US20110180235A1

US20110180235A1 - Microscale heat or heat and mass transfer system

Info

Publication number: US20110180235A1
Application number: US13/058,182
Authority: US
Inventors: Srinivas Garimella; Matthew Delos Determan
Original assignee: Georgia Tech Research Corp
Current assignee: Georgia Tech Research Corp
Priority date: 2008-07-31
Filing date: 2009-07-31
Publication date: 2011-07-28
Also published as: KR101727890B1; WO2010014878A1; EP2321605A4; JP2011530059A; EP2321605B1; CN102112837B; KR20110074970A; EP2321605A1; CN102112837A; JP5719296B2; KR20170005164A

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.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims benefit under 35 U.S.C. § 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

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

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.
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.
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.
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.
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.
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.
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.
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

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.
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.
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.
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.
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.
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

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:

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).

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.

FIG. 3 illustrates an exemplary, fully-assembled embodiment of the heat or heat and mass transfer apparatus as described herein.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

FIG. 18 illustrates the steps associated with one embodiment of the photochemical etching process for manufacturing exemplary microchannels as described herein.

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.

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.

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.

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.

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.

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

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

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.
Coefficient of performance (COP): ratio of a desired output (i.e., cooling or heating) from a system embodiment as compared to the input energy.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Monolithic: constituting one, undifferentiated whole or unit. Generally synonymous with integrated.
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.
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.
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.
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.
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.
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.
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

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.
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.
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.
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.
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.
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.
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.
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.
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.
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).
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, 102 a, 104 a, 102 b, 104 b, 102 c, 104 c, . . . 102 n, 104 n, 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.
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.
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.
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.
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.
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.
As shown in FIG. 2, the exemplary apparatus 10 generally comprises a rectangular prism shape, and has dimensions L×H×W (i.e., length×height×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×H×W dimensions of 200×200×34 mm³, respectively. However, even smaller embodiments (e.g., 120×120×25 mm³, 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.
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).
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.
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.
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.).
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.
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.
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.
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.
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).
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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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 800 a, 800 b, the condenser 1200 a, 1200 b, the recuperative refrigerant heat exchanger 1300 a, 1300 b, the evaporator 1400 a, 1400 b, and the absorber 1500 a, 1500 b.
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 1100 a, 1100 b, and rectifier 1150 a, 1150 b portions of the shims.
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.
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 800 a, 800 b, the desorber 1100 a, 1100 b, the rectifier 1150 a, 1150 b, the condenser 1200 a, 1200 b, the recuperative refrigerant heat exchanger 1300 a, 1300 b, the evaporator 1400 a, 1400 b, and the absorber 1500 a, 1500 b.
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 μm. 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.
As noted in the glossary, for example, even though an exemplary embodiment utilizes microchannels comprising hydraulic diameters of 306 μm, microchannel fluid flow and heat and mass transfer phenomena may be exploited in channels with hydraulic diameters ranging from 1 μm 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.
Further, according to one embodiment, the microchannel sizes are the same (e.g., hydraulic diameter of 306 μm) 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.
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

