Imaging of gas flow through a porous medium from a fuel cell bipolar plate by laser-induced fluorescence

The flow in a PEM fuel cell bipolar plate with a diagonal channel structure and across a carbon paper backing layer has been experimentally studied. To examine the flow inside the plate, a liquid analogue preserving dynamic similarity has been used, applying laser-induced fluorescence. This analogy, however, cannot be used to study the flow through the carbon paper, because gas and liquid surface tension are not equivalent and their flow through a porous medium will be different. For this analysis this paper proposes as a novel application, the use of acetone vapor planar induced fluorescence. With this technique, image sequences have been obtained to visualize the gas crossing the backing layer while the plate was filled with acetone-seeded air. It has been demonstrated that the pattern of the flow emerging from the diffusion layer follows that of the pressure distribution in the plate. Hence, even an apparently non-uniform velocity distribution of the reactant gases in the plate could result in an acceptable distribution over the catalyzed electrode if the pressure field is sufficiently smooth.