Performance analysis and parametric studies on the primary nozzle of ejectors in proton exchange membrane fuel cell systems

Ejectors are used for anode hydrogen recirculation in proton exchange membrane fuel cell (PEMFC) systems, and the geometric parameters of the primary nozzle of ejectors have essential effects on the ejector performance. A 3D numerical model was established to investigate ejectors, and the reliability of the numerical model was verified by experiments. The operating characteristics of ejectors in the PEMFC system were analyzed by numerical simulation. Moreover, the effects of four geometry parameters (throat diameter, convergent angle, divergent angle, and length) on entrainment performance were studied. The results showed that the angle and length of the divergent zone have a significant influence on entrainment performance. A larger divergent angle may cause over-expanded under low power conditions, resulting in lower entrainment performance. For PEMFC systems with stable operating conditions or high entrainment requirements, a supersonic ejector with an appropriate divergent angle and length is recommended. Conversely, a convergent primary nozzle is suggested to be employed for the PEMFC systems with the wide operating power range. This study may provide a helpful reference for the design of ejectors used in fuel cell systems.