A Numerical Study on the Impact of Capillary Pressure and Relative Permeability on Water Transport in Proton Exchange Membrane Fuel Cells

Effective water management is a key factor to maximise the performance and durability of Polymer Electrolyte Membrane Fuel Cells (PEMFCs), where the conflicting needs of maintaining adequate membrane hydration and avoiding pore flooding in the gas diffusion layers must be balanced. Therefore, accurate prediction of water accumulation and distribution within the porous media is crucial. To analyze multi-phase flows in fuel cells, several models exist, including the popular Two-Fluid (TF) and Multi-phase Mixture (M2) model. Despite existing comparisons, a clear assessment of how these models predict water accumulation remains necessary. Additionally, the influence of parameters such as irreducible water saturation and the impact of varying contact angles and capillary-pressure with relative permeability correlations have not been thoroughly investigated in PEMFCs modeling contexts. In this study, Simcenter STAR-CCM+ simulations were conducted to systematically compare the M2 and TF models regarding their capability to accurately predict water accumulation and distribution within PEMFCs. Additionally, a sensitivity analysis evaluated the impact of irreducible water saturation and contact angle variations. Finally, several capillary-pressure correlations combined with different relative permeability models were assessed against experimental data to identify the most reliable modeling approach. Results demonstrate that the TF model better predicts the magnitude of water accumulation compared to the M2 model. The analysis further indicates that incorporating irreducible water saturation does not significantly alter the simulation outcomes. In turn, variations in the contact angle influence water removal efficiency, but have limited effects on spatial distribution patterns. Among the evaluated capillary-pressure correlations, the Leverett correlation paired with the Brooks-Corey relative permeability model exhibited the highest accuracy, closely matching experimental data. These findings offer practical guidelines for the accurate simulation of multi-phase water transport in PEMFCs porous media, ultimately contributing to the advancement of simulation techniques that support the development of more efficient power generation and propulsion systems.