Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
1999-06-14
2001-10-23
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000
Reexamination Certificate
active
06306533
ABSTRACT:
FIELD OF THE INVENTION
The invention is directed to a novel cooling system for a battery of fuel cells that contains at least two fuel cells, each of which comprises a membrane-electrode unit and two collector plates.
BACKGROUND OF THE INVENTION
Up to now, fuel cell batteries with cooling systems are known wherein coolants flow in bipolar plates that are located between the individual fuel cell units of a battery. In addition, newer cooling systems have been disclosed for these batteries that are cooled without bipolar plates or filter press technology in a gas or in a fluid bath (see, e.g. German Letters Patent 44 42 285) and comprise fuel cell units that can be individually handled within the battery.
Sealing problems particularly arise in the battery cooling with bipolar plates because regions lie next to one another in which oxidant and fuel, which must be dependably sealed off from one another, are conducted. Given the fuel cell batteries without bipolar plates, which have only been known for a short time (see, e.g. German Letters Patent 44 42 285), fundamentally only two cooling systems have hitherto been known that both have the coolant flow through the battery in a free stream.
Under certain circumstances, however, the problem of uniform distribution and flow-through of the coolant within the fuel cell battery arises in the concept of fluid cooling because the areas close to inlet and discharge openings of the battery have a more intense flow and are thus more intensively cooled than the other areas of the battery. It can also be disadvantageous that many component parts of the battery enter into communication with the coolant—especially when coolants that are incompatible with the materials of the fuel cells are employed.
The full content of the patent bearing serial number German Letters Patent 44 42 285 is herewith referenced and the entire disclosure thereof is incorporated by reference into the subject matter of the present specification.
There is a need for economical batteries of fuel cells, i.e. batteries constructed without bipolar plates, wherein the cooling system assures an optimally uniform distribution of the coolant within the battery. There is also a need in fuel cell batteries with bipolar plates for a cooling capacity that can be added in when the battery must temporarily yield greater powers.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to make a cooling system for a fuel cell battery, particularly a PEM fuel cell battery, available that assures an optimally uniform flow-through of a fuel cell battery with coolant and/or that can be added in as needed to an existing cooling.
The subject matter of the present invention is therefore a battery and a method for the manufacture of a battery composed of at least two fuel cells each of which comprises a membrane-electrode unit and two collector plates, whereby a cooling card that has thermal contact to at least one of the neighboring fuel cells is located between the fuel cells.
In one embodiment of the invention, the individual cooling cards of a battery are connected by conduits in which coolant is conveyed. Electrically, however, the cooling cards are insulated from one another. It is cost-beneficial when the cooling cards of a battery (or of a plurality of batteries) are connected to one another but when they are also connected to an external heat exchanger that serves for regeneration of the coolant and that, for example, can also be fashioned in the form of a heat engine.
In one embodiment, the cooling card is filled such with endothermically reacting medium that exhaust gases of the endothermic reaction can escape via the sealing frame element (for example, alcohol), and enough cooling capacity is contained in a cooling card for the operating duration of the battery that no supply or disposal line of the cooling card are required.
In a practical development of the invention, the cooling cards themselves can be simply and cost-beneficially manufactured because they can be assembled by simple scaling and/or clamping and/or plugging of two coined plates.
In another advantageous development, the cooling cards are joined to the respectively adjacent collector plates of the adjoining fuel cells by and adhesive that is thermally and/or electrically conductive. In yet another embodiment, the cooling cards can be inserted as needed into the bipolar plates. Finally, the cooling cards of another embodiment of the invention can be respectively integrated in an intermediate element that is located between the collector plates of the individual fuel cells. Any element that serves for
transmission of the mechanical pressure between the individual fuel cells,
transmission of the electrical current between the individual fuel cells, and
elimination of the dissipated heat from the collector plate within a fuel cell battery is suited as intermediate element. For example, the intermediate element disclosed in the patent application bearing the German serial number 196 359 0.5 (of the same assignee) is especially well-suited.
What is understood here by “battery” is a unit or stack of at least two series-connected fuel cells. Dependent on the application of the fuel cell battery (stationary fields of employment of the PEM batteries are, for example, the applications in household energy supply and in decentralized power generating; electro-traction is a mobile application), practice will be a matter of units having a far greater number of individual, series-connected fuel cells.
Fuel cells that were disclosed by German Letters Patent 44 42 285 already cited above are preferably referred to here as “individual fuel cell” or “fuel cell unit”. Said fuel cells are not limited to the PEM fuel cells (see column 3, lines 18-27 of the German Patent) and are individually handled units that respectively comprise a negative pole plate, a membrane-electrode unit and a positive pole plate, whereby the aforementioned component parts are connected to one another by a frame element in a mechanically rigid, gas-tight and electronically insulating fashion. The invention, however, is not limited to batteries of these fuel cells but, as already mentioned, also covers batteries that are manufactured with the filter press technology upon employment of bipolar plates.
In the present case, the term “membrane-electrode unit” is used in its sense familiar to a person skilled in the art, as explained in the book “Brennstoffzellen”, edited by Ledjeff, and published by Müller Verlag or in the patent specifications that have been cited.
What is referred to here as “collector or contact plate” is every terminating plate of a fuel cell unit of the battery. This can thereby be a matter both of traditional “bipolar plates” or “bipolar plates” wherein two collector plates are combined to form bipolar plate as well as individual pole plates as disclosed, for example, by German Letters Patent 44 42 285. Among other things, traditional bipolar plates are described in the book “Brennstoffzellen” edited by Ledjeff.
What is understood by “cooling card” is every type of a welded or otherwise fashioned plate that forms a cavity for the coolant. For example, these are a matter of double plates that lie on top of one another and are joined to one another in sealing fashion along the edges. The cooling cards can contain openings for the acceptance and discharge of coolant that are surrounded such with seal elements or sealing lips that, by simply stacking the cooling cards, lines through which the coolant can flow are formed between them.
The cavities in the individual cooling cards of a fuel cell battery or of a plurality of batteries can be connected to one another via lines. These lines can be connected to any type of cooling circulation system, whereby the fashioning of the cooling circulation system is in turn completely arbitrary, for example can be fashioned from heat engine to simple beaters. The material of the plates that, together with the seal elements, form the cooling card must be electrically and thermally conductive mate
Helmolt Rittmar Von
Mund Konrad
Kalafut Stephen
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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