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.
Recuperative Solution Heat Exchanger
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.
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 802 a 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 802 b 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 808 a, 808 b 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.
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 810 a and 810 b in shims A 102 and B 104, respectively. According to the embodiment shown, and in an arrangement complementary to the voids 802 a, 802 b receiving dilute solution, void 810 b on shim B comprises a blind hole that does not allow fluid flow across the shim. The corresponding void 810 a on shim A, however, allows distributed concentrated solution flow from void 810 a into microscale passages 702. Upon exiting the microscale passages 702, concentrated solution enters void 812 a, and exits the solution heat exchanger through an exit header formed by alternating stacked voids 812 a, 812 b, where it is subsequently conveyed to the desorber 1100.
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 802 a and 802 b on shims A and B, respectively, for the dilute solution, as well as fluid passage 804 for carrying dilute solution from the void 802 b 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 812 a and 812 b for transferring concentrated solution out of the recuperative solution heat exchanger 800.
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.
According to various embodiments of the present system, voids 802 a, 802 b, 812 a, 812 b, 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).
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.
Desorber/Rectifier
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.
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.
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.
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.
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.).
Condenser
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 1202 a, 1202 b in shims A and B, respectively. Void 1202 b 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 1208 a, 1208 b on shims A and B, respectively, and is returned to the medium temperature hydronic fluid line (e.g., coupled to the ambient).
As shown, ammonia-water vapor from the rectifier 1150 enters the condenser component 1200 through inlet headers formed by the stacked-up voids 1210 a, 1210 b in shims A 102 and B 104, respectively. Void 1210 a 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 1212 a, 1212 b 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.
Recuperative Refrigerant Heat Exchanger
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 1302 a, 1302 b in shims A and B, respectively. As shown, void 1302 b 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 1308 a, 1308 b on shims A and B, respectively.
Low-pressure vapor from the evaporator 1400 enters the recuperative refrigerant heat exchanger 1300 through inlet headers formed by the stacked-up voids 1310 a, 1310 b in shims A 102 and B 104, respectively. Void 1310 a 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 1312 a, 1312 b 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.
Evaporator
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 1402 a, 1402 b in shims A and B, respectively. Void 1402 b 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 1408 a, 108 b on shims A and B, respectively, and is subsequently used for cooling a conditioned space, or other similar application.
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 1410 a, 1410 b in shims A and B, respectively. Void 1410 a 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 1412 a, 1412 b 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.
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 1502 a, 1502 b in shims A and B, respectively. As shown, void 1502 b 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 1508 a, 1508 b on shims A and B, respectively.
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 1510 a, 1510 b in shims A and B, respectively. Void 1510 a 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 1512 a, 1512 b in shims A and B, respectively.
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 1514 a, 1514 b in shims A and B, respectively. Void 1514 b 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.
According to the embodiment shown, microchannels 702 on shim A extend in length further toward inlet header 1510 a 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 1510 a 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 1512 a, 1512 b 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.
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

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.
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

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.
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.
Manufacturing Techniques
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.
Photochemical Etching
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.
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.
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.
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.
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.
Diffusion Bonding
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.
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.
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° 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.
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.
Cycle Design Calculations
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° 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.
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 2.7×10⁻³kg/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 1

State Points for Exemplary Absorption Heat Pump Cycle

			x,
State Point	T, ° 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

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.
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.
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.
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.
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.
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.
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.
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.
Component Design Calculations
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.
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.
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).
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.
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_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/m²-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.
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.
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 μm, 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.
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).
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,
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.
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.
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).
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.
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 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

High

Low

erant

ant

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_h,	306	400	NA
μm

indicates data missing or illegible when filed

Packaging and Bonding Considerations
FIG. 22 shows an enlarged plan view of a header (e.g., header created by stacked-up voids 808 a, 808 b 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 810 a 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.
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.
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.
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° C. to 900° C., while for low temperature waste heat recovery, the source temperature could be as low as 40° C. Similarly, for chiller applications, the cooled fluid temperature is typically about 5-15° C., whereas for refrigeration applications, the temperature could be well below 0° C. For heat rejection temperatures in air conditioning applications, ambient temperatures in 20-55° 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

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.
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 200×200×34 mm³, including 20 pairs of 0.5 mm thick shims A and B (i.e., 40 shims total), with previously described microchannels of 306 μm hydraulic diameter. The exemplary, manufactured system comprised other dimensions, system arrangements, etc., as described above.
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° 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 200×200×34 mm³, representing a volumetric cooling capacity of 221 kW/m³. 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 120×120×25 mm³, with a mass of 3 kg. The corresponding volumetric cooling capacity of such an embodiment comprises 833 kW/m³, while the specific cooling capacity is 0.10 kW/kg.
By comparison, conventional 10.55 kW cooling capacity residential electric-vapor compression systems are on the order of 0.91×0.91×0.91 m³and weigh about 225 kg, representing volumetric cooling capacities on the order of only 13.8 kW/m³and 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.
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.
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.
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.

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.