Effect of nitrogen concentration on the performance of a co-rotating scroll hydrogen recirculation pump in PEMFC systems

Nitrogen crossover and accumulation at the anode of a proton exchange membrane fuel cell are inevitable and significantly affect the performance of the hydrogen recirculation pump. This paper aims to investigate the performance of a co-rotating scroll hydrogen recirculation pump under varying inlet nitrogen concentrations, ranging from 0% to 25%, and to propose an optimized design solution to mitigate over-compression in the pump. Three-dimensional transient numerical simulations based on computational fluid dynamics were conducted on the co-rotating scroll hydrogen recirculation pump. The results indicate that increasing nitrogen concentration leads to a decrease in isentropic efficiency and an increase in volumetric efficiency. Furthermore, the pulsation of discharge velocity is reduced, while the pulsation of discharge pressure is enhanced. Higher nitrogen concentrations result in more significant flow losses, particularly concentrated in the chamber and closely linked to the discharge process. Notably, when the nitrogen concentration reaches 25%, counter vortices are observed in the chamber, which likely contribute to the increased flow losses. Following optimization, the degree of over-compression is significantly reduced, leading to improved overall performance of the pump. Specifically, at a nitrogen concentration of 25%, volumetric efficiency increases by 0.31%, and isentropic efficiency rises by 7.07%. These findings provide valuable insights for the efficient operation and optimized design of hydrogen recirculation pumps.