Flow field design patterns

Figure 636 Schematics of some common flow field design patterns. Many other basic design features have also been tried as well, including fractal and spotted post designs. (Image by Soowhan Kim.)...

To overcome the drawbacks of the straight parallel flow field design, a serpentine flow field pattern has been developed. As shown in Fig. 1.11, in the serpentine flow field, the reactant gas flows mainly along the flow channel, which leads to a uniform gas distribution inside the plate. In addition, the gas pressure drop from the inlet to the outlet is large, which favors water removal. 

Flow field layout plays an important role in flow field design, as it affects both reactant gas distribution and water removal. Several flow field layouts have been developed, according to their flow channels the pin-type flow field [95,96], the straight parallel flow field [97,98], the serpentine flow field [98,99], and the interdigitated flow field [100-103], as shown in Fig. 2.19. All these patterns have their own characteristics in terms of reactant gas distribution, water, and heat management, and their advantages and disadvantages have been extensively reviewed by Li and Sabir [86]. 

Once the reactant gases enter the individual cell they must be distributed over the entire active area. This is typically accomplished through a flow field, which may be in a form of channels covering the entire area in some pattern or porous structures. The following sections describe the key flow field design variables. 

Because of the complexity of designs and performance characteristics, it is difficult to select the optimum atomizer for a given appHcation. The best approach is to consult and work with atomizer manufacturers. Their technical staffs are familiar with diverse appHcations and can provide valuable assistance. However, they will usually require the foUowing information properties of the Hquid to be atomized, eg, density, viscosity, and surface tension operating conditions, such as flow rate, pressure, and temperature range required mean droplet size and size distribution desired spray pattern spray angle requirement ambient environment flow field velocity requirements dimensional restrictions flow rate tolerance material to be used for atomizer constmction cost and safety considerations. 

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