Energy efficiency assessment of hydrogen recirculation ejectors for proton exchange membrane fuel cell (PEMFC) system

The ejector is the core component for hydrogen recirculation in a proton exchange membrane fuel cell (PEMFC) system. However, in the past, the computational fluid dynamics (CFD) simulation of the ejector mainly focused on the influence of the change of the structural parameters on its performance, while the research on phase change condensation was lacking. Here, we proposed a two-phase flow model integrating the non-equilibrium phase change conservation equations and four categories of entropy transport equations, which analysed the phase change characteristics and the influence of different primary pressures on the property of ejector and internal entropy and exergy under the dry and wet gas models. We validated that the wet gas model has a good prediction ability with an MRE of only 2.53%. There was a significant difference between the dry and wet gas models, for example, the dry gas model predicted a larger Mach number and entrainment ratio, while the temperature and pressure were less than that of the wet gas model. Finally, the entropy and exergy were analysed, and the dry gas model overestimated the entropy generation, i.e, when the pressure of the primary inlet raised to 5.0 bar, the entropy generation overestimated by the dry gas model had reached 138.66 J kg^-1K⁻¹. The exergy destruction and exergy destruction ratio both increased with the rise of primary pressure. The dry gas model overestimated the exergy destruction and exergy destruction ratio, and the maximum overestimated values can reach 41.83 kJ/kg and 15.83%, respectively.