: a first row of microchannels for communicating a first
flow of the working fluid from an inlet fluid void associated with
the particular component of the heat and mass transfer system into
an outlet fluid void associated with the particular component of
the heat and mass transfer system; and a second row of
microchannels for communicating either a second flow of the working
fluid associated with the particular component of the heat and mass
transfer system or a flow of the coupling fluid for the heat
transfer function of the heat exchange regions, wherein the second
row of microchannels are in thermal contact with the first row of
microchannels to conduct heat between the first flow of the working
fluid in the first row of microchannels and either the second flow
of the working fluid or the flow of the coupling fluid in the
second row of microchannels for the heat transfer function of the
at least one heat exchange region; and wherein the system provides
a heating or cooling function via the thermally modified flow of
the coupling fluid.
216. The integrated heat and mass transfer apparatus of claim 215,
wherein the system is configured to operate as a heat pump, wherein
the fluid coupling means comprises: a first fluid coupling means
for coupling a first flow of a heated coupling fluid through a an
initial stage heat exchange region of the heat and mass transfer
system for receiving thermal energy into the system; a second fluid
coupling means for coupling a thermally modified second flow of
coupling fluid through a subsequent stage heat exchange region of
the heat and mass transfer system; and a third fluid coupling means
for coupling a heat rejection flow of coupling fluid through a heat
exchange region of a stage of the heat and mass transfer
system.
217. The integrated heat and mass transfer apparatus of claim 215,
wherein the plurality of shims are arranged as a plurality of pairs
of shims of a first type and a second type that when paired
together define the microchannels for communicating working fluid
and/or coupling fluid between fluid voids of the particular
component of the heat and mass transfer system.
218. The integrated heat and mass transfer apparatus of claim 217,
wherein each of the pairs of shims comprise a predetermined single
element of a multi-element array of the shims that have dimensions
determined by input/output thermal properties and fluid flow
characteristics of the heat and mass transfer system.
219. The integrated heat and mass transfer system of apparatus 215,
wherein the particular component of the heat and mass transfer
system comprises a refrigerant absorber, wherein a plurality of
vapor inlet holes formed in a row of the microchannels on a first
shim provide for vapor flowing from a passage in an adjacent second
shim to flow into the microchannels of the first shim and mix with
absorbent in the microchannels of the first shim.
220. The integrated heat and mass transfer apparatus of claim 215,
wherein one of the plurality fluid voids comprises a fluid header
for directing a flow of working fluid or coupling fluid for the
particular component into a fluid distribution passage that directs
the fluid into a row of microchannels.
221. The integrated heat and mass transfer apparatus of claim 215,
wherein the microscale indentations comprise a shape formed in a
top surface of a first shim of one of the plurality of shims for
conducting fluid alongside and thermal energy into a corresponding
and adjacent bottom surface of an adjacent second shim of the
plurality of shims that encloses the indentations so as to form the
microchannels.
222. The integrated heat and mass transfer apparatus of claim 215,
wherein the microscale indentations are selected from the group
consisting of machined grooves, cut grooves, photoetched grooves,
chemically etched grooves, laser etched grooves, molded grooves,
stamped grooves, and particle blasted grooves.
223. The integrated heat and mass transfer apparatus of claim 215,
wherein the plurality of stacked shims and pair of cover plates are
physically bonded to form a unitary structure.
224. The integrated heat and mass transfer apparatus of claim 223,
wherein the physical bonding is performed by a method selected from
the group consisting of diffusion bonding, gluing, brazing,
welding, and pressing.
225. The integrated heat and mass transfer apparatus of claim 215,
wherein a particular implementation of the heat and mass transfer
system comprises an absorption heat pump with the working fluid of
the absorption heat pump being selected from the group consisting
of ammonia-water and lithium-bromide-water admixture.
226. The integrated heat and mass transfer apparatus of claim 225,
wherein the heat pump is configured to be a single-effect, a
double-effect, a triple-effect, or a generator-absorber-heat
exchange (GAX) cycle.
227. The integrated heat and mass transfer apparatus of claim 215,
further comprising one or more fluid pumps for moving the working
fluid or the coupling fluid between the functional components.
228. The integrated heat and mass transfer apparatus of claim 215,
wherein the flow of working fluid in the first row of microchannels
is substantially counterflow, parallel-flow, co-flow or crossflow
in direction to the direction of flow of fluid in the second row of
microchannels.
229. The integrated heat and mass transfer apparatus of claim 215,
wherein the particular component of the heat and mass transfer
system comprises a refrigerant rectifier of an absorption heat
pump, and further comprises a plurality of fluid-retaining ribs
formed within the monolithic support structure that form trays for
containing a quantity of liquid and enable a flow of vapor and
liquid in opposite directions, with the fluid and vapor in direct
mass contact across a surface of liquid contained by the trays and
in thermal contact with a coupling fluid or working fluid, with a
reflux of liquid collecting and exiting the rectifier in a
generally downward fashion to join a desorber solution flow.
230. The integrated heat and mass transfer apparatus of claim 215,
wherein the heat and mass transfer system is an absorption heat
pump or a multi-component fluid processing system that includes a
forced convective flow of fluids in some regions within the system
and a gravity/buoyancy driven flow of fluids in other regions of
the system such that desired liquid or vapor temperatures, species
concentrations, and species concentration gradients during phase
change are achieved, and further comprising passages formed within
the monolithic structure that provide for downward liquid flow in
conjunction with upward vapor flow in a counterflow arrangement
within the passages, whereby conditions promoting the boiling or
desorption of vapor and/or higher refrigerant vapor purities are
effected.
231. A heat and mass transfer apparatus configured for use in a
heat and mass transfer system, the apparatus comprising: a pair of
cover plates that include ports for introducing a working fluid and
a coupling fluid into a plurality of functional components within a
support structure and for transporting the working fluid and the
coupling fluid out of at least one of the plurality of functional
components a plurality of shim pairs bonded to the pair of cover
plates to form an integrated heat and mass transfer system, the
plurality of shim pairs comprising a plurality of openings defining
a plurality of fluid voids and having microscale indentations
formed in a surface of the shim pairs defining a first row of
microchannels and a second row of microchannels; and a fluid
coupling means for coupling a thermally modified flow of coupling
fluid through a heat exchange region of a stage of the heat and
mass transfer apparatus, whereby the apparatus provides a heating
or cooling function via the thermally modified flow of coupling
fluid as appropriate for the heat and mass transfer system.
232. The heat and mass transfer apparatus of claim 231, wherein the
plurality of fluid voids contain the working fluid and the coupling
fluid employed for conveying thermal energy into or out of the
support structure, wherein the plurality of voids define one or
more integrally formed heat exchange regions defined and contained
within the support structure for effecting a heat transfer function
of at least one of the plurality of functional components of the
heat and mass transfer system.
233. The heat and mass transfer apparatus of claim 232, wherein
each heat exchange region comprises: the first row of microchannels
defined in the thermally conducting material for communicating a
first flow of the working fluid from an inlet fluid void associated
with a first functional component of the plurality of functional
components of the particular heat and mass transfer system into an
outlet fluid void associated with a second functional component of
the plurality of functional components of the heat and mass
transfer system; and the second row of microchannels defined in the
thermally conducting material for communicating either a second
flow of working fluid associated with the first functional
component of the plurality of functional components of the heat and
mass transfer system or a flow of the coupling fluid for the
particular heat transfer function of the heat exchange region.
234. The heat and mass transfer apparatus of claim 233, wherein the
first row of microchannels and the second row of microchannels are
arranged in thermal contact with each other within the support
structure so as to conduct heat between the first flow of working
fluid in the first row of microchannels and either the second flow
of working fluid or the flow of coupling fluid in the second row of
microchannels.
235. The heat and mass transfer apparatus of claim 231, wherein the
flow of the working fluid in the first row of microchannels is
substantially counterflow, parallel-flow, co-flow or crossflow in
direction to the direction of flow of fluid in the second row of
microchannels.
236. The heat and mass transfer apparatus of claim 231, wherein the
system is a heat pump, and wherein the fluid coupling means
comprises: a first fluid coupling means for coupling a first flow
of a heated coupling fluid through a heat exchange region defining
an initial stage of the heat and mass transfer system for receiving
thermal energy into the heat and mass transfer system; a second
fluid coupling means for coupling a thermally modified second flow
of coupling fluid through a heat exchange region defining a
subsequent stage of the heat and mass transfer system; and a third
fluid coupling means for coupling a heat rejection flow of coupling
fluid through a heat exchange region of a stage of the heat and
mass transfer system, whereby the system provides a heating or
cooling function via the thermally modified second flow of coupling
fluid for the heat and mass transfer system and a heat rejection
function via the heat rejection flow of coupling fluid.
237. The heat and mass transfer apparatus of claim 231, wherein
each of the plurality of pair of shims comprises a predetermined
single element of a multi-element array of the shims, the
multi-element array having dimensions determined by the
input/output thermal properties and fluid flow characteristics of
the heat and mass transfer system.
238. The heat and mass transfer apparatus of claim 231, wherein one
of the fluid voids comprises a fluid header formed within the
support structure for directing a flow of working fluid or coupling
fluid into a fluid distribution passage that directs the fluid into
a row of microchannels.
239. The heat and mass transfer apparatus of claim 238, wherein the
fluid header comprises a region within the plurality of shim pairs
defining: an opening for receiving fluid; and a fluid void defined
by the plurality of shim pairs within the fluid header; and a fluid
distribution passage defined in alternating shims of at least one
of the shims in the plurality of shim pairs.
240. The heat and mass transfer apparatus of claim 231, wherein the
microscale indentations comprise a shape formed in a top surface of
a first shim of one of the shims in a pair of the plurality of shim
pairs for conducting fluid alongside and thermal energy into a
corresponding and adjacent bottom surface of an adjacent second
shim that encloses the indentations so as to form the
microchannels.
241. The heat and mass transfer apparatus of claim 231, wherein the
microscale indentations are selected from the group consisting of
machined slots, machined grooves, cut grooves, photoetched grooves,
chemically etched grooves, laser etched grooves, molded grooves,
stamped grooves, and particle blasted grooves, or combinations
thereof.
242. The heat and mass transfer apparatus of claim 231, wherein the
working fluid is selected from the group consisting of
ammonia-water and lithium-bromide-water admixture.
243. The heat and mass transfer apparatus of claim 231, wherein the
system is a heat pump configured for operation selected from the
group consisting of a single-effect, double-effect, a
triple-effect, and a generator-absorber-heat exchange (GAX)
cycle.
244. The heat and mass transfer apparatus of claim 231, further
comprising one or more fluid pumps for moving the working fluid or
the coupling fluid between components.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims benefit under 35 U.S.C. .sctn.
119(e) of U.S. Provisional Patent Application No. 61/085,192, filed
Jul. 31, 2008, and entitled "Thermally Activated Cooling System",
which is incorporated by reference as if set forth herein in its
entirety.
TECHNICAL FIELD
[0002] The present system relates generally to microscale heat
transfer systems or heat and mass transfer systems, and more
particularly to monolithic or integrated microscale heat or heat
and mass transfer systems or apparatuses comprising a plurality of
shims or layers, each shim including a plurality of microchannels
for performing heat and/or mass exchange functions.
BACKGROUND
[0003] Traditionally, vapor-compression systems have been used in
various heating and cooling applications, such as residential and
commercial air conditioners, chillers, and heat pumps. These
systems generally comprise four basic components--an evaporator,
compressor, condenser, and expansion device. The evaporator and
condenser comprise heat exchangers that evaporate and condense
refrigerant while absorbing and rejecting heat. The compressor
takes the refrigerant vapor from the evaporator and raises its
pressure sufficiently to condense the vapor in the condenser. After
exiting the condenser, the flow of condensed refrigerant at higher
pressure is controlled by the expansion device back into the
evaporator, and the cycle repeats to produce continuous heating or
cooling effects.
[0004] Traditional vapor-compression systems, however, have several
disadvantages. For example, most vapor-compression systems rely on
synthetic refrigerants that have negative environmental impact.
Also, most vapor-compression systems utilize expensive, high-grade
electrical energy for power. Further, vapor-compressions systems
are often loud and unreliable due to the use of a compressor, and
often employ bulky overall system designs that prohibit small-scale
or portable use.
[0005] An absorption heat pump (also referred to herein as an
"absorption cooling and/or heating system") can be considered an
environmentally benign replacement for a traditional
vapor-compression system. In principle, the compressor of a
traditional vapor-compression system is replaced by a combination
of a desorber, absorber, liquid solution pump, and recuperative
solution heat exchanger to form an absorption heat pump. A benefit
of absorption heat pumps is the reduced concern about reliability
due to the absence of a major moving part, i.e., the compressor.
The lack of a compressor in the absorption heat pump also implies
much quieter operation as compared to a vapor-compression system.
Further, unlike vapor-compression systems that utilize high-grade
electrical energy as the input that drives the system, absorption
heat pumps typically run on more readily available and low-grade
thermal energy, which may be obtained from combustion of bio-fuels
and fossil fuels, from largely untapped waste heat sources (e.g.,
automobile exhaust, excess manufacturing heat, etc.), from solar
thermal energy, and other similar energy sources. In cooling mode
operation, this thermal energy input is used to provide cooling
and/or dehumidification, while in the heating mode, the heat input
is used to pump ambient heat to higher temperatures.
[0006] Because the compressor of a vapor-compression system is
replaced in an absorption heat pump by a combination of a desorber,
absorber, liquid solution pump, and recuperative solution heat
exchanger, absorption heat pumps are generally more heat and mass
exchange intensive than vapor-compression systems, thereby
requiring additional heat transfer surface area. Due to this
comparatively larger surface area requirement, absorption heat
pumps have typically been relegated to very large commercial and
industrial chiller applications, and achieving compact designs
while delivering high coefficients of performance (COPs) has been a
major challenge. Additionally, several advanced absorption cycles,
such as the double-effect, triple-effect, and Generator-Absorber
Heat Exchange cycles developed to improve COPs, rely on additional
internal recuperation to improve performance, further emphasizing
the need for high heat and mass transfer rates per volume. In fact,
these cycles have not been widely implemented primarily because of
a lack of practically feasible and compact heat and mass exchange
devices.
[0007] It is desirable, therefore, to achieve a compact absorption
cooling and/or heating system that delivers outputs comparable to
those of larger systems. However, in absorption systems that use
the two most common working fluid pairs (i.e., lithium
bromide-water and ammonia-water), processes such as absorption and
desorption naturally involve coupled heat and mass transfer in
binary fluids, leading to complexities and challenges in system
design. Particularly, in ammonia-water systems, due to the presence
of both absorbent (i.e., water) and refrigerant (i.e., ammonia) in
the liquid and vapor phases throughout the system, such binary
fluids processes occur in all components in the system (including
the condenser, evaporator, rectifier, and recuperative heat
exchangers). With other, less common working fluids (e.g.,
multi-component fluids), multi-component heat and mass transfer
processes are required. For the implementation of absorption
systems in compact, high-flux configurations that can take
advantage of disperse availability of waste heat, solar thermal
energy, or other energy in smaller capacities than at the
industrial scales, the heat and mass exchanger designs should
provide several features that are difficult to achieve
simultaneously. For example, the systems should include low heat
and mass transfer resistances for the working fluids, the requisite
transfer surface area for the working fluids and the fluids that
couple those working fluids to external heat sources and sinks in
compact volumes, and low resistances for the coupling fluids, among
other similar system properties.
