WO2009078866A1

WO2009078866A1 - Fuel cell systems and methods involving variable numbers of flow field passes

Info

Publication number: WO2009078866A1
Application number: PCT/US2007/087882
Authority: WO
Inventors: Paravastu Badrinarayanan; Sitaram Ramaswamy
Original assignee: Utc Power Corporation
Priority date: 2007-12-18
Filing date: 2007-12-18
Publication date: 2009-06-25

Abstract

Fuel cell systems (200) and methods involving variable numbers of flow field passes are provided. In this regard, a representative method for operating a fuel cell includes: operating a flow field (202) of a fuel cell with a first number of passes; and dynamically altering the flow field such that the flow field uses a different number of passes.

Description

FUEL CELL SYSTEMS AND METHODS INVOLVING VARIABLE NUMBERS OF FLOW FIELD PASSES

BACKGROUND Technical Field

The disclosure generally relates to fuel cells.

Description of the Related Art

Some fuel cell systems are designed to operate at both high power and low power ranges. In this regard, flow fields of fuel cell systems optimized for high power operation tend to exhibit instability during low power operation. This may be caused due to lower fluid flow velocities and consequent water hang-up within channels of the flow fields, for example. With respect to fuel cell systems designed for low power operation, high power operation tends to result in increased parasitic loads and system complexity.

SUMMARY

Fuel cell systems and methods involving variable numbers of flow field passes are provided. In this regard, an exemplary embodiment of a fuel cell system comprises: a fuel cell flow field having sets of channels operative to route fluid; the flow field being operative such that, in a first mode, fluid is routed through the sets of channels in a first number of passes and, in a second mode, fluid is routed through the sets of channels in a different number of passes. An exemplary embodiment of a fuel cell comprises: a flow field having a first set of channels, a second set of channels, a first manifold assembly and a second manifold assembly, the first set of channels extending between and communicating with the first manifold assembly and the second manifold assembly, the second set of channels extending between and communicating with the first manifold assembly and the second manifold assembly; the flow field being operative such that, in a first mode, fluid is routed from the first manifold assembly to the first set of channels and the second set of channels and, in a second mode, fluid is routed from the first manifold assembly to the first set of channels, through the second manifold assembly, and thereafter to the second set of channels.

An exemplary embodiment of a method for operating a fuel cell comprises: operating a flow field of a fuel cell with a first number of passes; and dynamically altering the flow field such that the flow field uses a different number of passes.

Other systems, methods, features and/or advantages of this disclosure will be or may become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features and/or advantages be included within this description and be within the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 is a schematic diagram partially depicting an exemplary embodiment of a fuel cell system.

FIG. 2 is a schematic diagram depicting the fuel cell system of FIG. 1 , showing detail of the flow field.

FIG. 3 is a schematic diagram of the embodiment of FIG. 1 being operated at a low power level.

FIG. 4 is the schematic diagram depicting another embodiment of a fuel cell system being operated at a low power level.

FIG. 5 is a schematic diagram depicting the embodiment of FIG. 4 being operated at a high power level.

DETAILED DESCRIPTION

Fuel cell systems and methods involving variable numbers of passes are provided. In this regard, several embodiments incorporate the use of manifold assemblies that can be dynamically altered to vary the number of passes through a flow field. By way of example, for low power operations, one or more valves can be selectively positioned such that a multi-pass configuration is provided. For high power operations, the valves can be repositioned to operate the flow field with fewer passes. For instance, the flow field can be operated as a single-pass flow field.

An exemplary embodiment of a fuel cell system is partially depicted in the schematic diagram of FIG. 1. As shown in FIG. 1 , fuel cell system 100 is configured as a Proton Exchange Membrane (PEM) fuel cell incorporating a membrane 102 that is oriented between catalyst layers 104, 106. The catalyst layers and membrane define a membrane electrode assembly 108. The membrane electrode assembly is positioned between opposing substrates 110, 112 that function as gas diffusion layers.

Adjacent to substrate 110 and opposing the membrane electrode assembly is an anode structure 111 that includes an array 113 of ribs (e.g., ribs 114, 116). Channels of array 113 (e.g., channel 118) that form a flow field are defined between the ribs. In particular, each channel of array 113 is defined by a pair of adjacent ribs, a corresponding channel wall of the anode, and a corresponding portion of substrate 110. By way of example, channel 118 is defined by ribs 114 and 116, channel wall 120, and a portion 122 of substrate 110. Notably, the channels of array 113 are reactant channels, with the reactant or fuel of this embodiment being a hydrogen-rich gas (e.g., hydrogen gas).

