1. Field
The present invention is generally directed to electrochemical converters such as fuel cells, and more particularly, to an apparatus and method for managing a flow of a cooling media in a fuel cell stack.
2. Description of the Related Art
Electrochemical cells comprising ion exchange membranes, such as proton exchange membranes (PEMS) may be operated as fuel cells, wherein a fuel and an oxidant are electrochemically converted at the cell electrodes to produce electrical power, or as electrolyzers, wherein an external electrical current is passed between the cell electrodes, typically through water, resulting in generation of hydrogen and oxygen at the respective electrodes.
Each fuel cell 10 comprises a membrane electrode assembly (MEA) 5 such as that illustrated in an exploded view in
In an individual fuel cell 10, illustrated in an exploded view in
Electrochemical fuel cells 10 with ion exchange membranes 2 such as PEM layers, sometimes called PEM cells, are typically advantageously stacked to form a stack 50 (see
The illustrated cell elements have openings 30 formed therein which, in the stacked assembly, align to form gas manifolds for supply and exhaust of reactants and products, respectively, and, if cooling spaces are provided, for a cooling medium.
Fluid reactant streams are supplied to and exhausted from internal manifolds and passages in the system 60 via inlet and outlet ports 76 in the end plate assemblies 62, 64. Aligned internal reactant manifold openings 78, 80 in the MEAs 68 and flow field plates 70, respectively, form internal reactant manifolds extending through the system 60. As one of ordinary skill in the art will appreciate, in other representative electrochemical fuel cell stacks, reactant manifold openings may instead be positioned to form edge or external reactant manifolds.
In the illustrated embodiment, a perimeter seal 82 is provided around an outer edge of both sides of the MEA 68. Furthermore manifold seals 84 circumscribe the internal reactant manifold openings 78 on both sides of the MEA 68. When the system 60 is secured in its assembled, compressed state, the seals 82, 84 cooperate with the adjacent pair of plates 70 to fluidly isolate fuel and oxidant reactant streams in internal reactant manifolds and passages, thereby isolating one reactant stream from the other and preventing the streams from leaking from the system 60.
As illustrated in
Instead of two plates 70, one plate 70 unitarily formed or alternatively fabricated from two half plates 70a, 70b can be positioned between the cells 66, forming bipolar plates as discussed above.
In the illustrated embodiment, the flow field plates 70 also have a plurality of typically parallel flow field channels 96 formed in the non-active surface thereof. The channels 96 on adjoining pairs of plates 70 cooperate to form coolant flow fields 98 extending laterally between the opposing non-active surfaces of the adjacent fuel cells 66 of the system 60 (generally perpendicular to the stacking direction). A coolant stream, such as air or other cooling media may flow through these flow fields 98 to remove heat generated by exothermic electrochemical reactions, which are induced inside the fuel cell system 60.
The reactant flow field channels 86 generally include design parameters that accommodate desired reactant flow. These parameters can also govern the design of coolant flow field channels 96 because plate design is typically constrained by forming limitations. Generally, the flow field channels 86 on one side of the plate are balanced by the flow field channels 96 on the other side of the plate, particularly if the plate is made by stamping (more typical of metal plates).
However, such manufacturing and design limitations impede optimizing the coolant flow field channels 96, resulting in suboptimal coolant flow, typically because the coolant flow field channels 96 are excessively large and therefore contain an undesirably large volume of coolant. A large volume of coolant may increase the stack thermal mass, thereby slowing a warming up process during freeze-starts and ambient startups, and may adversely affect a route or direction of desired heat transfer as well as water movement between the anode and cathode sides of the MEA 68.
Furthermore, flow field plate manufacturing limitations prescribe a shape of the coolant flow field channels 96 such that it is typically not possible with existing systems to introduce distinct cooling media through distinct coolant flow field channels and/or to control the rate and/or quantity of coolant media in distinct coolant flow field channels 98. For example, it may be desirable to direct less cooling medium through the coolant flow field channels 98 of the fuel cells 66 positioned toward the end plates 62, 64. Additionally, or alternatively, it may be desirable to flow less cooling medium through the coolant flow field channels 98 positioned at an edge of the flow field plates 70 as compared to that flowing through the coolant flow field channels 98 positioned toward a center of the flow field plates 70. Additionally, or alternatively, it may be desirable in certain applications to cool the anode side more than the cathode side of the MEA 68. In other applications, it may be desirable to cool the cathode side more than the anode side of the MEA. Conventional flow field plates 70 typically fail to allow such control over cooling of distinct regions in the fuel cell system 60.
Furthermore, conventional solutions have also failed to adequately address controlling a temperature of the distinct regions in a fuel cell system. Conventional solutions include molding and/or machining non-metal flow field plates to vary the thickness of the web of the plates, resulting in more costly and time-consuming manufacturing. Furthermore, this solution is not amenable to use with metal plates.
