Abstract:
An air humidifier is disclosed, the air humidifier including a caseless humidification module, wherein sealing properties of the humidification module are optimized.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/781,869 filed Mar. 13, 2006. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a fuel cell and more particularly to an air humidifier for a fuel cell including a caseless humidification module. 
     BACKGROUND OF THE INVENTION 
     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. The oxygen is typically supplied by an air stream. The hydrogen and oxygen combine to result in the formation of water. 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&#39;s”) or diffusion layers that are formed from a resilient, conductive, and gas permeable material such as carbon fabric or paper. The DM&#39;s serve as the primary current collectors for the anode and cathode as well as provide mechanical support for the MEA. The DM&#39;s and MEA are pressed between a pair of electrically 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. The channels supply the hydrogen and the oxygen to the electrodes on either side of the PEM. 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. 
     Many fuel cells use internal membranes, such as the PEM type fuel cell which includes proton exchange membranes, also referred to as polymer electrolyte membranes. In order to perform within a desired efficiency range, it is desirable to maintain the membranes in a moist condition. 
     Therefore, it is necessary to provide a means for maintaining the fuel cell membranes in the moist condition. This helps avoid damage to or a shortened life of the membranes, as well as to maintain the desired efficiency of operation. Humidification in a fuel cell is discussed in commonly owned U.S. patent application Ser. No. 10/797,671 to Goebel et al.; commonly owned U.S. patent application Ser. No. 10/912,298 to Sennoun et al.; and commonly owned U.S. patent application Ser. No. 11/087,911 to Forte, each of which is hereby incorporated herein by reference in its entirety. 
     To maintain a desired moisture level, an air humidifier is frequently used to humidify the air stream used in the fuel cell. The air humidifier normally consists of a round or box type air humidification module that is installed into a housing of the air humidifier. Examples of this type of air humidifier are shown and described in U.S. patent application Ser. No. 10/516,483 to Tanihara et al., hereby incorporated herein by reference in its entirety, and U.S. Pat. No. 6,471,195, hereby incorporated herein by reference in its entirety. A common structure used to seal the air humidification module with the housing of the air humidifier is a pair of spaced apart radial O-ring gaskets. The O-ring gaskets seal air streams within the housing from one another and minimize air leakage therebetween. 
     The O-ring gaskets have several advantages such as universal availability, usability, and serviceability. However, certain shortcomings also exist. Seating surfaces for the o-ring gaskets demand high precision in the geometry of the involved surfaces. Additionally, the gasket area becomes rather voluminous to militate against movement of the o-ring gaskets which results in leakage. Finally, the air humidification module requires an additional housing or an internal support to enhance the stiffness thereof during the assembly process of the air humidifier. 
     In order to achieve the demanded precision, complex manufacturing is necessary which results in a higher cost. The additional housing of the air humidification module is at present necessary for enhancing the stiffness, but the housing increases the complexity, cost, weight, and the required package space. For production of prototypes, the use of radial O-ring gaskets is acceptable since the cost and component space requirements are not as limiting as required for mass production. However, use of the O-ring gaskets in mass production is not practical. 
     It would be desirable to produce a humidifier including a caseless humidification module, wherein sealing properties of the humidification module are optimized. 
     SUMMARY OF THE INVENTION 
     Consistent and consonant with the present invention, a humidifier including a caseless humidification module, wherein sealing properties of the humidification module are optimized, has surprisingly been discovered. 
     In one embodiment, the humidifier comprises a hollow housing including a first channel and a second channel formed in an inner surface thereof; a humidification module having a first end and a second end, the first end having a first radially outwardly extending collar and the second end having a second radially outwardly extending collar, the first collar and the second collar respectively disposed in and substantially sealed in the first channel and the second channel of the housing to form a first chamber and a second chamber in the housing, wherein the first chamber is adapted to receive a first fluid and the second chamber is adapted to receive a second fluid; and a vapor permeable membrane disposed in the module and adapted to facilitate a vapor transfer between the first fluid and the second fluid. 
     In another embodiment, the humidifier comprises a hollow housing including a first channel and a second channel formed in an inner surface thereof, the housing having a first inlet aperture, a second inlet aperture, a first outlet aperture, and a second outlet aperture formed therein; a humidification module having a first end and a second end, the first end having a first radially outwardly extending collar and the second end having a second radially outwardly extending collar, each of the collars having a central aperture formed therein, the module including a water permeable membrane formed by a plurality of hollow fibers and disposed between the first collar and the second collar, wherein the first collar and the second collar are respectively disposed in the first channel and the second channel of the housing; and a sealing material disposed between each of the first collar and the first channel and the second collar and the second channel to form a substantially fluid-tight seal, the housing cooperating with the sealing material and the collars of the module to form a first chamber and a second chamber, the first chamber providing a first fluid conduit from the first inlet aperture around an exterior of the fibers of the membrane to the first outlet aperture, and the second chamber providing a second fluid conduit from the second inlet aperture through the central apertures formed in the collars and an interior of the fibers of the membrane to the second outlet aperture. 