Adjacent to substrate 112 and opposing the membrane electrode assembly is a cathode structure 121 that includes an array 123 of ribs (e.g., ribs 124, 126). Channels of array 123 (e.g., channel 128) that form a flow field are defined between the ribs. In particular, each channel of array 123 is defined by a pair of adjacent ribs, a corresponding channel wall of the cathode, and a corresponding portion of substrate 112. By way of example, channel 128 is defined by ribs 124 and 126, channel wall 130, and a portion 132 of substrate 112. In this embodiment, the channels of array 123 are reactant channels, with the reactant or oxidant being an oxygen-rich gas (e.g., air). Notably, during operation, water can be present in any of the reactant channels. The flow field of reactant channels of fuel cell system 100 is shown in greater detail in FIG. 2. As shown in FIG. 2, the channels extend from open ends located along a first side 140 of the flow field to open ends located along an opposing second side 142 of the flow field. By way of example, channel 108 extends between open ends 144 and 146, and channel 148 extends between open ends 154, 156. Although the channels are straight channels in this embodiment, various other configurations can be used, including those in which the open ends of a channel are not located along opposing sides of the fuel cell.

Fuel cell system 100 also includes two fluid manifold assemblies. In particular, a first manifold assembly 160 (which incorporates manifolds 162 and 164) is positioned along side 140 of the flow field, and a second manifold assembly 165 is positioned along side 142. Notably, a first set 166 of the channels (which includes channel 108) extends between and communicates with manifold 162 and manifold assembly 165. A second set 168 of the channels (which includes channel 148) extends between and communicates with manifold 164 and manifold assembly 165.

In operation in a high power mode, the flow field is operated so that fluid (e.g., air) enters each of the channels at side 140 of the fuel cell and departs the channels at side 142, thereby providing a single-pass configuration. Thus, the flow field is operated so that fluid is evenly distributed among all of the channels and effectively flows over the distance of the length of the channels. Such a single-pass configuration is considered adequate for reducing a tendency for water to hang-up in the channels since the high power operation uses relatively high fluid flow velocities through the flow field. This configuration also exhibits a relatively low pressure drop across the flow field. In contrast, operation in a low power mode typically involves lower fluid flow velocities through the flow field that might result in water hang-up if the flow field were operated in the single-pass configuration. In order to reduce the potential for water hang-up, the flow field can be dynamically altered (via the manifold assemblies in this embodiment) to exhibit a multi-pass configuration. Specifically, as shown in FIG. 3, manifold assembly 165 is altered so that fluid is redirected to flow through the second set of channels 168 and the manifold 164. That is, fluid, which directed through manifold 162 and the first set of channels 166 to manifold assembly 165, is also directed through the second set of channels 168 and manifold 164. Effectively, the cross-sectional area through which the fluid flows is reduced and the distance along which the fluid flows is increased.

This multi-pass configuration increases the fluid flow velocity through the channels (e.g., to a velocity comparable to that exhibited during the high power mode) and tends to assist in clearing the channels of hang-ups. It should be noted that although the embodiment of FIGS. 1 - 3 is configured to be selectively alterable between a multi-pass configuration (using only two passes) and a single-pass configuration, other numbers of passes can be used in other embodiments.

A portion of another embodiment of a fuel cell system is depicted schematically in FIG. 4. As shown in FIG. 4, fuel cell system 200 incorporates a flow field 202 of channels (e.g., channels 204 and 206). Each of the channels extends from an open end located along a first side 208 of the flow field to an open end located along an opposing second side 210. By way of example, channel 204 extends between open ends 214 and 216, and channel 222 extends between open ends 224 and 226. Fuel cell system 200 also includes two fluid manifold assemblies. In particular, a first manifold assembly 230 is positioned along side 208 of the flow field and a second manifold assembly 240 is positioned along side 210. Manifold assembly 230 incorporates manifolds 232, 234 and a valve 236. Similarly, manifold assembly 240 incorporates manifolds 242, 244 and a valve 246.

A first set 248 of the channels (which includes channel 204) extends between and communicates with manifold assemblies 230 and 240. Specifically, each of the channels of set 248 extends between manifolds 232 and 242. A second set 250 of the channels (which includes channel 206) also extends between and communicates with manifold assemblies 230 and 240. Specifically, each of the channels of set 250 extends between manifolds 234 and 244.

