FLEXIBLE HEAT/MASS EXCHANGER

RELATED APPLICATION DATA

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application Serial No. 60/915,558, filed May 2, 2007, and titled "Flexible Laminated Heat/Mass Exchangers," which is incorporated by reference herein in its entirety.

STATEMENT OF GOVERNMENT INTEREST

[0002] Subject matter of this disclosure was made with government support under U.S. Army

Contract No. W911QY-05-C-0008. The government may have certain rights in this subject matter.

FIELD OF THE INVENTION

[0003] The present invention generally relates to the field of heat exchangers and liquid cooling.

In particular, the present invention is directed to a flexible heat/mass exchanger.

BACKGROUND

[0004] There is a growing interest in small-scale power, refrigeration, and thermal management systems that require small and efficient liquid/air heat exchangers for heat rejection. Often these systems are meant to be integrated with human-portable equipment, such as chemical/biological protective suits, personal hydration systems, and soldier-portable power systems. The environments where these applications are needed are often remote and difficult to access. Heat must be rejected to an easily available heat sink, which almost always is ambient air. Typically the liquid will flow through an array of passages with large exposed surface area. Ambient air will flow past the outer surfaces of the flow passages and absorb heat from the liquid.

[0005] Typical heat transfer assemblies are formed from metal or ceramic components, and can be heavy and rigid. Furthermore, most heat rejection components are designed to transfer heat across a solid boundary. Systems like this have limited cooling potential because the circulating fluid cannot be cooled to a temperature that is lower than the temperature of the surrounding air. In hot environments, effective cooling using a typical heat exchanger can be impossible.

SUMMARY OF THE DISCLOSURE

[0006] In one implementation, the present disclosure is directed to a system for use with a working liquid. The system comprises a heat/mass exchanger that includes: a thin flexible body having a first face and a second face spaced from the first face, the thin flexible body comprising a

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plurality of layers defining a flow field region containing at least one passageway and having boundary margins, the plurality of layers fluidly sealingly attached to one another at least at the boundary margins, wherein at least one of the plurality of layers is permeable so as to allow mass transfer of a portion of the working liquid from the at least one passageway to the first face of the thin flexible laminate when the heat/mass exchanger is in use.

[0007] In another implementation, the present disclosure is directed to a heat/mass exchanger for use with a working fluid in an ambient environment. The heat/mass exchanger includes: a flexible laminate having a flexible first sheet and a flexible second sheet fluidly sealed around a boundary region, each of the flexible first and second sheets having an external face exposed to the ambient environment during use; a flow channel defined by the flexible first sheet, the flexible second sheet and the boundary region, the flow channel containing the working fluid during use; and either or both the flexible first and second sheets configured to transport a portion of the working fluid from the flow channel to the external face of either or both of the flexible first and second sheets.

[0008] In yet another implementation, the present disclosure is directed to a hydration system that includes: a hydration reservoir for storing potable water during use; and a heat/mass exchanger fluidly coupled with the hydration reservoir downstream thereof, the heat/mass exchanger including: a thin flexible body having a first face and a second face spaced from the first face, the thin flexible body comprising a plurality of layers defining a flow channel region containing a flow channel and having boundary margins, the plurality of layers fluidly sealingly attached to one another at the boundary margins so as to define the flow channel; a water inlet fluidly coupled between the hydration reservoir and the flow channel for providing the potable water thereto; and a water outlet fluidly coupled to the flow channel for conducting the potable water therefrom; wherein at least one of the plurality of layers is permeable so as to allow mass transfer of a portion of the working liquid from the flow channel to the first face of the thin flexible laminate when the heat/mass exchanger is in use.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] For the purpose of illustrating the invention, the drawings show aspects of one or more embodiments of the invention. However, it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein:

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FIG. 1 is a schematized cross-sectional view of a heat/mass exchanger made in accordance with concepts of the present disclosure;

FIG. 2 is a graph of temperature versus time for an example heat/mass exchanger made in accordance with the present disclosure, illustrating the cooling performance of the heat/mass exchanger at various flow rates and with and without an evaporation-assisting fan;

FIG. 3 A is an isometric exploded view of a four-layer rectangular laminate heat/mass exchanger made in accordance with concepts of the present disclosure;

FIG. 3B is a plan view of the two inner layers of FIG. 3A placed side-by-side;

FIG. 3C is a plan view of the two inner layers of FIG. 3A one superimposed on the other;

FIG. 4 is an isometric exploded view of another four-layer heat/mass exchanger made in accordance with concepts of the present disclosure that is flexible in any direction;

FIG. 5 is a perspective view of a personal hydration system having a cooling system that includes a heat/mass exchanger similar to the heat/mass exchanger of FIG. 4;

FIG. 6 A is a plan view of a flow matrix structure that includes elongated depressions in opposing faces of adjacent layers oriented substantially perpendicularly to each other;

FIG. 6B is a cross-sectional view as taken along line 6B-6B of FIG. 6A;

FIG. 7 A is a plan view of an alternative flow matrix structure having circular depressions that extend inwardly from opposing faces of adjacent layers;

FIG. 7B is a cross-sectional view as taken along line 7B-7B of FIG. 7A;

FIG. 8 is a plan view of yet another flow matrix structure for a four-layer exchanger formed by overlapping two patterns of circular holes cut in two separate layers;

FIG. 9 is a plan diagrammatic view of another alternative flow matrix structure formed by joining adjacent layers in a manner to direct fluid flow through the flow matrix in a serpentine pattern;

FIG. 10 is a partial perspective view/partial diagrammatic view of a personal evaporative cooling system having exchangers made in accordance with concepts of the present disclosure;

FIG. 11 is a plan view of the cooling module of FIG. 10 with the cover removed to expose the internal components to view;

FIG. 12 is a cross-sectional view as taken along line 12-12 of FIG. 11; and

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FIG. 13 is a perspective view of an evaporative cooling system made in accordance with concepts of the present disclosure.

