U.S. patent application number 13/440136 was filed with the patent office on 2012-07-26 for fuel cell water management system and method.
This patent application is currently assigned to FORD MOTOR COMPANY. Invention is credited to Simon Farrington, Cara N. Startek.
Application Number | 20120189945 13/440136 |
Document ID | / |
Family ID | 37983331 |
Filed Date | 2012-07-26 |
United States Patent
Application |
20120189945 |
Kind Code |
A1 |
Farrington; Simon ; et
al. |
July 26, 2012 |
FUEL CELL WATER MANAGEMENT SYSTEM AND METHOD
Abstract
Systems and methods for transporting accumulated water in a fuel
cell system are disclosed. Briefly described, in one aspect, a
system comprises a fuel cell flow field plate with at least one
channel disposed on a surface of the fuel cell flow field plate,
and at least one water management fin residing on a wall of the
channel such that when the accumulated water is transported along
the channel the water management fin guides the accumulated
water.
Inventors: |
Farrington; Simon;
(Vancouver, CA) ; Startek; Cara N.; (Vancouver,
CA) |
Assignee: |
FORD MOTOR COMPANY
Dearborn
MI
DAIMLER AG
Stuttgart
|
Family ID: |
37983331 |
Appl. No.: |
13/440136 |
Filed: |
April 5, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11318064 |
Dec 23, 2005 |
8173319 |
|
|
13440136 |
|
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Current U.S.
Class: |
429/512 |
Current CPC
Class: |
H01M 2008/1095 20130101;
H01M 8/04291 20130101; Y02E 60/50 20130101; H01M 8/0247 20130101;
H01M 8/026 20130101; H01M 8/04156 20130101 |
Class at
Publication: |
429/512 |
International
Class: |
H01M 8/04 20060101
H01M008/04 |
Claims
1-27. (canceled)
28. A method for transporting accumulated water from a fuel cell
system, the method comprising: guiding the accumulated water from a
top portion of a water management fin to a bottom portion of the
water management fin, the water management fin residing in a
channel of a fuel cell flow field plate; and guiding the
accumulated water from the bottom portion of the water management
fin to a channel root in the channel.
29. The method of claim 28, further comprising transporting the
accumulated water along the channel root to an outlet.
30. The method of claim 28, further comprising: collecting the
accumulated water from an edge of the channel, the edge of the
channel defined by a joining of a wall of the channel with a
surface of the fuel cell flow field plate; and guiding the
collected accumulated-water along the wall of the channel to the
water management fin.
31. The method of claim 28, further comprising: generating two
opposing vortices of gas, each gas vortex generated by one of two
opposing water management fins residing on opposite sides of the
channel, wherein each water management fin comprises the bottom
portion in proximity to the channel root, wherein each water
management fin is aligned with respect to the channel root at a
helix angle (.alpha.), and wherein the two gas vortices facilitate
transport of the accumulated water along the channel root.
32. The method of claim 28, further comprising: directing a flow of
a gas through at least the channel with a plurality of water
management microfins formed on a gas diffusion layer (GDL)
material, the GDL material adjacent to a surface of the fuel cell
flow field plate.
33. The method of claim 32 wherein the direction of the flow of the
gas corresponds to a direction of the channel, and wherein an
orientation of the plurality of water management microfins
corresponds to a helix angle (.alpha.) of the water management
fins.
34-38. (canceled)
39. A method for transporting accumulated water from a fuel cell
system, the method comprising: collecting an accumulation of water
in at least one channel of a flow field plate; and directing a flow
direction of a gas through at least the channel with a plurality of
water management microfins formed on a gas diffusion layer (GDL)
material, the GDL material adjacent to a surface of the fuel cell
flow field plate.
40. The method of claim 39 wherein the water management microfins
are aligned with the channel at a helix angle (.alpha.).
41. The method of claim 40 wherein the plurality of water
management microfins are formed by a plurality of fibers of the GDL
material oriented in a same direction, and wherein the alignment at
the helix angle (.alpha.) results from cutting the GDL
material.
42. The method of claim 41 wherein the water management microfins
are formed by a plurality of score lines on the surface of the GDL
material, and wherein the alignment at the helix angle (.alpha.)
results from rolling the GDL material with at least one score line
on a roller transporting the GDL material.
