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A Predictive Pressure Drop Model for a Designing and Optimizing Cathode Air Filters

Ryan A. Sothen and Bruce Tatarchuk. Chemical Engineering, Auburn University, 0322A Haley Center, Auburn, AL 36849

Proton Exchange Membrane (PEM) fuel cells are susceptible to damaging airborne molecular contaminants (AMCs) such as carbon monoxide, sulfur compounds, and volatile organic compounds (VOCs). Previous research indicts that the most effective method to deal with the presence of these AMCs is to increase the effectiveness of the cathode air filter. Adsorbent entrapped media, such as microfibrous materials engineered at Auburn University, provide a novel method to efficiently entrap particles as small as ten microns within a sinter-locked matrix of fibers. The small adsorbent diameters greatly increase the contacting efficiency and performance of the media; however, the particles also increase the pressure drop due to additional drag forces. Since the PEM fuel cell's compressor is self-powered, an increase in cathode filter resistance creates a rise in the parasitic power drain on the system. Thus, the prevention efforts can become self-defeating.

Pleating the media is a simple approach to enhance the capacity while reducing the flow resistance. A pleated filter achieves this by increasing the available filtration area. In turn, this reduces the velocity into the media and pressure drop across the media. Although the additional area reduces the pressure drop across the media, the presence of pleats creates a new resistance due to fluid-solid friction. Thus, construction of a pleated becomes an optimization process of balancing pleat resistance and media resistance to obtain the lowest pressure drop.

A comprehensive study was performed to identify the contributing flow resistance factors in order to optimize a cathode air filter. By employing various fundamental fluid dynamics equations and empirical data, the research established a predictive model capable of estimating pressure drop for flow through a pleated filter. The model can be used as a design tool to identify the contributions of pleat count, filter depth, media type, and number of filtering elements on the total resistance of the system. Using the model, the capacity and contacting performance of a pleated filter is compared to a packed bed at a fixed pressure drop and volumetric flows. Through the use of novel media and packaging techniques, the amount of adsorbent present in a cathode filter unit can be dramatically increased while maintaining a lower pressure drop to reduce the parasitic effects of the filter