Patent Application
20090017337
The invention relates to a pressure sensor and, more particularly, to a fuel cell pressure sensor adapted to sense a pressure within a flow channel of the fuel cell.
Fuel cell systems are increasingly being used as a power source in a wide variety of applications. Fuel cell systems have been proposed for use in power consumers such as vehicles as a replacement for internal combustion engines, for example. Such a system is disclosed in commonly owned U.S. patent application Ser. No. 10/418,536, hereby incorporated herein by reference in its entirety. Fuel cells may also be used as stationary electric power plants in buildings and residences, as portable power in video cameras, computers, and the like. Typically, the fuel cells generate electricity used to charge batteries or to provide power for an electric motor.
Fuel cells are electrochemical devices which directly combine a fuel such as hydrogen and an oxidant such as oxygen to produce electricity. Other fuels can be used such as natural gas, methanol, gasoline, and coal-derived synthetic fuels, for example.
The basic process employed by a fuel cell is efficient, substantially pollution-free, quiet, free from moving parts (other than an air compressor, cooling fans, pumps and actuators), and may be constructed to leave only heat and water as by-products. The term “fuel cell” is typically used to refer to either a single cell or a plurality of cells depending upon the context in which it is used. The plurality of cells is typically bundled together and arranged to form a stack with the plurality of cells commonly arranged in electrical series. Since single fuel cells can be assembled into stacks of varying sizes, systems can be designed to produce a desired energy output level providing flexibility of design for different applications.
Different fuel cell types can be provided such as phosphoric acid, alkaline, molten carbonate, solid oxide, and proton exchange membrane (PEM), for example. The basic components of a PEM-type fuel cell are two electrodes separated by a polymer membrane electrolyte. Each electrode is coated on one side with a thin catalyst layer. The electrodes, catalyst, and membrane together form a membrane electrode assembly (MEA).
In a typical PEM-type fuel cell, the MEA is sandwiched between “anode” and “cathode” diffusion mediums (hereinafter “DM's”) or diffusion layers that are formed from a resilient, conductive, and gas permeable material such as carbon fabric or paper. The DM's serve as the primary current collectors for the anode and cathode as well as provide mechanical support for the MEA. The DM's and MEA are pressed between a pair of electronically conductive plates which serve as secondary current collectors for collecting the current from the primary current collectors. The plates conduct current between adjacent cells internally of the stack in the case of bipolar plates and conduct current externally of the stack (in the case of monopolar plates at the end of the stack).
The secondary current collector plates each contain at least one active region that distributes the gaseous reactants over the major faces of the anode and cathode. These active regions, also known as flow fields, typically include a plurality of lands which engage the primary current collector and define a plurality of grooves or flow channels therebetween. In a hydrogen fuel cell, the channels supply the hydrogen and the oxygen to the electrodes on either side of the PEM from an intake manifold. In particular, the hydrogen flows through the channels to the anode where the catalyst promotes separation into protons and electrons. On the opposite side of the PEM, the oxygen flows through the channels to the cathode where the oxygen attracts the hydrogen protons through the PEM. The electrons are captured as useful energy through an external circuit and are combined with the protons and oxygen to produce water vapor at the cathode side.
The flow of the reactants through the channels must be precisely controlled to maintain the optimum performance of the fuel cell. The flows are typically monitored by one or more pressure sensors in communication with the flow paths of the reactants. False pressure readings by the sensors can result in a low reactant pressure within the fuel cell. Low reactant pressures can lead to an insufficient supply of the reactants needed to produce the required electrical output. Alternatively, false pressure readings by the sensors can result in a high reactant pressure that can permanently damage the fuel cell. Known pressure sensors are susceptible to such false readings when the fuel cell is operating at a sub-zero temperature, or a temperature below the freezing point of water. Such temperatures may cause the water vapor within the fuel cell to condense and freeze. The frozen water condensate can cause false readings in the known pressure sensors when the frozen condensate blocks the communication between the reactant flow path and the sensor.
It would be desirable to develop a pressure sensor that militates against a false pressure reading within a fuel cell under operating conditions below the freezing point of water.
Compatible and attuned with the present invention, a pressure sensor that militates against a false pressure reading within a fuel cell under operating conditions below the freezing point of water has surprisingly been discovered.
In one embodiment, a pressure sensor for use in a fuel cell comprises a body having a first end and a second end and including a cavity formed therein, the cavity adapted to contain a first fluid; and a membrane disposed at the second end of the body to seal off the cavity, wherein a pressure of a second fluid in communication with the membrane is transferred through the membrane to the first fluid.
In another embodiment, a fuel cell comprises at least one pressure sensor including a body having a first end and a second end and including a cavity formed therein, the cavity adapted to contain a first fluid; at least one flow channel adapted to provide a flow path for a second fluid, the second fluid being one of a fuel, an oxidant, and a coolant; a communication path disposed between the flow channel and the pressure sensor, the communication path adapted to contain the first fluid and including at least one membrane disposed therein, the membrane separating the first fluid from the second fluid, wherein a pressure of the second fluid is transferred through the membrane and the first fluid to the pressure sensor.
