WATER-VAPE SEPARATOR PLATE ARRANGEMENT AND METHOD FOR MAKING A WATER-VAPE TRANSFER ARRANGEMENT

Abstract

Water vapor separator plate arrangement (140), comprising: a pair of wet-side separator plates (150), each of which defines a wet-side flow channel area (54) therein; a pair of water vapor transfer membranes (170) arranged on respective surfaces of the pair of wet-side separator plates (150), such that a generally flat, dry-side flow channel region (164) is formed between them; and at least one spacer element (155) positioned between the pair of water vapor transfer membranes (170) such that the dry-side flow channel region, which has a thickness defined by the at least one spacer element (155), is formed; characterized in that several discrete supports (151, 153, 157) are positioned within the dry-side flow channel area (164) which is defined by the at least one spacer element (155); wherein the respective support (151, 153, 157) is a point (151) consisting of an adhesive material that hardens after application or a pressure-sensitive adhesive material with a self-adhesive backing.

Description

BACKGROUND OF THE INVENTION

[0001] This invention relates generally to a manner of improving the transfer of water vapor produced by a fuel cell, and more particularly to a water vapor transfer (WVT) separator plate assembly according to the preamble of claim 1 and a method of making such an assembly according to the preamble of claim 3, as of the type substantially known from US 8 091 868 B2.

[0002] Further state of the art can be found in US 2009 / 0 092 863 A1.

[0003] In many fuel cell systems, hydrogen or a hydrogen-rich gas is delivered to the anode side of a fuel cell through a flow field, while oxygen (such as atmospheric oxygen) is delivered to the cathode side of the fuel cell through a separate flow field. Typically, a suitable catalyst (e.g., platinum) is deposited as a layer on a porous diffusion medium, typically made of carbon cloth or paper, so that it exhibits elasticity, electrical conductivity, and gas permeability. The catalyzed diffusion medium is used to facilitate hydrogen oxidation at the anode side and oxygen reduction at the cathode side.An electric current generated by the decomposition of hydrogen at the anode is passed from the catalyzed portion of the diffusion media and through a separate circuit so that it can be the source of useful work, while the ionized hydrogen passes through the MEA to combine with the ionized oxygen at the cathode to form high-temperature water vapor as a reaction byproduct. In one form of fuel cell known as a proton exchange membrane or polymer electrolyte membrane (PEM) fuel cell, an electrolyte in the form of a perfluorinated sulfonic acid (PFSA) ionomer membrane (such as Nafion®) is sandwiched between the anode and cathode diffusion media. This layered structure is commonly referred to as a membrane electrode assembly (MEA) and forms a single fuel cell.Many such individual cells can be combined to form a fuel cell stack, thereby increasing its power output.

[0004] Fuel cells, especially PEM fuel cells, require balanced water levels to ensure proper operation. For example, it is important to avoid having too much water in the fuel cell, which can lead to flooding or subsequent blockage of the reactant flow field channels, thereby impeding cell operation. On the other hand, under-humidification limits the electrical conductivity of the membrane and can lead to premature cell failure. What makes maintaining a balanced water level even more difficult is that many competing reactions take place within a fuel cell, simultaneously increasing and decreasing local and overall hydration levels.

[0005] One method to ensure appropriate hydration levels throughout the fuel cell involves humidifying one or both reactants before they enter the fuel cell. For example, the water produced at the cathode can be used with a suitable humidification device to reduce the likelihood of dehydration of the anode or the PFSA ionomer membrane. An example of such a humidification device is a WVT unit (also called a membrane humidifier), which removes moisture from a humid fuel cell flow path (also called a flow channel) and introduces it into a feed path used to transport a low-humidity reactant. This is generally accomplished by using a WVT membrane sandwiched between adjacent high-humidity and low-humidity fluids.The membrane allows water vapor to pass through it from the higher humidity fluid to the lower humidity fluid, while preventing the undesirable direct passage of inlet gases from the low humidity fluid to the outlet containing the high humidity fluid without first passing through the fuel cell. In one construction, this membrane may be attached to a diffusion media layer (also referred to as a gas diffusion media (GDM)), which is generally similar (except for the catalyst layer) to the diffusion layer of the MEA discussed above. Such a combination of membrane and diffusion media layer may be referred to as a separator, a separator plate, or a membrane humidifier assembly. Many such separator plates may be stacked together so that the alternating layers facilitate the respective passages of the dry and wet fluids.In one form, a WVT unit consists of alternating layers of wet-side separator plates (also called wet-side plates) and dry-side separator plates (also called dry-side plates).

