Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2001-05-15
2004-02-03
Bell, Bruce F. (Department: 1746)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S006000, C429S006000, C429S010000, C429S006000, C429S006000, C429S010000, C429S010000
Reexamination Certificate
active
06686081
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to methods and apparatuses for driving fluids in a fuel cell, and more particularly, to methods and apparatuses for moving fluids, specifically water, fuel, a fuel mixture and liquid effluent, in a direct methanol fuel cell system using self-generated pressure differentials.
2. Background of the Prior Art
Substantial research has been dedicated to development of direct oxidation fuel cell systems, including but not limited to direct methanol fuel cell systems for use in portable electronics in recent years. Those skilled in the art will recognize a direct oxidation fuel cell is one that does not require fuel to be processed following its introduction into the fuel cell system. For a direct methanol fuel cell system to operate properly, it is inperative that the fluids in the system are available to the fuel cell for the generation of electricity.
Currently, direct oxidation fuel cell systems, including direct methanol fuel cell systems (DMFC Systems) are typically operated in a particular physical orientation in order for the system to properly operate (e.g., fuel supply, water supply). However, because many potential applications for DMFC Systems are operated in a variety of orientations, it is imperative that the DMFC System be able to operate regardless of its orientation.
Previous methods of supplying fuel to a fuel cell have focused on directing the fuel with a pump or series of pumps, as shown in FIG.
1
. Alternatively, pressurized fuel tanks or cartridges may be used to drive fuel into the system. However, pumps result in parasitic power loss, and fabrication of pressurized fuel tanks that will effectively deliver fuel to a direct methanol fuel cell (DMFC) is cost prohibitive and difficult. In addition, in a DMFC System that recirculates the unreacted methanol/water fuel mixture and adds neat methanol to provide adequate fuel to the system, it is necessary to ensure that the new methanol is evenly mixed in the mixture prior to introduction into the anode.
It is therefore desirable to have a fuel delivery and mixture maintaining system that does not require that a pump or other power consuming device be used to manage fluid flow and composition within the fuel cell system.
SUMMARY OF THE INVENTION
The present invention provides unique methods and apparatuses for driving fluids throughout a fuel cell system, and for mixing fuel and water into a fuel mixture using pressure differentials produced by an effluent gas. Thus, the present invention allows for the movement and mixing of fluids in a direct oxidation fuel cell system without the use of electrically driven pumps or other electrically driven apparatuses.
The present invention presents novel apparatuses and methods to utilize anodically generated CO
2
to maintain and provide a sufficient flow of methanol and water ultimately to the anode chamber of a fuel cell. It will be understood by those skilled in the art that the invention can be used with a variety of fuel cell configurations, including but not limited to configurations utilizing a bipolar stack, as well as those that use multiple Protonically Conductive
Membranes assembled in a single plane, or single-cell Direct Methanol Fuel Cell System designs.
Accordingly, it is an object of the present invention to provide a means to ensure that a consistent supply of the fuel mixture is provided to an anode chamber of a fuel cell to enable electricity generating reactions to continue
It is also an object of the present invention to provide orientation independence for a fuel cell system. That is, the present invention allows a fuel cell system to operate in any variety of orientations. In prior art direct oxidation fuel cell systems, the fuel cell is typically required to remain in a single position, so that gravity is used to aid in movement of liquids/gases in the system. Accordingly, the present invention allows for direct oxidation fuel cell systems to be used in portable electronics.
It is yet a further object of the present invention to provide a fuel cell system to ensure that proper amounts of the constituents that comprise the fuel mixture are supplied to a mixing chamber.
It is another object of the present invention to ensure that proper flow of the fuel mixture, liquid anode effluent comprised of unreacted fuel and water, added fuel and/or added water, occurs. Moreover, the present invention allows for the accelerated and enhanced mixing of “neat” methanol with—the liquid anode effluent and cathodically generated water.
In each of the embodiments of the invention, it is important to note that the fuel may be delivered to the system via a cartridge (similar to that used in a fountain pen) or through a tank that may be refilled. It should be further understood that the valves described in the present invention are preferably electrically actuated and allow the flow of fluid only when open, and preferably only in one direction.
Accordingly, in a first aspect of the present invention, a fuel cell system includes a housing defining an anode chamber and a cathode chamber and includes a catalyst, a protonically conductive (but electronically non-conductive) membrane positioned between the anode chamber and the cathode chamber and a first vent connecting said anode chamber with the ambient environment. The catalyst is preferably applied to the anode and cathode faces of the protonically conductive membrane. The system also includes a fuel chamber in gaseous communication with the anode chamber via a first valve, a water chamber in gaseous communication with the anode chamber via a second valve, and a mixing chamber having a second vent. The mixing chamber is in gaseous communication with the anode chamber via a third valve and receives fuel from the fuel chamber through a fuel valve, water from said water chamber via a water valve, and liquid effluent from the anode chamber via a liquid effluent valve. The mixing chamber also provides a fuel mixture to the anode chamber via a fuel mixture valve.
In yet another aspect of the present invention, a method for moving a liquid between chambers of a fuel cell system includes sealing off an anode chamber and a first chamber having a liquid stored therein of a fuel cell system from external pressure creating a closed sub-system, while allowing an effluent gas produced in the anode chamber to freely flow between the anode chamber and the first chamber, and storing a portion of said effluent gas in the first chamber. A first pressure of the sub-system increases due to an increasing volume of effluent gas being produced—in the anode chamber. The method also includes sealing off in the first chamber from the anode chamber, substantially ceasing the flow of the effluent gas between the anode chamber and the first chamber, creating a pressure differential between a second chamber and the first chamber by lowering a second pressure in the second chamber to a point below the first pressure, opening a conduit between the first chamber and the second chamber, where, as a result of the pressure differential, the liquid stored in the first chamber flows into the second chamber via the second conduit.
In the above aspect, the first and second chambers may be the following:
First Chamber
Liquid
Second Chamber
mixing chamber
fuel mixture
anode chamber
water chamber
water
mixing chamber
fuel chamber
fuel
mixing chamber
anode chamber
liquid effluent
mixing chamber
In yet another aspect of the present invention, a method for agitating a liquid stored in a first chamber of a fuel cell system includes sealing off the anode chamber from external pressure, storing an effluent gas produced in the anode chamber within the anode chamber, where pressure within the anode chamber increases over a period of time due to an increasing volume of effluent gas being produced. The method also includes creating a pressure differential between the first chamber and the anode chamber by lowering a first pressure of a first chamber to a point below the anode pressure, and op
Bell Bruce F.
Mintz Levin Cohn Ferris Glovsky and Popeo P.C.
MTI Microfuel Cells Inc.
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