In another embodiment, a fuel cell stack comprises at least one pressure sensor including a body having a first end and a second end and including a cavity formed therein, the cavity adapted to contain a first fluid, and a membrane disposed at the second end of the body to seal off the cavity, wherein a pressure of a second fluid in communication with the membrane is transferred through the membrane to the first fluid; and at least one fuel cell including at least one flow channel adapted to provide a flow path for the second fluid, the second fluid being one of a fuel, an oxidant, and a coolant.
The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which:
The following detailed description and appended drawings describe and illustrate various exemplary embodiments of the invention. The description and drawings serve to enable one skilled in the art to make and use the invention, and are not intended to limit the scope of the invention in any manner.
One end of the pressure sensor 10 includes a connection 16 to a measuring device (not shown). An opposite end of the pressure sensor 10 includes a communication path 18 formed therein and in fluid communication with the flow channel 14. An o-ring 20 is provided between the pressure sensor 10 and the fuel cell 12 to provide a substantially fluid tight seal therebetween. It should be understood that other sealing means can be used as desired to achieve the substantially fluid tight seal.
In operation the fluid 15 in the flow channel 14 is in communication with the pressure sensor 10 through the communication path 18. The pressure sensor 10 includes a transducer (not shown) within the body 11 that converts a pressure of the fluid 15 into a representative electrical signal. The electrical signal is then relayed through the connection 16 to the measuring device. The measuring device interprets the electrical signal as a pressure reading of the fluid 15. The measuring device cooperates with other control devices (not shown) such as a pressure regulator that adjust a flow of the fluid 15 in the flow channel 14 to maintain a desired fluid pressure therein.
The fluid 15 within the flow channel 14 is often a gas that includes water vapor. At operating temperatures below the freezing point of water, droplets of water condensate can form and freeze on a surface of the flow channel 14. As shown in
One end of the pressure sensor 50 includes a connection 16′ to a measuring device (not shown). An opposite end of the pressure sensor 50 includes a substantially conical shaped cavity 54 formed therein. It should be understood that the cavity 54 may be cubical, cylindrical, or otherwise shaped, as desired. A fluid 56 is provided in the cavity 54. A membrane 58 is disposed on the body 52 to seal off the cavity 54 and seal the fluid 56 therein. In the embodiment shown, the fluid 56 is a freeze-resistant liquid such as an ethylene glycol and water solution that has a freeze point lower than water, and the low temperature operating conditions of the fuel cell 12′. The low freezing point of the freeze-resistant liquid prevents the freeze-resistant liquid from freezing while the fuel cell 12′ is operating at such low temperatures. It should be understood that other fluids can be used as desired. An o-ring 60 is provided between the pressure sensor 50 and the fuel cell 12′ to provide a substantially fluid tight seal therebetween. It should be understood that other sealing means can be used as desired to achieve the substantially fluid tight seal.
In operation, the fluid 15′ in the flow channel 14′ is in communication with the membrane 58. The fluid 15′ exerts a pressure on the membrane 58 which is transferred to the fluid 56. The membrane 58 is adapted to cooperate with the fluid 56 to communicate the pressure of the fluid 15′ to a transducer (not shown) within the body 52 of the pressure sensor 50. The transducer converts the pressure of the fluid 15′ into a representative electrical signal. The electrical signal is then relayed through the connection 16′ to a measuring device (not shown). The measuring device interprets the electrical signal as a pressure reading of the fluid 15′. The measuring device then cooperates with other control devices (not shown) such as a pressure regulator that adjust a flow of the fluid 15′ in the flow channel 14′ to maintain the desired fluid pressure therein. It is understood that other systems could be used to read, convert, and relay a pressure reading in place of the electrical system such as pneumatic, for example.
As discussed above, the droplets of water condensate can form within the flow channel 14′ and freeze on a surface thereof.
The blockage of the communication between the flow channel 14′ and the transducer within the body 52 of the pressure sensor 50 can lead to a low pressure within the flow channel 14′ or a high pressure within the flow channel 14′. Either condition can result in a shutting down of the production of electricity by the fuel cell 12′. The loss of the electrical production from the fuel cell 12′ is often referred to as a “walk home failure”. A vehicle using the electrical output from the fuel cell 12′ to power an electrical drive motor will be rendered inoperable upon such loss of electrical production. The pressure sensor 50 militates against fuel cell shutdown and the inconvenience caused to a person relying on the continued uninterrupted electrical supply from the fuel cell 12′.
The pressure sensor 50 shown in
A communication path 112 is formed within the structural member of the fuel cell 12″. The communication path 112 is a channel or conduit formed in a selected portion of the fuel cell 12″. The communication path 112 has a first section 116 having a substantially conically shape and a second section 118 having a substantially constant cross-sectional shape. The fluid 106 fills the communication path 112 and the cavity 104 in the pressure sensor 100. In the embodiment shown, the fluid 106 is a freeze-resistant liquid such as an ethylene glycol and water solution that has a freeze point lower than water, and the low temperature operating conditions of the fuel cell 12″. The low freezing point of the freeze-resistant liquid prevents the freeze-resistant liquid from freezing while the fuel cell 12″ is operating at such low temperatures. It should be understood that other fluids can be used as desired. A membrane 124 is disposed on the fuel cell 12″ to seal off the communication path 112 and seal the fluid 106 therein.
In operation, the pressure sensor 100 shown in
From the foregoing description, one ordinarily skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications to the invention to adapt it to various usages and conditions.