[0006] It is known to manufacture a WVT separator assembly consisting of plastic plates with integrated flow channels, with the gas diffusion and membrane layers attached to the plastic plate using a pressure-sensitive adhesive (PSA). Such a procedure is time-consuming and expensive to manufacture, repair, or replace. Furthermore, the use of a plastic plate increases the overall dimensions of the separator plate.

[0007] An exemplary membrane humidifier for a fuel cell system that does not include a plastic plate is disclosed in US 2009 / 0 092 863 A1 by Skala, owned by the assignee of the present invention. The apparatus presented in this application describes a membrane humidifier assembly for a WVT unit having upper and lower layers formed from a diffusion media, which in turn is formed from a glass fiber impregnated with an uncured resin. An array of substantially planar, elongated ribbons is disposed between the upper and lower diffusion media layers to provide reinforcement to the upper and lower layers and to maintain separation between them.While the Skala system eliminates many of the shortcomings of previous WVT separator plate designs, it would be desirable to further reduce the overall size, weight, and complexity of a WVT unit using a stack of separator plate assemblies.

[0008] The invention is based on the task of meeting this requirement. SUMMARY OF THE INVENTION

[0009] This object is achieved with a water vapor separator plate arrangement having the features of claim 1 and with a method having the features of claim 3.

[0010] According to one aspect of the present invention, a separator plate assembly can be made thinner, lighter, and simpler to achieve efficient transfer of water vapor between adjacent flow fields in a WVT device to provide humidification of the dry WVT side. The assembly can include a pair of wet-side separators (or separator plates) spaced apart from each other. A pair of WVT membranes is disposed on or adjacent the outer surfaces of the pair of wet-side separators such that the membranes face each other to define a dry-side flow channel between them. Spacer elements positioned between the facing surfaces of the pair of WVT membranes define the thickness of a dry-side region between adjacent wet-side separator plates.With such a design, the channel formed in place of the conventional dry-side plate has a thickness substantially defined by the spacer elements rather than the conventional fiber and additional diffusion media. Thus, even if additional support structure is present in the dry-side flow channel, they do not contribute to an increase in the thickness of the dry-side flow channel beyond that created by the spacer elements. Furthermore, the presence of the wet-side WVT membranes defining the opposing upper and lower (or, depending on the fuel cell orientation, side-by-side) surfaces of the dry-side flow channel means that redundant membrane structure is absent or eliminated, further contributing to fuel cell thickness and parts count.In a preferred form, the spacing elements may be formed in the form of strips arranged along opposite edges along the direction of reactant flow.

[0011] According to another aspect of the present invention, a method for manufacturing the various plates of such a separator plate assembly can be used to fabricate simpler, lighter, and more cost-effective WVT units. The method includes providing a pair of wet-side separators having first and second surfaces, applying a WVT membrane to the first surface of the pair of wet-side separators, applying edge strips positioned on opposite edges of a surface of at least one of the WVT membranes, and sandwiching the pair of wet-side separators to the facing WVT membranes. In this manner, the edge strips positioned between the pair of WVT membranes define a substantial entirety of the thickness of a flow channel formed between the pair of water vapor transfer membranes.

[0012] As explained in connection with at least the above aspects of the present invention, a separator plate assembly can be fabricated without the traditional dry-side separator plate, which is replaced by edge spacers as well as intermittent (i.e., discrete) support locations across the plate surface. The configuration resembles multiple wet-side plates stacked such that between each adjacent stacked plate or layer there is a thin, dry-side flow region formed by the edge spacers and the discrete supports between adjacent wet-side plates. Membranes located between the wet-side and dry-side flow fields allow the passage of moisture from the former to the latter.

[0013] The spacers and discrete supports, combined with the relatively balanced pressure on opposite sides of the wet-side separators (e.g., due to the relatively uniform incoming dry-side air pressure from the cathode feed compressor), are sufficient to prevent flutter and similar vibration phenomena that might otherwise occur during operation of the WVT unit. Furthermore, the discrete supports ensure uniform spacing between the plates, resulting in a uniformly distributed dry-side mass flow throughout the entire WVT stack.

