Effect of Secondary-Flow Humidity on Phase Change Characteristics of Hydrogen Recirculation Ejector in a PEMFC System

The recovery and reuse of hydrogen is an essential step in proton exchange membrane fuel cell (PEMFC) systems. Compared to other hydrogen recirculation devices, the ejector offers advantages such as stable operation and no additional energy consumption, and is therefore widely used in hydrogen recirculation subsystems. The driving force of the ejector is the internal working fluid, and its entrainment performance exhibits significant sensitivity to changes in operating conditions. This study aims to elucidate the influence of humidity variations in the secondary flow on phase-change condensation and entrainment performance. The results show that when the secondary-flow humidity is in a saturated state, the outlet liquid flow rate is 0.582 mg/s and the maximum flow rate of droplets in the constant-volume mixing region is 0.63 mg/s. The occurrence of condensation causes the temperature in the parallel mixing region to increase by 5.48 K. When the secondary-flow humidity rises from 20% to 100%, the total entrainment ratio of the ejector increases by 16%, while the hydrogen entrainment ratio decreases by 18.7%.