Exergy performance analysis of hydrogen recirculation ejectors exhibiting phase change behaviour in PEMFC applications

Abstract

A comprehensive analysis of flow behavior and exergy performance was conducted in hydrogen recirculation ejector, taking into account the phase change of humid hydrogen for proton exchange membrane fuel cell (PEMFC) systems. A two-phase nonequilibrium condensation CFD model integrating the entropy transport equations was established. The effect of phase change on ejectors’ performance under various primary pressure, secondary pressure and temperature, and back pressure were analyzed. When primary pressure was adjusted into 3.0 bar, a liquid fraction of 4.56 % was observed at the outlet, while the liquid fraction will increase to 15.35 % when the inlet pressure got to 5.0 bar. Then, the values of mass flow rate and liquid mass fraction on different sections under variable secondary temperature and back pressure were calculated. Finally, it is found that a larger primary pressure brought an increase in exergy destruction. So was exergy destruction ratio. However, increasing secondary pressure leads to the opposite result. With the increase of secondary temperature from 60 to 80 °C, exergy destruction increases from 330.28 to 390.23 kJ/kg but the destruction ratio decreases from 29.85 % to 26.19 %.