Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
1999-08-25
2001-04-17
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S010000, C429S006000, C429S006000, C429S066000, C029S623200
Reexamination Certificate
active
06218039
ABSTRACT:
BACKGROUND
The invention relates to clamping apparatus and methods for fuel cells.
Fuel cells have been used to produce electrical power. A fuel cell is an electrochemical device that converts energy produced by a chemical reaction into electrical energy. Fuel cells generally employ an ion exchange membrane or solid polymer electrolyte disposed between two electrodes that form the anode and cathode. One type of fuel cell includes a proton exchange membrane (PEM) fuel cell. At the anode of the PEM fuel cell, diatomic hydrogen (a fuel) is oxidized to produce hydrogen protons that pass through the membrane. The electrons produced by this oxidation travel through electrical circuitry that is external to the fuel cell to form an electrical current. At the cathode, oxygen is reduced and reacts with the hydrogen protons to form water.
Multiple fuel cells can be connected together, generally in series, to increase the voltage output of the fuel cell assembly. Several serially connected fuel cells may be formed in an arrangement called a fuel cell stack. The fuel cell stack may include different plates that are stacked one on top of the other in the appropriate order, and each plate may be associated with more than one fuel cell of the stack. The plates may be formed of metal or a graphite composite material and may include various channels and orifices to route the above-described reactants and products through the fuel cell stack. Several PEMs (each one being associated with a particular fuel cell) may be dispersed throughout the stack between the anodes and cathodes of the different fuel cells.
Referring to
FIG. 1
, as an example, a fuel cell stack
10
may be formed out of repeating units called plate modules
12
. Each plate module
12
includes a set of composite plates that may form several fuel cells. For the arrangement depicted in
FIG. 1
, an exemplary plate module
12
a
may include a cathode cooler plate
14
, a bipolar plate
16
, a cathode cooler plate
18
, an anode cooler plate
20
, a bipolar plate
22
and an anode cooler plate
24
that are stacked from bottom to top in the listed order. Each cooler plate acts as a heat exchanger by routing a coolant through flow channels in either the upper or lower surface of the cooler plate to remove heat from the plate module
12
a
. The other surface of each cooler plate includes flow channels to route either hydrogen (for the anode cooler plates
20
and
24
) or oxygen (for the cathode cooler plates
14
and
28
) to an associated fuel cell. The bipolar plates
16
and
22
include flow channels on one surface (top or bottom surface) to route hydrogen to an associated fuel cell and flow channels on the opposing surface to route oxygen to another associated fuel cell. In this arrangement, each fuel cell may be formed in part from one bipolar plate and one cooler plate, as an example. Other fuel cell stacks have other arrangements.
To achieve optimal fuel cell performance, the components of a stack, such as the stack
10
, are assembled and operated under a load or compressive force, which is also referred to as a clamping force, that is applied using a vertical press. The applied clamping force is used to compress gaskets for sealing the mating surfaces between adjacent plates to prevent leakage of the different gases and liquids in the fuel stack. In addition, the applied clamping force is used to provide a consistent pressure across the area of gas diffusion layers (GDLs) to achieve sufficient electrical conductivity between the GDLs and corresponding lands of the fuel cell plates in a stack. As illustrated in
FIG. 1
, one technique of applying the compressive force is by use of tie rods
24
attaching top and bottom end plates
20
and
22
. The number of tie rods used may range from four to twelve. The tie rods
24
may be attached to the end plates
20
and
22
by use of washers and nuts. Typically, the end plates
20
and
22
are relatively thick and are formed of stainless steel or some other metal to provide structural support under the applied clamping force provided by the tie rods
24
. However, the use of heavy stainless steel end plates and numerous tie rods, washers, and nuts lead to a relatively heavy assembly. Further, connecting the tie rods
24
to the end plates
20
and
22
to form the fuel cell assembly involves a relatively large number of steps, which may be time consuming.
Other techniques for applying a compressive force onto a fuel cell stack also exist. One such technique uses compression bands that extend around the end plates of the fuel stack assembly. However, these and other conventional clamping mechanisms are also associated with shortcomings. A need thus continues to exist for an improved apparatus and method for clamping fuel cell stack assemblies.
SUMMARY
In general, according to one embodiment, a fuel cell assembly includes a stack assembly having fuel cell plates. The fuel cell assembly further includes a frame having a bottom section and at least two side sections integrally formed with the bottom section. The stack assembly is placed on the frame bottom section, and one or more fasteners are used to attach the frame to an upper portion of the stack assembly to apply a compressive force on the stack assembly.
Other features of the invention will become apparent from the following description, from the drawing, and from the claims.
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Brunner Adam K.
Mease Kevin L.
Pitts Larry A.
Winslow Alan F.
Kalafut Stephen
Martin Angela J.
Plug Power Inc.
Trop Pruner & Hu P.C.
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