Intermediate element for thermal, electrical and mechanical...

Details Intermediate element for thermal, electrical and mechanical... Intermediate element for thermal, electrical and mechanical...

1999-03-04

2001-10-09

Brouillette, Gabrielle (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

C429S010000, C429S006000

Reexamination Certificate

active

06299999

ABSTRACT:

FIELD OF THE INVENTION
The invention is directed to an intermediate element for thermal, electrical and mechanical connection of two parts, particularly two fuel cells.
BACKGROUND OF THE INVENTION
For example, bipolar plates are known for the electrical, thermal and mechanical connection of fuel cells, whereby these bipolar plates are fashioned continuous, i.e. without holes or clearances, so that a reaction medium that flows along the active surface of a bipolar plate can be located either above or below this plate according to the Prior Art. All other known intermediate elements that are not bipolar plates respectively use only one surface for the contact with the medium.
The continuous fashioning of the bipolar plates also has the disadvantage that the cooling or reaction medium is conducted over the active surface in a flow without an exchange of the medium occurring from the middle of the flow to the outer region of the flow. When the medium at the outside of the flow has been used, it cannot be replaced by unused reaction agent proceeding from the middle of the flow but must be replaced by new agent located at the outside of the flow, so that, to be brief, a high flow velocity of agent is required given optimally small agent flow diameters. It is thereby disadvantageous that, even given small agent flow diameters, the part of the agent that is in the middle of the flow always flows through the system unused.
Finally, the known bipolar plates or intermediate elements exhibit the disadvantage that the pressure transmission occurs non-uniform, namely with peak loads at the highest elevations of the bipolar plates.
The known bipolar plates and/or intermediate elements thus not only lack a possibility of effecting an exchange of the agent from the middle of the agent flow toward the outside of the flow within the agent flow on their active surface, a possibility of using the surface present at both sides (and, for example, effective in the cooling system) for contacting with agent but also lack the capability of forwarding mechanical pressure as uniformly as possible across their entire surface.
There is thus a need for bipolar plates that, just like the known bipolar plates, can be utilized as electrically, mechanically and thermally connecting intermediate elements in fuel cell stacks and that simultaneously reduce or entirely eliminate the aforementioned disadvantages.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to make an intermediate element or a bipolar plate available that is fashioned such that an exchange of the agent toward the outside regions from the middle of the agent flow is possible on its active surface. It is also an object of the invention to create an intermediate element that uniformly transfers the mechanical pressure. Finally, another object of the invention is to optimize the actively used surface of intermediate elements.
A general perception of the invention is that, due to the fashioning of sharp edges along the active surface of the intermediate element of the bipolar plate, the agent experiences turbulence when it flows along the active surface that effects an exchange of agent from the middle of the agent stream or flow toward the outer regions. It is also a general perception of the invention that the active surface of a bipolar plate can be multiplied by the formation of holes and clearances given the same outlay for material. Finally, it has been recognized in the framework of the invention that a plurality of elevations and depressions on an intermediate element leads to a uniform pressure transmission.
The subject matter of the invention is a corrugated intermediate element for thermal, mechanical and electrical connection of two parts, whereby each corrugation is multiply interrupted along its wave hill of wave valley and is coined upward and downward in alternation.
The intermediate element is preferably made of a material with good thermal and electrical conductivity that also comprises suitable elastic properties for the transmission of mechanical pressure.
In a preferred embodiment, the intermediate element is made of a metal such as, for example, spring bronze or other copper or aluminum alloys. For reducing the contact resistance in the formation of a “stack”, i.e. of a fuel cell stack, for example of a battery, the inventive intermediate elements can be subject to a surface treatment before their incorporation such as, for example, a gold plating. Such a surface treatment is usually implemented for improving the electrical and thermal conductivity of bipolar plates.
The thickness of the intermediate elements can amount to up to 0.5 mm; it preferably amounts to between 0.001 and 0.4 mm, and intermediate elements with a thickness of approximately 0.05 are especially preferred.
What are referred to here as “corrugated intermediate element” or “corrugated bipolar plate” are flat, thermally, mechanically and electrically conductive plates, sheets, disks or other, more planarly fashioned bodies that exhibit a corrugated structure similar to a corrugated sheet. The height of the wave hills or, respectively, the difference of the heights between wave hill and wave valley are thereby arbitrary and correspond to the standard dimensions of intermediate elements, particularly those that are utilized in fuel cell stacks.
What are referred to as “individual interruption of the corrugation along its wave hill or wave valley” are the clearances that enable the fashioning of individual lamellae bent down and up in alternation that are bent out similar to blades. The term “blades” can thereby refer to “bent out portions” rounded off at the top as well as pointed at the top up to entirely pointed (labeled
2
,
2
a
and
2
b
in FIG.
1
).
What is achieved as a result of this simple design measure of the aforementioned interruptions is that the agent can flow not only either above or below the intermediate element; rather, it is thus possible to simultaneously conduct the agent at the top and bottom along the intermediate element. The surface of the intermediate element is thereby substantially increased, i.e. up to a factor of more than 10. As a result of enlarging the surface, the “active surface”, i.w., for example, the contact surface that is available for the thermal contact of the bipolar plate with the coolant, is also increased. That serves to increase the efficiency of the affected system.
By coining the lamellae—upward and downward in alternation—, edges are created along a corrugation, so that the agent stream or flow flowing along experiences turbulence. What is here referred to as “agent stream” is the flow or stream of the reaction agent respectively under consideration (for example, the coolant) that flows along the active surface of an intermediate element or of a bipolar plate that is relevant to it and thereby reacts in conformity with the system or is consumed or is heated.
Both the enlargement of the active surface of the intermediate element as well as the creation of turbulence in the agent stream of the coolant or reaction agent improve the efficiency, i.e. the effective utilization of the agent in the system.
A further advantage of the inventive design of the intermediate elements with respect to the pressure transmission is that the alternating coining of the lamellae toward the top and bottom effects that the pressure is uniformly transmitted from one part to the next, for example from one fuel cell to the next.
Any type of coolant such as, for example, air, inert gas, other gasses or fluids is referred to here as coolant. However, the coolant air or some other gaseous coolant is preferably inventively employed.
The invention is applicable to all types of fuel cells, but preferably to the PEM (polymer electrolyte membrane) fuel cell. In particular, the manufacture of fuel cell stacks or “stack” of PEM fuel cells that are operated with air cooling (air-cooled PEM batteries) was taken into consideration in this invention.
In an embodiment, the present invention provides an intermediate element fo

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