A complete three-dimensional model for proton exchange membrane (PEM) fuel cells is used to investigate the effect of the channel depth on the performance of the straight flow field at different stoichiometries of air. Therefore there is a complete cell model that includes all the parts of the PEM fuel cell, flow channels, gas diffusion electrodes, catalyst layers and the membrane. Coupled transport and electrochemical kinetics equations are solved in a single domain; therefore, no interfacial boundary condition is required at the internal boundaries between cell components. This computational fluid dynamics code is used as the direct problem solver, intended to simulate the three-dimensional mass, momentum and species transport phenomena, as well as the electron- and- proton-transfer process taking place in a PEMFC. The results show that the predicted polarization curves are in good agreement with the experimental data, and a high performance was observed at the channel depth of 1 mm for the cathode and 1.5 mm for the anode. Furthermore, the results show that the increase of the stoichiometry of air can enhance the performance of the cell. Also it is observed that the current density distribution is more uniform for channel depth 1mm for anode and 1.5mm for cathode and for channel depth 1.5 mm for anode and 1 mm for cathode than the other two designs and by moving in the channel, mole fraction of oxygen decreases due to consumption.

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