DETAILED DESCRIPTION OF THE DRAWINGS

[0010] Referring now to the drawings, FIG. 1 illustrates a heat/mass exchanger 100 made in accordance with concepts of the present disclosure. At a high level, heat/mass exchanger 100 has first and second outer faces 104, 108 spaced from one another, with a flow channel 112 located between the first and second outer faces. As will be discussed below in detail, exemplary heat/mass exchanger 100 includes a number of beneficial features, including a resilient highly flexible construction (e.g., it can be folded back on itself without permanent deformation), a permeable construction that allows for mass transfer from fluid in the flow channel 112 through either or both of the first and second outer faces (depending on the location(s) of permeable material) to a cooling medium outside the exchanger, and fabrication materials and techniques that favor creation of integral design features such as either or both of an inlet manifold 116 and outlet manifold 120 placed adjacent to the flow channel 112. In addition, although not explicitly shown in FIG. 1 but explained in more detail below, flow channel 112 may be configured for highly efficient heat and/or mass transfer across a large extent of the expanse of the flow matrix, i.e., both along the "length" of the flow channel between inlet and outlet manifolds 116, 120 and along the "width" of the flow channel in a direction perpendicular to the length.

[0011] In this connection, flexible heat/mass exchangers made in accordance with concepts of the present disclosure, such as flexible heat/mass exchanger 100, are characterizable as "thin" structures, i.e., structures having widths and lengths much greater than their thicknesses. Minimum width:thickness and length/thickness ratios are each about 100:1 and 300:1. Examples of structures meeting this criterion are sometimes characterized as sheets and ribbons, among others. Exemplary configurations of such highly efficient configurations for flow channel 112 are presented below in connection with FIGS. 3A-C, 4, and 6A-9. It is noted that while heat/mass exchanger 100 includes all of these features, those skilled in the art will readily understand that other embodiments of a heat/mass exchanger made in accordance with the present disclosure does not need to include all of these features, but rather may include only one or two of these features.

[0012] Heat/mass exchanger 100 may be conveniently described as comprising three layers, i.e., first and second outer layers 124, 128 and an intermediate layer 132 that contains flow channel 112. It is to be understood that while each of these layers 124, 128, 132 is shown in FIG. 1 as a discrete

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layer relative to the others so as to suggest that each layer consists of a single sheet of material, this need not necessarily be so. For example, in various embodiments, each layer 124, 128, 132 may comprise one, two or three or more sheets. Alternatively, regarding intermediate layer 132, this layer may not include any discrete sheets at all, but rather may be formed from portions of sheets that make up the first and/or second outer layers. In an extreme example (albeit one that would likely be challenging to manufacture but nonetheless possible), heat/mass exchanger 100 could be made of a single sheet of material, and layers 124, 128, 132 in this context would correspond to "zones" within the single sheet. At the other extreme, examples could be made where a plurality of internal layers 132, each created by one or more sheets or by portions of adjacent sheets, are used to construct the flow channel 112. Specific examples of heat/mass exchangers of the present disclosure having two- and four-sheet laminated construction are shown and described below in connection with FIGS. 3A-C, 4, 6A-9.

[0013] First and second outer layers 124 and 128 may themselves comprise multiple layers of various materials. For example, some of the layers that make up the outer layers can serve as structural support, some may provide permeability to the exchanger's working fluid, and some may be present to simplify fabrication (for example by enabling bonding to the intermediate layer 132). Typically commercial "membrane" materials are assembled from multiple layers, each of which performs a separate function.

[0014] Exemplary materials of construction for layers 124, 128, and 132 include thin flexible polymeric sheets. Thin polymeric sheets provide enhanced heat and mass transfer as well as flexibility. The sheets may be formed in non-planer shapes for specific applications where form- fitting heat/mass transfer area is desirable. The sheets may be permeable or impermeable to the working liquid, or combinations thereof, though at least one sheet should exhibit at least partial permeability to facilitate mass transfer to or from an outer face, such as first outer face 104 or second outer face 108, of an external layer 124 or 128 respectively, of the heat/mass exchanger 100. For example, a permeable sheet may be composed of a material that is inherently impermeable but contain sufficient porosity to permit mass transfer, such as ePTFE (expanded polytetrafluoroethylene). Alternatively, a sheet may be formed from a solid hydrophilic membrane, such as urethane. Fluid may dissolve into the sheet and diffuse through the sheet material without passing through openings or other porous structures.

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[0015] Intermediate layer 132 need not facilitate mass transfer through its solid components to an external face and so, if provided as one or more separate and distinct layers, may be manufactured from inherently permeable or inherently impermeable materials so as to promote flow of working fluid along the direction of arrows 136. In some embodiments, flow channel 112 includes interconnecting flow passageways that form a flow matrix (not explicitly shown in FIG. 1, but see 3A-C, 4, 6A-B, 7A-B, 8 and 9) formed in intermediate layer 132 that allow fluid contact with outer layers 124, 128 bounding the flow matrix, thereby permitting mass transfer to one or both of first and second outer faces 104, 108. It is noted that in the embodiments shown in FIGS. 3A-C, 4, 6A-B, 7A-B, 8 and 9 the flow matrices that each provide flow channel 112 to the respective heat/mass exchanger are defined by sheets of material provided with various openings, depressions or other structures when the sheets are overlain with one another. In other embodiments, the structure of flow matrix may be provided in other ways, such as using a sheet of fibrous material formed into a three-dimensional matrix. In yet other embodiments, flow channel 112 may simply be a single passageway without any sort of flow matrix structure. In differing embodiments, possible materials composing the heat/mass exchanger include urethane, polyimide, nylon, and others. When flexibility is not needed, thin metal sheets can also be used to assemble intermediate layer 132. Typically, though not necessarily, the intermediate layer will have a thickness in the range 0.025 mm to 1 mm.

