Effect of gas diffusion layer fiber shape on cathode two-phase dynamics in proton exchange membrane fuel cells

Commercially available Gas Diffusion Layers (GDLs) are fabricated using different shapes of carbon fibers to suit different types of Proton Exchange Membrane Fuel Cells (PEMFCs). However, the impact of this difference on the GDL properties and fluid behavior remains unclear. In this study, a two-phase flow numerical study is conducted to investigate this influence by considering GDLs consisting of curved and straight carbon fibers. A periodic surface model is adopted to reconstruct the two types of GDLs, using the same through-plane porosity distribution, domain size, and fiber diameter. Pore Size Distribution (PSD) comparison between two stochastically reconstructed GDLs shows a similar trend. Besides, the liquid transport through these two GDLs and the assembled Gas Channels (GCs) is simulated using the Volume of Fluid (VOF) method implemented in OpenFOAM 7.0. The results show the total water saturation and capillary pressure in these two GDLs are similar, whereas their through-plane local water saturation level and the liquid breakthrough locations are substantially different. In addition, the total water saturation variation in the GCs exhibits an increasing difference over time. In the case of straight-fiber GDL, bigger water slugs are observed in the later simulation, which are located in the corner of the top and side surfaces of the GC. Besides, the case with a curved-fiber GDL has more separated droplets in the GC domain, which flow out of the GC faster than the slug flow in another case. However, it also increases the formation of discrete water cross-section regions, resulting in a higher GC pressure drop accompanied by more noticeable oscillations.