[0008] Most of the available absorption component concepts fall
short in one or more of these features essential for achieving
compact, high-flux designs. For example, the primary configuration
employed currently in commercial absorption chillers (i.e.,
absorption of vapor into solution films falling over tube banks
carrying coolant liquid) suffers from high coolant-side resistances
and poor wetting of the transfer surface by the liquid film.
Additionally, some prior designs enhance absorption/desorption
processes, but fail to reduce single-phase resistance on the other
side (i.e., coupling fluid side), thereby requiring large system
components, and resulting in high working fluid and coupling fluid
pressure drop, which results in high parasitic power consumption
and also results in losses in driving temperature differences due
to decrease in saturation temperatures brought about by pressure
drops within system components.
[0009] In addition to absorption cooling and/or heating systems, it
is further desirable to provide various other heat transfer or heat
and mass transfer systems for performing other functions, such as
related cooling or heating functions, basic heat transfer,
distillation, and other similar functionalities as will occur to
one of ordinary skill in the art.
[0010] Therefore, there is a long-felt but unresolved need for a
microscale heat or heat and mass transfer system or apparatus that
provides compact, modular, versatile design that can be applied for
high flux heat and mass transfer, both in individual system
components and in the overall system assembly, while overcoming the
weaknesses of currently-used configurations. There is a further
need for a microscale, monolithic absorption heat pump that
provides significant heating and cooling outputs from a portable,
integrated system. The principal embodiments of the present system,
and variants thereof, represent a miniaturization technology highly
adaptable to a variety of design conditions, and also to several
systems in multiple industries involved in binary, ternary, and
other multi-component fluid heat and mass transfer.
BRIEF SUMMARY OF THE DISCLOSURE
[0011] Briefly described, and according to one embodiment, aspects
of the present disclosure generally relate to systems and
apparatuses for absorption cooling and/or heating, or performing
other heat and/or mass transfer functions. More particularly,
according to one aspect, an array of parallel, aligned alternating
shims with integral microscale passages and voids, fluid inlet and
outlet passages, and vapor-liquid spaces as necessary, enclosed
between cover plates, define the heat and mass transfer system
components of a thermally-activated absorption heat pump. The
assembly of parallel shims with microscale features directs fluid
flow through a defined absorber, recuperative solution heat
exchanger, desorber, rectifier (in applications using a working
fluid with a volatile absorbent), condenser, recuperative
refrigerant heat exchanger, and an evaporator, which together
comprise the heat and mass transfer system components of a
single-effect absorption heat pump. As described in greater detail
herein, in a particular embodiment, the heat and mass transfer
components are defined within a microscale, monolithic apparatus or
assembly via pairs of alternating shims. In embodiments in which a
double-effect, triple-effect, generator-absorber-heat exchange
(GAX) cycle, or other advanced absorption cycle is desired,
additional microscale features arranged into additional, defined,
heat and mass transfer system components are incorporated into the
apparatus to accomplish the requisite recuperative heat and mass
transfer.
[0012] According to one aspect, the absorption cycle working fluid
flows in microscale and other passages incorporated into one side
of a shim, while the high (heat source), medium (heat rejection),
and low (chilled stream) temperature coupling fluids flow on the
other side of the shim in thermal contact with the respective
working fluid streams on the initial side. Therefore, sets of two
shims ("shim pairs"), with somewhat differentiated microscale
feature geometries, comprise building blocks of an entire
absorption heat pump or other heat or heat and mass transfer system
that are duplicated in numbers required to accomplish the desired
overall cooling or heating load. The features incorporated into
each shim are arrayed in groups, with each group representing the
corresponding passages for each heat or heat and mass transfer
system component in a heat pump (e.g., absorber, desorber, etc.).
Fluid connections between the respective, defined heat and mass
transfer system components is achieved through connecting fluid
lines external to the system, or through specifically designed
routing passages between different parts of the shims or cover
plates, or via some other similar connection mechanism. Generally,
the working fluid is largely contained within the assembly of
shims, therefore reducing fluid inventories several fold over
conventional heat pumps that deliver similar capacities.
[0013] According to an additional aspect, cooling, heat rejection,
and heat source fluid streams enter and leave the heat or heat and
mass transfer apparatus through appropriate inlet and outlet
connections, enabling versatile deployment of heating or cooling
loads, irrespective of the physical location of the heat or heat
and mass transfer apparatus. In one aspect, a working solution pump
is provided external to the system assembly to pump the working
fluid through the heat and mass transfer components and
microchannels arrayed across each shim in the assembly. During the
heat pump cycle, and according to a further aspect, expansion of
the refrigerant stream and the refrigerant-absorbent solution from
the low to high-side pressures (and intermediate pressures as
necessary for advanced absorption cycles) is accomplished through
integral tailored constrictions within the shims or through
externally connected valves.
[0014] According to various aspects, the microchannels and other
microscale passages in the shims comprise square, rectangular,
semi-circular, semi-elliptical, triangular or other
singly-connected cross-sections to enable fluid flow in
single-phase or two-phase state, as necessary, with the microscale
cross-section shape and dimensions determined based on heat and
mass transfer requirements, operating pressures, structural
strength of the assembled apparatus, manufacturing constraints for
dimensional tolerances and bonding of the shims and cover plates,
and other factors. Generally, the microscale channels in the shims
are formed through processes such as lithography, etching,
machining, stamping, or other appropriate processes based on
overall assembly dimensions as well as microscale channel
dimensions. Joining and assembly of a plurality of shim pairs and
cover plates to form an embodiment of the microscale heat or heat
and mass transfer system is accomplished through processes such as
diffusion bonding and brazing for the most commonly utilized
metallic assemblies, and if permitted or dictated by the working
fluid, operating conditions, and desired loads, by gluing for
plastic, ceramic, or other nonmetallic apparatus parts. Modularity
in heat duties is achieved by varying the microscale channel
dimensions, number of channels, length and width of the shims, and
number of shim pairs.
[0015] According to another aspect, for large scale implementation
of microscale heat or heat and mass transfer assemblies as
described herein, multiple assemblies are connected in series
and/or parallel arrangements through external plumbing to form a
plurality of connected heat or heat and mass transfer assemblies.
According to various aspects, for larger capacities, the shims are
subdivided into individual assemblies representing each heat and
mass transfer system component of the heat or heat and mass
transfer system rather than a monolithic heat or heat and mass
transfer assembly, to facilitate flexibility in connections, and
largely unconstrained increases in delivered loads.
[0016] These and other aspects, features, and benefits of the
claimed invention(s) will become apparent from the following
detailed written description of the preferred embodiments and
aspects taken in conjunction with the following drawings, although
variations and modifications thereto may be effected without
departing from the spirit and scope of the novel concepts of the
disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The accompanying drawings illustrate one or more embodiments
and/or aspects of the disclosure and, together with the written
description, serve to explain the principles of the disclosure.
Wherever possible, the same reference numbers are used throughout
the drawings to refer to the same or like elements of an
embodiment, and wherein:
[0018] FIG. 1 illustrates an embodiment of a monolithic, microscale
heat or heat and mass transfer apparatus constructed and operated
in accordance with various aspects of the claimed invention(s).
[0019] FIG. 2 shows an embodiment of the heat or heat and mass
transfer apparatus as described herein with a cut out area
illustrating a section of the cover plates removed from the
apparatus to display a portion of the heat and mass transfer system
components formed via the shims.
[0020] FIG. 3 illustrates an exemplary, fully-assembled embodiment
of the heat or heat and mass transfer apparatus as described
herein.
[0021] FIGS. 4A-4D show exploded perspective views of the exemplary
microscale, heat or heat and mass transfer apparatus according to
an embodiment of the present system.
[0022] FIG. 5 illustrates a schematic functional representation of
the internal heat and mass transfer system components and the fluid
flows between the components according to one embodiment of the
present heat or heat and mass transfer apparatus.
[0023] FIGS. 6A and 6B are perspective views illustrating exemplary
representations of shim A and shim B, respectively, according to
one embodiment of the present system.
[0024] FIGS. 7A and 7B are front plan views illustrating exemplary
representations of shim A and shim B, respectively, according to
one embodiment of the present system.
[0025] FIGS. 8A and 8B show perspective views of portions of shims
A and B, respectively, associated with a recuperative solution heat
exchanger according to an embodiment of the present apparatus.
[0026] FIGS. 9A and 9B are enlarged perspective views of portions
of shims A and B, respectively, associated with a recuperative
solution heat exchanger according to an embodiment of the present
apparatus (i.e., these figures are enlarged views of FIGS. 8A and
8B).
[0027] FIGS. 10A and 10B illustrate enlarged, perspective views of
portions of a plurality of stacked shims A and B associated with a
recuperative solution heat exchanger according to an embodiment of
the present apparatus.
[0028] FIGS. 11A and 11B illustrate perspective views of portions
of shims A and B, respectively, associated with a desorber and
rectifier, according to an embodiment of the present apparatus.
[0029] FIGS. 12A and 12B illustrate perspective views of portions
of shims A and B, respectively, associated with a condenser
according to an embodiment of the present apparatus.
[0030] FIGS. 13A and 13B illustrate perspective views of portions
of shims A and B, respectively, associated with a recuperative
refrigerant heat exchanger according to an embodiment of the
present apparatus.
[0031] FIGS. 14A and 14B illustrate perspective views of portions
of shims A and B, respectively, associated with an evaporator
according to an embodiment of the present apparatus.
[0032] FIGS. 15A and 15B illustrate perspective views of portions
of shims A and B, respectively, associated with an absorber
according to an embodiment of the present apparatus.
[0033] FIGS. 16A and 16B are enlarged perspective views of portions
of shims A and B, respectively, associated with an absorber, and
specifically illustrating locations of vapor inlet holes and
passages in shims A and B according to an embodiment of the present
apparatus.
[0034] FIG. 17 illustrates a modular embodiment of the present
system comprising discrete heat and mass transfer system components
associated with an absorption cooling and/or heating system.
[0035] FIG. 18 illustrates the steps associated with one embodiment
of the photochemical etching process for manufacturing exemplary
microchannels as described herein.
[0036] FIG. 19 illustrates a representation of a hot press vacuum
furnace for diffusion bonding various shims, cover plates, and
other system components together according to one embodiment of the
present system.
[0037] FIG. 20 illustrates a cross-section of a portion of a
plurality of stacked shims A and B showing representative
arrangements of microchannels within the shims according to an
exemplary embodiment of the present system.
[0038] FIG. 21 illustrates an enlarged cross-section of shims A and
B illustrating a close-up view of specific, exemplary shim and
microchannel dimensions according to an exemplary embodiment of the
present system.
[0039] FIG. 22 shows an enlarged plan view of a header used in a
heat and mass transfer system component according to an embodiment
of the present system.
[0040] FIG. 23 shows a representative cross-section of alternating
shims A and B taken from cross-section XX of the header in FIG. 22
according to one embodiment of the present system.
[0041] FIG. 24 illustrates a front plan view of exemplary fluid
connections and external plumbing arrangements for testing an
embodiment of the present system.
DETAILED DESCRIPTION
[0042] Prior to a detailed description of the disclosure, the
following definitions are provided as an aid to understanding the
subject matter and terminology of aspects of the present systems
and methods, are exemplary, and not necessarily limiting of the
aspects of the systems and methods, which are expressed in the
claims. Whether or not a term is capitalized is not considered
definitive or limiting of the meaning of a term. As used in this
document, a capitalized term shall have the same meaning as an
uncapitalized term, unless the context of the usage specifically
indicates that a more restrictive meaning for the capitalized term
is intended. However, the capitalization or lack thereof within the
remainder of this document is not intended to be necessarily
limiting unless the context clearly indicates that such limitation
is intended.
Definitions/Glossary
[0043] Absorbent: material or fluid that, either by itself or in
multi-component form combined with ammonia or another refrigerant,
comprises a working fluid or portion of a working fluid for
performing the heat and mass transfer functions of a heat or heat
and mass transfer system (e.g., an absorption heat pump) as
described herein. Examples include, but are not limited to, water
(in ammonia-water mixtures), lithium bromide (in lithium
bromide-water mixtures), and other similar materials.
[0044] Coefficient of performance (COP): ratio of a desired output
(i.e., cooling or heating) from a system embodiment as compared to
the input energy.
[0045] Coupling fluid: fluid used to transfer heating and/or
cooling to and from embodiments of the present system. Generally
connects embodiments of the present system to one or more heat
sources, heat sinks, ambient spaces, conditioned spaces, etc.,
generally via hydronic coupling. Examples include, but are not
limited to, ethylene glycol-water solution, propylene glycol-water
solution, calcium chloride-water solution, high temperature heat
transfer fluids (e.g., synthetic oil), and other similar fluids.
Sometimes referred to herein as coolant.
[0046] Cover plate: rigid outer layer on outer sides of embodiments
of the present system to provide structure, support, and, in some
embodiments, fluid transfer channels to shims contained between
cover plates. Cover plates generally include holes or inlet and
outlet openings for transferring coupling fluid and working fluid
flow streams entering and exiting embodiments of the system.
[0047] Fluid distribution passage: channel or passage that
transports fluid from voids formed by stacked-up shims (i.e.,
headers) to microchannels within heat and mass transfer system
components or heat exchange components in embodiments of the
present system. Generally synonymous with distribution passage,
fluid passage, passage, or passageway.
[0048] Header: element within a heat and mass transfer system
component that provides an opening or port to receive or expunge
fluid. Generally formed by a plurality of stacked-up voids
associated with individual shims that, when combined, form a
passageway for fluid flow. Types generally comprise inlet headers
and outlet headers.
[0049] Heat or heat and mass transfer system: a system for
transferring heat or heat and mass comprising properties, features,
dimensions, components, etc., as described herein. As will be
understood and appreciated, generally describes a heat transfer
system or a heat and mass transfer system formed by one or more
heat and mass transfer system components, as described herein.
Generally synonymous with heat or heat and mass transfer apparatus,
heat or heat and mass transfer assembly, or heat and/or mass
transfer system.
[0050] Heat and mass transfer system component: generic term used
to describe any component capable of performing heat and/or mass
transfer, generally (although not always) within a larger heat or
heat and mass transfer system. Examples include, but are not
limited to, an absorber, recuperative solution heat exchanger,
desorber, rectifier, condenser, recuperative refrigerant heat
exchanger, evaporator, or other similar component. Generally
(although not always) includes or comprises at least one heat
exchange component. Generally synonymous with heat and mass
transfer component. Sometimes synonymous with heat exchanger.
[0051] Heat exchange component: generic term used to describe any
component capable of performing heat transfer. May comprise a heat
and mass transfer system component, or a sub-component thereof.
Generally synonymous with heat exchanger.
[0052] Microchannel: channel or passage of microscale dimensions
formed in a shim as described herein for transferring fluid in
single-phase or multi-phase state to accomplish heat and/or mass
transfer functionality. Generally characterized by circular (or
non-circular) cross-sections with hydraulic diameters less than 1
mm (although, as will be understood, channels larger than 1 mm may
exhibit fluid flow and heat and mass transfer phenomena similar to
microchannels at somewhat larger hydraulic diameters, depending
upon the given fluid properties and operating conditions).
Generally synonymous with microscale passage or microscale
channel.
[0053] Microscale: relatively smaller in size as compared to other
systems or components of similar functionality and/or output.
Generally miniature, as understood in the art.
[0054] Monolithic: constituting one, undifferentiated whole or
unit. Generally synonymous with integrated.
