Numerical and experimental study of two-phase flow uniformity in channels of parallel PEM fuel cells with modified Z-type flow-fields

The aim of this study is to improve two-phase flow uniformity of proton exchange membrane fuel cells (PEMFCs) with parallel flow-fields. Therefore, a series of experiments are performed to find the relevance of cathode stoichiometry ratio, unsteady distribution of water coverage ratios and power of a PEMFC with Z-type flow-field. The experimental results indicate that at high cathode stoichiometry ratios, the power and efficiency are stable but their magnitudes are low. In addition, the fuel cell later reaches to its stable power and efficiency. However, the duration of this stability is higher than low cathode stoichiometry ratios. A 3D numerical model is proposed in order to simulate two-phase flow in channels of parallel flow-fields. This model, which is validated by the experimental results, considers the microstructure of gas diffusion layers. By using this model, a modified flow-field with uniform distribution of single-phase and two-phase flow is introduced. Unlike the simple flow-field, the plugs do not exist in the modified flow-field. It has lower two-phase pressure drop than the simple flow-field. The simulation results show that the parasitic power for the air supply system of this modified flow-field is lower than the simple flow-field and therefore its overall efficiency is higher.