CONDENSATION BASED PORE NETWORK MODELLING OF WATER TRANSPORT IN HYDROPHOBIC PEM FUEL CELL GDLS

摘要

In this work, a novel pore network model is employed to simulate water transport originating from condensation in the polymer electrolyte membrane (PEM) fuel cell gas diffusion layer (GDL). Liquid water transport follows the rules of invasion percolation with trapping, where two mobile phases are considered. Flow conditions are based on dynamic pressure changes in the network. The GDL is assumed to be a hydrophobic pore network, where capillary forces dominate over gravitational and viscous forces. The model follows a condensation based algorithm that begins with a single nucleation site from where liquid water spreads with continuing condensation. To account for a humidity gradient within the GDL, water flow is assumed to originate from condensation occurring in pores facing the cathode catalyst layer. Modelling parameters and their effect on the saturation profile are discussed. Little impact was found on the saturation profile when trapping logic was made more sophisticated, recognizing conditions leading to air trapping in a single throat. It is shown that saturation profiles for slow flow (I.e. slow condensation rates) can be predicted with reasonable accuracy from a known throat topology alone. However, as condensation rates are increased, raising network viscous forces to levels comparable to network capillary forces, the flow patterns begin to depend on a number of variables such as pore sizes and pore filling rates. At such condensation rates, flow patterns show high sensitivity to variance in condensation rates and become much less predictable from simple geometries.