[0055] Multi-component fluid: fluid comprising more than one
discrete substance (i.e., more than one species). Examples include,
but are not limited to, ammonia-water mixtures and lithium
bromide-water mixtures. Generally synonymous with multi-constituent
fluid, multi part fluid, binary fluid, ternary fluid, quaternary
fluid, fluid pair, etc.
[0056] Refrigerant: material or fluid that, either by itself or in
multi-component form combined with water or another absorbent,
comprises a working fluid or portion of a working fluid for
performing the heat and mass transfer functions of a heat or heat
and mass transfer system (e.g., an absorption heat pump) as
described herein. Examples include, but are not limited to, ammonia
(in ammonia-water mixtures), water (in lithium bromide-water
mixtures), and other similar materials. Generally synonymous with
ammonia, as used herein.
[0057] Shim: thin, rigid layer defining features associated with
one or more heat or heat and mass transfer components as described
herein. Generally includes a plurality of microchannels, fluid
distribution passages, and voids for transferring working fluid
and/or coupling fluid across the shim. Generally synonymous with
layer or laminate.
[0058] Shim group: combination of a plurality of shim pairs bonded
or otherwise combined together to define one or more heat or heat
and mass transfer system components.
[0059] Shim pair: combination of two discrete shim types (e.g., A
and B, described herein) bonded or otherwise combined together to
enable heat and/or mass transfer between fluids flowing in
microchannels, voids, and other passages in each shim.
[0060] Void: hole or space defined by a plurality of stacked-up
shims that enables fluid flow in to our out of a heat or heat and
mass transfer system component. Generally relates to the space
within or formed by a header. Generally synonymous with stacked-up
void or vapor-liquid space.
[0061] Working fluid: fluid transferred throughout embodiments of
the present system to accomplish heat and/or mass transfer
functions. At various stages in an absorption cycle process or
other similar heat cycle, can be in liquid state, vapor state, or
liquid-vapor mixture. Examples include, but are not limited to,
ammonia-water mixtures and lithium bromide-water mixtures.
Generally comprises multi-component fluids, but also comprises
single-component fluid as needed.
Overview
[0062] For the purpose of promoting an understanding of the
principles of the present disclosure, reference will now be made to
the embodiments illustrated in the drawings and specific language
will be used to describe the same. It will, nevertheless, be
understood that no limitation of the scope of the disclosure is
thereby intended; any alterations and further modifications of the
described or illustrated embodiments, and any further applications
of the principles of the disclosure as illustrated therein are
contemplated as would normally occur to one skilled in the art to
which the disclosure relates. All limitations of scope should be
determined in accordance with and as expressed in the claims.
[0063] Aspects of the present disclosure generally relate to heat
or heat and mass transfer systems or apparatuses. Particularly, one
embodiment of the present apparatus comprises a plurality of shims
assembled or pressed between two outer plates that, when combined,
form discrete but integrated heat and mass transfer system
components that make up a microscale, monolithic absorption cooling
and/or heating system or absorption heat pump, or other heat or
heat and mass transfer system. The shims generally include a
plurality of microchannels, voids, and other heat transfer features
for transferring working fluids and coupling fluids between defined
heat and mass transfer system components throughout the apparatus,
and into and out of the apparatus to and from heating and cooling
sources and sinks as needed. According to one embodiment, two
distinct shim types are used (i.e., shims A and B, described in
greater detail below), and the shims are combined (e.g., bonded
together) as a plurality of shim pairs, wherein the two distinct
shims in each pair comprise slightly different microchannel and
fluid passage arrangements as compared to each other to enable
thermal contact between the fluids flowing within the microchannels
in each shim pair.
[0064] According to one aspect, each shim includes the geometries
of all of the necessary heat and mass transfer system components
that comprise an absorption cooling and/or heating system, namely,
an absorber, recuperative solution heat exchanger, desorber,
rectifier, condenser, recuperative refrigerant heat exchanger, and
an evaporator. As will be appreciated, these heat and mass transfer
components perform their conventional functions as understood by
one of ordinary skill in the art. Thus, in one embodiment, when a
plurality of shim pairs are combined, a microscale absorption
heating and/or cooling system is formed. Further, as pairs of shims
are stacked and combined together, the number of microchannels
(and, hence, the overall heat exchange surface area) of each heat
and mass transfer component increases, thereby increasing the heat
exchange capacity of each component and the overall system. In this
way, embodiments of the present apparatus comprise monolithic,
microscale heat or heat and mass transfer systems that can be
scaled to meet individual application requirements as desired.
[0065] As described in greater detail herein, embodiments of the
present invention(s) yield compact overall geometries for
absorption heat pumps and other heat or heat and mass transfer
apparatuses, with several fold reductions in system volume as
compared to conventional systems for equivalent cooling and/or
heating loads. As described previously, conventional absorption
heat pumps require additional heat and mass transfer components as
compared to vapor-compression systems, leading to larger overall
system sizes. Accordingly, it has previously not been possible to
implement heat-driven absorption heat pumps in small geometries.
Embodiments of the present invention(s), however, exploit the
inherent and novel advantages of fluid flow and heat and mass
transfer phenomena at microscales to enable high cooling and
heating capacity systems in relatively small system packages.
Therefore, embodiments of the present system are able to take
advantage of: a) high heat and mass transfer coefficients in small
hydraulic diameter microscale passages, b) large surface-to-volume
ratios at small hydraulic diameters, c) flexibility of parallel
flows in pluralities of microchannels in multiple parallel shim
assemblies to achieve high heat and/or mass transfer rates with low
pressure drops, and d) the ability to modify microchannel
dimensions, the numbers of microchannels used in each heat and mass
transfer component, the number of shims used in the system, and
overall system envelope width and length to precisely tailor system
size to desired loads. Further, as described in greater detail
below, hydronic coupling and the absence of long interconnecting
lines between heat and mass transfer system components (due to the
relatively small size of system embodiments) minimizes working
fluid inventories, overall system size and mass, fluid pressure
drops, parasitic power requirements, and undesirable heat losses
and gains to and from the ambient.
[0066] Generally, embodiments of the present system utilize thermal
energy as the input energy source, such as waste heat, solar
energy, energy from primary fuel combustion, etc. A wide range of
source energy temperatures are utilized to provide cooling and/or
heating, and a wide range of heating and cooling loads are supplied
using the present system. Accordingly, embodiments of the system
inherently allow for modular design of heating or cooling
capacities ranging from a few Watts to Megawatts. Generally, the
utilization of microscale fluid flow and heat and mass transfer
principles enables the realization of compact system assemblies
that deliver substantially higher cooling and heating capacities in
equivalent system volumes as compared to conventional or prior
systems. Embodiments of the system require relatively minimal use
of electrical energy to pump the working fluids. Preferably,
multi-component fluid mixtures are used as working fluids so that
the system need not use synthetic fluids with ozone-depleting and
global warming potential, and therefore the system has minimal
adverse environmental impact.
[0067] As will be appreciated, embodiments of the present system
are useful for a variety of commercial applications. Generally,
embodiments of the present system can be implemented as
replacements for conventional vapor-compression systems or
absorption heat pumps in most applications, especially when
small-scale applications are needed. However, as will be
understood, embodiments of the present apparatus can be utilized in
a variety of applications, including but not limited to, waste heat
recovery and upgrade applications, heat-driven chillers and heating
and air-conditioning systems, cogeneration systems, heat
transformers, integrated cooling, heating, and power systems,
vehicular, marine, naval, and stationary climate control systems,
processing and refrigerated transport of food, medicines, vaccines,
and other perishable items, harvesting of ambient moisture for
potable water using thermal energy input, micro-reactors and
combustors, and a variety of other applications as will occur to
one of ordinary skill in the art.
[0068] For purposes of example and explanation of the fundamental
functions and components of the disclosed systems and apparatuses,
reference is made to FIG. 1, which illustrates an embodiment of a
monolithic, microscale heat or heat and mass transfer apparatus 10
constructed and operated in accordance with various aspects of the
claimed invention(s). The particular embodiment shown in FIG. 1
(and referenced throughout this disclosure) comprises a monolithic,
microscale absorption cooling and/or heating system (i.e.,
absorption heat pump) including various heat and mass transfer
system components as described herein. As will be understood and
appreciated, however, the exemplary microscale heat or heat and
mass transfer system 10 shown in FIG. 1 represents merely one
approach or embodiment of the present system, and other aspects are
used and contemplated as described herein and as understood by one
of ordinary skill in the art.
[0069] As shown, the heat or heat and mass transfer apparatus 10
includes two cover plates 110, 111, a shim group 108 (generally
comprising a plurality of shims 102, 104, described in greater
detail below) sandwiched between the cover plates, and a plurality
of coupling fluid lines 120 for transferring coupling fluid into
and out of the apparatus 10.
[0070] As shown, the cover plates comprise two cover plate types,
namely, front cover plate 110 and back cover plate 111, that,
depending on the particular embodiment, include various holes 122
for transporting fluid to and from the apparatus 10. As will be
understood, the arrangement of holes 122 and overall structure of
the cover plates 110, 111 may or may not vary between each cover
plate 110, 111 depending on the particular system embodiment.
[0071] As described herein, shim group 108 generally includes a
plurality of shims 102, 104. Referring briefly to FIG. 10A, an
enlarged, perspective view of a portion of a plurality of stacked
shims 102, 104 associated with a shim group 108 within an exemplary
heat and mass transfer system component according to an embodiment
of the present apparatus is shown. The specifics and particulars of
FIG. 10A are discussed in greater detail below; the figure is
discussed here, however, to illustrate the stacked-up arrangement
of shims in a shim group 108 according to one embodiment of the
present apparatus 10. The shims 102, 104 include a plurality of
microchannels, voids, and other heat transfer features (described
in greater detail below) for effectuating fluid transfer between
the shims and between heat and mass transfer components (and,
accordingly, for effectuating heat and mass transfer throughout the
assembly 10).
[0072] According to one embodiment, the shims comprise two shim
types (i.e., shims A 102 and B 104, described in greater detail
below), such that the shims are stacked and aligned in alternating
fashion within the heat transfer apparatus 10 to form a plurality
of shim pairs (each pair including one of each shim type, A and B).
In the embodiment shown in FIG. 10A, the shims are arranged in
alternating fashion of the two, described shim types, 102a, 104a,
102b, 104b, 102c, 104c, . . . 102n, 104n, where "n" represents the
total number of shim pairs in the shim group used to perform the
desired heat and/or mass transfer functionality. As is described in
detail herein, the two disparate shim types include differing
microchannel arrangements to enable alternating fluid flows and
heat and mass transfer functionality throughout the apparatus
10.
[0073] Returning to FIG. 1, cut out area 112 illustrates a section
of the cover plates 110, 111 removed from the apparatus 10 to
display a portion of the heat and mass transfer system components
formed via the shim group 108 (and the shims 102, 104). As shown in
cut out area 112, one of the heat and mass transfer system
components of the exemplary heat pump is shown in its entirety
(specifically, the condenser), as defined by a plurality of
combined shims. The design and aspects of each heat and mass
transfer system component and its operation with respect to the
exemplary, overall absorption cooling and/or heating assembly, is
described in greater detail below.
[0074] According to various embodiments, the shims 102, 104 are
manufactured from steel or other thermally conductive metals,
ceramics, plastics (in low temperature applications), and other
similar materials as will occur to one of ordinary skill in the
art. The cover plates 110, 111 are manufactured from materials
similar or dissimilar to those of the shims, as long as the
resulting cover plates have adequate strength and rigidity
characteristics to hold the assembly 10 together during operation.
The microchannels (discussed below) in the shims 102, 104 are
generally formed via a photochemical etching process or other
etching process, lithography, stamping or machining during shim
manufacturing, or other similar micro-cutting technique. Once
manufactured, the shims 102, 104 and cover plates 110, 111 are
bonded together via diffusion bonding, brazing, or gluing (in low
temperature applications), or combined via a bolted or clamped
assembly, or otherwise assembled via similar bonding or assembly
techniques, to form a monolithic, microscale heat or heat and mass
transfer system 10.
[0075] As shown in FIG. 1, the heat or heat and mass transfer
system 10 (shown in FIG. 1 as an absorption heat pump) receives
input heat from heat source 130 via conventional fluid coupling
through coupling fluid lines 120. The coupling fluid lines are
attached to the apparatus 10 via holes 122 in the cover plates 110,
111 to transport coupling fluid into our out of the heat or heat
and mass transfer apparatus. According to various embodiments,
holes 122 can also be used to transport working fluids from one
internal heat and mass transfer component to another via external
working fluid lines (not shown). As will be understood, however,
working fluids may also be transferred between heat and mass
transfer components within the assembly 10 via connections
incorporated into the cover plates 110, 111 or the shims 102, 104
themselves. As will be understood, external heating and cooling is
not necessarily supplied via hydronic coupling in all embodiments,
and it may be supplied via a hot gas stream, e.g., a flue gas
stream, condensing steam, or other high temperature condensing
fluid, or externally-heated solid conductive heaters, or some other
similar technique depending on the particular embodiment.
Additionally, although the embodiment of the apparatus 10 shown in
FIG. 1 receives heat from a heat source 130 and expunges heating
output 140 and/or cooling output 150, embodiments of the present
system can be designed to perform a variety of heating and/or
cooling functions as will occur to one of ordinary skill in the
art.
[0076] As listed in FIG. 1, examples of heat sources 130 include
fuel combustion, automotive exhaust, engine coolant, marine engine
heat, naval gas turbine heat, diesel engine heat, or heat from
chemical processes, metals processing, food processing, and a
variety of other manufacturing processes. As described previously,
the heat source is derived from thermal energy. Examples of heating
outputs 140 (i.e., applications or uses for heat expelled by the
system) include space heating (e.g., home or office heating), water
heating, and drying. Examples of cooling outputs 150 (i.e.,
applications or uses for cooling expelled by the system) include
building or automotive air-conditioning, dehumidification, chilling
water, refrigeration, electronics cooling, wearable cooling
applications (e.g., cooling systems in firefighter uniforms),
medicine storage, and food preservation. As will be understood and
appreciated, the lists of potential heating sources, and heating
and cooling outputs (applications) are provided for exemplary
purposes only, and are not intended to limit the scope of the
present disclosure or the embodiments described herein.
[0077] FIG. 2 shows an embodiment of the heat or heat and mass
transfer apparatus 10 as described herein with cut out area 202
illustrating a section of the cover plates 110, 111 removed from
the apparatus 10 to display a portion of the heat and mass transfer
system components formed via the shims 102, 104 in shim group 108.
Portions of shim group 108 are also illustrated as removed to
further illustrate the inner workings and geometry of an exemplary
embodiment of the present system. As shown, the embodiment in FIG.
2 does not include the coupling fluid lines 120 to facilitate
easier viewing of the illustrated system embodiment.
[0078] As shown in FIG. 2, the exemplary apparatus 10 generally
comprises a rectangular prism shape, and has dimensions
L.times.H.times.W (i.e., length.times.height.times.width). As will
be understood, however, other system shapes are used according to
other embodiments as needed. As previously described, embodiments
of the present system generally comprise micro scale systems that
are much smaller in size as compared to conventional heat and mass
transfer systems (e.g., conventional absorption heat pumps and
other related systems). However, as will be understood, embodiments
of the present apparatus 10 can be scaled to fit virtually any
application. For example, one specific, exemplary embodiment
(described in greater detail below) includes L.times.H.times.W
dimensions of 200.times.200.times.34 mm.sup.3, respectively.