[0016] It is noted that some of the materials used to make heat/mass exchangers of the present disclosure and the configurations of such heat/mass exchangers allow the heat/mass exchangers to be readily made/formed into a variety of shapes. For example, in some embodiments, the various layers 124, 128, 132 may be made of corresponding respective sheets of material that may be cut to any shape and suitably secured to one another while engaged with a shaping form, such as a convex of concave form, or engaged in a shaping mold, such as a mold having two parts that together define a cavity that contains the heat/mass exchanger during molding. As an illustrative example, a heat/mass exchanger of the present disclosure, such as heat/mass exchanger 100 of FIG. 1, may be molded to conform to the shape of the outer surface of a military personnel combat helmet. During use, the molded heat/mass exchanger would be secured to the outer surface of the helmet with a permeable outer layer facing outward. Mass transfer of a working liquid, e.g., water, through the permeable layer would provide evaporative cooling as described below, thereby providing cooling to the helmet and relief to the wearer.

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[0017] When: 1) a liquid working fluid (represented in FIG. 1 by arrows 136) resides in or passes through the flow channel 112 in a cooling mode; 2) first outer layer 124 is permeable and second outer layer 128 is impermeable to the working liquid and its vapor and 3) heat/mass exchanger 100 is located in an ambient air environment 144 that is not saturated with the vapor phase of the working fluid, the heat/mass exchanger works as follows. Working liquid 136, such as water to be cooled for personal hydration, flows into inlet manifold 116, for example, via an inlet fluid port 140. Manifold 116 delivers working liquid 136 to flow channel 112 and distributes it substantially evenly across the width of the flow matrix. Because the ambient air 144 is not saturated with vapor, there is a difference in chemical potential that favors mass transfer from the working fluid to the ambient air. As working fluid 136 flows through flow channel 112, a very small fraction of fluid will transfer through the permeable outer layer 124 and enter the surrounding air 144 as vapor. Substantial heat is absorbed in this process by evaporation of the working fluid. Heat needed to drive this evaporation is drawn from the working fluid and the surrounding air.

[0018] The primary driving force for this process is the difference in chemical potential of the working fluid 136 between the flow channels 112 and surrounding air 144, not the difference in temperature. Therefore this cooling process can proceed even if the temperature of the surrounding air is greater than the temperature of the working fluid. The remaining portion of working fluid 136 transiting through flow channel 112 passes through the outlet manifold 120 and exits the heat/mass exchanger through an outlet fluid port 142. The additional cooling achieved through the evaporation mechanism provided by permeable first outer layer 124 is highlighted by FIG. 2, which contains a graph 200 of data collected using a working example of a heat/mass exchanger made in accordance with the present disclosure. For context, this working example was a 15 in. (38.1 cm) X 8 in. (20.3 cm) rectangular heat exchanger constructed in the manner of heat exchanger 300 of FIG. 3 A, wherein the thickness of the outer layers was on the order of 125 μm (0.005 inches).

[0019] Referring now to FIG. 2, and also to FIGS. 1 and 3A, FIG. 2 contains a graph 200 illustrating the performance of a heat/mass exchanger having the general configuration of heat/mass exchanger 300 of FIG. 3 A. In this working example, heat/mass exchanger 300 had a working liquid of water passing through flow channel 112. First and second outer layers 124, 128 (corresponding to first and second outer sheets 304, 308 of FIG. 3A) were constructed of ePTFE porous polymer membranes. Intermediate layer 132 (which corresponds to the composite formed by first and second intermediate sheets 312, 316 of FIG. 3 A-C) incorporating flow channel 112 was constructed of a pair of urethane sheets, each sheet containing a diagonal pattern of parallel channels 320, 324 fully

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penetrating the sheet thickness as shown in FIG. 3B. Two such sheets were overlain with one another so that parallel channels 320 in each intermediate sheet 312, 316 run along opposite diagonals, creating a crisscrossing pattern of interconnected flow channels that constitute the flow channel 112. The porosity of the ePTFE material in each of first and second outer layer 124, 128 (first and second outer sheets 304, 308 of FIG. 3A) permitted a portion of the water from flow channel 112 to migrate to some part of each of first and second outer faces 104, 108 where unsaturated ambient air induced evaporative cooling at the two outer faces. The water was thereby cooled by conduction through the flexible laminate structure of heat exchanger 300, which in turn was cooled by evaporative cooling at first and second outer faces 104, 108.

[0020] Referring to FIG. 2 in greater detail, graph 200 displays the ambient air temperature 204, water inlet temperature 208, and water outlet temperature 212 as a function of time for an embodiment similar to that shown in FIG 3A as operational conditions were varied. Before any flow through the exchanger (until approximately 10 minutes into the test), all three temperatures 204, 208, 212 were approximately the same (7O ⁰ F -72 ⁰ F). The relative humidity of the ambient air was such that the wet bulb temperature was 51 ⁰ F, which would be the lowest achievable fluid temperature at equilibrium. When water flow through the exchanger began at approximately 10 minutes, the water cooled to an outlet temperature 212 of about 63 ⁰ F by natural convection with the surrounding air. When the velocity of the ambient air 144 across the outer faces (104, 108 in FIG. 1) was increased by starting a fan at 25 minutes, evaporative cooling was enhanced by forced convection, resulting in increased cooling of the water (working liquid). This is evident in graph 200 by the drop in water outlet temperature 212 from approximately 63 ⁰ F at time t = 25 minutes, to approximately 55 ⁰ F when the fan is turned on. Water outlet temperature 212 does not reach the wet bulb temperature, suggesting insufficient area to completely reach equilibrium. As the working liquid flow rate was increased from 1.8 L/hr to 3.3L/hr at approximately t = 90 minutes, the residence time of the working liquid decreases and the volume of fluid that must be cooled in a given time increases. As a result, the outlet temperature of the working fluid 136 rose slightly, to approximately 57 ⁰ F. An apparatus without the ability to utilize a portion of the working liquid for evaporative cooling would have been unable to achieve exit working liquid temperatures lower than the ambient air temperature.

