Modeling of gas-water transport in the porous transport layer of a proton exchange membrane electrolyzer

In this work, the mechanism of gas invasion into a saturated thin porous medium, specifically the Porous Transport Layer used in a Proton Exchange Membrane electrolyzer, is investigated. The phase-field model based on the Cahn-Hilliard theory is employed to capture the dynamics of the water-air interface in the presence of solid surfaces within the porous material. Numerical simulations are performed on 2 mm× 6 mm domain geometries composed of cylindrical solid grains, characterized by different pore sizes from 10 to 30 µm and porosities from 0.47 to 0.59, to examine the influence of pore architecture and inlet air velocity on two-phase distribution. Additionally, mesh dependency, relative tolerance, and mobility sensitivity studies are conducted to identify the optimal simulation parameters. Quantitative evaluation of the phase distributions reveals that increasing inlet air velocity shifts the system from capillary-dominated to viscous-dominated flow. The boundaries of this regime transition depend on the Capillary number, pore microstructure, sample thickness, and fluid properties.