However, even smaller embodiments (e.g., 120.times.120.times.25
mm.sup.3, and smaller) are used depending on the necessary cooling
and heating loads of the particular application. Additionally,
individual shim thickness (i.e., width) is variable as well, but an
exemplary thickness of 0.5 mm is associated with an exemplary
embodiment as described herein.
[0079] Alternatively, in applications in which size is a relatively
insignificant factor, and greater heating and cooling loads and
capacities are needed, embodiments of the present system can be
scaled to large-scale apparatuses limited only by available storage
space and manufacturing constraints. Further, according to various
embodiments, the individual heat and mass transfer system
components are removed from the overall assembly 10 (i.e., the
shims define a singular heat and mass transfer component instead of
a plurality of components) to enable modularity in overall system
design (described in greater detail below in conjunction with FIG.
17).
[0080] FIG. 3 illustrates an exemplary, fully-assembled embodiment
of the heat or heat and mass transfer apparatus 10 as described
herein. The apparatus shown in FIG. 3 represents a system wherein
all included shims 102, 104 in the shim group 108 and cover plates
110, 111 have been bonded (e.g., via diffusion bonding, brazing,
etc.) or otherwise combined together. As shown, all optional holes
122 for the particular embodiment shown have been removed from the
cover plates 110, 111, such that only coupling fluids transferring
heat and cooling into and out of the apparatus are entering or
exiting the apparatus 10 via the coupling fluid lines 120. The
apparatus 10 shown in FIG. 3 represents an embodiment of the
present system, as described previously, that transfers all working
fluids internally (i.e., via connections or channels in the cover
plates 110, 111 or shims 102, 104 themselves). Accordingly, holes
for connecting external working fluid lines to transfer working
fluids between internal heat and mass transfer system components
are unnecessary in the shown embodiment.
[0081] The coupling fluid lines 120 in FIG. 3 illustrate exemplary
coupling fluid flow into and out of the apparatus 10. The coupling
fluid lines 120 transfer coupling fluid to and from the heat source
130 to supply heat to the apparatus 10, to and from the heat
rejection (output) 140 to expel heat to an external application,
and to and from the cooling output 150 to transfer cooling to a
conditioned space. As described previously, however, in some
embodiments, heat input is provided not via coupling fluid lines
and coupling fluid, but via a hot gas stream, conductive heaters,
or other similar techniques.
[0082] FIGS. 4A-4D show exploded perspective views of the exemplary
microscale, heat or heat and mass transfer apparatus 10 according
to an embodiment of the present system. FIG. 4A shows a perspective
view of an embodiment of the apparatus 10 with a cover plate 110
removed from the remainder of the apparatus (i.e., from the
combined plurality of shims 102, 104 in shim group 108 and the
cover plate 111 on the alternate side of the apparatus). As shown,
a plurality of shim pairs (each shim pair comprising shim A bonded
to shim B, the details of each shim described in greater detail
below) are combined to form a group of shims 108. The number of
shim pairs included within the apparatus varies depending on the
particular application in which the apparatus is used (e.g., based
on heating and cooling loads needed, size and weight constraints,
etc.).
[0083] As will be understood, as more shims (and shim pairs) are
combined in the shim group 108, the corresponding number of
microchannels increases, as does the resulting surface area for
thermal contact associated with the microchannels in each heat and
mass transfer system component within the apparatus 10 (described
in greater detail below). Thus, for applications that require
greater cooling and or heating outputs, greater numbers of (and/or
larger) shim pairs are needed. For example, in its most basic
implementation, a single shim pair comprising one shim A 102 and
one shim B 104 may be adequate to form the shim group 108 to
perform the necessary heat and mass transfer functions of a given
application. In other embodiments, tens, hundreds, or more shim
pairs may be used. As will be understood, the number of shims used
and overall shim and apparatus size depends on the particular use
and application of each particular system embodiment.
[0084] Still referring to FIG. 4A, exemplary shim group 108 defines
the heat and mass transfer system components of an absorption
cooling and/or heating system. As shown, each heat and mass
transfer system component is formed by a plurality of stacked or
combined shim pairs that define the features and geometries of each
component in the shim group 108. The specifics of these heat and
mass transfer components and the fluid transfer within and between
each component are described in greater detail below.
[0085] FIG. 4B shows a perspective exploded view of an embodiment
of the apparatus 10 with cover plates 110, 111 separated from shim
group 108. In the embodiment shown, the arrangement of holes 122 is
different for each of the two cover plates 110, 111. This
difference in hole arrangements is attributed to differences in
attachment points for various coupling fluid lines and working
fluid lines on either side of the apparatus 10. As mentioned
previously, various embodiments of the present apparatus include
varying numbers and locations of holes 122 depending on the manner
in which working fluid is transferred between internal heat and
mass transfer components (e.g., through connections or channels in
the cover plates or via external working fluid lines, etc.), and
also depending on how and whether coupling is used to provide and
receive heating and cooling to and from the apparatus, etc.
[0086] FIG. 4C shows a perspective exploded view of an embodiment
of the apparatus 10 with cover plates 110, 111 separated from shim
group 108', and with a single shim A 102 separated from the shim
group 108'. Shim group 108' is similar to shim group 108 shown
previously in FIGS. 4A and 4B, except that one of the plurality of
shim A's has been separated from the shim group. FIG. 4D shows a
perspective exploded view of an embodiment of the apparatus 10 with
cover plates 110, 111 separated from shim group 108'', and with a
single shim A 102 and a single shim B 104 separated from the shim
group 108''. Shim group 108'' is similar to shim group 108' shown
previously in FIG. 4C, except that one of the plurality of shim B's
has been separated from the shim group. As described previously,
shims A and B together form a shim pair. Thus, shim group 108''
comprises a plurality of shim pairs, but with one less shim pair as
compared to shim group 108 (shown in FIGS. 4A and 4B). As also
described previously, when the apparatus 10 is fully assembled, the
shims 102, 104 and cover plates 110, 111 are bonded or otherwise
combined together to define the necessary heat and mass transfer
components of an absorption cooling and/or heating system, or some
other similar heat and/or mass transfer device.
[0087] FIG. 5 illustrates a schematic functional representation 500
of the internal heat and mass transfer system components and the
fluid flows between the components according to one embodiment of
the present heat or heat and mass transfer apparatus 10. The
fundamental functions and processes of the heat and mass transfer
components in the exemplary apparatus 10 are shown and described in
relation to FIG. 5, whereas an exemplary architecture and geometry
of these components as defined by the shims 102, 104 is shown and
described in greater detail in relation to subsequent figures
below. In the exemplary embodiment shown, the system is arranged
for operation as a single-effect, ammonia-water (i.e., working
fluid) absorption heat pump in cooling mode. As will be
appreciated, however, other arrangements are used according to
various embodiments, such as double-effect, triple-effect, and
other multi-effect systems utilizing various types of working
fluids and multi-component fluids (e.g., lithium bromide-water), as
described in greater detail below. Additionally, minor
modifications to the system shown in FIG. 5 enable heating mode
operation (also described in greater detail below).
[0088] With reference to the schematic representation 500 shown in
FIG. 5, fluid coupling is used to connect the heat source 130,
ambient for heat rejection 140, and the conditioned space 150 to
the internal heat and mass transfer components within the apparatus
10 carrying the working fluid pair (e.g., ammonia-water). As shown,
concentrated ammonia-water solution (i.e., working fluid) exiting
the solution pump 502 at the system high-side pressure is carried
by fluid line 504 to the recuperative solution heat exchanger 800.
Upon recuperative heating in the recuperative solution heat
exchanger 800, the ammonia-water solution further proceeds via
fluid line 506 to the desorber component 1100, where an
ammonia-water vapor mixture is desorbed from the ammonia-water
solution. The ammonia-water solution (i.e., dilute solution) exits
the desorber by fluid line 508, and flows to the previously
mentioned recuperative solution heat exchanger 800. The dilute
solution is cooled in the recuperative solution heat exchanger 800,
and subsequently exits through fluid line 510, which carries it to
the solution expansion valve 512.
[0089] Upon expansion in the expansion valve 512 to the low-side
pressure of the system, the dilute solution exiting through line
514 enters the absorber component 1500, where it absorbs
refrigerant (i.e., ammonia) vapor arriving from the recuperative
refrigerant heat exchanger 1300 through line 516 (described in
greater detail below). As shown, dashed lines (e.g., line 516)
represent a vapor phase of the working fluid, whereas solid lines
(e.g., line 510) represent a liquid phase. As referred to herein
and as understood in the art, when describing ammonia-water working
fluid, "ammonia" is generally synonymous with "refrigerant", and
"water" is generally synonymous with "absorbent" (although, as is
understood, refrigerant may not comprise pure ammonia, as some
relatively minimal or trace amounts of water may be present, and
vice versa). Alternatively, when describing lithium bromide-water
working fluid, "lithium bromide" is generally synonymous with
"absorbent", and "water" is again generally synonymous with
"refrigerant". These terms are understood in the art as applicable
to any refrigerant-absorbent working fluid pair.
[0090] Still referring to FIG. 5, heat of absorption rejected by
the dilute solution in the absorber 1500 is removed by a medium
temperature coupling fluid line 518 that eventually rejects heat to
the ambient (e.g., heating output 140). Upon absorption of
refrigerant vapor into the dilute solution in the absorber 1500,
the resulting concentrated ammonia-water solution leaves the
absorber through fluid line 520 to the previously described
solution pump 502, where it is again pumped to the recuperative
solution heat exchanger 800 (described previously).
[0091] Returning to discussion of the desorber 1100, heat of
desorption is conveyed to the desorber by a high-temperature heat
transfer fluid line 522, which is in turn connected to the heat
source 130 that drives the system (i.e., fluid coupling with heat
source). Ammonia-water vapor leaving the desorber component 1100
(described previously) enters the rectifier component 1150, wherein
a cooling fluid line 524 is employed to rectify the ammonia-water
vapor to a higher concentration of ammonia. As shown, the rectifier
1150 and desorber 1100 are combined in a single component; however,
as will be understood, these components may be separated according
to various embodiments as desired. Depending on the particular
embodiment, the cooling fluid employed in cooling fluid line 524 is
a medium temperature hydronic fluid, or the concentrated solution
exiting the solution pump 502, or some other fluid depending on the
particular system design and operating conditions.
[0092] Reflux ammonia-water solution from the rectifier 1150
returns to the desorber 1100, where it is expunged through fluid
line 508 (described previously). High concentration ammonia (i.e.,
refrigerant) vapor exiting the rectifier 1150 is conveyed to the
condenser component 1200 via fluid line 526. In the condenser 1200,
the concentrated ammonia vapor is condensed and subcooled to liquid
refrigerant (i.e., ammonia) by medium temperature hydronic fluid
line 528 that eventually rejects heat of condensation to the
ambient (e.g., heat rejection 140). Liquid refrigerant leaving the
condenser 1200 through fluid line 530 enters the
previously-mentioned recuperative refrigerant heat exchanger 1300,
where it is further cooled by vapor-phase refrigerant exiting the
evaporator component 1400 (described below). The cooled liquid
refrigerant exits the recuperative refrigerant heat exchanger 1300
through fluid line 532, which carries it to the refrigerant
expansion valve 534. Upon expansion to the system low-side
pressure, the resulting two-phase refrigerant mixture is conveyed
to the evaporator component 1400 by fluid line 536.
[0093] In the evaporator component 1400, vaporization of the
two-phase refrigerant mixture effects cooling of the
low-temperature coupling fluid entering through line 538. Fluid
line 538 is eventually connected (via hydronic coupling) to the
conditioned space where the desired cooling (e.g.,
space-conditioning 150) is achieved. Vaporized refrigerant exits
the evaporator 1400 through line 540 and flows to the
previously-discussed recuperative refrigerant heat exchanger 1300,
where it serves as coolant for the liquid (high pressure)
refrigerant exiting the condenser 1200 and entering the
recuperative refrigerant heat exchanger 1300 through line 530. The
heated refrigerant vapor exits the recuperative refrigerant heat
exchanger 1300 through line 516 and flows to the absorber component
1500 (as described previously) to complete the cycle.
[0094] As described previously, minor modifications to the system
shown in FIG. 5 enable heating mode operation (as opposed to
cooling mode, as shown). For example, coupling the low temperature
fluid line 538 of the evaporator 1400 to an outdoor ambient as
opposed to a conditioned space, and coupling the medium temperature
fluid lines 528, 518 of the condenser 1200 and absorber 1500 to a
conditioned space as opposed to outdoor ambient for heat rejection,
would enable heating mode operation without changing the assembly
or components of the apparatus 10. As will be understood and
appreciated, various arrangements of connections between heat and
mass transfer system components and external heating and cooling
sources enable various modes of operation of embodiments of the
present system.
[0095] As also described previously, FIG. 5 illustrates a
single-effect system according to one embodiment of the present
invention(s). However, other system arrangements (as opposed to the
single-effect arrangement) are used according to various other
embodiments, such as double-effect, triple-effect, and other
multi-effect systems utilizing ammonia-water and other various
types of working fluids and multi-component fluids (e.g., lithium
bromide-water). Additional recuperative components configured in a
similar manner to those shown in FIG. 5 would achieve multi-effect
and other advanced heat pump thermodynamic cycle operation. Thus,
for example, double-effect operation is achieved for applications
with high temperature heat sources by including a second-effect
desorber that generates additional refrigerant by recuperatively
recovering heat from the vapor exiting desorber 1100 shown in the
present embodiment before it flows through the rectifier 1150 and
condenser 1200. Additional examples include a combination of
solution-cooled and hydronically-cooled absorbers instead of the
solely hydronically-cooled absorber shown in the single-effect
embodiment in FIG. 5. Further embodiments comprising other, similar
recuperative heat exchange components would yield Generator
Absorber Heat Exchange (GAX) heat pump configurations. As will be
understood, in embodiments in which relatively high heat source
input temperatures are used, greater heating or cooling effect is
achieved (as compared to single-effect systems using the same input
temperature) through the inclusion of additional recuperative heat
exchange components or heat and mass transfer components.
[0096] FIGS. 6A and 6B are perspective views illustrating exemplary
representations of shim A 102 and shim B 104, respectively,
according to one embodiment of the present system. The shims 102,
104 illustrate the arrangement of heat and mass transfer system
components to achieve the specific heat and mass transfer functions
for an exemplary absorption heat pump as described herein. As
described previously, according to one embodiment, shims A and B
are combined to form a shim pair, wherein a plurality of shim pairs
are further combined to form the shim group 108. The number of shim
pairs used to comprise shim group 108 is generally dependent upon
the desired cooling or heating loads of each particular
application. Further, as described in greater detail below, certain
features (e.g., number and arrangement of microchannels, microscale
passages, and other fluid connecting lines) of shims A 102 and B
104 are similar or identical, whereas others are different. This
difference generally corresponds to the notion that one type of
shims (e.g., shim A) convey working fluid throughout an embodiment
of the apparatus 10, whereas the other type of shims (e.g., shim B)
convey coupling fluid throughout the apparatus (although this is
not necessarily the case for each embodiment of the present system
or each heat and mass transfer component within a particular
embodiment). The specific fluid flows through the exemplary shims A
and B are described in greater detail below.