43. A method for transporting accumulated water from a fuel cell
system, the fuel cell system comprising: a fuel cell flow field
plate; at least one channel having a generally "U" shaped
cross-section disposed on a surface of the fuel cell flow field
plate, the channel having a top portion approximate the surface of
the fuel cell flow field plate and a channel root away from the
surface of the fuel cell flow field plate; and at least one water
management fin residing on a wall of the channel and arranged
within the channel and contacting the flow field plate surface,
such that when the accumulated water is transported along the
channel, the water management fin guides at least some of the
accumulated water towards a channel root, wherein the water
management fin comprises: a top portion approximately at least
substantially flush with the flow field plate surface; a bottom
portion extending towards a channel root of the channel; and a face
portion disposed between the top and bottom portions and protruding
outward from the wall of the channel, wherein the accumulated water
transported along the channel is guided by the fin face from
proximate the top portion of the fin towards the bottom portion of
the fin to the channel root, and wherein the method comprises:
guiding the accumulated water from a top portion of a water
management fin to a bottom portion of the water management fin; and
guiding the accumulated water from the bottom portion of the water
management fin to a channel root in the channel.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to fuel cell
systems, and, more particularly, to water management in a fuel cell
system.
[0003] 2. Description of the Related Art
[0004] Electrochemical fuel cells convert reactants, namely fuel
and oxidant fluid streams, to generate electric power and reaction
products. Electrochemical fuel cells generally employ an
electrolyte disposed between two electrodes, namely a cathode and
an anode. An electrocatalyst, disposed at the interfaces between
the electrolyte and the electrodes, typically induces the desired
electrochemical reactions at the electrodes. The location of the
electrocatalyst generally defines the electrochemically active
area:
[0005] One type of electrochemical fuel cell is the proton exchange
membrane (PEM) fuel cell. PEM fuel cells generally employ a
membrane electrode assembly (MEA) comprising a solid polymer
electrolyte or ion-exchange membrane disposed between two
electrodes. Each electrode typically comprises a porous,
electrically conductive substrate, such as carbon fiber paper or
carbon cloth, which provides structural support to the membrane and
serves as a fluid diffusion layer. The membrane is ion conductive,
typically proton conductive, and acts both as a barrier for
isolating the reactant streams from each other and as an electrical
insulator between the two electrodes. A typical commercial PEM is a
sulfonated perfluorocarbon membrane sold by E.I. Du Pont de Nemours
and Company under the trade designation NAFION.RTM.. The
electrocatalyst is typically a precious metal composition (e.g.,
platinum metal black or an alloy thereof) and may be provided on a
suitable support (e.g., fine platinum particles supported on a
carbon black support).
[0006] In a fuel cell, an MEA is typically interposed between two
separator plates that are substantially impermeable to the reactant
fluid streams. Such plates are referred to hereinafter as flow
field plates. The flow field plates provide support for the MEA. In
addition, the flow field plates have channels, trenches or the like
formed therein which serve as paths to provide access for the
reactant and the oxidant fluid streams to the respective porous
electrodes. Also, the fluid paths provide for the removal of
reaction byproducts and depleted gases formed during operation of
the fuel cell.
[0007] In a fuel cell stack, a plurality of fuel cells are
connected together, typically in series, to increase the overall
output power of the fuel cell system. In such an arrangement, one
side of a given separator flow field plate may be referred to as an
anode flow field plate for one cell and the other side of the plate
may be referred to as the cathode flow field plate for the adjacent
cell.
[0008] A plurality of inlet ports, supply manifolds, exhaust
manifolds and outlet ports are utilized to direct the reactant
fluid to the reactant channels in the flow field plates. The supply
and exhaust manifolds may be internal manifolds, which extend
through aligned openings formed in the flow field plates and MEAs,
or may comprise external or edge manifolds, attached to the edges
of the flow field plates. A variety of configurations are
possible.
[0009] A broad range of reactants can be used in PEM fuel cells.
For example, the fuel stream may be substantially pure hydrogen
gas, a gaseous hydrogen-containing reformate stream, or methanol in
a direct methanol fuel cell. The oxidant may be, for example,
substantially pure oxygen or a dilute oxygen stream such as
air.
[0010] During normal operation of a PEM fuel cell, fuel is
electrochemically oxidized on the anode side, typically resulting
in the generation of protons, electrons, and possibly other species
depending on the fuel employed. The protons are conducted from the
reaction sites at which they are generated, through the membrane,
to electrochemically react with the oxidant on the cathode side.