     In yet another embodiment, the humidifier comprises a hollow housing including a first channel and a second channel formed in an inner surface thereof, the housing having a first inlet aperture, a second inlet aperture, a first outlet aperture, and a second outlet aperture formed therein; a humidification module having a first end and a second end, the first end having a first radially outwardly extending collar and the second end having a second radially outwardly extending collar, each of the collars having a central aperture formed therein, the first collar and the second collar respectively disposed in and substantially sealed in the first channel and the second channel of the housing to form a first chamber and a second chamber in the housing, the first chamber providing a first fluid conduit from the first inlet aperture to the first outlet aperture and the second chamber providing a second fluid conduit from the second inlet aperture through the central apertures formed in the collars to the second outlet aperture; and a water vapor permeable membrane disposed in the module and adapted to facilitate a water vapor transfer between the first fluid conduit and the second fluid conduit. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is a perspective view of an air humidification module for a humidifier for a fuel cell according to the prior art; 
         FIG. 2  is a perspective view of a humidifier for a fuel cell according to an embodiment of the invention and showing a housing of the humidifier in an open condition to facilitate a viewing of an air humidification module disposed in the housing; and 
         FIG. 3  is a fragmentary perspective view of the air humidification module of  FIG. 2  and showing a portion of the housing in section. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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. In respect of the methods disclosed, the steps presented are exemplary in nature, and thus, the order of the steps is not necessary or critical. 
       FIG. 1  shows an air humidification module  10  according to the prior art. The module  10  is generally cylindrical with a circular cross-section. Other cross-sectional shapes are also used such as rectangular. The module  10  includes a longitudinal aperture  12  formed therein. A housing (not shown) surrounds the module  10 . The housing includes a first inlet (not shown) and a first outlet (not shown) formed therein to facilitate a flow of a first fluid therethrough and communicate with the aperture  12 . A second inlet (not shown) and a second outlet (not shown) are also formed in the housing to facilitate a flow of a second fluid therethrough and respectively communicate with an inlet  27  and an outlet  28  of the module  10 . Typically, the first fluid and the second fluid are oxygen or air having different water vapor partial pressures or humidity levels, although other fluids can be used. 
     Each end of the module  10  includes a first annular ring  14  and a spaced apart second annular ring  16 . The first annular ring  14  is disposed adjacent the end of the module  10 . A groove  18  is formed in an outer surface of the first annular ring  14 . A first O-ring  20  is disposed in the groove  18 . 
     The second annular ring  16  is spaced from the first annular ring  14  in a direction away from the end of the module  10 . A groove  22  is formed in an outer surface of the second annular ring  16  which receives a second O-ring  24  therein. 
     An outer wall  26  of the module  10  surrounds a membrane  29  such as a hollow fiber membrane. The membrane  29  is a water vapor permeable membrane. It is desirable that a permeation rate of water vapor through the membrane  29  is higher than a permeation rate of the first fluid and the second fluid through the membrane  29 . A ratio of the water vapor permeation rate to the fluid permeation rate of 10:1 or more has been found to provide satisfactory results, although other ratios can be used. 
     In operation, the first fluid flows into the housing through the first inlet, through the aperture  12  and an inner portion of the hollow tubes forming the membrane  29 , and exits the housing through the first outlet. The second fluid flows into the inlet  27 , between the hollow tubes forming the membrane  29  to communicate with an outer portion of the hollow tubes forming the membrane  29  and out through the second outlet. Water vapor in the fluid having the higher water vapor partial pressure permeates through the membrane  29  and into the fluid having the lower water vapor partial pressure. Thus, the humidity level in the fluid having the higher water vapor partial pressure is decreased and the humidity level in the fluid having the lower water vapor partial pressure increased. The first O-ring  20  and the second O-ring  24  militate against a mixing of the first fluid and the second fluid by sealingly engaging an inner surface of the housing. 
       FIG. 2  illustrates a humidifier  30  for an air stream of a fuel cell (not shown) according to an embodiment of the invention. It is understood that the humidifier  30  can be used in other applications as desired without departing from the scope and spirit of the invention. The humidifier  30  includes a housing  32  and an air humidification module  34  disposed in the housing  32 . The housing  32  has a generally cylindrical shape with a substantially circular cross-section. It is understood that other cross-sectional shapes can be used as desired. The housing  32  includes a first housing section  36  and a second housing section  38 . It is understood that the first section  36  and the second section  38  can be separately formed or formed having a common portion such as a living hinge, for example. The housing  32  is shown in  FIG. 2  in an open position. 
