Effects of Working Fluids on the Performance of a Roots Pump for Hydrogen Recirculation in a PEM Fuel Cell System

In this paper, the performance of a Roots pump for hydrogen recirculation in proton exchange membrane (PEM) fuel cell system is simulated based on CFD modeling. The Roots pump is in a three-lobe configuration with helical rotors, and it is developed specifically for fuel cell systems between 60 to 110 kW. A three-dimensional model of the Roots pump is established to predict the pump performance, including the flow rate and power consumption under various operating conditions. Extensive simulations were conducted and then verified experimentally by operating with working fluids of air and helium. Based on the validated CFD model, the contents of water vapor and nitrogen in the hydrogen recirculated are taken into account to evaluate the Roots pump performance numerically according to the actual conditions of the recirculating hydrogen at the stack outlet. It is shown that the volumetric efficiency and isentropic efficiency are improved with the increase fraction of water vapor and nitrogen. It is found that the performance of the Roots pump integrated in the PEM fuel cell system is between the performance of the pump working with air and helium. Finally, correlations of volumetric efficiency and isentropic efficiency are given based on the CFD results to show the general pattern of this kind of hydrogen pump. It is believed that these equations are very helpful to the design and operation control of the PEM fuel cell system.