[0021] The embodiment shown in FIG. 1 has been described in terms of heat/mass transfer that involves cooling of the working fluid 136 in conjunction with transport and evaporation of working fluid from the first or second outer faces 104, 108 into the ambient air 144. It should be recognized

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that this process may be reversed, using a chemical potential gradient to transport moisture from the ambient air 144 and into the working fluid 136. This dehumidification process requires that the external layers 124, 128 have the same properties for transporting fluid (in liquid or vapor form) as are utilized in the evaporation mode. Various chemical and physical means for controlling the chemical potential gradient are well known in the engineering arts.

[0022] In addition, while channel 112 of exemplary heat/mass exchanger 100 of FIG. 1 is denoted as a "flow channel," it should be appreciated that working fluid 136 does not need to be moving to be cooled. For example, when working fluid 136 is not moving, channel 112 may be considered a reservoir. In this case, the stagnant working fluid 136 is cooled by the same evaporative effect described above. An example of a useful device in which channel 112 intermittently acts as a reservoir for stagnant working fluid 136 is described below in the context of personal hydration system 500 of FIG. 5.

[0023] Referring now to FIGS. 3A-C, FIG. 3 A illustrates an exemplary heat/mass exchanger 300 having the basic configuration of heat/mass exchanger 100 of FIG. 1 executed with a four-sheet construction that includes first and second outer sheets 304, 308 and first and second intermediate sheets 312, 316. Comparing heat/mass exchanger 300 of FIG. 3A to diagrammatic heat/mass exchanger 100 of FIG. 1, it is seen that first and second outer sheets 304, 308 correspond, respectively, to first and second outer layers 124, 128, and first and second intermediate sheets 312, 316 together correspond to intermediate layer 132. For additional clarity, FIG. 3B shows intermediate sheets 312, 316 oriented as they would be when overlain with one another in the assembled heat/mass exchanger 300, with first sheet 312 containing a diagonal pattern of parallel channels 320 fully penetrating the sheet thickness, and second sheet 316 containing a complementary diagonal pattern of parallel channels 324 fully penetrating the sheet thickness. The flow matrix (112 in FIG. 1) is constructed by overlaying the two intermediate sheets 312, 316 so that parallel channels 320, 324 in corresponding respective sheets run on opposite diagonals, creating a crisscrossing pattern of interconnected flow channels that constitute the flow matrix. This aspect of the embodiment is perhaps best illustrated in FIG. 3C. Channels 320, 324 may be created in intermediate sheets 312, 316 by means well known to those practiced in the arts, such as by mechanical or laser cutting a finished sheet or in the sheet manufacturing process by molding or casting techniques. FIG. 3B illustrates a case in which intermediate sheets 312, 316 are actually the same design rotated and flipped in two different orientations. However the intermediate sheets 312,

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316 can be patterned with different designs as well, depending on the specific requirements for the exchanger.

[0024] In this example, heat/mass exchanger 300 includes integrated inlet/outlet manifolds 328, 332 formed in corresponding respective ones of first and second intermediate sheets 312, 316. This example also includes a pair of inlet/outlet ports 336, 340 in fluid communication with corresponding respective ones of integrated inlet/outlet manifolds 328, 332 for carrying a working liquid (not shown) to and from the respective inlet/outlet manifolds. Inlet/outlet ports 336, 340 are roughly positioned in the diagonal corners of the two overlain intermediate sheets 312, 316 in small tab-like extensions 344, 348 of the otherwise rectangular sheets, but still located over their respective inlet/outlet manifolds 328, 332. As those skilled in the art will readily appreciate, manifolds 328, 332 and ports 336, 340 are conveniently characterized as "inlet/outlet" simply because whether each manifold and port is an inlet-type or outlet-type depends only on the direction the working liquid flows through heat/mass exchanger 300. This convention is also used relative to heat/mass exchanger 400 of FIG. 4.

[0025] In the example shown in FIG. 3A, first and second outer sheets 304, 308 each include corresponding respective openings 304A-B, 308A-B provided to receive therethrough corresponding ones of inlet/outlet fluid ports 336, 340 and inlet/outlet manifolds 328, 332 formed in intermediate sheets 312, 316. It is noted that in alternative embodiments, any one or more of openings 304A-B, 308A-B need not be provided. For example, in some other embodiments, first outer sheet 304 may be continuous over inlet/outlet manifold 328 and include an embossment (not shown) that conformally receives therein that inlet/outlet manifold, and likewise, second outer sheet may be continuous over inlet/outlet manifold 332 and include an embossment (not shown) that conformally receives therein that inlet/outlet manifold. In yet other embodiments, the inlet/outlet manifolds may be defined by corresponding respective embossments or like structures (similar to manifolds 328, 332) formed in corresponding respective ones of the first and second outer sheets rather than in the first and second intermediate sheets.