In operation in a high power mode (FIG. 5), flow field 202 is operated so that fluid (e.g., air) enters each of the channels via manifold assembly 230 and departs the channels via manifold assembly 240. Such a single-pass configuration is considered adequate for reducing a tendency for water to hang-up in the channels since the high power operation uses relatively high fluid flow velocities. Notably, the single-pass configuration of this embodiment is facilitated by moving valves 236 and 246 to respective first positions. Specifically, in the first position, valve 236 is configured so that fluid flow directed to valve 236 is routed to manifold 234. As such, fluid is first routed to the open ends of the channels of the flow field that communicate with manifold assembly 230. Valve 246 in the first position is configured to route fluid provided via manifold assembly 240 away from the flow field. In contrast, operation in a low power mode typically involves lower fluid flow velocities that might result in water hang-up if the flow field were operated in the single- pass configuration. In order to reduce the potential for water hang-up, the flow field can be dynamically altered to exhibit a multi-pass configuration. Specifically, as shown in FIG. 4, the multi-pass configuration of this embodiment is facilitated by moving valves 236 and 246 to respective second positions. In particular, valve 246 is moved to the second position in which valve 246 is configured to direct fluid from the first set of channels (and manifold 242) to (manifold 244 and) set 250 of the channels. Thus, the effective number of channels is reduced and the distance along which the fluid flows is increased. This configuration increases the fluid flow velocity through the channels (e.g., to a velocity comparable to that exhibited during the high power mode for flow rates that are proportional to the low power mode) and tends to assist in clearing the channels of hang-ups. Additionally, in the second position, valve 236 is configured to receive fluid provided by manifold 234 and set 250 of the channels.

It should be emphasized that the above-described embodiments are merely possible examples of implementations set forth for a clear understanding of the principles of this disclosure. Many variations and modifications may be made to the above-described embodiments without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the accompanying claims.

Claims

1. A fuel cell system comprising: a fuel cell flow field having sets of channels operative to route fluid; the flow field being operative such that, in a first mode, fluid is routed through the sets of channels in a first number of passes and, in a second mode, fluid is routed through the sets of channels in a different number of passes.

2. The system of claim 1 , wherein, in the first mode, the flow field is operated as a single-pass flow field.

3. The system of claim 1 , wherein: the sets of channels include a first set of channels and a second set of channels; the system further comprises a first valve movable between a first position corresponding to the first mode, in which fluid is routed to both the first set of channels and the second set of channels, and a second position corresponding to the second mode, in which fluid is not routed to the second set of channels.

4. The system of claim 3, further comprising a second valve movable between a first position corresponding to the first mode, in which fluid from both the first set of channels and the second set of channels is received at the second valve, and a second position corresponding to the second mode, in which fluid passed through the first set of channels is routed via the second valve to the second set of channels.

5. The system of claim 1 , wherein the flow field is a Proton Exchange Membrane (PEM) fuel cell flow field.

6. The system of claim 1 , wherein the sets of channels are reactant channels.

7. The system of claim 6, wherein the fluid used as a reactant is air.

8. A fuel cell comprising: a flow field having a first set of channels, a second set of channels, a first manifold assembly and a second manifold assembly, the first set of channels extending between and communicating with the first manifold assembly and the second manifold assembly, the second set of channels extending between and communicating with the first manifold assembly and the second manifold assembly; the flow field being operative such that, in a first mode, fluid is routed from the first manifold assembly to the first set of channels and the second set of channels and, in a second mode, fluid is routed from the first manifold assembly to the first set of channels, through the second manifold assembly, and thereafter to the second set of channels.

9. The fuel cell of claim 8, wherein: the first manifold assembly comprises a first manifold and a second manifold; the first set of channels communicates with the first manifold; and the second set of channels communicates with the second manifold.

10. The fuel cell of claim 9, wherein: the fuel cell further comprises a valve; in the first mode, the valve is operative to route fluid to the second manifold; and in the second mode, the valve is operative to prevent fluid from being routed to the second manifold.

11. The fuel cell of claim 8, wherein: the second manifold assembly comprises a first manifold and a second manifold; the first set of channels communicates with the first manifold; and the second set of channels communicates with the second manifold.

12. The fuel cell of claim 11 , wherein: the fuel cell further comprises a valve; in the first mode, the valve is operative to receive fluid from both the first manifold and the second manifold; and in the second mode, the valve is operative to route fluid from the first manifold to the second manifold.

13. The fuel cell of claim 8, wherein the fuel cell is a Proton Exchange Membrane (PEM) fuel cell.

14. A method for operating a fuel cell comprising: operating a flow field of a fuel cell with a first number of passes; and dynamically altering the flow field such that the flow field uses a different number of passes.

15. The method of claim 14, wherein the different number is a higher number of passes than the first number.

16. The method of claim 15, wherein the first number is one and the different number is two.

17. The method of claim 15, wherein the different number is a lower number of passes than the first number.

18. The method of claim 14, wherein the flow field is a Proton Exchange Membrane (PEM) fuel cell flow field.

19. The method of claim 14, wherein the flow field comprises reactant channels.

20. The method of claim 19, wherein the fluid used as a reactant is air.