[0014] The WVT assembly can be manufactured using a process that eliminates plate stacking operations while producing a finished product, if desired. A roll-based process can be used, facilitating continuous formation of the wet-side separator plates, with a stack consisting of a continuous roll of material that is, for example, creased and folded into a Z-shape. In one form, the elimination of the dry-side plates results in a significant reduction in the height of the dry-side flow channels compared to a conventional "paper and string" plate configuration or a plastic plate configuration.The present inventors have found that a reduction of up to about 67% of the height of the dry-side flow channel in the gap between successive wet-side plates, or up to about 75% for the plastic plate configuration, can be achieved by replacing the dry-side "paper and string" plate with the procedure of the present invention.

[0015] The WVT assembly with individually supported wet-side plates may have one or more of the following advantages. In some embodiments, the WVT assembly may exhibit improved water transfer rate performance, with increases of about 5% at low flows and about 25% at high flows, for example, having been demonstrated in prototype WVT assemblies. This allows for a reduction in the required active membrane area and a concomitant reduction in the number of separator assemblies. Thus, the WVT assembly may be more cost-effective as a result of (1) eliminating the active membrane area (and the associated number of plates) and / or (2) eliminating the dry-side separator assembly components and / or (3) stacking the WVT core as part of the separator assembly manufacturing process. The WVT assembly may exhibit improved water transfer rate performance due to the elimination of the dry-side separator assembly components (e.g.,3.4 grams per dry-side separator assembly, which could be about 350 grams per core (depending on the number of wet- and dry-side assemblies in the WVT assembly) or about 13.5% of 2.6 kilograms target. The WVT assembly could have a lower parts count due to the elimination of dry-side assembly parts (e.g., approximately ten thousand parts per core for dry-side plates utilizing a two-piece GDM with 87 cords). The WVT assembly can have a reduced dry-side channel height (e.g., approximately 400 micrometers reduction per cell or 40 millimeters on a WVT core containing one hundred dry-side flow channels, or, if desired, a corresponding reduction in footprint instead). The WVT assembly can have reduced dry-side flow channel height variation due to the elimination of the two pieces of GDM previously contained in the dry-side plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The following detailed description of specific embodiments is best understood when read in conjunction with the following drawings, wherein like structures are designated by like reference numerals, and in which: Fig. 1 is a schematic diagram showing portions of a fuel cell system with a representative WVT unit arrangement relative to a fuel cell stack; Fig. Figure 2 is an exploded view of an alternating stack of wet-side and dry-side separator plates for the prior art WVT; Fig. 3 an edge view of a separator plate assembly section with three plates of the WVT of Fig. 2 shows; Fig. 4 shows an edge view taken along the dry-side flow channels of a comparable portion of a separator plate assembly comprised of wet-side plates according to one aspect of the present invention; Fig. 5 shows different possible single support configurations for a wet-side plate; Fig. 6 shows a hot pressing process for producing the individually supported wet-side plate of the present invention; Fig. Figure 7 shows a simplified illustration of a roll-based process for manufacturing the individually supported wet-side plate of the present invention; and Fig. 8A to 8H various steps for forming the individually supported WVT separator plate assemblies from the rolling process of Fig. Show 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] First referring to Fig. 1 shows a fuel cell system 1 consisting of a fuel cell stack 10 with several individual fuel cells, each having an anode 12 and a cathode 14. Various flow paths are used to transport reactants and their byproducts to and from the respective anode 12 and cathode 14. A WVT unit 30 is fluidly coupled to corresponding portions of the flow path 20 to facilitate the exchange of moisture between the outlet 24 and the inlet 22. As shown particularly for the cathode 14, dry air from a compressor (not shown) is supplied through the inlet 22 over a range of pressures and low humidity (typically around 0%) into the WVT unit 30. Likewise, the exhaust gas discharged from the cathode 14 flows through the outlet 24 to the WVT unit 30.The cathode discharge 24 is at a lower pressure and higher humidity than the air entering the WVT unit 30 on the inlet 22 side. Within the WVT unit 30 is a core consisting of many wet-side and dry-side plates stacked in an alternating arrangement such that (except for the outermost plates) each plate is sandwiched between plates of the opposite flow path.