[0097] Still referring to FIGS. 6A and 6B, the exemplary heat and
mass transfer system components shown and discussed previously in
conjunction with FIG. 5 are shown (or specifically, individual
layers of the heat exchange components defined by shims A and B are
shown) as they are arranged in exemplary shims 102, 104. As shown,
each discrete heat and mass transfer system component that makes up
an exemplary absorption cooling and/or heating system is formed by
and is a part of each shim 102, 104. Specifically, individual
layers of the recuperative solution heat exchanger 800, desorber
1100, rectifier 1150, condenser 1200, recuperative refrigerant heat
exchanger 1300, evaporator 1400, and absorber 1500 for performing
their individual functions described previously in conjunction with
FIG. 5 (and elsewhere herein) are represented in each of shims A
102 and B 104, respectively, in FIGS. 6A and 6B.
[0098] As described previously, for some heat and mass transfer
components, the features (e.g., microchannel arrangement, etc.) of
shim A 102 as compared to shim B 104 vary within each individual
heat and mass transfer component. According to one embodiment,
these differences enable the desired fluid flows and heat transfer
functions between the working fluid and coupling fluids exchanging
heat therein (e.g., one shim type carries working fluids, whereas
the other shim type carries coupling fluids). These differences are
shown and described in greater detail below and in subsequent
figures. Specifically, the heat and mass transfer components that
include internal shim differences to achieve necessary heat
transfer functions are the recuperative solution heat exchanger
800a, 800b, the condenser 1200a, 1200b, the recuperative
refrigerant heat exchanger 1300a, 1300b, the evaporator 1400a,
1400b, and the absorber 1500a, 1500b.
[0099] Alternatively, the features within each of shims A and B for
the desorber 1100 and rectifier 1150 are the same as compared to
each other (e.g., the arrangement of microchannels and other
microscale passages are similar). Based on the functions of these
heat exchange components, arrangement of internal shim features,
and the fluid flows within the shims, disparate arrangements of
shim features are not necessary (in one embodiment) for these shim
types. Accordingly, shims A 102 and B 104 are identical for the
exemplary embodiment shown for the desorber 1100a, 1100b, and
rectifier 1150a, 1150b portions of the shims.
[0100] Additionally, alignment notches 602 and 604 in each shim A
102 and B 104 provide holes in the shims to facilitate precise
alignment, assembly, and joining of the plurality of shim pairs and
cover plates 110, 111 as desired within each heat transfer
apparatus. As shown, exemplary notches 602 and 604 have varying
cross sections as compared to each other (i.e., notch 602 is
circular-shaped, whereas notch 604 is square-shaped) to enable easy
joining and alignment of the shims within the overall assembly
(e.g., such that shims are not accidentally reversed during system
assembly). As will be understood, depending on the particular
embodiment, notches 602, 604 define virtually any cross-sectional
shape, or, in some embodiments, are entirely unnecessary and thus
not included.
[0101] FIGS. 7A and 7B are front plan views illustrating exemplary
representations of shim A 102 and shim B 104, respectively,
according to one embodiment of the present system. FIGS. 7A and 7B
essentially illustrate front plan views of the layers of the heat
and mass transfer system components defined by pluralities of shims
A and B as shown and described previously in conjunction with FIGS.
6A and 6B. Accordingly, each of the heat and mass transfer system
components in an exemplary microscale, absorption heat pump is
shown; specifically, the recuperative solution heat exchanger 800a,
800b, the desorber 1100a, 1100b, the rectifier 1150a, 1150b, the
condenser 1200a, 1200b, the recuperative refrigerant heat exchanger
1300a, 1300b, the evaporator 1400a, 1400b, and the absorber 1500a,
1500b.
[0102] Also shown in FIGS. 7A and 7B are microchannels 702 that
enable fluid flow and resulting heat transfer within individual
heat and mass transfer components within the system. As will be
understood and appreciated, these microchannels 702 comprise
varying dimensions and are included in varying numbers according to
various embodiments of the present apparatus. According to one
exemplary embodiment described herein, these microchannels have
dimensions comprising a channel etch depth of approximately half
the shim thickness (e.g., 0.25 mm), a channel width of
approximately 0.5 mm, and a nominal channel hydraulic diameter of
approximately 306 .mu.m. Again, however, these microchannel
dimensions are provided for illustrative purposes only, and are not
intended to limit the scope of the present invention(s) in any way.
Representative dimensions and microchannel cross-sections are shown
and described in greater detail below in conjunction with FIGS. 20
and 21 associated with an exemplary system embodiment.
[0103] As noted in the glossary, for example, even though an
exemplary embodiment utilizes microchannels comprising hydraulic
diameters of 306 .mu.m, microchannel fluid flow and heat and mass
transfer phenomena may be exploited in channels with hydraulic
diameters ranging from 1 .mu.m to about 1 mm (and greater). In
fact, channels may exhibit fluid flow and heat transfer phenomena
specific to microchannels at somewhat larger hydraulic diameters,
even up to about 3 mm, depending upon the fluid properties and
operating conditions, the corresponding vapor bubble formation
phenomena and critical bubble diameters, and varying effects of
surface tension, gravity, and inertial forces in these channels at
different pressures and temperatures for different fluids and fluid
mixtures.
[0104] Further, according to one embodiment, the microchannel sizes
are the same (e.g., hydraulic diameter of 306 .mu.m) throughout
each heat and mass transfer system component in the system. In
other embodiments, the microchannel dimensions vary on a
per-component basis (e.g., microchannels in the absorber 1500 may
comprise different dimensions than those in the condenser 1200).
Additionally, in still other embodiments, microchannel dimensions
may vary for shim A 102 as compared to shim B 104, even within the
same heat and mass transfer component. As will be understood and
appreciated, various microchannel dimensions are used according to
various system embodiments as needed.
[0105] Additionally, according to various embodiments, the
microchannels are formed via photochemical etching, stamping,
cutting, or other machining techniques. Further, the
cross-sectional shapes of the microchannels in the shims comprise,
depending on the embodiment, square, rectangular, semi-circular,
semi-elliptical, triangular, or other singly-connected
cross-sections to enable fluid flow in single-phase or two-phase
state, as necessary, wherein the microchannel cross-section shape
and dimensions are determined based on heat and mass transfer
requirements, operating pressures, structural strength of the
assembled apparatus, manufacturing constraints for dimensional
tolerances and bonding of the shims and cover plates, and other
similar application-specific factors.
Discussion of Discrete, Exemplary Heat and Mass Transfer System
Components
[0106] As described, embodiments of the present system generally
comprise microscale heat or heat and mass transfer systems or
heat-driven cycle apparatuses. More particularly, exemplary
embodiments comprise monolithic, microscale absorption heating
and/or cooling apparatuses including discrete but integrated heat
and mass transfer system components, such as recuperative solution
heat exchangers, desorbers, rectifiers, condensers, recuperative
refrigerant heat exchangers, evaporators, absorbers, and other
similar components. The particular architectures and functions of
these discrete components and the operative connections between the
components as represented by an exemplary embodiment (e.g.,
absorption heat pump) of the present system are described in
greater detail below.
[0107] Recuperative Solution Heat Exchanger
[0108] FIGS. 8A and 8B show perspective views of portions of shims
A 102 and B 104, respectively, associated with a recuperative
solution heat exchanger 800 according to an embodiment of the
present apparatus 10. As shown, dilute ammonia-water solution
enters the apparatus (and, specifically, the recuperative solution
heat exchanger 800) at an inlet header through void 802 (also
referred to herein as a "stacked-up void") formed by a plurality of
shim pairs combined together (shown and described in more detail in
conjunction with FIGS. 10A and 10B). As described below, the void
802 (and other system voids) enables fluid flow in to or out of
individual heat and mass transfer components or microchannels
within the system, and also allows or restricts flow in to or out
of particular shims.
[0109] The dilute ammonia-water solution enters the recuperative
solution heat exchanger 800 via external tubing (not shown) from
solution pump 502 (generally initiated from absorber 1500). In the
exemplary embodiment shown in FIG. 8A, in the plane of shim A 102,
the void 802a comprises a blind hole that does not allow fluid flow
across the shim. In the plane of shim B 104 shown in FIG. 8B,
however, the void 802b includes an entrance to fluid distribution
passage 804, which allows the dilute ammonia-water solution to be
distributed into the plurality of microchannels 702, which are in
thermal contact with similar microchannels in shim A 102 (which
are, in turn, carrying concentrated ammonia-water solution received
from the desorber 1100 in an orientation counterflow to the dilute
ammonia-water solution). Upon flowing through the plurality of
microscale channels 702 in shim B, dilute solution exits through an
exit passage 806, similar in construction to distribution passage
804 at the inlet. Passage 806 conveys the dilute solution to the
voids 808a, 808b formed by the assembly of stacked shims A 102 and
B 104, wherein this void serves as the exit header for the dilute
solution (wherein the dilute solution is subsequently conveyed to
the solution expansion valve 512.
[0110] Still referring to FIGS. 8A and 8B, concentrated
ammonia-water solution enters the recuperative solution heat
exchanger 800 through the stacked assembly of alternating voids
810a and 810b in shims A 102 and B 104, respectively. According to
the embodiment shown, and in an arrangement complementary to the
voids 802a, 802b receiving dilute solution, void 810b on shim B
comprises a blind hole that does not allow fluid flow across the
shim. The corresponding void 810a on shim A, however, allows
distributed concentrated solution flow from void 810a into
microscale passages 702. Upon exiting the microscale passages 702,
concentrated solution enters void 812a, and exits the solution heat
exchanger through an exit header formed by alternating stacked
voids 812a, 812b, where it is subsequently conveyed to the desorber
1100.
[0111] FIGS. 9A and 9B are enlarged perspective views of portions
of shims A 102 and B 104, respectively, associated with a
recuperative solution heat exchanger 800 according to an embodiment
of the present apparatus 10 (i.e., these figures are enlarged views
of FIGS. 8A and 8B). FIGS. 9A and 9B illustrate in more detail the
arrangement of inlet voids 802a and 802b on shims A and B,
respectively, for the dilute solution, as well as fluid passage 804
for carrying dilute solution from the void 802b to the plurality of
microscale channels 702 in shim B. Also shown are the corresponding
plurality of microscale channels 702 in shim A for carrying
concentrated (ammonia-water) solution, and exit voids 812a and 812b
for transferring concentrated solution out of the recuperative
solution heat exchanger 800.
[0112] As shown in FIG. 9B, distribution passage 804 includes a
rectangular, uniform cross-section. In other embodiments, however,
if necessary to ensure uniform flow distribution through the
microchannels 702 in shim B 104, this cross-section is tapered in
the direction of fluid flow to better manage the fluid pressure
drops in distribution passage 804, as well as in the microchannels
702, which leads to improved flow distribution. According to
various embodiments, the cross-sections of the microchannels 702 in
shims A 102 and B 104, respectively, are square, rectangular,
semi-circular, semi-elliptical, triangular, or comprise other
similar singly-connected shapes based on the desired flow rates and
heat transfer rates for each specific application. Further, the
cross-sections of the microchannels 702 on shims A and B are not
necessarily the same; different microscale passage geometries can
be adopted for the two sets of passages (on shims A and B,
respectively) to accommodate different flow rates and thermal
capacities of the dilute and concentrated solution streams flowing
therein, resulting in better matching of thermal resistances.
[0113] According to various embodiments of the present system,
voids 802a, 802b, 812a, 812b, and other voids associated with the
recuperative solution heat exchanger 800, as well as other heat and
mass transfer system components of the apparatus described herein,
comprise varying cross-sections as desired or necessitated by the
particular embodiment. For example, voids 812 comprise a square
cross-section, whereas voids 802 comprise a circular cross-section
for the embodiment shown in FIGS. 9A and 9B. Other shapes are
utilized according to other embodiments, however, such as
rectangular shapes, and other similar cross-sections. In one
embodiment, D-shaped voids are used, such that the straight line
portion of the "D" is aligned along the entrance to the
microchannels to reduce pressure resistance (but simultaneously
ensure that the microchannels have identical flow lengths).
[0114] As briefly discussed previously, FIGS. 10A and 10B
illustrate enlarged, perspective views of portions of a plurality
of stacked shims A 102 and B 104 associated with a recuperative
solution heat exchanger 800 according to an embodiment of the
present apparatus 10. As shown, the top shim in FIG. 10A is a
representative shim A 102, whereas the top shim in FIG. 10B is a
representative shim B 104. The plurality of stacked shims shown in
FIGS. 10A and 10B illustrate in more detail the operative
connections between voids 802 and distribution passages 804, as
well as voids 812 and microchannels 702. As described previously,
the geometries of passages 804 on shim B enable solution to pass
into shim B from void 802. Additionally, microchannels 702 on shim
A enable solution to pass from the microchannels to void 812. As
also shown, because shims A do not include distribution passages
804, solution is restricted from flowing into shims A from void
802. Further, because shims B do not include microchannel
connections to void 812, solution is restricted from passing in to
or out of this void 812 from shim B. As will be understood and
appreciated, other similar passages, voids, and microchannel
arrangements are utilized in other heat and mass transfer
components within embodiments of the present system, as described
in greater detail below.
[0115] Desorber/Rectifier
[0116] FIGS. 11A and 11B illustrate perspective views of portions
of shims A 102 and B 104, respectively, associated with a desorber
1100 and rectifier 1150, according to an embodiment of the present
apparatus 10. As described previously, the features, arrangement of
passages, etc., for the desorber 1100 are the same for shim A as
compared to shim B. Similarly, the features, arrangement of
passages, etc., for the rectifier 1150 are the same for shim A as
compared to shim B. Thus, the representations of the embodiments
shown in FIGS. 11A and 11B are identical. As will be understood and
appreciated, however, alternate embodiments of the present system
utilize alternating or counterflow microscale passages (similarly
to other heat and mass transfer components herein described), such
that the arrangement of microscale features in shims A and B need
not be the same.
[0117] Referring to the embodiment of the desorber 1100 shown in
FIGS. 11A and 11B, concentrated ammonia-water solution enters the
desorber from the recuperative solution heat exchanger 800 via
inlet headers 1102 formed by the stacked-up voids defined by the
plurality of shim pairs A and B. The concentrated solution then
enters a plurality of passages 1104 on shims A and B, and as the
solution flows through these passages, is heated by an external
heat source (via voids 1106), therefore producing ammonia-water
refrigerant vapor and dilute ammonia-water solution. As shown, the
external heat source is provided to the concentrated solution
through a plurality of voids 1106 in shims A and B, respectively.
According to various embodiments, heat from the heat source is
provided through voids 1106 by a hot gas stream, e.g., a flue gas
stream, condensing steam, or other high pressure condensing fluid,
or externally-heated solid conductive heaters, or a heat transfer
coupling fluid coupled to an external heat source, or by other
similar techniques. The crossflow orientation between the
concentrated ammonia-water solution in passages 1104 and the
external heat source in voids 1106 shown in the embodiment in FIGS.
11A and 11B is but one possible configuration for this flow. For
example, in alternate embodiments, counterflow orientation between
the ammonia-water solution and the external heat source is provided
by orienting the voids 1106 in shims A and B in parallel with the
corresponding solution passages 1104, as opposed to the
perpendicular orientation to the shims, as shown in FIGS. 11A and
11B.
[0118] Slot voids 1110 in shims A and B near the inlet headers 1102
provide thermal isolation between the recuperative solution heat
exchanger component 800 and the desorber heat source voids 1106, so
that the external heat is maximally applied to the concentrated
solution. According to other embodiments and aspects, similar voids
are used in various locations throughout the present system to
effect thermal separation between heat exchange components that
should be maintained at hot and cold temperatures. The dilute
ammonia-water solution and ammonia-water vapor mixture exiting the
desorber passages 1104 collect in the desorber outlet headers 1108
formed by the stacked-up voids defined by the plurality of shim
pairs A and B, and subsequently flow into the rectifier 1150.
