Friday October 29
Chem. Sci & Engineering Room 211
Presenter: Dr. Jeffrey S. Allen, Michigan Technological University Mechanical Engineering—Engineering Mechanics
Abstract: The standard proton exchange membrane (PEM) fuel cell consist of a series of nonwetting porous layers compressed between the bipolar plates. The layers can be categorized as anode and cathode porous transport layers (PTL), also known as gas diffusion layers, each with a catalyst layer and a proton exchange membrane. The cathode PTL has the dual role of facilitating the access of the reactants to the catalyst layer while removing the water produced by the electrochemical reaction. In a PEM fuel cell, liquid water may percolate through the non-wetting PTL forming conduits or fingers that are influenced by capillary pressure and the PTL morphology. Using a specially designed ex-situ experimental setup, images of the water percolation and the pressure required to inject the water in a PTL were simultaneously recorded. The time evolution of projected area occupied by water and the percolation pressure are indicative of the drainage flow pattern taking place. Scaling of key parameters in conjunction with the capillary number and the viscosity ratio has resulted in a non-dimensional number correlating the pressure-area data; two variables which are usually analyzed separately in two-phase porous media flow. Using this non-dimensional number a simple logarithmic dependence for all injection flow rates was obtained for a given PTL sample; effectively collapsing the drainage phase diagram to a single curve. When a PTL sample with different morphological and wetting properties was tested, a new linear relationship was obtained. Each type of PTL has a unique curve and, based on preliminary results, the slope of this curve can be used to characterize PTLs with respect to water percolation. This scaling technique can also be used as a validation method for numerical simulation of drainage in porous media.rous media.