[0018] Next, referring to the Fig. 2 and Fig. 3, details of known separator plates are shown. The core 40 of the WVT unit 30 consists of a stack of plates 50, 60, one used as a wet-side plate and the other used as a dry-side plate. Each plate 50 and 60 includes generally planar upper and lower layers 52 and 62, respectively, made of GDM. The upper and lower layers 52 and 62 within each of the plates 50 and 60 are spaced apart to define flow channels 54 and 64, which facilitate the flow of the respective wet effluent 24 and feed 22 through the plate edges. In one form according to the prior art, the channels 54, 64 may be formed integrally as a part of the respective plate, while in another they may be formed separately with band-like (or cord-like) structures 66 (shown representatively inside the channel 64 of the plate 60) which are bonded with an adhesive 68 (e.g.a hot melt adhesive) to the respective diffusion media forming an adjacent upper or lower plate surface. Those skilled in the art will appreciate that a comparable cord and adhesive may be used in the plates 50, and that such cord-like structures 66 may define a substantially rectangular profile, a substantially cylindrical profile, or other well-known shape. Edge strips 55 and 65 (only the latter of which is shown here) are aligned with the flow channels 54 and 64 along their length. The edge strips 55, 65 help provide the spacing that defines the thickness of the channels 54 and 64; for example, the height of the wet-side channel 64 is defined by the thickness of either the edge strips 65 or the cord 66, while the additional thickness of the GDM 62 contributes to the overall thickness of the plate 60.

[0019] The WVT membrane 70 defines a water vapor permeable barrier between the facing GDM surfaces 52, 62 of the adjacent stacked plates 50 and 60. The WVT membranes 70 are made of a material suitable for permitting water transport from the wet-side flow path to the dry-side flow path while inhibiting the passage of inlet air, which would otherwise pass directly into the exhaust stream without first passing through the fuel cell cathode. As can be seen, a significant portion of the thickness of the plate 60 is defined by the thickness of the cord 66. In one example, a gap (defined as the thickness between the surrounding membranes 70 and consisting of the combined thickness of the cord 66 and the diffusion layers 62 immediately above and below the cord 66) is approximately 0.63 millimeters.The thickness of the plates 50 (and the accompanying gap) is also largely defined by the cord 66; however, they are less amenable to the removal of the channel-defining cord 66 or a similar structure because the plates 50 are subjected to higher stress due to the lower internal pressure than the dry side.

[0020] Next, referring to Fig. 4, a plate assembly 140 according to one aspect of the present invention forming a portion of a WVT core and including a plate 160 sandwiched between two plates 150 is shown. In the present context, the term "assembly" shall refer to two or more parts fixed, attached, or otherwise joined together by a manufacturing means such that a collection of parts so assembled forms a complete machine, structure, or unit of a machine. As such, the assembly 140 may comprise a single plate 150 and a single plate 160 sandwiched together as shown, as well as a larger layered or multi-layered stack of many alternating plates 150, 160 such that the assembly 140 defines part or all of the core of a WVT unit (e.g., the WVT unit 30 shown previously).The plates 150 include upper and lower diffusion media 152 defining a channel 154 therebetween. The diffusion media 152 may be formed from any conventional material, such as a glass fiber, a glass (or other) paper, a carbon fiber, or the like. Likewise, the WVT membrane 170 may be any conventional membrane, such as the aforementioned PFSA ionomer membrane for use in the MEA of a fuel cell, a hydrophilic polymer membrane, or a polymer composite membrane. Edge strips 155 (in . Fig. 5) help to define the generally coextensive flow path (ie, a flow channel) in a manner that is generally similar to that shown in Fig. 2 is similar.