The electrons travel through an external circuit providing useable
power and then react with the protons and oxidant on the cathode
side to generate water reaction product.
[0011] As noted above, the channels of the flow field plate serve
two functions: to deliver reactants/oxidants to the active region
of the membrane, and to remove byproducts and depleted gasses
resulting from the electrochemical generation process. When
hydrogen is used as the reactant and oxygen is used as the oxidant,
one of the byproducts of the electrochemical generation process is
water. Although some amount of water in the active region of the
membrane is desirable, the accumulation of water can result in
undesirable amounts of water in some regions of the fuel cell.
[0012] Water may accumulate in the flow field channels. As gas is
injected into the flow field plate channels (reactants and/or
oxidants), gas pressure and movement may "flush" the accumulated
water through the above-described outlets.
[0013] If a relatively large amount of water collects in a
localized region of a flow field plate channel, however, the
channel may become blocked by the water. If the channel becomes
blocked by accumulated water, gas flow stops. Consequently, as the
reactants and/or oxidants in the gas residing in the blocked
channel are depleted, electrical output of the fuel cell decreases.
Maintaining fuel cell efficiency is very desirable.
[0014] In some fuel cell systems, other problems may arise from the
accumulation of water in and around the membrane. Droplets of water
may divert gas flow into less-than-optimal patterns over the
membrane. Water droplets reduce the hydraulic diameter of the flow
field plate channel, thereby increasing gas flow resistance in the
region around the water droplet. Furthermore, because the gas must
diffuse around a water droplet, gas diffusion distance is
increased. Because gas (reactants and/or oxidants) cannot reach the
membrane where the water droplet has formed, that area of the
membrane will become inactive and result in distortions of the
current density distribution in the fuel cell membrane, thereby
reducing fuel cell efficiency. Furthermore, if left standing in a
region of the membrane, flow field plate channel and/or other
location of the fuel cell, the accumulated water may result in
corrosion or deformation to the membrane or other parts of the fuel
cell system.
BRIEF SUMMARY OF THE INVENTION
[0015] The present invention is directed to systems and methods for
transporting accumulated water in a fuel cell system. In one
aspect, a system comprises a fuel cell flow field plate with at
least one channel disposed on a surface thereof, and at least one
water management fin residing on a wall of the channel such that
when accumulated water is transported along the channel the water
management fin guides the accumulated water.
[0016] In another aspect, a method comprises guiding accumulated
water from a top portion of a water management fin to a bottom
portion of the water management fin, the water management fin
residing in a channel of a fuel cell flow field plate; and guiding
the accumulated water from the bottom portion of the water
management fin to a channel root.
[0017] These and-other aspects of the invention will be evident
upon reference to the following detailed description and attached
drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
[0018] In the drawings, identical reference numbers identify
similar elements or acts. The sizes and relative positions of
elements in the drawings are not necessarily drawn to scale. For
example, the shapes of various elements and angles are not drawn to
scale, and some of these elements are arbitrarily enlarged and
positioned to improve drawing legibility. Further, the particular
shapes of the elements as drawn, are not intended to convey any
information regarding the actual shape of the particular elements,
and have been solely selected for ease of recognition in the
drawings.
[0019] FIG. 1 is an exploded cross-sectional view of a portion of a
fuel cell stack according to one embodiment of the present
invention.
[0020] FIG. 2 is a cross-sectional perspective view of a portion of
a flow field plate from the fuel cell stack of FIG. 1.
[0021] FIG. 3 is a plan view of a water management fin from the
flow field plate of FIG. 2.
[0022] FIG. 4 is a plan view of a portion of a flow field plate
according to another embodiment of the present invention,
schematically illustrating accumulated water being transported by a
water management fin.
[0023] FIG. 5 is a plan view schematically illustrating two water
management fins according to yet another embodiment of the present
invention.
[0024] FIGS. 6-10B illustrate several alternate embodiments of
water management fin and channel root configurations according to
the present invention.
[0025] FIGS. 11A and 11B illustrate one embodiment of a method for
forming water management microfins on a gas diffusion layer
structure.
[0026] FIGS. 12A, 12B and 12C illustrate another embodiment of a
method for forming water management microfins on a gas diffusion
layer structure.
[0027] FIGS. 13 and 14 schematically illustrate additional
alternative embodiments of water management fins.
