Flow field design considerations

M. V. Williams, E. Begg, A. A. Peracchio, H. R. Kunz, and J. M. Fenton. Gonvection considerations in PEMFC flow field design. 203rd Electrochemical Society Meeting, Paris (Abstract 1246) (2003). 

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. 

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. 

Our treatment of Chemical Reaction Engineering begins in Chapters 1 and 2 and continues in Chapters 11-24. After an introduction (Chapter 11) surveying the field, the next five Chapters (12-16) are devoted to performance and design characteristics of four ideal reactor models (batch, CSTR, plug-flow, and laminar-flow), and to the characteristics of various types of ideal flow involved in continuous-flow reactors. Chapter 17 deals with comparisons and combinations of ideal reactors. Chapter 18 deals with ideal reactors for complex (multireaction) systems. Chapters 19 and 20 treat nonideal flow and reactor considerations taking this into account. Chapters 21-24 provide an introduction to reactors for multiphase systems, including fixed-bed catalytic reactors, fluidized-bed reactors, and reactors for gas-solid and gas-liquid reactions. 

This design practically or to a considerable extent eliminates particles collisions in the separation zone, which sharpens separation. As the flow field in the chamber has no inherent vortexes the device has lower air resistance and energy consumption. Several prototypes of this classifier were used in phosphate industry for separation of crushed phosphate ore at 1 mm cut size. One such plant with output of 251 per hour and pressure drop of 800-900 Pa yielded 96-98% cleanness of fines and 78-85% of coarse fraction [8],... 

Research and development effort has been concentrated on the bipolar plate designs to reduce the cost and increase the performance of the fuel cell. Improvements can occur in the performance of a fuel cell through optimization of the channel dimensions and shape in the flow field of bipolar plates. The contact surface area of the reactant gas on the bipolar plates has an effective contribution on the overall reaction of the gases. The reactant gas pressure has an important role in the overall functioning of the fuel cell. Consideration of fluid flow, heat, and mass transfer phenomenon is impor-fanf while designing the bipolar plate channels. 

Design Considerations There are many different flow field configurations that have been used for fuel cells in general and PEFCs in particular. The design of a flow field is a complex balance between many coupled constraints, many with opposing functional dependencies on the fuel cell performance, so that trade-offs must be made. The design constraints include the following ... 

Several field test studies have been undertaken utilizing the SEPAREX process in a 2-in. diameter element size Due to the modular configuration of membrane systems, a full size system can be directly designed from the test results with a small pilot plant. Although the flow rates for a pilot unit are considerably lower than might be encountered in a full-size system, all process parameters such as product purities, pressure drop, product recoveries, optimum pressure and temperature, membrane area required and series/parallel arrangement of the elements can be directly determined. 

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