[0119] Generally, the ammonia-water vapor from the desorber outlet
headers 1108 flows into the rectifier vapor space 1122 formed by
rectifier trays 1112 on shims A and B. As the vapor proceeds along
the rectifier 1150, cooling by a coupling fluid flowing in
counterflow orientation to the ammonia-water vapor through passages
1116 along the side walls of the vapor space chamber 1122 effects
rectification of the vapor. Depending on the particular embodiment,
this coupling fluid comprises medium temperature coupling fluid or
concentrated ammonia-water solution exiting the solution pump 502
(described previously). The coupling fluid enters the assembly 10
at inlet headers formed by stacked-up voids 1118 in shims A and B,
and exits from outlet headers formed by stacked-up voids 1120 in
shims A and B. During the rectification process, reflux liquid
(i.e., dilute ammonia-water solution) collects in trays 1112 and
flows back into the desorber exit headers 1108 where it mixes with
the dilute ammonia-water solution therein before exiting the
desorber. According to one embodiment, the dilute ammonia-water
solution exits the desorber exit headers 1108 via a hole in a cover
plate (not shown). Rectified, high concentration ammonia-water
vapor exits the rectifier vapor space 1122 through vapor outlet
headers formed by stacked-up voids 1114 in shims A and B, and is
subsequently transferred to the condenser 1200.
[0120] According to one embodiment, coupling fluid flowing between
stacked-up voids 1118 and 1120 via passage 1116 in shims A and B is
in forced-convective flow. On the other hand, as the ammonia-water
vapor passes through the rectifier 1150 and is rectified, reflux
liquid flows back down the rectifier and collects at exit header
1108. This counterflow of vapor and reflux liquid within the
rectifier 1150 comprises a gravity/buoyancy-driven flow (unlike the
forced-convective flow on the coupling fluid side) that further
enhances the rectification of the vapor from the dilute
ammonia-water solution. The varying geometries possible due to the
shim, passage, and microchannel geometries incorporated into
various embodiments of the present system enable the combination of
co- and counterflow forced-convective and gravity/buoyancy-driven
flows for different fluid streams, as desired, in the various heat
and mass transfer system components, such as the rectifier 1150 and
desorber 1100, in embodiments of the heat or heat and mass transfer
system. As will be understood and appreciated, for this flow to
occur, the overall system 10 should be oriented such that the
rectifier 1150 is aligned vertically above the desorber 1100. Thus,
for example, when in use, the embodiment of the system herein
described should be oriented similarly to that shown in FIGS. 1, 2,
etc., and not in a relatively flat arrangement (as shown in FIGS.
4A-4D, etc.).
[0121] Condenser
[0122] FIGS. 12A and 12B illustrate perspective views of portions
of shims A 102 and B 104, respectively, associated with a condenser
1200 according to an embodiment of the present apparatus 10. The
architecture and geometry of the condenser is relatively similar to
that of the recuperative solution heat exchanger 800 discussed
previously in conjunction with FIGS. 8A and 8B. In the embodiment
shown, medium-temperature coupling fluid enters the condenser 1200
through inlet headers formed by stacked-up voids 1202a, 1202b in
shims A and B, respectively. Void 1202b in shim B leads to passage
1204 that enables distributed flow of coupling fluid into the
plurality of microchannels 702 on shim B. As the coupling fluid
passes through these microchannels 702, it is heated by the working
fluid passing through microchannels in shim A. The heated coupling
fluid then flows to exit passage 1206 on shim B, which in turn
leads to exit headers formed by stacked-up voids 1208a, 1208b on
shims A and B, respectively, and is returned to the medium
temperature hydronic fluid line (e.g., coupled to the ambient).
[0123] As shown, ammonia-water vapor from the rectifier 1150 enters
the condenser component 1200 through inlet headers formed by the
stacked-up voids 1210a, 1210b in shims A 102 and B 104,
respectively. Void 1210a in shim A leads to a plurality of
microchannels 702, which enable flow of condensing vapor in
counterflow orientation to, and in thermal contact with, the
coupling fluid flowing through similar microchannels 702 on shim B.
The condensed and subcooled refrigerant liquid exits microscale
channels 702 in shim A and flows into outlet headers formed by the
stacked-up voids 1212a, 1212b in shims A and B, respectively.
Variations, options, and other details associated with microchannel
geometries, coupling fluid inlet and outlet passages 1204, 1206,
and voids for the condenser 1200, including shapes, cross-sections,
and dimensions, apply equally and are similar to those described
previously in conjunction with the recuperative solution heat
exchanger 800.
[0124] Recuperative Refrigerant Heat Exchanger
[0125] FIGS. 13A and 13B illustrate perspective views of portions
of shims A 102 and B 104, respectively, associated with a
recuperative refrigerant heat exchanger 1300 according to an
embodiment of the present apparatus 10. The architecture and
geometry of the recuperative refrigerant heat exchanger is
relatively similar to that of the recuperative solution heat
exchanger 800 discussed previously in conjunction with FIGS. 8A and
8B. In the embodiment shown, high-pressure liquid refrigerant
(i.e., ammonia) from the condenser 1200 enters the recuperative
refrigerant heat exchanger through inlet headers formed by the
stacked-up voids 1302a, 1302b in shims A and B, respectively. As
shown, void 1302b in shim B leads to passage 1304 that enables
distributed flow of liquid refrigerant into the plurality of
microchannels 702 on shim B. As the liquid refrigerant flows
through the microchannels on shim B, the liquid refrigerant is
cooled by low-pressure refrigerant vapor simultaneously flowing
through microchannels 702 in shim A. Subsequently, the cooled
refrigerant fluid flows to exit passage 1306 on shim B, which in
turn leads to exit headers formed by stacked-up voids 1308a, 1308b
on shims A and B, respectively.
[0126] Low-pressure vapor from the evaporator 1400 enters the
recuperative refrigerant heat exchanger 1300 through inlet headers
formed by the stacked-up voids 1310a, 1310b in shims A 102 and B
104, respectively. Void 1310a in shim A leads to a plurality of
microscale passages 702, which enable flow of low-pressure
refrigerant vapor as coolant for, in counterflow orientation to,
and in thermal contact with, high-pressure refrigerant liquid
flowing through similar microscale passages 702 on shim B. The
refrigerant vapor exits microscale passages 702 and flows into
outlet headers formed by the stacked-up voids 1312a, 1312b in shims
A and B, respectively. Variations, options, and other details
associated with microchannel geometries, high-pressure refrigerant
liquid inlet and outlet passages 1304, 1306, and voids for the
recuperative refrigerant heat exchanger 1300, including shapes,
cross-sections, and dimensions, apply equally and are similar to
those described previously in conjunction with the recuperative
solution heat exchanger 800.
[0127] Evaporator
[0128] FIGS. 14A and 14B illustrate perspective views of portions
of shims A 102 and B 104, respectively, associated with an
evaporator 1400 according to an embodiment of the present apparatus
10. The architecture and geometry of the evaporator is relatively
similar to that of the condenser 1200 discussed previously in
conjunction with FIGS. 12A and 12B. In the embodiment shown,
low-temperature coupling fluid enters the evaporator through inlet
headers formed by voids 1402a, 1402b in shims A and B,
respectively. Void 1402b in shim B leads to passage 1404 that
enables distributed flow of coupling fluid into the plurality of
microchannels 702 on shim B. As the coupling fluid flows through
the microchannels on shim B, it is cooled by the ammonia-water
two-phase mixture (from the recuperative refrigerant heat exchanger
1300 via the expansion valve 534) flowing through microchannels 702
in shim A. The cooled coupling fluid then flows to the exit passage
1406 on shim B, which in turn leads to exit headers formed by voids
1408a, 108b on shims A and B, respectively, and is subsequently
used for cooling a conditioned space, or other similar
application.
[0129] As shown, ammonia-water two-phase mixture from fluid line
536 (see FIG. 5 and associated discussion) leaving the expansion
valve 534 enters the evaporator component 1400 through inlet
headers formed by voids 1410a, 1410b in shims A and B,
respectively. Void 1410a in shim A leads to a plurality of
microchannels 702, which enable flow of evaporating vapor in
counterflow orientation to, and in thermal contact with, the
coupling fluid flowing through similar microchannels 702 on shim B.
The evaporated refrigerant vapor exits the microchannels in shim A
and flows into outlet headers formed by voids 1412a, 1412b in shims
A and B, respectively. Variations, options, and other details
associated with microchannel geometries, coupling fluid inlet and
outlet passages 1404, 1406, and voids for the evaporator 1400,
including shapes, cross-sections, and dimensions, apply equally and
are similar to those described previously in conjunction with the
recuperative solution heat exchanger 800.
[0130] Absorber FIGS. 15A and 15B illustrate perspective views of
portions of shims A 102 and B 104, respectively, associated with an
absorber 1500 according to an embodiment of the present apparatus
10. In the embodiment shown, medium-temperature coupling fluid
enters the absorber 1500 through inlet headers formed by voids
1502a, 1502b in shims A and B, respectively. As shown, void 1502b
in shim B leads to passage 1504 that enables distributed flow of
coupling fluid into the plurality of microchannels 702 on shim B.
The coupling fluid is heated via thermal contact with dilute
ammonia-water solution and refrigerant vapor flowing through
microchannels 702 on shim A. The heated coupling fluid then flows
to the exit passage 1506 on shim B, which in turn leads to exit
headers formed by voids 1508a, 1508b on shims A and B,
respectively.
[0131] In the embodiment shown, dilute ammonia-water solution from
fluid line 514 (see FIG. 5 and associated discussion) leaving the
solution expansion valve 512 enters the absorber component 1500
through inlet headers formed by voids 1510a, 1510b in shims A and
B, respectively. Void 1510a in shim A leads to a plurality of
microchannels 702, which enable flow of dilute solution and
refrigerant vapor (the mixture of which is described below) in
counterflow orientation to, and in thermal contact with, the
coupling fluid flowing through similar microchannels 702 on shim B.
The medium temperature coupling fluid removes heat of absorption
from the dilute solution and refrigerant vapor mixture, thereby
forming concentrated ammonia-water solution in the microchannels in
shim A. The concentrated ammonia-water solution exits microchannels
702 and flows into outlet headers formed by voids 1512a, 1512b in
shims A and B, respectively.
[0132] According to one embodiment, ammonia-water vapor from fluid
line 516 (see FIG. 5 and associated discussion) leaving the
recuperative refrigerant heat exchanger 1300 enters the absorber
1500 through inlet headers formed by voids 1514a, 1514b in shims A
and B, respectively. Void 1514b in shim B leads to passage 1516
that supplies the ammonia-water vapor stream to microchannels 702
in shim A through vapor inlet holes 1518 in shim A. The location of
inlet holes 1518 is indicated in FIG. 15A, and is shown in greater
detail in FIG. 16A.
[0133] According to the embodiment shown, microchannels 702 on shim
A extend in length further toward inlet header 1510a than do
microchannels 702 on shim B for purposes of enabling entry of
incoming ammonia-water vapor into the microchannels on shim A
through vapor inlet holes 1518. The mixed two-phase flow of dilute
ammonia-water solution entering microchannels 702 on shim A through
header 1510a and the ammonia-water vapor entering these same
microchannels through inlet holes 1518, upon absorption, exits the
microchannels as concentrated solution into outlet headers formed
by voids 1512a, 1512b in shims A and B, respectively. As will be
understood, the vapor enters microchannels 702 via inlet holes 1518
based on forced convective flow, which also prevents the dilute
solution from flowing into inlet holes 1518. Variations, options,
and other details associated with microchannel geometries, coupling
fluid inlet and outletpassages 1504, 1506, 1516, and voids for the
absorber 1500, including shapes, cross-sections, and dimensions,
apply equally and are similar to those described previously in
conjunction with the recuperative solution heat exchanger 800.
[0134] FIGS. 16A and 16B are enlarged perspective views of portions
of shims A 102 and B 104, respectively, associated with an absorber
1500 according to an embodiment of the present apparatus 10.
Specifically, FIGS. 16A and 16B illustrate one embodiment of the
locations of vapor inlet holes 1518 in microchannels 702 in shim A
102. As shown, the inlet holes 1518 in shim A map to passage 1516
in shim B to enable vapor flowing from passage 1516 to flow into
microchannels 702 in shim A and mix with dilute ammonia-water
solution in the microchannels. As will be understood and
appreciated, vapor inlet holes 1518 comprise various
cross-sectional shapes, areas, arrangements, etc., according to
various embodiments of the present system.
Alternate Embodiment Comprising Modular Components
[0135] FIG. 17 illustrates a modular embodiment of the present
system comprising discrete heat and mass transfer components
associated with an exemplary absorption cooling and/or heating
system. The discrete heat and mass transfer components shown in
FIG. 17 define an exemplary absorption heat pump in discrete
component-by-component assemblies, which facilitates modular and
versatile assembly of absorption heat pumps (and/or other heat or
heat and mass transfer systems) with larger cooling and/or heating
capacities than those typically associated with the preferred,
monolithic apparatus previously discussed. The heat and mass
transfer components comprising the recuperative solution heat
exchanger 800, desorber 1100, rectifier 1150, condenser 1200,
recuperative refrigerant heat exchanger 1300, evaporator 1400, and
absorber 1500 are shown as individual heat and/or mass exchangers
arranged according to one layout for the system assembly.
Generally, the system architectures, features, and functions of
each of these heat and mass transfer components are similar to
those previously described. For example, each component shown in
FIG. 17 includes a plurality of shim pairs; however, each shim only
includes the microscale features necessary to accomplish the
individual heat and mass transfer functions of its respective
component.
[0136] To avoid unnecessary cluttering, the fluid lines and
connections to coupling fluids, etc., are not shown in FIG. 17. As
will be understood, however, fluid connecting lines or other
passages should be included in system embodiments to transfer
working fluids and coupling fluids within and/or between components
as appropriate. According to one embodiment, the discrete
components shown in FIG. 17 are incorporated into an integrated
structure, such as a large, insulated unit, such that although the
individual heat and mass transfer components are formed as discrete
components, the overall absorption heating and/or cooling assembly
may be contained in an integral package, if necessary.
Description of Particular Exemplary Embodiment
[0137] The discussion below relates to specifics for a particular,
exemplary embodiment of the present system described herein.
Specifically, described below are calculations, manufacturing
processes, design details, dimensions, feature arrangements,
exemplary working fluids and coupling fluids, and other similar
details associated with the described, exemplary embodiment and
methods of making the same. As will be understood and appreciated,
the specific embodiment and application described below is but one
embodiment of the present system, and is not intended to limit the
scope of the present disclosure, or the invention(s) and systems
described herein, in any way.
[0138] Specifically, the discussion below describes the design and
fabrication of a miniaturized (i.e., microscale), monolithic
absorption heat pump system utilizing microchannel heat and mass
transfer system components. An exemplary embodiment of the present
system was built according to the specifications, parameters, etc.,
outlined below, and the achieved performance results for the
exemplary embodiment under specified parameters are provided
herein.
[0139] Manufacturing Techniques
[0140] The manufacturing techniques used to build the exemplary
apparatus allow multiple microchannel heat and mass transfer
components or heat exchange components (i.e., heat exchangers) to
be fabricated at the same time in a single, monolithic structure.