DETAILED DESCRIPTION OF THE INVENTION
[0028] In the following description and enclosed drawings, certain
specific details are set forth in order to provide a thorough
understanding of various embodiments of the invention. One skilled
in the art will understand, however, that the invention may be
practiced without all of these details. In other instances,
well-known structures associated with fuel cell systems have not
been shown or described in detail to avoid unnecessarily obscuring
descriptions of the embodiments of the invention.
[0029] FIGS. 1-3 illustrate a fuel cell stack 102 having two fuel
cells 103, anode and cathode fuel cell flow field plates 104 and
106, respectively, and a pair of membrane electrode assemblies
(MEAs) 108. Each MEA 108 includes an anode gas diffusion electrode
(GDE) 110, a cathode gas diffusion electrode (GDE) 112 and a
membrane 113 therebetween. A plurality of channels 114 in the upper
flow field plates 104 provide for the flow of reactant gasses into
the anode GDE 110. Similarly, channels in the lower flow field
plates 106 provide for the flow of oxidant gasses into the cathode
GDE 112. In some types of fuel cell systems, adjacent flow field
plates may be made from a single piece of material, with the
channels 114 being formed on opposing sides thereof.
[0030] During operation, water droplets (not shown) form in the
membrane 113 and in the anode and cathode GDEs 110 and 112. As a
water droplet is wicked out to a surface of the anode GDE 110 or
the cathode GDE 112, further capillary action draws the water
droplet into the flow field plate channel 114. When the water is
drawn into the channel 114, at least one water management fin 100
protruding from a wall of the channel 114 guides the water to a
channel root 115 at a base of the channel. Water entering the
channel root 115 joins other accumulated water, and gas movement
through the channels 114, and/or gas pressure in the channels,
causes the accumulated water on the channel-root to form a rivulet
along-which the accumulated water exits the fuel cell stack
102.
[0031] FIG. 2 better illustrates one of the flow field plates 106
and one of the water management fins 100 extending outward from a
wall 204 of the flow field channel 114. For clarity, only one water
management fin 100 is illustrated in FIG. 2. A top portion 206 of
the water management fin 100 (as oriented in FIG. 2) is aligned
approximately with a top surface 208 of the flow field plate 106.
For example, in one embodiment, the top portion 206 is flush with
the surface 208; however, it is appreciated that the top portion
206 may be above or below the surface 208.
[0032] The water management fins 100 may be employed in channels
114 of the anode flow field plate 104, the cathode flow field plate
106, or both flow field plates 104, 106. Furthermore, the water
management fins 100 may be used in all of the channels 114,
selected ones of the channels 114, and/or in selected portions of
some or all of the channels 114.
[0033] Gas movement and/or pressure transports accumulated water
over an edge 210 and into the channel 114. The water enters the
flow channel 114, and the water management fin 100 guides at least
some of the water from the top portion 206 to an opposing bottom
portion 212 and onto the channel root 115 where the water forms a
rivulet exiting the fuel cell stack 102.
[0034] The channel root 115 is denoted in FIG. 2 as a line
extending down the central portion of the channel 114. The channel
root 115 may be merely a low point in the channel 114. In some
embodiments, however, the channel root 115 may have a structure or
features or may otherwise be formed to facilitate water flow.
[0035] FIG. 3 is a plan view of the water management fin 100 of
this particular embodiment. The shape of an inside edge 302 of the
water management fin 100 corresponds to the shape of the wall 204
(FIG. 2). Because the channel 114 illustrated in FIGS. 1 and 2 is
elliptical in cross-section, the general shape of the illustrated
water management fin 100 is elliptical to conform to the shape of
the channel. Along its length, the illustrated water management fin
100 is tapered from its widest at the top portion 206 to its
narrowest at the bottom portion 212. An outside edge 304 joins
with, or may be approximately aligned with, the inside edge 302 at
the bottom portion 212. The illustrated water management fin 100
has a triangular cross-section.
[0036] FIG. 4 schematically illustrates accumulated water 402 being
transported to the channel root 115 by another embodiment of a
water management fin 400. In this embodiment, the water management
fin 400 extends not only from the top surface 208 to the channel
root 115, but also in a longitudinal direction along the channel
114, giving the fin a helical shape.
[0037] As a water droplet 401 emerges from the anode GDE 110 or the
cathode GDE 112 into the flow channel 114, if the surface of the
anode GDE 110 or cathode GDE 112 is hydrophilic, the water droplet
401 will disperse into a film, as conceptually illustrated by the
shape of the "accumulated water" 402a. (If the surface were
hydrophobic, the accumulated water 402a could have been
conceptually illustrated as an elliptical-shaped water droplet.)