[0021] In contrast to the Fig. 3, the plate 160 does not include a diffusion medium. A generally planar-shaped region forming a dry-side flow channel 164 is defined by membranes 170 attached to corresponding surfaces of the wet-side diffusion medium 152 of the plate 150, while the wet-side flow channel 154 (in Fig. 4 as extending between the left and right edges of the plates 150) runs along a generally perpendicular path to promote increased moisture exchange between the alternating plates 150, 160. The elimination of the diffusion medium from the plate 160, as well as the use of discrete supports as a way to avoid the use of the reinforcing cords discussed above, allows the assembly 140 to have a lower (i.e., thinner) profile. Such individual supports significantly reduce the profile of the assembly 140 over the prior art. Examples of such individual supports are shown in the Fig. 4 and Fig. 5 as points 151, protrusions 153, and threads 157, but according to the invention, the supports are / are formed as points 151. In one example, the height of the channel 164 (which coincides with the gap thickness) in the plate 160 is reduced from about 0.63 millimeters to about 0.22 millimeters, representing a reduction in thickness in the channel 164 of approximately 67% when individual supports are used. In the present context, an individual support is one that is either discontinuous (e.g., in the case of points 151) or, if continuous, causes such a large reduction in the channel thickness (such as that of the channel 164, as shown) that the overall profile of the assembly 140 is greatly reduced due to the minimal size of the support.This removal of the diffusion media and reinforcement cords from the dry-side plates is equivalent to a complete removal of the plates 160, with the only remaining structure being the spacer elements (shown in the form of edge strips 165) present to define the height in the aforementioned channel 174 to permit the flow of dry-side fluid therethrough. It has been determined that a continuous reinforcement structure is not required across the entire dry-side channel 164 because the pressure of the dry-side fluid introduced into the assembly by a compressor is sufficient to keep the channel 164 from collapsing.

[0022] In some embodiments, to avoid flutter, to maintain uniform plate spacing, or to avoid similar structural problems associated with the operation of a WVT unit including an assembly 140, individual supports may optionally be disposed in the channel 164 of the plates 160 to take the place of the now-absent cord or similar reinforcing structure that would otherwise be pressed against the opposite side of the WVT membranes 170. These individual supports are preferably formed on, or to contact, the membrane 170. With reference to Fig. Figure 5 shows a surface of a diffusion medium 152 for a plate 150 with the side comprising various shapes of individual supports to be placed against or on the membrane 170, wherein three different approaches may be used. In a first approach, a repeating pattern of hot-melt or cure-in-place (CIP) dots 151 is applied to the surface of the membrane 170. The dots 151 may be applied to the membrane 170 as part of a rolling process, which is explained in more detail below, or could be made of any material that can be dispensed in liquid or semi-liquid form and then cured. In one form, the dots 151 may be approximately 200 micrometers thick.

[0023] Contrary to the invention, offset, heat-formed protrusions 153 may be formed in the edge strip material along the edges of the plate 150, defining the flow path inlets and outlets; in one form, heated tools could be used to fabricate the protrusions 153; such protrusions 153 could be thermoformed into the edge strips 155 on the plate 150. The various shapes of individual supports also allow for a reduction in the gap between the cells while preventing airflow-induced flutter when the cords or similar separator devices are eliminated. Like the points 151, the edge protrusions 153 may be approximately 200 micrometers thick in one form.Those skilled in the art will appreciate that this 200 micrometer thickness of the dots 151 or edge protrusions 153 is considerably less than the approximately 0.50 to 0.60 millimeter thickness of conventional cords such as those shown and described above in connection with the prior art. Contrary to the invention, threads 157 may extend from an inlet edge of the plate 150 to an outlet edge. Contrary to the invention, when threads 157 are used as individual supports, their number and diameter (or similar thickness dimension) are limited with respect to those shown in the structure of FIG. Fig. 3. Such threads 157 can be incorporated during a stacking process, where they can be heat-embossed into position on the respective inlet and outlet edges using a hot-melt adhesive. These approaches can be used alone or in combination with one another to achieve the desired degree of individual reinforcement. In cases where the threads 157 are retained, they could (in one form) be individually attached to the plates 160 using an adhesive, while in another they would be in a woven form that can be placed between the plates 160 during the stacking process.The edge strips 155, which extend along the length of the plate 150 along its flow path dimension, may comprise a hot-melt or other adhesive applied thereto using a small dot (not shown) of pressure-sensitive adhesive (PSA) (e.g., during the aforementioned rolling process). Subsequent reactivation of the hot-melt adhesive may be used to achieve edge sealing.