[0026] In this example, both first and second outer sheets 304, 308 are constructed from materials that permit working fluid mass, in either liquid or vapor form, to migrate to the respective first and second outer faces 352, 356 from the flow matrix, such as ePTFE or urethane. The construction of the various layers (i.e., layers 124, 128, 132 of diagrammatic heat/mass exchanger 100 of FIG. 1) from thin flexible sheets as done in heat/mass exchanger 300 of FIGS. 3A-C can

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create concerns with ballooning of the heat/mass exchanger in the region of the flow matrix under pressure of the flowing working liquid. This is overcome by implementing any one or more of various techniques for joining, adhering, or otherwise sealingly securing sheets 304, 308, 312, 316 at points of contact with adjacent sheets, for example, adhesive bonding, thermal bonding, sonic welding, or other similar technologies appropriate for the particular materials of construction used. The same or similar techniques may be used to fluidly seal the various sheets 304, 308, 312, 316 of heat/mass exchanger 300 to one another around the perimeter of the flow matrix so as to laterally define the flow matrix.

[0027] FIG. 4 illustrates another exemplary heat/mass exchanger 400 having the basic configuration of heat/mass exchanger 100 of FIG. 1 and executed with a four-sheet construction in a manner similar to heat/mass exchanger 300 of FIGS. 3A-C. In particular and relating heat/mass exchanger 400 to heat/mass exchanger 100 of FIG. 1, heat/mass exchanger 400 includes first and second outer sheets 404, 408 that correspond, respectively, to first and second outer layers 124, 128 of FIG. 1 and first and second intermediate sheets 412, 416 that together correspond to intermediate layer 132 of FIG. 1. Flow channel 112 of FIG. 1 is generally formed from the two intermediate sheets 412, 416, each of which has diagonal cutouts 420 and that are overlain with one another in a manner to cause the cutouts portions of the sheets to intersect in a crisscross pattern.

[0028] In contrast to heat/mass exchanger 300 of FIG. 3A-C, each fluid inlet/outlet port 424 of heat/mass exchanger 400 of FIG. 4 (only one visible in FIG. 4) is centrally located relative to a corresponding one of a pair of inlet/outlet flow manifolds 428, 432. Both fluid inlet/outlet ports 424 in this example are provided in second outer sheet 404. First outer sheet 408 includes a pair of recesses 436, 440 that accommodate corresponding respective inlet/outlet flow manifolds 428, 432, which are generally formed in first intermediate sheet 412. Depending on the materials of construction, recesses 436, 440 may be specifically formed, for example, by molding or embossing, or, if first outer sheet 408 is essentially flat and sufficiently flexible, may simply be an artifact of laying the first outer sheet over inlet/outlet manifolds 428, 432 that are relatively rigidly formed in first intermediate sheet 412. Second interior sheet 416 includes a pair of openings 444 (only one visible in FIG. 4) for allowing fluid communication between inlet/outlet flow manifolds 428, 432 and corresponding respective ones of fluid inlet/outlet ports 424 (again, only one is visible in FIG. 4). In this example, each of the four corners of heat/mass exchanger 400 is provided with an attachment point 448, 452, 456, 460 for securing the heat/mass exchanger to some other structure. FIG. 5 illustrates one example of utilization of attachment points 448, 452, 456, 460 in which

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heat/mass exchanger 400 of FIG. 4 is secured to a hydration pack 500 via the attachment points to form an integrated personal hydration system 504. The materials of sheets 404, 408, 412, 416 may be the same as the materials described above for layers 124, 128, 132 of heat/mass exchanger 100 of FIG. 1.

[0029] Referring now to FIG. 5, hydration pack 500 provides a reservoir for potable water for drinking by a user (not shown) of personal hydration system 504. Hydration pack 500 can be any conventional or custom pack adapted for supporting or otherwise integrating heat/mass exchanger 400 and for fluidly communicating the potable water to and from the heat/mass exchanger. Hydration system 504 shown includes a handle 508 for hand-carrying and -wielding, as well as shoulder straps 512 (one visible in FIG. 5) for allowing the system to be carried on the back of a wearer. In this example, heat/mass exchanger 400 is secured to hydration pack 500 with a set of four straps 516 and four cinch buckles 520 (only three of each shown) secured to attachment points 448, 452, 456, 460 (see FIG. 4). Manifolds 428, 432 of FIG. 4 and the corresponding respective embossments 436, 440 have corrugated features to afford sufficient flexibility along the width of the heat/mass exchanger 400 and prevent the manifolds 428, 432 from being closed off when exchanger 400 is bent in the "width" direction. It is noted that the curvature of heat/mass exchanger 400 of this example is due to its highly flexible nature, rather than being molded to this shape (although in alternative embodiments, the latter could be done, if desired). Regarding the structure of heat/mass exchanger 400, visible in FIG. 5 is a flow field region 524 containing the plurality of interconnecting flow channels of the flow matrix (corresponding to flow channel 112 of FIG. 1) formed by the oppositely angled cutouts 420 of first and second intermediate sheets 412, 416 of FIG. 4. Flow field region 524 (FIG. 5) is bounded by a boundary margin 528 where all sheets 404, 408, 412, 416 (FIG. 4) are fluidly sealed to one another to fluidly seal the flow matrix along the boundary margin.