Gas movement and/or pressure transports the accumulated water 402a
to the edge 210 of the flow channel 114, as generally denoted by
the arrows 404. The accumulated water 402a is transported to edge
210 where the accumulated water 402a is generally transported in
the direction of gas flow traveling through channel 114,
illustrated by the dashed-arrow 406. That is, the accumulated water
402a is moved generally in the direction of arrow 408.
[0038] The top surface 208 is typically in contact with the MEA
under high load, and therefore water droplets 401 forming in the
anode GDE 110 or cathode GDE 112 over this region will emerge at an
edge 210 of the flow channel 114, and be generally transported in
the direction of gas flow traveling through channel 114,
illustrated by dashed-arrow 406.
[0039] As the accumulated water 402b comes into contact with the
water management fin 400, the accumulated water 402b is guided
along the face 306 of the water management fin 400 towards the
channel root 115. Furthermore, the fins 400 may induce a transverse
component of gas flow, as denoted by arrow 407, which further
guides the accumulated water 402b towards the channel root 115. As
the accumulated water 402c reaches the bottom portion 212 of the
water management fin 400, the accumulated water 402c is directed
onto the channel root 115, forming a rivulet. The rivulet of
accumulated water 402c is transported along the channel root 115 by
the gas movement and/or pressure, as denoted by arrow 412. The
accumulated water 402d exits the channel 114 through an outlet (not
shown), as generally denoted by arrow 412.
[0040] FIG. 5 illustrates a top view of two water management fins
500a and 500b angled at a helix angle (.alpha.) with respect to the
length of the channel root 115. With respect to the water
management fin 500a, the helix angle .alpha..sub.1 may be generally
defined by a vector 502 drawn from the bottom portion 212 to the
top portion 206. The helix angle .alpha. may be designed to have
any suitable magnitude, from zero degrees (0.degree.), wherein the
water management fin 500a would be oriented parallel to the channel
root 115, to nearly ninety degrees (.+-.90.degree.), wherein the
water management fin would be oriented nearly perpendicular to the
channel root 115 (see, e.g., FIG. 2).
[0041] In some embodiments, the helix angle .alpha. may be selected
based upon anticipated or computed gas movement and/or pressure in
the channel 114. In other embodiments, the helix angle .alpha. may
be selected based upon manufacturing considerations or other
parameters.
[0042] As noted above, any suitable helix angle .alpha. may be
used. Furthermore, because gas movement and/or pressure may not be
constant along the entire length of the channel 114, the helix
angle .alpha. of individual water management fins along a
particular channel may vary to change the effect of water
management along the length of channel in some embodiments.
[0043] A second water management fin 500b is also illustrated in
FIG. 5. With respect to water management fin 500b, the helix angle
.alpha..sub.2 may be similarly defined by a vector 504. In FIG. 5,
the illustrated helix angle .alpha..sub.2 has the same magnitude as
the helix angle .alpha..sub.1 for convenience. The helix angles
.alpha..sub.1 and .alpha..sub.2 may be different, depending upon
the embodiment.
[0044] FIGS. 6 and 7 are plan views of additional embodiments of
water management fin configurations angled with respect to the
channel root 115. In FIG. 6, the alignment of the water management
fins 600a on the left side of the channel 114 is parallel to the
alignment of the water management fins 600b on the right side of
the channel 114. The left side and the right side water management
fins 600a, 600b are staggered along the length of the channel root
115. In some embodiments the left side water management fins 600a
may be aligned with the corresponding bottom portions of the right
side water management fins 600b.
[0045] In FIG. 7, the alignment of the water management fins 700 on
the left side of the channel 114 are symmetrical bilaterally with
the water management fins 700 on the right side of the channel 114.
The bottom portions 712 of the water management fins 700 on the
left and right sides are positioned approximately adjacent to each
other (with respect to the channel root 115). That is, the bottom
portions 712 of the plurality of the left side water management
fins 700 are aligned with the corresponding bottom portions of the
plurality of the right side water management fins 700. In some
embodiments the left side and the right side water management fins
may be staggered along the length of the channel root 115.
[0046] In this double-opposed helix embodiment of FIG. 7, two
opposing vortices of gas (illustrated by arrows 702) are generated
by each pair of opposing water management fins 700. The opposing
gas vortices 702 may facilitate transport of accumulated water into
and/or down the channel root 115.