     The first section  36  forms a hollow interior  42 . The interior  42  of the first section  36  is adapted to receive a portion of the air humidification module  34  therein. An inner surface  44  of the first section  36  includes a first groove or channel  46  and a second groove or channel  48  formed therein. A first inlet aperture  50  is formed in the first section  36  and is adapted to provide fluid communication between a source of a first fluid and the hollow interior  42  of the first section  36 . Typically, the first fluid is oxygen or air, although other fluids can be used. 
     A first end  39  of the first section  36  has a second inlet aperture  40  formed therein and a second end  41  of the first section  36  has a second outlet aperture  43  formed therein. The second inlet aperture  40  is adapted to provide fluid communication with a source of second fluid and the interior  42  of the first section  36 . The second outlet aperture  43  is adapted to discharge the second fluid from the hollow interior  42  of the first section  36 . Typically, the second fluid is oxygen or air, although other fluids can be used. Additionally, the first fluid and the second fluid may have different water vapor partial pressures or humidity levels. 
     The second section  38  has a hollow interior  52  formed therein. The interior  52  of the second section  38  is adapted to receive a portion of the air humidification module  34 . The interior  42  of the first section  36  and the interior  52  of the second section  38  cooperate to form a hollow chamber within the housing  32  which receives the air humidification module  34  therein. 
     A first groove or channel  54  and a second groove or channel  56  are formed in an inner surface  58  of the second section  38 , as more clearly shown in  FIG. 3 . The first channel  54  and the second channel  56  of the second section  38  are respectively aligned with the first channel  46  and the second channel  48  of the first section  36  to form a first annular groove or channel and a second annular groove or channel in the housing  32 . An outlet aperture  60  is formed in the second section  38  and is adapted to discharge the first fluid from the hollow interior  52  of the second section  38 . 
     A first end  62  of the second section  38  has a second inlet aperture  64  formed therein and a second end  66  of the second section  38  has a second outlet aperture  65  formed therein. The second inlet aperture  64  is adapted to provide fluid communication with the source of second fluid and the interior  52  of the second section  38 . The second outlet aperture  65  is adapted to discharge the second fluid from the hollow interior  52  of the second section  38 . When the first section  36  and the second section  38  are assembled to form the housing  32 , the second inlet aperture  40  and the second inlet aperture  64  cooperate to form a second inlet aperture of the housing  32  and the second outlet aperture  43  and the second outlet aperture  65  cooperate to form a second outlet aperture of the housing  32 . 
     The module  34  has a generally cylindrical shape with a substantially circular cross-section. It is understood that other cross-sectional shapes can be used as desired. A radially outwardly extending annular collar  70  is formed at a first end  72  of the module  34  and a radially outwardly extending annular collar  74  is formed at a second end  76  of the module  34 . An aperture  68  is formed in each of the collars  70 ,  74 . The collars  70 ,  74  are adapted to be respectively disposed in the first channel  54  and the second channel  56 . 
     A sealing material  78  is disposed between the collars  70 ,  74  and walls forming the channels  54 ,  56  to create a substantially air-tight seal therebetween. Although the sealing material  78  can be any conventional sealing material, a viscous liquid sealing material such as glue, for example, has been found to provide satisfactory results. It is also understood that gaskets such as deformable gaskets can be used. Other conventional sealing materials that may be used such include a UV-curable elastic glue, a polyurethane, a silicon rubber, a thermoplastic elastomer, and a hot-melt adhesive, for example. 
     A water permeable membrane  80  of the module  34  is disposed between the collars  70 ,  74 . It is desirable that a permeation rate of water vapor through the membrane is higher than a permeation rate of the first fluid and the second fluid through the membrane. A ratio of the water vapor permeation rate to the fluid permeation rate 10:1 or more has been found to provide satisfactory results. However, it is understood that other ratios can be used without departing from the scope and spirit of the invention. 
