Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
2000-11-14
2003-06-10
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S006000, C429S006000
Reexamination Certificate
active
06576357
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a polymer electrolyte membrane (PEM) fuel cell system with a wetting and/or a cooling with a liquid medium. The polymer electrolyte membrane fuel cell system includes a fuel cell stack and a liquid distributor.
Published, Non-Prosecuted European Patent Application EP 0 743 693 A1, which corresponds to U.S. Pat. No. 5,958,613, discloses a fuel cell system with an anode-side liquid wetting. A gas/liquid mixture is produced with a bubbler, which is made from sintered metal. The bubbler extends over the entire length of the fuel supply line. For this purpose, the fuel gas is fed, via the bubbler, as bubbles into the liquid stream, which flows along the supply line. In the process, the liquid, which in this case is water, forms a coherent film. A disadvantage of this fuel cell system or other water-cooled fuel cell stacks is that water causes corrosion problems in the fuel cell stack. The high consumption of water and process gas is a further disadvantage of this type of wetting. This system is therefore also not suited for electrotraction, because large tanks have to be carried along. Furthermore, the water flow is such that it adequately cools the fuel cell system even in the case of power peaks. Consequently, when the system is used to drive a vehicle, the air stream is never utilised for cooling, which reduces the overall energy efficiency of the vehicle.
Published, Non-Prosecuted German Patent Application DE-A 196 41 143 discloses a wetted polymer electrolyte membrane (PEM) fuel cell in which water is supplied to the active cell faces in the form of drops which can be suspended as an aerosol in the process gas flow or the water can be supplied to the active cell faces through the use of a number of thin lines. In the latter case, there is no appreciable mixing of the gas and water phases in the process, and this reduces the free surface of the water, in other words, the “useful” surface of the water is reduced. A disadvantage of the first-mentioned alternative, that is to say the wetting with the aerosol, is the formation of suspended droplets which prematurely deposit along the feed lines and supply lines. Consequently, only a fraction of the water quantity used reaches the active cell face, and the overall result is an unbalanced wetting of the individual cells. The efficiency of the wetting, in view of the amount of water that is used, is low in both of the wetting and/or cooling systems described. In the case of the configuration with the plurality of thin lines for each active face, a high outlay for its construction is to be expected. This results in high production costs and an increased size and weight of the resulting fuel cell stack.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a polymer electrolyte membrane (PEM) fuel cell system, in particular for mobile applications, which overcomes the above-mentioned disadvantages of the heretofore-known fuel cell systems of this general type and which achieves a uniform and balanced wetting and/or cooling in conjunction with a high efficiency of its water consumption and which can be implemented with the lowest possible constructional outlay, so that the weight and size of the fuel cell system are burdened as little as possible by the system for wetting and/or cooling with a liquid medium. The fuel cell system should furthermore be cost-effective in its production and should in particular be suited for mass production. It is a further object of the invention to provide a method for wetting and/or cooling a fuel cell stack of a fuel cell system which is suitable for mobile applications.
With the foregoing and other objects in view there is provided, in accordance with the invention, a polymer electrolyte membrane fuel cell system, including:
a fuel cell stack having a start plate, an end plate, and at least two fuel cell units disposed between the start plate and the end plate;
two supply lines connected to the fuel cell stack for supplying process gases to the fuel cell units;
two removal lines connected to the fuel cell stack; and
a liquid distributor provided in at least one of the supply a lines and disposed within the fuel cell stack; and
at least one acoustic wave generator connected to the liquid distributor.
In other words, the subject matter of the invention is a polymer electrolyte membrane (PEM) fuel cell system which uses a wetting and/or cooling with a liquid medium and which includes the following elements:
at least two fuel cell units which, together with
a start plate and an end plate, form a fuel cell stack,
two supply lines for the process gases, and
the respective removal lines,
a liquid distributor, which is connected to at least one device for producing acoustic waves, is provided in at least one of the process gas supply lines inside the fuel cell stack.
According to a preferred embodiment of the invention, the device for producing acoustic waves, to which the liquid distributor is connected, generates a standing wave in the liquid distributor and/or into the liquid column in such a way that the standing wave in the liquid distributor and/or in the liquid column has an antinode at the level or height of the gas inlet of each fuel cell unit.
It is preferable to generate in the liquid distributor and/or in the liquid column a standing wave whose wavelength is such that one half of the wavelength corresponds to the spacing distance between two successive fuel cell units.
The device for producing acoustic waves preferably includes at least one piezo actor, which are for example used for producing extremely small droplets (cf. S. Brand and T. Laux: “Einsatzmöglichkeiten und -Bereiche von piezokeramischen Aktoren” [“Possible applications and fields of use of piezoceramic actors”], Volume 1 of the VDI series “Technologiestudien und Marktprognosen zur Mikrosystemtechnik” [“Technological studies and market forecasts for Microsystems technology”]).
The liquid distributor is an essential element of the invention and designates a component which can become saturated with a liquid medium and can be made to oscillate with an acoustic wave generator. This component is configured such that the latter can be accommodated in a process gas supply line without much constructional outlay, that is to say it should be capable of being inserted simply by being pushed or pulled into the process gas supply line. Alternatively, the water distributor is formed from a plurality of pieces and is formed by stacking the fuel cell units when assembling the fuel cell stack.
The liquid distributor can be formed from any material which is suitable for transporting a liquid medium, for example textile (cotton, hemp) and/or plastic (for example nylon, glass fiber and/or carbon fiber and arbitrary mixtures thereof) and/or metal (for example iron, steel, etc.). The liquid distributor is accommodated in one or in both axial supply channel (channels) of a fuel cell stack, and is made to oscillate through the use of acoustic waves. Examples of the liquid distributor are a small tube, a wire, a wick or a hose filled with liquid medium in which an oscillating element, for example a wire, is located. In this case, the hose must be porous, having bores or nozzles through which the liquid medium can exit and be atomised by the oscillation of the hose.
Suitable as liquid medium are all liquids which are also suitable for the system disclosed in the simultaneously filed application entitled “Polymer Electrolyte Membrane Fuel Cell And Method For Operating a Polymer Electrolyte Membrane Fuel Cell System With Liquid Wetting And/Or Cooling” Ser. No. 09/712,395 (Attorney Docket No. GR 98 P 8040). It is preferred in this case to use water or water with additives such as surfactants or similar additives. The invention is not limited to water but includes all other liquid media suitable for cooling and/or wetting of the polymer electrolyte membrane of the fuel cell.
According to a preferred embodiment of the invention, the fuel cell
Chaney Carol
Greenberg Laurence A.
Locher Ralph E.
Siemens Aktiengesellschaft
Stemer Werner H.
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