Other methods include additional manufacturing steps such as machining, forming, etching, and/or molding that are typically carried out to form reactant and coolant flow field channels in separate manufacturing steps in order to achieve coolant flow field channels having a shape distinct from reactant flow field channels. Additionally, these processes are typically limited to specific materials, for example, they typically cannot be used for thin metal plates, the thickness of which may not be easily adjusted.
Accordingly, there is a need for a system and a method to manage a utilization of coolant flow field channels to accommodate a desired flow of distinct cooling media through the coolant flow field channels and selectively control a temperature of distinct regions of a fuel cell and/or of a fuel cell system by managing the cooling media flow through coolant flow field channels of flow field plates fabricated from any suitable material.
According to one embodiment, a flow field plate assembly for use in a fuel cell stack having more than one fuel cell, each fuel cell including a membrane electrode assembly (MEA) having an ion-exchange membrane interposed between anode and cathode electrode layers, comprises a first flow field plate positionable on an anode side of the MEA of a first fuel cell, at least one reactant flow field channel formed in at least a portion of a first side of the first flow field plate adapted to direct a fuel to at least a portion of the anode electrode layer of the first fuel cell, a second flow field plate positionable on a cathode side of the MEA of a second fuel cell, adjacent the first fuel cell, at least one reactant flow field channel formed in at least a portion of a first side of the second flow field plate adapted to direct an oxygen-containing gas to at least a portion of the cathode electrode layer of the second fuel cell, at least one coolant flow field channel formed in at least a portion of a second side of the first and second flow field plates, respectively, the coolant flow field channels of the second side of the first flow field plate being positioned substantially opposite the coolant flow field channels of the second side of the second flow field plate to define an aggregate volume therebetween configured to direct a cooling medium therethrough, and at least one dividing member extending across at least one coolant flow field channel of at least one of the second sides to selectively divide the aggregate volume into at least first and second volumes, the first volume being configured to circulate or seal a first fluid having a first flow characteristic when circulated and a first composition, and the second volume being configured to circulate or seal a second fluid having a second flow characteristic when circulated and a second composition, to allow selective control over an aggregate cooling characteristic of the fuel cell stack, when the flow field plate assembly is installed in the fuel cell stack and the fuel cell stack is in operation.
According to another embodiment, a fuel cell stack comprises more than one fuel cell, each fuel cell including a membrane electrode assembly (MEA) having an ion-exchange membrane interposed between anode and cathode electrode layers, a first flow field plate positioned on an anode side of the MEA, at least one reactant flow field channel formed in at least a portion of a first side of the first flow field plate adapted to direct a fuel to at least a portion of the anode electrode layer, a second flow field plate positioned on a cathode side of the MEA, at least one reactant flow field channel formed in at least a portion of a first side of the second flow field plate adapted to direct an oxygen-containing gas to at least a portion of the cathode electrode layer, at least one coolant flow field channel formed in at least a portion of a second side of the first and second flow field plates, respectively, the coolant flow field channels of the second side of the first flow field plate of each fuel cell respectively positioned substantially opposite the coolant flow field channels of the second side of the second flow field plate of an adjacent fuel cell to define an aggregate volume therebetween configured to direct a cooling medium therethrough, and at least one dividing member extending across at least one coolant flow field channel of at least one of the second sides to selectively divide the aggregate volume into at least first and second volumes, the first volume being configured to circulate or seal a first fluid having a first flow characteristic when circulated and a first composition, and the second volume being configured to circulate or seal a second fluid having a second flow characteristic when circulated and a second composition, to allow selective control over an aggregate cooling characteristic of the fuel cell stack, when the flow field plate assembly is installed in the fuel cell stack and the fuel cell stack is in operation.
According to yet another embodiment, a method of selectively managing cooling characteristics of a fuel cell stack in distinct regions thereof, the fuel cell stack having a plurality of fuel cells, each fuel cell comprising a membrane electrode assembly (MEA) having an ion-exchange membrane interposed between anode and cathode electrode layers, at least one flow field plate interposed between the MEAs of adjacent fuel cells, the flow field plates forming a plurality of coolant flow field channels on a side of the flow field plates opposing the MEAs and a plurality of reactant flow field channels on a side of the flow field plates adjacent the MEAs, comprises positioning the coolant flow field channels of each flow field plate substantially opposite the coolant flow field channels of an adjacent flow field plate to define an aggregate volume between each pair of opposing coolant flow field channels, dividing each aggregate volume into at least two volumes, and at least one of directing and sealing at least two fluids through the at least two volumes, respectively, the two fluids comprising at least one of distinct flow characteristics when circulated and distinct compositions, to variably manage a rate of cooling in at least one of distinct regions of each fuel cell and distinct regions of the fuel cell stack.