[0024] Next, referring to Fig. 6 shows a simplified version of a hot press 200. In such an approach, the hot press 200 includes an upper tooling portion 210 and a lower tooling portion 220. The lower tooling portion 220 may be fabricated to fit within the space defined by a thread weaving support 230, which acts as a frame to hold the lower diffusion medium 152 in position while the spacer elements in the form of edge strips 155 and the aforementioned threads 157 from the third reinforcement approach discussed above are applied for attachment to the diffusion medium 152 by a hot melt adhesive or the like. In one form, the thread 157 may be made of polypropylene, glass, or a similar structural material, while the edge strip 155 may be made of polypropylene coated with a hot melt adhesive.Once all parts to be assembled are in position within the press 200, the upper tool portion 210 is brought against the lower tool portion 220 under considerable pressure and temperature to force the parts and adhesive to bond. Details related to the hot-press approach are explained in the aforementioned published application to Skala.

[0025] In one form, the plates 150 may be manufactured in a rolled process, with the membrane 170 attached to or otherwise adjacent to both sides of the plate 150 formed by the diffusion medium 152. Referring next to Fig. 7, a more automated rolling process 300 is shown using exemplary threads 315 (which may be the same as those shown in Fig. 5). As will be appreciated by those skilled in the art, an automated rolling process can be adapted to point 151 or other individual supports such as those shown in Fig. 5. Unlike the hot press 200 discussed above, the roll process 300 utilizes continuous production of the board 150 via a roll-based paper station 335 and membrane station 375. The configuration of the paper station 335 and membrane station 375 is such that one or a series of rolls can be used sequentially to achieve the desired degree of interlamination. Spools 310 of a thread 315 or similar reinforcement (which, as noted above, may be coated with an adhesive if desired) are fed from a spool stand through an alignment tool 320 so that they are introduced as a generally planar array of threads 315 between the layers of the wet-side diffusion media 152 fed from opposing rolls 300. The diffusion media 152 may be preheated prior to joining with the reinforcing threads 315, if desired.Suitable preheating methods include heated rollers and infrared means. The edge strip 165, fed from the roller 360, is inserted between the upper and lower diffusion media layers 152 along their lateral edges. As with the threads 315, the edge strip 165 may be coated with an adhesive, if desired. The composite layer of upper diffusion media 152 / thread 315 / edge strip 165 / lower diffusion media 152 is then consolidated by passing it through heated rollers 340 so that the adhesive (if present) cures it. The rollers 340 may be made of or treated with silicone, if desired, to facilitate the release of the upper and lower diffusion media 152 from their respective feed rollers once the diffusion media 152 has bonded to the thread 315 or the edge strip 165.

[0026] The hot-melt adhesive on the surface of the diffusion media 152 is reheated and used to bond the membrane 170 coming off the roll 370. If necessary, additional adhesive is applied at station 350 prior to a membrane station 375. An optional cooling station (not shown) may be included between the paper station 335 and the membrane station 375 to accelerate the curing process of the laminate. The membrane station 375 is configured in a generally similar manner to that of the paper station 335 in that it deposits a layer of the membrane 170 from the roll 370 onto the outer surfaces of the diffusion media 152 forming the laminate. Similarly, pressure rollers 380 force the membrane 170 onto the adhesive for secure assembly. An additional cooling station (not shown) may be included to more rapidly cure the adhesive, whether from the adhesive station 350 or elsewhere.Following these, a print head and cutting station (none of which are shown, the latter exemplified in the form of cutting rollers) may be used to cut the assembled laminate to a desired length. From here, the laminate may be punched into a separator plate shape at a punching station (not shown). The parts themselves may be die-cut using tooling, lasers, water jets, or the like. Additional steps may be employed, including stacking the various plates into a core or similar package. Likewise, a manifold station may be used on the line to apply plate-to-plate adhesive to the parts for in-line stacking after they have been cut to length.