For this exemplary embodiment, the microchannels 702 are first
formed on stainless steel shims 102, 104 by a wet chemical etching
process. The shims are then diffusion bonded together to form the
overall apparatus 10. By placing shims with different microchannel
configurations in an alternating pattern, the fluid streams of each
heat and mass transfer component are allowed to come into close
thermal contact. The steps according to one embodiment of the
microchannel manufacturing process are outlined in greater detail
below.
[0141] Photochemical Etching
[0142] FIG. 18 illustrates the steps associated with one embodiment
of the photochemical etching process for manufacturing
microchannels 702 according to an exemplary embodiment as described
herein. As will be understood and appreciated, other processes and
manufacturing techniques may be used to manufacture microchannels,
as described previously. The photochemical etching process begins
with cleaning the stainless steel shims 102, 104 to remove any
oils, greases, metal working fluids or other contaminants on the
surface. The shims are then cleaned with hydrochloric acid to
remove any scale or oxides on the surface of the metal.
[0143] A photosensitive material (photoresist) is then applied to
both sides of the given shim 102, 104. The photo resist material
used in the production of the exemplary apparatus is a dry film,
negative resist. The portions of the resist exposed to UV light
cure and protect the underlying steel during the etching
process.
[0144] A mask containing the image of the required flow channels
(i.e., microchannels) is created for both sides of each of the two
shim designs (i.e., shims A 102 and B 104). The mask is a film with
opaque sections representing the areas to be etched and transparent
sections representing areas wherein the photo resist should remain
to protect the base material from the etching chemicals. The masks
are mounted to both sides of the shim and aligned to ensure
features match up on both sides of the steel.
[0145] The arrangement of the steel, photoresist, and mask is then
exposed to ultra violet light to cure the photoresist. The uncured
photoresist is then removed in a developing process. The metal with
the cured photoresist is then passed through the etching process,
wherein a ferric chloride solution (i.e., acid solution) is used as
the etchant. This acid solution removes the exposed metal and forms
the microchannels and holes in the steel shim.
[0146] Once the shim is removed from the etching process, the
remaining photoresist material is similarly removed. During the
etching process, the shims remain connected to the process sheets
by several tabs. Leaving the shims tabbed to the sheets ensures
consistent etching. After the photoresist material is removed, the
individual shims are removed from the process sheet. The
photoresist application and the etching process are generally
conducted in a clean room to reduce the risk of dust contamination
which could cause manufacturing defects during the etching
process.
[0147] Diffusion Bonding
[0148] In the exemplary embodiment described herein, the shims are
joined using a diffusion bonding process. As will be understood,
the shims may be combined via other bonding or combination
processes according to various embodiments, as described
previously. The diffusion bonding process begins with cleaning the
shims 102, 104 and an inspection to ensure there are no burrs or
foreign objects on the shim material. The shims are coated with a
nickel plating in an electroless nickel plating procedure. The
nickel coating is applied to aid in creating a hermetic seal during
the diffusion bonding process.
[0149] The shims 102, 104 and cover plates 110, 111 are then
arranged in the correct order (e.g., alternating shims A and B) and
proper alignment of the shims is carefully monitored (e.g., via
alignment notches 602, 604 described previously). Two pins are
inserted into alignment notches in the front plate 110, end plate
111, and shim group 108, respectively. In this particular
embodiment, all shims and the back end cover plate 111 each have at
least one alignment notch. This alignment scheme enables the steel
shims to lie flat, even if there are minor inconsistencies in the
position of the alignment notches. It also allows the steel to
expand and contract due to thermal expansion during the bonding
process without causing buckling or delimitation while achieving
alignment tolerances of .+-.0.05 mm.
[0150] The assembled system 10 is then placed in a hot press vacuum
furnace 1900, illustrated and represented by FIG. 19. The
evacuation in the hot press furnace 1900 removes any air from
between the shims (i.e., laminates) as well as from the voids
within the assembled shims. The system is then raised to an
elevated temperature (e.g., approximately 1000.degree. C.) in the
vacuum conditions and a load is applied to the system to raise the
interfacial stress between adjoining components to a required value
(e.g., approximately 10 MPa). The system remains at these
conditions for a sufficient period of time (e.g., approximately 5
hours) for the bonding process to occur.
[0151] During the bonding process, the surface asperities on
contacting surfaces begin to deform plastically. The deformation
continues until the pores between the surfaces have been
eliminated. The atoms from adjacent surfaces can then diffuse
across the interface, allowing the grain boundaries to reorganize
in the interface region. This process forms a bond with a strength
approaching the yield strength of the bulk material.
[0152] Cycle Design Calculations
[0153] A thermodynamic model for the exemplary system was developed
by choosing representative design conditions for the operation of a
single-effect absorption cycle in the cooling mode. Throughout this
section and for ease of reference, previously-presented reference
numerals are used to identify various system components.
Particularly, reference is made to FIG. 5, which shows the
schematic functional representation of the internal heat and mass
transfer components and the fluid flows between the components
according to one embodiment of the present system. Principally, the
external heat source input, desired cooling, and ambient conditions
are established to enable the cycle design. With a representative
heat sink (i.e., heat rejection 140) temperature of 37.degree. C.,
a thermal power input (i.e., heat source 130) of 800 W, and
specified desired cooling 150 of 300 W, system design calculations
are initiated. As mentioned, these selected parameters are chosen
purely for purposes of describing an exemplary system embodiment,
and are in no way intended to limit system parameters, capacities,
etc.
[0154] These specified representative external conditions for heat
source and sink, combined with allowances for temperature
differences between the external conditions and the working fluid
that yield reasonable component surface area requirements, result
in high and low side operating pressures of approximately l 1600
and 400 kPa, respectively. Thus, the high-side pressure is
established by the choice of a driving temperature difference
between the condensed refrigerant (i.e., ammonia) and an ambient
sink in the condenser 1200. Similar consideration of the driving
temperature difference at the desorber component 1100 and the
already established high-side pressure yields a dilute solution
outlet temperature and concentration, i.e., fraction of ammonia in
an ammonia-water solution. Using the corresponding concentrated
solution inlet temperature at the desorber 1100, the high-side
pressure, and the equilibrium properties of ammonia-water mixtures,
a solution inlet enthalpy is obtained. Coupled with the dilute
solution outlet enthalpy at the desorber 1100, the heat input is
related to the concentrated solution flow rate through an energy
balance between the heat source and the working fluid. For the
representative design point calculation, the resulting concentrated
solution mass flow rate and ammonia mass fraction are
2.7.times.10.sup.-3 kg/s and 0.37, respectively. The energy balance
calculation and the equilibrium relationships also yield the vapor
quality (ratio of ammonia-water vapor mixture to total
ammonia-water two-phase flow rate) and concentration at the
desorber 1100 outlet. A summary of key operating conditions for
this representative, exemplary cycle is provided in Table 1.
TABLE-US-00001 TABLE 1 State Points for Exemplary Absorption Heat
Pump Cycle x, State Point T, .degree. C. P, kPa kg/kg
Solution/Refrigerant State Points Absorber Concentrated Solution
out 50.4 400 0.37 Rectifier Concentrated Solution In 50.8 1600 0.37
Recuperative Solution Heat Exchanger 63.7 1600 0.37 Concentrated
Solution In Recuperative Solution Heat Exchanger 109 1600 0.37
Concentrated Solution Out Desorber Out 128.2 1600 0.37 Rectifier
Vapor In 128.2 1600 0.876 Rectifier Reflux Out 128.2 1600 0.285
Recuperative Solution Heat Exchanger Dilute 128.2 1600 0.285
Solution In Recuperative Solution Heat Exchanger Dilute 75.7 1600
0.285 Solution Out Absorber Dilute Solution In 73.2 400 0.285
Rectifier Refrigerant Out 85 1600 0.984 Condenser Refrigerant Out
39.6 1600 0.984 Recuperative Refrigerant Heat Exchanger High 30.2
1600 0.984 Out Evaporator Refrigerant In -1.4 400 0.984 Evaporator
Refrigerant Out 8.6 400 0.984 Recuperative Refrigerant Heat
Exchanger Low 18 400 0.984 Out Coolant State Points Evaporator
Coolant In 9 101.3 NA Evaporator Coolant Out 5.5 101.3 NA Absorber
Coolant In 37 101.3 NA Absorber Coolant Out 45.6 101.3 NA Condenser
Coolant In 37 101.3 NA Condenser Coolant Out 42.6 101.3 NA
[0155] A low vapor concentration exiting the desorber 1100 would
cause severe temperature glide penalties in the evaporator 1400,
resulting in rising refrigerant temperatures that would unduly
restrict cooling. To ensure an adequately pure ammonia refrigerant
stream, the vapor stream should be cooled in the rectifier 1150 to
strip off extra water vapor. Accordingly, the design outlet
temperature of the saturated vapor stream leaving the rectifier is
set to provide a minimum ammonia concentration of 98% for this
exemplary embodiment.
[0156] Generally, the reflux liquid that is condensed out of the
refrigerant stream in the rectifier 1150 flows back into the
separation chamber where it mixes with the dilute solution before
exiting the desorber 1100. An energy balance on the rectifier vapor
inlet and outlet and liquid streams yields the rectifier cooling
load.
[0157] In this embodiment, for the design calculations to provide
the required cooling, the concentrated solution stream leaving the
solution pump 502 (see FIG. 5) is assumed to be the cooling source
for the rectifier 1150 (i.e., via cooling fluid line 524). The
aforementioned energy balance also yields the outlet enthalpy and
temperature of the concentrated solution upon cooling the vapor
stream in the rectifier. Additionally, mass and species balances on
the rectifier yield the refrigerant and reflux mass flowrates. The
reflux mixes with the remaining liquid solution in the separation
chamber in the bottom of the rectifier and exits towards the
recuperative solution heat exchanger 800. Mass and species balances
on this mixing process yield the dilute solution flowrate and
concentration.
[0158] The refrigerant vapor leaving the rectifier 1150 flows to
the condenser 1200. With an assumption of a subcooled liquid
refrigerant outlet from the condenser, the refrigerant
concentration and the high-side pressure, and the condenser
refrigerant outlet temperature are established. The condenser heat
load is also calculated using an energy balance. In addition, this
condenser heat load is used in combination with a set coolant
(i.e., coupling fluid) flow rate to determine the coolant outlet
temperature from the condenser (i.e., via medium temperature fluid
line 528). After leaving the condenser 1200, the refrigerant flows
through the recuperative refrigerant heat exchanger 1300 where it
is further cooled by the refrigerant leaving the evaporator.
[0159] The expansion of the refrigerant exiting the recuperative
refrigerant heat exchanger 1300 through the expansion valve 534
(see FIG. 5) is assumed to be isenthalpic for this exemplary
embodiment, which yields the evaporator 1400 inlet temperature.
With a fixed evaporator temperature glide requirement, the
evaporator outlet temperature is determined, which also yields the
cooling load in the evaporator.
[0160] The calculated cooling load, in conjunction with a set
chilled water (i.e., coupling fluid) flowrate and inlet
temperature, yields the chilled water outlet temperature (i.e., to
desired cooling 150) from an energy balance. A similar energy
balance is conducted on the recuperative refrigerant heat exchanger
1300 to obtain the low pressure vapor state at the outlet of this
heat exchanger, which is also the absorber refrigerant inlet
condition for this exemplary embodiment.
[0161] Returning to the solution circuit, according to the
described exemplary embodiment, the concentrated solution inlet to
the recuperative solution heat exchanger 800 is determined by the
outlet of the rectifier 1150. An energy balance on the recuperative
solution heat exchanger yields the dilute solution and concentrated
solution outlet conditions from this heat exchanger, as well as its
heat load. The solution expansion valve 534 is assumed to be
isenthalpic. Regarding the absorber 1500, with the inlet conditions
to the absorber fixed (as described above), and with an assumed
solution subcooling at the absorber outlet, the absorber heat load
is calculated from an energy balance.
[0162] Once the state points are fixed (as described above) using
mass, species and enthalpy balances for each exemplary heat and
mass transfer system component, the heat transfer rates of each
component necessary to yield the desired cooling load are also
fixed. Subsequent calculations are conducted to obtain the required
heat and mass transfer component surface area requirements based on
these desired heat loads and the relevant heat and mass transfer
models and correlations. Varying levels of detail may be
incorporated into such component design calculations, but for the
fabrication of this particular exemplary embodiment, the component
heat and mass transfer calculations are conducted by treating each
component as one single, integrated component, with the fluid
properties averaged over the component. Thus, the heat and mass
transfer component sizes are obtained based on the component heat
loads, the coupled heat and mass transfer resistances, and the
driving log-mean temperature differences. This technique is valid
for heat exchangers where the heat capacity rates of the two fluid
streams (e.g., the working fluid and coupling fluid) are constant
along the length of the heat exchanger. For ammonia-water systems,
in some components, the thermal capacities vary along the length,
but this technique may be applied to obtain reasonable estimates of
component sizes, with proper accounting of the driving temperature
differences. The heat and mass transfer component geometries are
generally determined based on these heat and mass transfer
calculations to satisfy the required heat loads, as well as on
dimensional requirements based on manufacturing techniques
discussed herein.
[0163] Component Design Calculations
[0164] As described above, according to the described exemplary
embodiment, the required size (overall heat transfer conductance,
UA) of each heat transfer component is determined from the cycle
model. The specific fluid channel configuration (i.e.,
microchannels, voids, and distribution passages) of each heat and
mass transfer component is determined by estimating the overall
heat transfer resistance of each individual component.
[0165] FIG. 20 illustrates a cross-section 2000 of a portion of a
plurality of stacked shims A 102 and B 104 showing representative
arrangements of microchannels 702 within the shims according to an
exemplary embodiment of the present system. The cross-section 2000
specifically illustrates the relative positioning, sizing, thermal
contact, etc., of microchannels 702 in combined shims A and B for a
given heat exchange component described herein. As will be
understood and appreciated, the cross-section arrangement 2000
illustrated in FIG. 20 is shown for exemplary purposes only, and
other embodiments of the present system utilize other microchannel
arrangements as will occur to one of ordinary skill in the art.
[0166] As shown in FIG. 20, heat exchange fluids (e.g., coupling
fluids and working fluids) flow through the microchannels on
alternating shims A 102 and B 104 in a counterflow arrangement
(although, as is understood, the flows do not necessarily have to
be counterflow depending on the specific embodiment). The analysis
of each heat exchange component begins by considering the extracted
and enlarged cross-section 2002, which illustrates various
microchannel and shim dimensions (described in greater detail
below).
[0167] According to the described embodiment and as shown in FIG.
20, the wet chemical etching process to create microchannels
creates channel cross-sections of rounded rectangular shape. During
the etching process, the etchant acts laterally as well as
vertically, removing material under the edge of the cured
photoresist, creating rounded features as shown in FIG. 20.
[0168] According to the described, exemplary embodiment, each heat
and mass transfer component in the system is modeled by computing
the thermal resistance presented by each fluid flowing through the
respective microchannels in shims A 102 and B 104, in addition to
the conductive thermal resistance presented by the intervening
metal wall between the shims (as illustrated in FIG. 20 as
t.sub.wall). Furthermore, the total surface area of the
microchannels is treated as a combination of surfaces in direct and
indirect thermal contact with the fluid on the other side of the
wall. The indirect thermal contact presented by the microchannel
side walls is accounted for by computing the effective heat
transfer area based on the appropriate fin efficiencies. (For the
range of heat transfer coefficients encountered in this design
process (380-38,000 W/m.sup.2-K), and the range of channel and shim
geometries of interest, the fin efficiencies approach unity and the
entire area of the microchannel walls can be treated as prime
surface.) The heat transfer coefficient for each of the fluid
streams is determined from applicable correlations.
