Visualization experiments and pore network simulations for invasion-percolation transport of a non-wetting fluid through multiple porous layers

A similarity model experiment was developed to investigate the liquid water transport in hydrophobic porous layers of polymer electrolyte membrane fuel cells (PEMFCs). The dimensionless numbers in the similarity model experiment were closely matched to those in operating PEMFCs. This allowed the visual inspection of invasion-percolation transport of a non-wetting fluid with active capillary fingering in multiple porous layers, similar to the liquid water transport in porous layers of PEMFCs. The experimental results showed that inserting an intermediate layer between a fine layer and a coarse layer suppresses the capillary fingering of the non-wetting fluid inside the coarse layer. Thus, it could be expected that the steady-state volume of the non-wetting fluid in the multiple porous layers decreases as the thickness of the intermediate layer increases. In fact, this trend was quantitatively verified by measuring the volume of the breakthrough droplets formed by the non-wetting fluid that emerged out of multiple porous layers. In addition, pore network simulations were also conducted to reproduce the observed non-wetting fluid transport in multi-layer porous media, and relatively good agreements between experimental and numerical results were obtained.