[0027] With particular reference to the Fig. 8A to 8H, various handling and stacking approaches of a continuous roll 400 of a laminate may also be used. In one form, such handling includes scoring 405 ( Fig. 8B) and Z-shaped folds ( Fig. 8C to 8E) of the continuous layered composite 400; such an approach is roughly analogous to that used in rolls of lottery (or similar gaming) tickets. Edge strips 155, 165 could be added as explained above at the notches 405 (to create the dry flow field), while the roll 400 would be folded until the number of cells is reached and then cut to create a complete WVT core. This approach could significantly reduce the core part count; in an example of a WVT dimensioned for automotive applications, such an approach could reduce the part count by approximately 3500. Such an approach could also lead to the use of the aforementioned single filament adhesive, which in turn could result in an even more porous diffusion media 152. In particular, since the Z-folded stack 500 would now utilize a series of continuous filaments like those used in the process in Fig. 7, an intermittent hot melt adhesive application could be used instead of a continuous hot melt coated thread, thereby reducing the amount of hot melt impregnated diffusion medium 152, which in turn would reduce the transfer resistance in the diffusion medium 152 as it progresses along its production path.

[0028] A cutting station (not shown) could score both the top and bottom of the plate 150 of the roll 400 to create the wet stream flow path. Once enough pleats are arranged in the plate 150, an accordion-shaped series of pleats ( Fig. 8E to 8G). In addition to a conventional blade, other approaches could be used. In a special form, a laser tuned to an appropriate power level could be used.

[0029] As particularly in the Fig. 8F and Fig. 8G, some spacer elements or similar supports could be added to the scribed plate 150. In addition to providing the spacing required between adjacent cells when folded, these spacer elements (e.g., the previously mentioned dots 151, protrusions (or spikes) 153, and continuous threads 157 from above Fig. 5 as well as the edge strips 155) are useful in preventing flutter and similar problems. It is also believed, as explained above, that a certain spacing (e.g., about 200 micrometers) between the cells will be advantageous to allow the dry air to flow between adjacent, facing cells. Once the spacers and supports are added, the various sections of the plate 150 are folded along the creases adjacent to the notch to complete the assembly, as shown in Fig.8H, to produce a Z-folded stack 500. The above-mentioned spacing, although not necessarily a minimum, can be dimensioned to produce a desired pressure drop for a fluid as it flows through the channel. In one exemplary form, the spacing is 600 micrometers and includes a 400-micrometer channel and two 100-micrometer layers of diffusion media 152.

Claims

[1] A water vapor separator plate assembly (140) comprising: a pair of wet-side separator plates (150), each defining a wet-side flow channel region (54) therein; a pair of water vapor transfer membranes (170) disposed on respective surfaces of the pair of wet-side separator plates (150) so that a generally planar, dry-side flow channel region (164) is formed therebetween; and at least one spacer element (155) positioned between the pair of water vapor transfer membranes (170) to form the dry-side flow channel region having a thickness defined by the at least one spacer element (155); characterized by , that a plurality of discrete supports (151, 153, 157) are positioned within the dry-side flow channel region (164) defined by the at least one spacing element (155); wherein the respective support (151, 153, 157) is a point (151) consisting of an adhesive material which hardens after application or a pressure-sensitive adhesive material with a self-adhesive backing. [2] The water vapor separator plate assembly (140) of claim 1, wherein the at least one spacing element (155) comprises at least one edge strip. [3] A method of manufacturing a water vapor transfer assembly (140), the method comprising: a plurality of wet-side separator plates (150), each having at least one wet-side flow channel region formed therein, is provided, each of the wet-side separator plates (150) comprising at least one diffusion medium having a water vapor transfer membrane (170) attached thereto; spacing elements (155) positioned on oppositely facing surfaces of at least two of the plurality of wet-side separator plates (150) are applied so that a dry-side flow channel region (164) is formed therebetween; and the at least two wet-side separator plates (150) are layer-bonded to one another; characterized by , that a plurality of discrete supports (151, 153, 157) are applied within the dry-side flow channel region (164) defined by the spacing elements (155) prior to layer bonding; wherein the respective support (151, 153, 157) is a dot (151) made of an adhesive or pressure-sensitive adhesive material with a self-adhesive backing which hardens after application. [4] The method of claim 3, further comprising applying an adhesive to the supports (151, 153, 157). [5] The method of claim 3, wherein the spacing elements (155) comprise a pair of edge strips on at least one of the gas diffusion media layers such that upon layer bonding, the gas diffusion media and the pair of edge strips form a plurality of wet-side separator plates.

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