Convective flow through polymer electrolyte fuel cells
Date
2005
Authors
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Publisher
University of Delaware
Abstract
Hydrogen powered PEM fuel cells have three primary loss mechanisms: activation over-potential, ohmic overpotential, and the mass-transport limited over-potential. It is suggested that convection in the form of channel bypass can be used to increase reactant concentrations in the catalyst layer which will improve reaction kinetics. Further, if convection can be made the dominant mechanism for gas transport, the diffusion-limited mass-transport overpotential can be reduced or removed. In order to determine under what conditions this can take place, an analytic model was developed for convective flow within a single serpentine channel configuration. The model shows that the channel length and in-plane permeability of the gas diffusion layers are most important factors. ☐ Particle Image Velocimetry was used to observe the velocity fields in representative test sections of an interdigitated and a serpentine fuel cell. Using ex-situ methods, it was shown that it is possible observe secondary flows with primary-to-secondary velocity ratios approaching 100-to-1. Channel bypass was observed in both configurations. Local variation in permeability appears to cause local variation in velocity fields in the channel. ☐ A radial permeability experiment designed and fabricated to characterize and differentiate in-plane permeability of three gas diffusion layers manufactured by different techniques. It was shown that experiments can use either a wetting liquid or a gas of known viscosity as the host fluid and reach identical conclusions. However, flowrates' dependence on pressure is different for gases and liquids and must be recognized when large pressure differentials are present.