Two-Phase Flow Simulation of Multi-Droplet Motion Relevant for Polymer Electrolyte Fuel Cell Gas Channel Using the Volume of Fluid Approach

This study develops a 3D computational fluid dynamics model of a polymer electrolyte fuel cell cathode gas channel with seven discrete liquid breakthrough inlets, one gas inlet, and a two-phase outlet. Two-phase flow and droplet evolution on the gas diffusion layer are simulated using the volume-of-fluid method in OpenFOAM. The model agrees well with reported experimental and numerical data in terms of droplet size, morphology, and detachment behavior. Results show that breakthrough geometry governs droplet dynamics: circular openings promote stronger aerodynamic loading and earlier detachment, while sharp-cornered geometries (e.g., triangular and polygonal) stabilize droplets and prolong residence time. Among all investigated geometries, the circular breakthrough exhibits the highest drainage efficiency, in agreement with recent experimental studies demonstrating that laser-drilled circular pores facilitate water removal and reduce oxygen mass-transfer resistance in polymer electrolyte fuel cells. Complex interactions with the gas diffusion layer surface, gas channel walls, and corners lead to coalescence, sliding, and rivulet formation. Force decomposition reveals the competition among aerodynamic, capillary, adhesion, and shear forces. The study provides a mechanistic basis for geometry-controlled water transport and guidance for gas diffusion layer design and water management.