Gas flow-field design

There are two major considerations for the design of the bipolar plate (1) selection of materials for bipolar plafes and (2) gas flow-field design. A detailed description of fhese two aspecfs of the bipolar plate design is given in the following section. 

Straight parallel channel gas flow-field design, (a) Straight parallel flow channels, (b) Gas distribution primarily by diffusion in the gas diffusion layer. 

Kumar A and Reddy R G (2005) Effect of gas flow-field design in the bipolar/end plates on the steady and transient state performance of polymer electrolyte membrane fuel cells. Journal of Power Sources (In Press). 

Velocity seals are more recent developments in air seal design. They use conical baffles to redirect and focus the purge gas flow field just below the flare tip to sweep air from the flare stack. Some velocity seal designs can reduce the purge gas flow rate requirement to about 1/10 of the rate needed without the seal. Also, some velocity seal designs reportedly require only about 25 to 33 percent of the purge gas used in diffusion seals (AICliE-CCPS, 1998). More details about air (purge reduction) seals may be found in API RP 521 (2007). 

Figure 5.2. Calculated gas flow fields in the near-nozzle region of free-fall atomizers. Primary gas pressure 0.140 MPa secondary gas pressure 0.189 MPa angle of secondary gas nozzle relative to the spray centerline 10° angle of primary gas nozzle relative to the spray centerline (a) 0°, (b) 22.5°, and (c) 30° designed for minimizing recirculation gas flow. (Reprinted from Ref. 612.)...

K. Yoshizawa, K. Ikezoe, Y. Tasaki, et al. Analysis of gas diffusion layer and flow-field design in a PEMFC using neutron radiography. Journal of the Electrochemical Society 155 (2008) B223-B227. 

In a multichannel flow-field design the channels with normal and lowered pressure may alternate and one may expect that the latter will effectively remove excessive water from the cathode compartment. Such a flow field may have advantages over the interdigitated flow field since gas flow in the water-draining (Red) channels is externally driven and can be varied to reach optimal conditions. 

In the L79 design, both the gas flow fields and electrodes are made from single sided copper clad circuit board. Copper clad circuit board comes in a variety of sizes and is either clad with copper on one side only, or both sides. Boards also differ in the type of base material they are made of. This fuel cell requires the FR-4 glass epoxy resin base, clad with copper on one side only. We used a 1 ounce, which is coated with copper to a thickness of. 0014". 

Developed a unique flow field design via modeling and basic principles of gas transport that optimizes the uniformity of hydrogen and air mass flow velocities for the matched EB media and increases high current density performance over conventional designs. 

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