Numerical Predictions of Water Transport in a Proton Exchange Membrane Fuel Cell

摘要

Water transport plays a critical role in a proton exchange membrane(PEM)fuel cell performance. Due to the dominance of electro-osmotic drag over back diffusion,over-water-saturation and dehydration usually happen simultaneously on both sides of the membrane,which damage the performance of a PEM fuel cell.Balancing the water content distribution within the membrane involves judicious water and heat managements.Physical and chemical phenomena are modeled by four major aspects:Heat and mass transfer,electrochemistry and potential field.Mass transport includes multi-species gaseous mass transfer in the channels and porous media with species generation and consumption at the interfaces. Water migration through the membrane is attributed to electro-osmotic drag and back diffusion mechanisms.Heat generated by the electrochemical reactions,Ohmic heating,contact resistance and activation are taken into consideration.Electrical potential is established through the electrochemical reactions taking place on both sides of the membrane, where the change in Gibb’s free energy of formation is turned into electrical potential.Numerical simulations of a full scale industrial PEM fuel cell unit have shown the strong dependence of water transport through the membrane on the temperature, current density distributions,mass flow rates and inlet humidity level.The obtained polarization curve reflects the voltage loss due to the activation and Ohmic loss.Parametric study of water transport for different inlet water saturation level are discussed in detail.