     The membrane  80  typically includes a large number (generally in the range of tens of thousands to hundreds of thousands) of hollow fiber membranes bundled nearly in parallel to form a hollow fiber membrane bundle, although more or fewer hollow fiber membranes can be used. Additionally, other membrane types can be used as desired. The ends of the hollow fiber membranes are maintained in an opened state. The hollow fiber membranes can be bundled in a so-called twilled state by alternately cross-arranging the hollow fiber membranes with respect to an axial direction of the hollow fiber membrane bundle 
     The membrane  80  can be any conventional water permeable membrane and can be either a porous membrane or a non-porous membrane. A non-porous membrane is typically more desirable since the porous membrane permits components other than water vapor to pass therethrough. Additionally, the membrane  80  preferably has material properties (heat resistance, chemical resistance, durability and hydrolysis resistance) suitable for use with water vapor or oxygen gas at a high temperature of about 80 degrees Celsius. The porous membrane can be produced from any conventional porous material such as perfluorocarbon resin having a sulfonic acid group, polyethylene resin, polypropylene resin, polyvinylidene fluoride resin, polyethylene tetrafluoride resin, polysulfone resin, polyethersulfone resin, polyamide resin, polyamidoimide resin, polyetherimide resin, polycarbonate resin, and cellulose derivative resin, for example. The non-porous membrane can be produced from any conventional non-porous material such as polyimide resin, polysulfone resin, perfluorocarbon resin having a sulfonic acid group, polyethersulfone resin, polyamide resin, polyamidoimide resin, polyetherimide resin, polycarbonate resin, polyphenylene oxide resin, polyacetylene resin, and cellulose derivative resin, for example. 
     The humidifier  30  is assembled by applying the sealing material  78  to at least one of the surfaces forming the channels  46 ,  48 ,  54 ,  56  and the collars  70 ,  74 . Where a viscous liquid sealing material  78  is used, the application is typically done shortly prior to insertion of the collars  70 ,  74  into the channels  54 ,  56 . The viscous liquid sealing material  78  also adheres the collars  70 ,  74  to the surfaces forming the channels  46 ,  48 ,  54 ,  56 . Any spaces or voids between the collars  70 ,  74  and the surfaces forming the channels  46 ,  48 ,  54 ,  56  are occupied by the sealing material  78 . 
     The first section  36  is then placed on the second section  38  to insert the collars  70 ,  74  into the channels  46 ,  48 . The first section  36  and the second section  38  are then joined to form the housing  32 . Any conventional joining method can be used to join the first section  36  and the second section  38  such as gluing or welding, for example. When assembled, the housing  32  cooperates with the sealing material  78  and the collars  70 ,  74  to form two separate chambers within the housing  32 . The first chamber provides a first fluid conduit from the first inlet aperture  50  formed in the first section  36 , around an exterior of the fibers of the membrane  80 , to the first outlet aperture  60  formed in the second section  38 . The second chamber provides a second fluid conduit from the second inlet aperture of the housing  32 , through the apertures  68  formed in the collars  70 ,  74  and an interior portion of fibers forming the membrane  80  of the module  34 , to the second outlet aperture of the housing  32 . 
     After application of the sealing material  78  and insertion of the collars  70 ,  74  into the channels  46 ,  48 ,  54 ,  56 , the sealing material  78  is permitted to solidify or polymerize, if necessary. The sealing material  78  may be light induced or chemically induced to polymerize. Additionally, the sealing material  78  may be cured or simply permitted to cool down to seal the interface between the collars  70 ,  74  and the surfaces forming the channels  54 ,  56 . 
     Due to the use of the sealing material  78 , the channels  54 ,  56  need not be precisely formed, since the sealing material  78  occupies any spaces or voids formed between the collars  70 ,  74  and the surfaces forming the channels  54 ,  56 . Satisfactory results have been obtained using the sealing material  78  with channels  54 ,  56  having a depth of approximately 0.1 to 5 mm. It is understood that channels having different depths can be used. 
     In operation, the first fluid flows through the first inlet aperture  50 , around an exterior of the fibers of the membrane  80  to communicate with the outer portion of the fibers, and out of the first outlet aperture  60 . The second fluid flows into the housing  32  through the second inlet aperture of the housing, through the apertures  68  formed in the collars  70 ,  74  and the interior portion of the fibers forming the membrane  80  of the module  34 , and exits the housing  32  through the second outlet aperture of the housing. Water vapor in the fluid having the higher water vapor partial pressure permeates through the membrane  80  into the fluid having the lower water vapor partial pressure. Thus, the humidity level in the fluid having the higher water vapor partial pressure is decreased and the humidity level in the fluid having the lower water vapor partial pressure increased. Typically, the first fluid is the fluid having the higher water vapor partial pressure and the second fluid is the fluid having the lower water vapor partial pressure. The substantially air-tight seal created by the sealing material  78  helps the sealing material  78  to militate against a mixing of the first fluid and the second fluid. 
     The humidifier  30  having the housing  32  produced from two sections  36 ,  38  minimizes a complexity of manufacturing. Due to the minimized complexity of manufacturing, the cost thereof is minimized. A reliability of the seal created by the sealing material  78  is also maximized. 
     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.