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
Forming the coolant flow field channels 122, 124 simultaneously with forming the reactant flow field channels 118, 120 can eliminate additional manufacturing steps such as machining, forming, and/or etching that are typically carried out to form reactant and coolant flow field channels in separate manufacturing steps in order to achieve coolant flow field channels having a shape distinct from reactant flow field channels. Additionally, these processes are typically limited to specific materials, for example they typically cannot be used for thin metal plates, the thickness of which may not easily be adjusted. However, forming the coolant and reactant flow field channels 118, 120, 122, 124 in a single process such as molding or embossing graphite plates and/or stamping metal plates is less expensive, and more expedient and versatile toward different materials.
The flow field channels 118, 120, 122, 124 are sized based on reactant flow design parameters. These parameters determine a shape of the reactant flow field channels 118, 120, which in turn govern a shape of the coolant flow field channels 122, 124, particularly when stamping metal plates to form the flow field channels thereon. Accordingly, the coolant flow field channels 122, 124 need not necessarily be sized at this point in manufacturing to optimize the flow of the cooling medium directed therethrough, thereby reducing manufacturing time and costs.
According to an embodiment of the present invention, the fuel cell stack 100 further comprises a dividing member 126 that acts as an obstruction medium, selectively isolating a volume 107a, 107b of the coolant flow field channels 122 of the first flow field plate 106 from the volume 107a of other flow field channels 122 of the first flow field plate 106 and from the volume 107b of other coolant flow field channels 124 formed on the second flow field plate 108, permitting fluid flow, or blocking fluid from flowing, on either side of the dividing member 126. Therefore, if desired the volume 107a, 107b can selectively circulate or seal at least one of an oxygen-containing gas such as air, an inert gas such as nitrogen, and a liquid such as water and/or glycol or any other suitable cooling media. Introducing air into at least a portion of the volumes 107a, 107b promotes reducing the thermal mass in the coolant flow field channels 122, 124. Such a configuration can be used to induce a desired or controlled temperature gradient between the cathode and anode sides of the MEA 104 and force water movement to one of the cathode and anode sides of the MEA 104. Furthermore, the volumes 107a, 107b can selectively direct additional cooling medium where heightened cooling is desired.
For example, during ambient and freeze startups, cooling media can be directed and/or circulated through only certain isolated coolant flow field channels 122, 124, such as directing less cooling media through the coolant flow field channels 122, 124 positioned toward an edge of the flow field plates 106, 108 than that directed through the coolant flow field channels 122, 124 positioned toward a center of the flow field plates 106, 108. Additionally, or alternatively, less cooling media can be directed through the coolant flow field channels 122, 124 of the fuel cells 102 (
Additionally, or alternatively, at least some of the volumes 107a, 107b, or all of the volumes 107a, 107b of one of the flow field plates 106, 108 may stagnantly store and seal fluids such as water and/or air, for example sealing air in at least a portion of at least one of the volumes 107a, 107b, to obtain insulation qualities, control the thermal mass of the flow field plates 106, 108, or for any other suitable purpose depending on the application.
Furthermore,
In any of the embodiments described herein, the dividing member 126, 226, 326 may comprise thermal insulation properties obtained through a material of the dividing member 126, 226, 326 and/or an insulating coating applied to at least a portion thereof for a particular application of the fuel cell stack 100, 200, 300. Furthermore, in any of the embodiments described, the dividing member 126, 226, 326 can be fluid-tight to fluidly isolate the volumes thereof.
The following describes an example of an embodiment of a method of selectively controlling characteristics of distinct cooling media through distinct isolated flow field channels 122, 124 separated by a dividing member 126 in a fuel cell stack according to one embodiment, such as the stack 100 illustrated in
In some embodiments, the method may include directing lesser or no cooling media through isolated volumes 107a, 107b of the coolant flow field channels 122, 124 positioned toward an end of at least one fuel cell 102 and/or the fuel cell stack 100. In some embodiments, the two distinct fluids may respectively include air and a cooling medium. In some embodiments, the two distinct fluids may respectively comprise distinct cooling media. In some embodiments, the two distinct fluids may respectively comprise air, water and/or glycol.
In some embodiments, the method may comprise directing a larger flow rate of cooling media through one of the two volumes 107a, 107b adjacent the flow field plate 106 of at least one fuel cell 102 proximate the anode electrode layer 109 of the at least one fuel cell 102 to cool a region proximate the anode electrode layer 109 of the at least one fuel cell 102 more than cooling a region proximate the cathode electrode layer 111 of the at least one fuel cell 102.
In some embodiments, the method may comprise directing a larger flow rate of cooling media through one of the two volumes 107a, 107b adjacent the flow field plate 106 of at least one fuel cell 102 proximate the cathode electrode layer 111 of the at least one fuel cell 102 to cool a region proximate the cathode electrode layer 111 of the at least one fuel cell 102 more than cooling a region proximate the anode electrode layer 109 of the at least one fuel cell 102.
The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments.
These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.
This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 60/______, filed Aug. 25, 2006 (formerly U.S. application Ser. No. 11/467,307, converted to provisional by Petition dated Aug. 9, 2007), which provisional application is incorporated herein by reference in its entirety.
Number | Date | Country | |
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60966525 | Aug 2006 | US |