Clamping system for a fuel cell stack

Details Clamping system for a fuel cell stack Clamping system for a fuel cell stack

2000-02-11

2002-04-16

Kalafut, Stephen (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

C429S010000, C429S006000, C429S006000, C429S006000, C429S006000

Reexamination Certificate

active

06372372

ABSTRACT:

BACKGROUND
The invention relates to a clamping system for a fuel cell stack.
A fuel cell is an electrochemical device that converts chemical energy that is produced by a reaction directly into electrical energy. For example, one type of fuel cell includes a proton exchange membrane (PEM), often called a polymer electrolyte membrane, that permits only protons to pass between an anode and a cathode of the fuel cell. At the anode, diatomic hydrogen (a fuel) is reacted to produce hydrogen protons that pass through the PEM. The electrons produced by this reaction travel through 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. The anodic and cathodic reactions are described by the following equations:
H
2
→2H
+
+2
e
−
at the anode of the cell, and
O
2
+4H
+
+4
e
−
→2H
2
O
at the cathode of the cell.
A typical fuel cell has a terminal voltage near one volt DC. For purposes of producing much larger voltages, several fuel cells may be assembled together to form an arrangement called a fuel cell stack, an arrangement in which the fuel cells are electrically coupled together in series to form a larger DC voltage (a voltage near 100 volts DC, for example) and to provide a larger amount of power.
The fuel cell stack may include flow plates (graphite composite or metal plates, as examples) that are stacked one on top of the other, and each plate may be associated with more than one fuel cell of the stack. The plates may include various surface flow channels and orifices to, as examples, route the 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.
For purposes of directing the reactant, coolant and product flows into and out of the flow channels of the flow plates, the flow plates typically include aligned openings to form manifold passageways in the stack. Gaskets may be located between the flow plates to seal off these manifold passageways and seal off the flow channels that are formed by the flow plates.
FIG. 1
depicts an exemplary fuel cell stack assembly
10
, an assembly that includes a stack
12
of flow plates that are clamped together under a compressive force. To accomplish this, the assembly
10
typically includes end plate
16
and spring plate
20
that are located on opposite ends of the stack
12
to compress the flow plates that are located between the plates. Besides the end plate
16
and spring plate
20
, the assembly
10
may include a mechanism to ensure that a compressive force is maintained on the stack
12
over time, as components within the stack
12
may settle, or flatten, over time and otherwise relieve any applied compressive force.
As an example of this compressive mechanism, the assembly
10
may include another end plate
14
that is secured to the end plate
16
through tie rods
18
that extend through corresponding holes of the spring plate
20
. The spring plate
20
is located between the end plate
14
and the stack
12
, and coiled compression springs
22
may reside between the end plate
14
and spring plate
20
. The tie rods
18
slide through openings in the spring plate
20
and are secured at their ends to the end plates
14
and
16
through nuts
15
and
17
. Due to this arrangement, the springs
22
remain compressed to exert a compressive force on the stack
12
over time even if the components of the stack
12
compress.
To establish connections for external conduits (hoses and/or pipes) to communicate the reactants, coolants and product with the manifold passageways of the stack
12
, the assembly
10
may include short connector conduits, or pipes
24
, that may be integrally formed with the end plate
16
to form a one piece end plate assembly (for example, pipes
24
may be welded to end plate
16
). The pipes
24
form the complex part of the end plate assembly, making the end plate assembly difficult to mass manufacture due to the high cost of the required materials and the multiple operations that may be needed to manufacture the end plate assembly.
Thus, there is a continuing need for an arrangement that addresses one or more of the problems that are stated above, or that improves such functionality and features.
SUMMARY
In an embodiment of the invention, a fuel cell stack assembly includes a stack of fuel cell flow plates that include fluid passageways; pipes to communicate fluids with the fluid passageways; an end plate; and a dielectric manifold. The end plate supports a compressive load to compress the stack, and the end plate includes openings. The manifold is located between the end plate and the stack to communicate the fluids between the pipes and the fluid passageways. The manifold at least partially extends through the openings in the end plate to form a sealed connection between the manifold and the pipes.
In another embodiment of the invention, a fuel cell stack assembly includes first and second end plates; a fuel cell stack of flow plates; at least one spring; and tie rods. The stack is located between the first and second end plates, and the spring(s) have ends that extend across different edges of the first end plate. Each tie rod has a first end that is connected to one of the ends of said at least one spring and a second end that is connected to the second end plate to cause the first and second end plates to apply a compressive force to the stack.
Advantages and other features of the invention will become apparent from the following description, from the drawing and from the claims.


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