[0030] Referring again to FIG. 5, heat/mass exchanger 400 is fluidly coupled to hydration pack 500 by a pair of flexible tubes (only an upper tube 532 is shown) connected to corresponding respective ones of inlet/outlet ports 424 (see FIG. 4). In the setup shown, one of the tubes (not shown) fluidly connects the lower (relative to FIG. 5) inlet/outlet port 424 of heat/mass exchanger 400 to the bottom of the reservoir inside hydration pack 500, and upper tube 532 is fluidly connected to the upper inlet/outlet port 424. A mouthpiece 536, which can be a conventional hydration-pack-type mouthpiece, is coupled to upper tube 532. During use of personal hydration system 504, a user, using mouthpiece 536, draws water from hydration pack 500 through the lower

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tube (not shown) and into and through heat/mass exchanger 400, where the water is cooled via the thermal processes and mechanisms described above relative to graph 200 of FIG. 2, but without the additional cooling enhanced by the fan. The water then exits heat/mass exchanger 400 cooler than it entered the heat/mass exchanger from hydration pack 500, providing the user with water of a more refreshing temperature. Those skilled in the art will readily appreciate that many variations of personal hydration and other liquid systems could be made using the broad underlying principles disclosed herein.

[0031] The volume of the flow channel in flow field region 524 may be any suitable size. For example, if compactness of heat/mass exchanger 400 is important, this volume may be limited to a single drink or sip by the user. In this example, cooling of the water in heat/mass exchanger 400 occurs primarily between drinks by the user while the water is stagnant. This single-drink volume of heat/mass exchanger 400 is best suited for occasional hydration since each time the user takes a drink, the entire volume of the heat/mass exchanger is refilled with warm uncooled water from hydration pack 500. In other embodiments, the liquid volume of the flow channel may be greater than the volume of one drink. This way, a greater volume of cooled water is available to the user at one time.

[0032] As seen in FIGS. 3A-C and 4, both heat/mass exchangers 300, 400 shown there have flow matrices formed by two intermediate layers 312, 316, 412, 416 having corresponding respective channels 320, 324 or cutouts 420 extending along differing diagonal directions. As those skilled in the art will appreciate, suitable flow matrices for a heat/mass exchanger made in accordance with principles and concepts disclosed herein may have any one or more of a variety of configurations and executions. FIGS. 6A through 9 illustrate a few alternative configurations and executions of flow matrices to illustrate this variety.

[0033] Referring now to FIGS. 6A-B, these figures illustrate a flow matrix structure 600 executed in a two-sheet construction consisting of a first sheet 604 and a second sheet 608 that each have corresponding respective set 612, 616 of depressions 620 therein that together define the serpentine flow channels 624 within the flow matrix. Flow matrix structure 600 has the similarity relative to the flow matrices of heat/mass exchangers 300, 400 of FIGS. 3A-C and 4, respectively, of comprising flow channels 624 formed from elongate spaces that cross one another. A difference, however, is that flow channels 624 of flow matrix structure 600 are executed with just two sheets 604, 608 as opposed to the four sheets 304, 308, 312, 316 or 404, 408, 412, 416 of heat/mass

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exchangers 300, 400, respectively. In the present context, a "depression" is defined as an internal space (relative to flow matrix structure 600) that extends away from a plane 628 that contains all of the joints where first and second sheets 604, 608 contact one another or are joined to one another. Depending on the nature of the materials of first and second sheets 604, 608, which may be made of any of the materials described above relative to layers 124, 128 of heat/mass exchanger 100 of FIG. 1, depressions 620 may be, for example, molded into the sheets or formed by the ballooning of the sheets under positive internal pressure within flow channels 624 (in such an embodiment the sheets must be joined to one another at locations other than at the depressions). As best seen in FIG. 6B, the outer faces 632, 636 of first and second sheets 604, 608 may follow the contours of depressions 620 or, alternatively, may be planar, as would be the case when depressions are provided such that the thickness of each sheet at locations other than the depressions is greater than the thickness of that sheet at the depression.

[0034] The views of FIGS. 6A-B show only the relative positions of depressions 620 and, for the sake of clarity, intentionally omit other features of an entire heat/mass exchanger that includes flow matrix structure 600. Those skilled in the art would readily appreciate how to incorporate such other features as desired upon reviewing the entire present disclosure. Explicitly comparing the structure of flow matrix structure 600 of FIGS. 6A-B to the structure of diagrammatic heat/mass exchanger 100 of FIG. 1, it is seen that the portions of first and second sheets 604, 608 that form flow channels 620 and are exposed to the ambient environment would make up first and second outer layers 124, 128 of heat/mass exchanger 100 and that the space within flow channels 620 themselves would make up intermediate layer 132 of the heat/mass exchanger. As discussed above relative to other examples, it should be clear that one, the other, or both, of first and second sheets 604, 608, or portions thereof, will be permeable so as to provide flow matrix structure 600 with mass-exchange ability.

[0035] FIGS. 7A-B illustrate another flow matrix structure 700 that is made of just two sheets (first and second sheets 704, 708) in a manner similar to flow matrix structure 600 of FIGS. 6A-B. Relating flow matrix structure 700 of FIGS. 7A-B to flow matrix structure 600 of FIGS. 6A-B, flow matrix structure 700 may be considered to have "reverse" depressions 712 in each of first and second sheets 704, 708. That is, depressions 712 extend inward relative to flow matrix structure 700, whereas depressions 620 of FIGS. 6A-B extend outward relative to flow matrix structure 600. In the embodiment shown in FIGS. 7A-B, depressions 712 in first sheet 704 are formed at locations different from the depressions formed in second sheet 708, but with the same height, so that when

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the first and second sheets are fastened together (at the depressions), the depressions on one sheet are staggered relative to the depressions on the other sheet. Consequently, the "height" of the flow channels 716 formed among depressions 712 is equal to the height of the depressions. In alternative embodiments, the depressions may be formed in only one of sheets 704, 708 and the other sheet remains planar. In yet other embodiments, the depressions may be formed in both sheets but located so that when the two sheets are put together, the depressions of one sheet contact the depressions of the other sheet. In such embodiments, the "height" of the flow channels formed amongst the depressions would be the sum of the heights of each pair of contacting depressions.