[0047] It is appreciated from FIGS. 5-7 that the position,
orientation and helix angle (.alpha.) of the water management fins
may be varied in any desired manner to facilitate water management
objectives of interest. Such objectives may be based upon the
particular nature of the fuel cell system and/or the particular
nature of the flow field plate channel configurations.
[0048] Furthermore, in FIGS. 6 and 7 the water management fins are
shown as being evenly spaced apart from each other along the length
of the channel 114. In other embodiments; the spacing between water
management fins may vary. For example, in regions of relatively
greater amounts of water accumulation, water management fins more
closely spaced together may be desirable. In regions of relatively
lesser amounts of water accumulation, water management fins spaced
farther apart may be desirable. All such various configurations of
the orientation and placement of water management fins in a channel
114 are intended to be included within the scope of this
disclosure.
[0049] FIG. 8 is a perspective view of one embodiment of a channel
root 814. The channel root 814 provides a guide directing the flow
of the rivulet of accumulated water. The illustrated channel root
814 runs along the length of the channel 114, starting where
accumulated water is directed by a water management fin 800, and
ending at an outlet where the accumulated water exits the fuel
cell. In FIG. 8, the channel root 814 is illustrated as an edge or
as a discontinuity in the wall 204. As noted above, gas movement
and/or pressure transports the accumulated water along the channel
root 814. In one embodiment, the channel root 814 may result from
an offset in opposing wall portions 204 of the channel 114. Such an
offset or discontinuity may be formed by a die used to form the
channel 114 or may be machined (i.e.; cut) or scored into the
channel 114.
[0050] FIGS. 9A, 9B, 10A and 10B illustrate alternative embodiments
of a channel root 914, 1014. In FIG. 9A, the channel root 914a is a
V-shaped gutter and in FIG. 9B, the channel root 914b is a V-shaped
curb. In FIG. 10A, the channel root 1014a is a rectalinear gutter
and in FIG. 10B, the channel root 1014b is a rectangular curb. Any
suitable channel or protruding ridge cross-section may be employed.
The channel root 914, 1014 may be formed by a protrusion or
extension on the die used to form the channel 114, or it may be
machined or scored into the channel 114.
[0051] FIGS. 11A and 11B illustrate a method of forming water
management microfins 1100 using existing fibers 1104 in a gas
diffusion layer (GDL) material 1102. When a GDL is made of a woven,
calendered, or other similarly formed material 1102, the
orientation of the fibers 1104 of the material is typically biased
in a common direction, as denoted by the arrow 1106, this in turn
biases the shape and orientation of surface porosity. When a
section 1110 is cut from the material to make the GDL, the fibers
1104 or fiber portions at the surface of the material 1102 can act
as water management microfins 1100. The helix angle (.alpha.) may
be controlled by selecting the angle of the section 1110 with
respect to the direction of fiber orientation 1106.
[0052] FIGS. 12A, 12B and 12C illustrate a method of forming water
management microfins 1202 using score lines 1204 on the surface of
one or more rollers 1208 that calender a gas diffusion layer (GDL)
material 1203. Score lines 1204 may be any trench-like marks cut or
scored into one or more rollers 1208. The helix angle (.alpha.) may
be controlled by selecting the orientation of the score lines 1204
with respect to the direction of calendering. As the material 1203
is calendered by the helically scored rollers 1208, the material
1203 is urged into the score lines 1204, thereby forming the
relatively small fins 1202, referred to herein as microfins.
[0053] In an alternative embodiment, the score lines 1204 may be
protrusions on the surface of the rollers 1208 (such as, but not
limited to, knife edges or the like), which cut or impress
trenches, grooves or the like into the material 1203 as the rollers
1208 calender the material 1203, thereby forming inverse water
management microfins 1206. GDLs cut from the material 1203 having
such inverse microfins 1206 facilitate water management by
directing the flow of water along the surface of the GDL.
[0054] Some embodiments may employ both microfins 1202 and inverse
microfins 1206. In alternative embodiments, the score lines 1204
may be oriented in the same direction as fibers 1104 or fiber
portions at the surface of the material 1102 (FIG. 11). Thus, the
microfins 1202 formed by score lines 1204 are oriented in the
direction of fiber orientation. These embodiments, accordingly, may
be viewed as a combination of one or more of the above-described
embodiments.