[0169] Based on the heat exchange component heat and mass transfer
design approach outlined above, the microchannel width,
microchannel length, and number of microchannels for each component
are determined to satisfy the design heat loads at the pertinent
operating conditions computed from thermodynamic cycle analyses. As
will be understood, however, the approach outline above is but one
approach to determine appropriate microchannel dimensions, and
other approaches are used in other embodiments as will occur to one
of skill in the art.
[0170] FIG. 21 illustrates an enlarged cross-section 2100 of shims
A 102 and B 104 illustrating a close-up view of specific, exemplary
shim and microchannel dimensions according to an exemplary
embodiment of the present system. In order to simplify the design
procedure for this exemplary embodiment, a single microchannel size
is used for all heat exchange components and/or heat and mass
transfer system components mentioned above, as shown in FIG. 21. As
shown, a shim thickness of 0.5 mm (i.e., approximately 0.02 in) is
chosen based, in part, on the range of microchannel sizes that can
be fabricated on the shim. With a microchannel etch depth of half
the shim thickness and a microchannel width of 0.5 mm, the nominal
channel hydraulic diameter for this exemplary embodiment is 306
.mu.m, with a channel horizontal transverse pitch of 1 mm and
vertical pitch of 0.5 mm. These dimensions are illustrated in FIG.
21. As will be understood, these dimensions are presented for
illustrative purposes only, and embodiments of the present system
are not limited in any way by the indicated dimensions shown and
described.
[0171] In the described, exemplary embodiment, the flows of all
coupling fluids are in single-phase laminar liquid flow. Similarly,
working fluid flows in the recuperative solution heat exchanger 800
and the recuperative refrigerant heat exchanger 1300 are in
single-phase laminar flow. According to the described embodiment,
the heat transfer coefficient and friction factor for such
single-phase flows in the exemplary microchannel shape (shown in
FIG. 21) and other similar shapes (such as rectangular channels for
the coolant in the rectifier 1150) are estimated using the
correlations reported in Kakac et al., Handbook of Single-Phase
Convective Heat Transfer, New York, Wiley (1987).
[0172] According to one embodiment, for vapor-to-liquid phase
change processes such as condensation, correlations described in
Shah, M. M., A General Correlation for Heat Transfer During Film
Condensation Inside Pipes, International Journal of Heat and Mass
Transfer, Vol. 22(4), pp. 547-556 (1979), and Kandlikar, S.,
Garimella, S., Li, D., Colin, S. and King, M. R., Heat Transfer and
Fluid Flow in Minichannels and Microchannels, Elsevier Science
(2005), are used, as applicable, for each particular phase change
process. Other guidance for addressing single-component and
multi-component phase-change heat and mass transfer in condensers,
absorbers, evaporators, desorbers, and rectifiers is taken from the
models, correlations, and techniques outlined in Carey, V. P.,
Liquid-Vapor Phase-Change Phenomena: An Introduction to the
Thermophysics of Vaporization and Condensation Processes in Heat
Transfer Equipment, Washington, D.C., Taylor & Francis Series,
Hemisphere Pub. Corp. (1992), and Hewitt, G. F., Shires, G. L. and
Bott,
[0173] T. R., Process Heat Transfer, Boca Raton, CRC Press, Begell
House (1994). Two-phase pressure drops are estimated using the
two-phase pressure drop multiplier approach of Mishima et al., Some
Characteristics of Air-Water Two-Phase Flow in Small Diameter
Vertical Tubes, International Journal of Multiphase Flow, Vol.
22(4), pp. 703-712 (1996). Nonlinear variations of vapor quality
with heat exchanger length, even in these integrated analyses, are
accounted for by evaluating these correlations at the integrated
average properties along the component length. Conservative
estimates of two-phase pressure drops are obtained by computing the
greatest pressure gradient in the heat and mass transfer component
as a function of vapor quality or component length and applying
that to the total length of the heat and mass transfer
component.
[0174] Generally, evaporation heat transfer coefficients are
calculated using the correlation from Kandlikar et al., Predicting
Heat Transfer During Flow Boiling in Minichannels and
Microchannels, Chicago, IL, Soc. Heating, Ref. Air-Conditioning
Eng. Inc., pp. 667-676 (2003) and Kandlikar et al., An Extension of
the Flow Boiling Correlation to Transition, Laminar, and Deep
Laminar Flows and Microchannels, Heat Transfer Engineering, Vol.
25(3), pp. 86-93 (2004). The mean heat transfer coefficient for the
evaporating stream is calculated at a representative integrated
average vapor quality along the evaporator length to account for
the non-linear variation of vapor quality with evaporator
length.
[0175] According to the described exemplary embodiment, desorption
(vapor generation from the concentrated solution) is achieved in
the desorber 1100 using eight 150 W electrical cartridge heaters
for a maximum heat input of 1200 W. Heat fluxes supplied by the
heaters at a design desorber heat input rate of 800 W were found to
be well below critical heat flux limitations estimated using the
correlation for parallel mini/microchannels from Qu et
al.,Measurement and Correlation of Critical Heat Flux in Two-Phase
Micro-Channel Heat Sinks, International Journal of Heat and Mass
Transfer, Vol. 47(10-11), pp. 2045-2059 (2004).
[0176] For the exemplary rectifier 1150 design, the liquid reflux
and the vapor stream are assumed to be in thermal equilibrium so
that the temperature of the reflux leaving the rectifier is equal
to the temperature of the vapor entering the rectifier. In order to
facilitate the approach to this equilibrium, four trays are
included in the exemplary rectifier to hold the liquid reflux and
allow heat and mass transfer interaction with the counterflow
vapor. The heat transfer coefficient on the refrigerant side is
estimated using the laminar film condensation correlation from
Sadasivan et al., Sensible Heat Correction in Laminar Film Boiling
and Condensation, Journal of Heat Transfer, Transactions ASME, Vol.
109(2), pp. 545-547 (1987). Only the area of the single wall in
thermal contact with the concentrated solution is used for heat
transfer estimation in the rectifier for the particular exemplary
embodiment of the present system. The heat and mass transfer area
associated with the trays is not included in this calculation in
order to produce a more conservative result. The additional area of
the trays further enhances the performance of this heat and mass
transfer component.
[0177] Further details of the correlations mentioned above in
reference to various articles and texts can be found in the cited
literature. Representative dimensions of the exemplary heat and
mass transfer system components resulting from the calculations
described above are presented in Table 2. As will be understood and
appreciated, the dimensions and geometric details shown in Table 2
are presented for illustrative purposes only, and pertain to the
specific, described, exemplary embodiment of a single-effect
absorption cycle, and are in no way intended to limit or exclude
other combinations of system geometries, arrangements of various
heat exchange components or heat and mass transfer components,
channel hydraulic diameters, numbers of channels, shim thicknesses,
numbers of shims, etc., used in other embodiments of the present
system.
TABLE-US-00002 TABLE 2 Representative Dimensions of Exemplary
Embodiment of Single-Effect Absorption Heat Pump Cycle Recuperative
Solution Heat Exchanger (800) Recuperative Evaporator Rectifier
(1150) Concen- Refrigerant Heat (1400) Desorber Concen- Absorber
(1500) Condenser (1200) trated Exchanger (1300) Refrig- Cool-
(1100) trated Refrig- Solution Coolant Refrigerant Collant Solution
Solution High Low erant ant Solution Solution erant Cycle Analysis
Q, W 748 414 562 15 354 800 152 Heat Exchanger Geometry Channel 50
60 40 40 80 55 38 NA Length, mm Channels/ 12 12 8 8 10 10 5 5 15 15
4 1 NA shim Channel D.sub.h, 306 400 NA .mu.m indicates data
missing or illegible when filed
[0178] Packaging and Bonding Considerations
[0179] FIG. 22 shows an enlarged plan view of a header (e.g.,
header created by stacked-up voids 808a, 808b in the recuperative
solution heat exchanger 800) used in a heat and mass transfer
component according to an embodiment of the present system. In the
embodiment shown, the fluid distribution passage (e.g., passage 806
in the recuperative solution heat exchanger 800) within necked
region 2202 creates an area where bonding pressure is not
transmitted directly through the stacked shims during the diffusion
bonding process. A similar area is present below the microchannels
702 as they enter a heat exchanger core from a header (e.g.,
microchannel entry from void 810a in the recuperative solution heat
exchanger); however, the fluid distribution passages (e.g., 806)
are generally much wider than individual microchannels, and thus
the fluid distribution passages represent a critical bonding
point.
[0180] FIG. 23 shows a representative cross-section 2300 of a
portion of alternating shims A 102 and B 104 taken from
cross-section XX of the header in FIG. 22 according to one
embodiment of the present system. According to the exemplary,
described embodiment, the bonding pressure should be transmitted
laterally underneath the fluid distribution passages on shims B 104
to ensure a hermetic seal at the critical bonding point 2302.
Passage widths of 2 mm are used in this exemplary embodiment to
ensure sufficient bonding, although wider or narrower widths are
used according to other system embodiments.
[0181] As described previously, preferred embodiments of the
present system comprise microscale, monolithic heat or heat and
mass transfer systems. Because it is often desirable, depending on
the particular embodiment, to include more than one heat and mass
transfer system component within an integrated, monolithic
structure, system embodiments should account for extraneous heat
transferred between internal heat and mass transfer system
components. To account for this extraneous heat transfer, certain
factors are taken into account in various embodiments, such as
overall size of the microscale heat or heat and mass transfer
system, spacing between heat and mass transfer components within
the system, arrangement and type of fluid connections between
various system components, and other similar factors as will occur
to one of ordinary skill in the art.
[0182] As will be understood and as described previously, the
exemplary embodiment described herein, and its associated operating
parameters, temperature ranges, etc., are provided for illustrative
purposes only, and are not intended to limit the scope of the
present systems or apparatuses in any way. Generally, various
operating temperature and pressure ranges are envisioned depending
on the application under consideration. Thus, for example, when
applied for waste heat recovery from high temperature combustion
processes such as automotive exhaust, the heat source temperature
could range from 300.degree. C. to 900.degree. C., while for low
temperature waste heat recovery, the source temperature could be as
low as 40.degree. C. Similarly, for chiller applications, the
cooled fluid temperature is typically about 5-15.degree. C.,
whereas for refrigeration applications, the temperature could be
well below 0.degree. C. For heat rejection temperatures in air
conditioning applications, ambient temperatures in 20-55.degree. C.
are contemplated. However, as will be understood, the specific
values of these individual external temperatures are less important
than the relationship between the heat source, heat sink, and the
cooling temperature. Because a thermally-activated heat pump is
generally known as a three temperature (i.e., low temperature
cooling, medium temperature heat rejection, and high temperature
input heat source) system, the temperatures for which the subject
heat and mass transfer system may be applied should provide at
least a minimal lift, i.e., temperature difference, between the low
and medium temperatures to effect the desired output, and the
medium and high temperatures to provide the driving force necessary
to effect the desired output.
Form Factor Comparison and Representative Parameters of Exemplary
Embodiment
[0183] As described previously, one exemplary embodiment of the
present system comprises a microscale, monolithic absorption
cooling and/or heating system. The following section provides a
comparison of the described, exemplary embodiment of the present
system in the form of such an absorption cooling and/or heating
system to a traditional vapor-compression system used for
residential cooling. This section also provides representative
parameters associated with the exemplary embodiment described
herein. As will be understood and appreciated, the following
discussion is provided for illustrative purposes only, and is in no
way intended to limit the scope of the present disclosure, or the
invention(s) and systems described herein.
[0184] The exemplary embodiment of the present system described
above (i.e., a microscale, monolithic absorption heat pump) was
manufactured and tested under realistic ambient, chilled fluid, and
heat source conditions on a breadboard test facility. FIG. 24
illustrates a front plan view of exemplary fluid connections and
external plumbing arrangements for testing an embodiment of the
present system. The manufactured exemplary system embodiment
comprised overall dimensions of 200.times.200.times.34 mm.sup.3,
including 20 pairs of 0.5 mm thick shims A and B (i.e., 40 shims
total), with previously described microchannels of 306 .mu.m
hydraulic diameter. The exemplary, manufactured system comprised
other dimensions, system arrangements, etc., as described
above.
[0185] During testing of the exemplary embodiment, nominal 300 W of
cooling were delivered for an 800 W heat input at representative
ambient and chilled fluid conditions. Furthermore, the exemplary
system was demonstrated to operate in cooling mode over a wide
range of ambient temperatures (i.e., 20-35.degree. C.) and at
different heat input rates (i.e., 500-800 W). A nominal coefficient
of performance (COP) of 0.375 was achieved in a system volume of
200.times.200.times.34 mm.sup.3, representing a volumetric cooling
capacity of 221 kW/m.sup.3. With a system mass of 7 kg, the
corresponding specific cooling capacity is 0.043 kW/kg. The
exemplary embodiment was purposely designed with all heat and mass
transfer system component fluid inlets and outlets external (i.e.,
outside) to the apparatus, with wide spacing to enable installation
of temperature and pressure instrumentation at the inlet and/or
outlet of each component. An alternate embodiment, with internal
flow passages and elimination of extra space for instrumentation,
comprises projected dimensions of 120.times.120.times.25 mm.sup.3,
with a mass of 3 kg. The corresponding volumetric cooling capacity
of such an embodiment comprises 833 kW/m.sup.3, while the specific
cooling capacity is 0.10 kW/kg.
[0186] By comparison, conventional 10.55 kW cooling capacity
residential electric-vapor compression systems are on the order of
0.91.times.0.91.times.0.91 m.sup.3 and weigh about 225 kg,
representing volumetric cooling capacities on the order of only
13.8 kW/m.sup.3and specific cooling capacities of 0.047 kW/kg.
Therefore, on both volumetric and mass bases, the subject exemplary
system embodiment represents a substantial reduction in size of
cooling systems, while providing a similar cooling capacity to
those of much larger, conventional vapor-compression systems.
[0187] When compared to conventional absorption cooling systems (as
opposed to vapor-compression systems), the benefits of the
exemplary system embodiment described above become even more
evident. As described previously, absorption cooling systems are
generally much larger than vapor-compression systems due to the
additional heat and mass transfer components needed in absorption
systems. Thus, as will be understood, comparison of the exemplary,
described embodiment to a conventional 10.55 kW cooling capacity
absorption cooling system indicates advanced volumetric or specific
cooling capacities of the exemplary embodiment (due to the larger
size and weight of conventional absorption cooling systems
exhibiting an unchanged cooling capacity, as compared to the
vapor-compression system discussed above). Additionally, because
many fluid connections between heat and mass transfer system
components are included within a monolithic, microscale structure
of a system embodiment, leak reduction is enhanced, and required
fluid inventory is substantially lower than that of conventional
systems.
[0188] The foregoing description of the exemplary embodiments has
been presented only for the purposes of illustration and
description and is not intended to be exhaustive or to limit the
inventions to the precise forms disclosed. Many modifications and
variations are possible in light of the above teaching.
[0189] The embodiments were chosen and described in order to
explain the principles of the inventions and their practical
application so as to enable others skilled in the art to utilize
the inventions and various embodiments and with various
modifications as are suited to the particular use contemplated.
Alternative embodiments will become apparent to those skilled in
the art to which the present inventions pertain without departing
from their spirit and scope. Accordingly, the scope of the present
inventions is defined by the appended claims rather than the
foregoing description and the exemplary embodiments described
therein.
* * * * *