Two-phase flow and evaporation in model fibrous media - Application to the gas diffusion layer of PEM fuel cells

Two-phase flow dominated by capillary effects in model fibrous media is studied combining pore-network simulations and visualisations on transparent micromodels. It is shown that the process of liquid water invasion in a hydrophobic medium can be simulated using the classical invasion percolation algorithm provided that the contact angle (measured in air, which is the wetting phase) is sufficiently far below 90 degrees. For contact angles approaching 90 degrees. changes in the interface local growth mechanisms lead to changes in the invasion pattern. Then it is shown that the invasion pattern is dramatically different in a hydrophilic medium. Impact of wettability (hydrophobic vs. hydrophilic) on evaporation pattern is also analysed. In a last part implications of the study findings on the water management problem in the gas diffusion layers (GDLs) of PEMFC are discussed. Our results provide pore-scale explanations to the advantages of hydrophobic GDLs. (c) 2007 Elsevier B.V. All rights reserved.