[0036] First and second sheets 704, 708 may be made of any suitable material, such as any one or more of the non-permeable and permeable materials mentioned above relative to heat/mass exchangers 100, 300 of FIGS. 1 and 3A-C, respectively. One, the other, or both, of first and second sheets 704, 708 will be permeable so as to make flow matrix structure 700 provide the mass exchange functionality described above relative to, for example, heat/mass exchanger 100. The spacing, size, and height of depressions 712 may be determined as a function of one or more of a number of variables, such as the pressure of the liquid that will flow within flow channels 716, the amount of ballooning tolerable between depressions, and the physical properties of first and second sheets 704, 708, among others. First and second sheets 704, 708 may be fastened at depressions 712 using any fastening technique suitable for the materials chosen for the sheets, such as any one or more of the fastening techniques mentioned above relative to heat/mass exchanger 300 of FIGS. 3A- C. The structure of flow matrix structure 700 corresponds to the three-layer (or zone) construction of heat/mass exchanger 100 of FIG. 1 in essentially the same manner as described above relative to flow matrix structure 600 of FIGS. 6A-B.

[0037] FIG. 8 illustrates another flow matrix structure 800 that could be utilized in a heat/mass exchanger made in accordance with concepts disclosed herein, such as heat/mass exchanger 100 of FIG. 1. Flow matrix structure 800 corresponds to flow channel 112 in FIG. 1 and takes the place of the inner two layers (312, 316 or 412, 416) of the four-layer exchangers 300 and 400 assemblies described above. In this example, flow matrix structure 800 is largely defined by overlaying with one another two sheets 804, 808 each containing a two-dimensional array 812, 816 of holes 820 (here full thickness circular openings). Holes 820 in each array 812, 816 are arranged so that when sheets 804, 808 are overlain, portions of the holes in one sheet overlap with the holes in the other sheet. In a finished heat/mass exchanger, flow matrix structure 800 shown would be sandwiched between first and second outer layers (not shown, but corresponding to first and second outer layers

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124, 128 of heat/mass exchanger 100 of FIG. 1). These outer layers would contain a working liquid that flows through the holes in flow matrix 800. The overlapping portions of the holes allow the liquid to flow through the flow matrix by defining continuous flow channels 824 through the final structure.

[0038] Sheets 804, 808 may be made of any suitable material(s) for the design contemplated and may be secured to one another by any suitable technique compatible with the materials used. The sizing and spacing of holes 820 and locations of connections between sheets 804, 808 may be determined as a function of a number of variables, such as the pressure of the liquid that will flow within flow channels 824, the amount of ballooning tolerable in the outer layers at the depressions, and the physical properties of the outer layers, among others. The basic structure of flow matrix structure 800 lends itself to many variations. For example, the shapes of holes 820 may be other than circular, such as oval, rectangular, and octagonal, one or both of single sheets 804, 808 may be replaced with multiple sheets. Similarly, the holes may be replaced by depressions that do not extend all the way through the respective sheets. In this last case, the resulting flow matrix structure could be executed in as few as two sheets, since the material of each sheet remaining at each depression would function as one or the other of first and second outer layers 124, 128 of heat/mass exchanger 100 of FIG. 1.

[0039] FIG. 9 illustrates a flow matrix structure 900 in which the flow matrix 904 (generically denoted by crosshatching) is provided with a set of flow baffles 908A-D arranged relative to one another to direct the flow within the flow matrix in a predetermined manner, here along a generally serpentine path 912. Relating flow matrix structure 900 to heat/mass exchanger 100 of FIG. 1, it is noted that first and second outer layers 124, 128 that would bound flow matrix 904 are omitted from FIG. 9 for clarity and simplicity. In FIG. 9, flow baffles 908A-D are formed by bonding all layers together at the locations of the baffles. Those skilled in the art will readily appreciate that flow matrix 904 may be made in any suitable manner, such as any one or more of the manners illustrated in FIGS. 3A-C, 4 and 6A-8. Those skilled in the art will also appreciate that more or fewer than four baffles may be provided, that the baffles need not be straight (e.g., they could be curved, segmented, etc.), and that the baffles may be used to force the flow along a path that is other than the simple back-and- forth serpentine path shown. It will also be understood that flow matrix structure 900 need not be rectangular in shape as shown, but rather may have any shape desirable to conform to particular design constraints. This is also true of other flow matrix structures and entire heat/mass

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exchangers disclosed herein, such as flow matrix structures 600, 700, 800 of FIGS. 6A-8 and heat/mass exchangers 300, 400 of FIGS. 3A-5.

[0040] Under the harsh and mobile conditions envisioned for many of the applications of a heat/mass exchanger made in accordance with the present disclosure, such heat/mass exchanger may be a component of a modularized unit which can be easily installed or replaced in the application it services. For example and referring to FIGS. 10-12, these figures illustrate a liquid-based personal cooling system 1000 that includes at least one liquid-cooled garment 1004 and a cooling unit 1008 that together form a liquid/thermal circuit in which heat gained by the garment from a wearer (not shown) of the garment is conveyed by a working liquid (e.g., water) to the cooling unit, where it is given up to the environment. Garment 1004 may be any type of garment, such as a vest, portion of a garment, or other wearable device, such as a helmet cover and lining, containing at least one flow channel for conducting the liquid through the garment and absorbing heat from the wearer. Liquid- cooled garments suitable for use as garment 1004 are generally known in the art and, therefore, need not be described in any more detail herein. The heated liquid from garment 1004 is conveyed from the garment to cooling unit 1008, via one or more feed conduits 1012, where it is cooled by a heat/mass transfer process similar to the heat/mass transfer process described above relative to FIGS. 1 and 2. After this cooling, the cooled liquid is returned to garment 1004 via one or more return conduits 1016 so that it can again be used to absorb heat from the wearer of the garment.