[0055] Furthermore, with respect to the above-described MEAs having
microfins 1100, 1202 and/or inverse microfins 1206, the microfins
also improve the effect of the gas movement and/or pressure that
transports the accumulated water along the channel root 115. A
cyclone effect induced by the water management microfins 1202 on
the surface of the MEA increases force applied to the accumulated
water, thereby facilitating the process of removing accumulated
water.
[0056] FIGS. 13 and 14 illustrate alternative embodiments of water
management fins 1300, 1400. The above-described water management
fin 100 in FIG. 3 was described as tapering in thickness from the
top portion 206 to the bottom portion 212. FIG. 13 illustrates a
water management fin 1300 that is not tapered in thickness. That
is, the thickness at the top portion 1306 is the same, or
approximately the same, as the bottom portion 1312. Other
embodiments may vary the thickness in any manner.
[0057] The water management fin 100 in FIG. 3 was described as
having a straight alignment from the top portion 206 to the bottom
portion 212. FIG. 14 illustrates a water management fin 1400 that
is curved from the top portion 1406 to the bottom portion 1412.
That is, the helix angle (.alpha.) varies along the length of the
water management fin 1400. In other embodiments, the curvature of
the water management fin 100 can vary in any suitable manner.
[0058] In some alternative embodiments, the thickness and the
curvature of mater management fins may both vary. This embodiment,
accordingly, may be viewed as a combination of the embodiments of
FIGS. 13 and 14.
[0059] The water management fin 100 was described as having a
triangular cross-section in FIG. 3. In other embodiments, different
cross-sectional shapes may be used. For example, the
cross-sectional shape of a water management fin 100 may be
rectangular, trapezoidal, elliptical, half-round, quarter-round,
tapered or may have any other suitable shape.
[0060] The water management fins 100 were described as residing in
channels 114 having an elliptical cross-section. In other
embodiments, different cross-sections of the channels 114 may be
used. For example, the cross-sectional shape of the channels 114
may be, among other shapes, circular, square, rectangular, or
trapezoidal. Any of these channels 114 may have one-or more water
management fins 100 residing on its wall 204.
[0061] The water management fins 100 were described as protruding
outward from the walls 204 of the channel 114. In such an
embodiment, the dies or other devices used to form the channels 114
may be scored or have grooves thereon which correspond to negative
images of the desired water management fins 100. When the dies are
used to form the channels 114, portions of the material of the
plate fill the void of the scores or grooves, thereby forming a
protruding water management fin 100.
[0062] It is appreciated that the size of water management fins 100
may vary along the length of a channel 114. For example, smaller
water management fins 100 may be used where there is relatively
smaller amounts of water accumulation. In fuel cell regions subject
to relatively large amounts of water accumulation, larger water
management fins 100 may be used. The height, thickness and/or
length of the water management fins 100 may be varied.
[0063] In other embodiments, the water management fins 100 may be
inverted. That is, the water management fins may be grooves,
channels or the like residing in a channel 114. In such an
embodiment, the dies or other devices used to form the channels 114
may have outwardly extending fins, ridges or the like which
correspond to negative images of the desired water management fins
100. When such dies are used to form the channels 114, portions of
the material are compressed, thereby forming inverted water
management fins 100. Inverted water management fins 100 could
instead be machined or scored into the walls 204 after
fabrication.
[0064] In the various above-described embodiments, the water
management fins 100 were described and illustrated as residing in
the channels 114 of the fuel cell flow field plates. Depending upon
the type of fuel cell system, the water management fins 100 may
reside in the channels 114 of fuel cell flow field plates
associated with both the anode side and the cathode side of the
fuel cell system. In other embodiments, water management fins 100
reside only in the channels 114 of fuel cell flow field plates on
the anode side of the fuel cell system. Accordingly, such
embodiments may be suitable for fuel cells operating in a
dead-ended mode of operation.
[0065] Unless the context requires otherwise, throughout the
specification and claims which follow, the word "comprise" and
variations thereof, such as, "comprises" and "comprising" are to be
construed in an open, inclusive sense, that is as "including, but
not limited to."
[0066] 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 of the present invention. 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.
[0067] From the foregoing it will be appreciated that, although
specific embodiments of the invention have been described herein
for purposes of illustration, various modifications may be made
without deviating from the spirit and scope of the invention.
Accordingly, the invention is not limited except as by the appended
claims.
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