[0041] As best seen in FIG. 11, the interior of cooling unit 1008 contains one or more heat/mass exchanger assemblies 1100, a liquid reservoir 1104, a liquid circulation pump 1108, air circulation fans 1112, and a power supply, here rechargeable batteries 1116. An electrical charge port 1120 is provided for recharging batteries 1116 when needed. Cooling unit 1008 also includes various conduits 1124, 1128, 1132 and fittings 1136, 1140 for conveying the working liquid from component to component and connecting the cooling unit to garment 1004 (FIG. 10). During use, circulation pump 1108 draws the heated working fluid from garment 1004 (FIG. 10) and forces fluid through heat/mass exchanger assembly 1100, where the working liquid is cooled, and then back to the garment to complete the thermal loop. At the same time, air circulation fans 1112 draw ambient air into the interior of cooling unit 1008 via an air inlet 1020 (FIG. 10) and across heat/mass exchanger assembly 1100 before exhausting the air back to the environment via an exhaust outlet 1024 (FIG. 10). The air moving across heat/mass exchanger assembly 1100 enhances evaporation of the working liquid from the outer surface(s) of the heat/mass exchanger assembly, and may aid in removing convective heat from cooling unit 1008 (if the ambient temperature is lower than the

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cooling fluid's temperature). Liquid reservoir 1104 stores a makeup supply of the working liquid, for example, water, to make up for the liquid lost to evaporation through the mass-exchange cooling process.

[0042] Referring to FIG. 12, in this example heat/mass exchanger assembly 1100 includes a plurality of parallel, spaced heat/mass exchangers 1200 fluidly connected at opposite ends to common inlet and outlet manifolds 1204, 1208. Each heat/mass exchanger 1200 may be, for example, a mass-transfer-enabled heat exchanger having a suitable combination of the features described above in connection with FIGS. 1-9. Parallel heat/mass exchangers 1200 are held in spaced relation from one another via three multi-slot supports 1212 spaced from one another along the lengths of the heat/mass exchangers. Providing multiple heat/mass exchangers 1200 in this manner increases the surface area of heat/mass exchanger assembly 1100 to increase its heat-transfer ability not only by increasing the surface area available for heat transfer and evaporation, but also by increasing the flow capacity of the heat/mass exchanger assembly. In other embodiments, such increases in surface area per unit volume of a region occupied by a heat/mass exchanger assembly can be achieved in other ways, such as by pleating a single sheet-like heat/mass exchanger by creating a plurality of alternating opposite direction folds or by rolling a large sheet- like heat/mass exchanger with suitable spacers to provide a spirally configured heat/mass exchanger assembly, among others.

[0043] The variety of useable materials of construction and variety of methods of bonding these materials together create many possible embodiments of a heat/mass exchanger assembly made in accordance with the present disclosure that may have various configurations to meet different design and/or geometric requirements. In this connection, FIG. 13 illustrates a heat/mass exchanger assembly 1300 that utilizes a stack 1304 of, in this case, substantially annular heat/mass exchangers 1308 and a motorized convection fan 1312 to actively draw air over the surfaces of the heat/mass exchangers to facilitate cooling. Each heat/mass exchanger 1308 may be, for example, a mass-transfer-enabled heat exchanger having an appropriate set of the features described above in connection with FIGS. 1-9. The multiple heat/mass exchangers 1308 may be considered to be stacked with one another along a central stacking axis 1316, though immediately adjacent ones of the heat/mass exchangers are spaced from one another so that air drawn by fan 1312 is drawn across the expansive faces of the heat/mass exchangers as indicated by arrows 1320. Since heat/mass exchangers 1308 are substantially annular in shape, the inner peripheries 1324 of the heat/mass exchangers define substantially circular openings 1328.

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[0044] In one embodiment, the heat/mass exchangers are fluidly connected in a parallel flow configuration. In this embodiment, an inlet port 1332 provides a working liquid, for example, water, to all heat/mass exchangers 1308 via an inlet header, which in this embodiment is formed by the inlets of the individual heat/mass exchangers. An outlet header, which in this embodiment is formed by the outlets of the individual heat/mass exchangers 1308, collects the working liquid from the heat/mass exchangers that has flowed through heat/mass exchanger assembly 1300 as indicated by arrows 1336 and communicates it to an outlet port 1340. In another embodiment, the heat/mass exchangers 1308 are fluidly connected in a series flow configuration. In this case, outlet port 1340 would connect with bottom-most heat/mass exchanger, on the side of stack 1304 that is opposite from inlet port 1332 (and not visible in FIG. 13). Other embodiments may encompass one or more heat/mass exchanger units connected and/or formed in helical, cylindrical, or other useful shapes; pleated or unpleated; have heat/mass exchanger surfaces having variable orientation to convective air flow or different orientation than those shown; or may be operated with steady or intermittent flow of working fluid.

[0045] As will be understood by those skilled in the art, in a complete semi-closed system inlet and outlet ports 1332, 1340 would be connected, for example, to a liquid circulating loop that is coupled to a heat source desired to be cooled. An example of a semi-closed system is the personal cooling system 1000 of FIGS. 10-12. In a complete open system, such as the personal hydration system 504 of FIG. 5, inlet port 1332 would be connected to a reservoir of liquid desired to be cooled and outlet port 1340 would provide the cooled liquid to a user of the cooled liquid. Many more mass/heat exchangers/assemblies and open and closed systems are possible using the broad underlying concepts of the present disclosure.

[0046] Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the spirit and scope of the present invention.

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