Study on a multi-nozzle structured ejector for recirculating hydrogen in PEMFC systems

The ejector-based hydrogen recirculation system in a proton exchange membrane fuel cell has many advantages, such as no moving parts, no extra energy consumption, compact structure, reliable operation, no pollution, and low cost. However, the problem that hinders its application is the narrow working range of the ejector. In this work, aiming at extending the working range of the ejector, a novel multi-nozzle structured ejector is proposed and designed using the gas dynamic method, meanwhile a 3-D numerical model is developed and validated. The flow field characteristics inside the ejector under five different working modes are studied, and the effects of ejector back pressure and primary flow pressure on ejector performance are investigated. The optimum working mode for each stack power in the range of 17.9 kW to 84 kW is obtained. Comparisons are made with the traditional and twin-nozzle hydrogen ejectors; results show that the novel structured ejector has a wider operating range and can work better at relatively low stack power. At 17.9 kW, the entrainment ratio of the novel structured ejector increased by 66.2 % compared to that of the twin-nozzle ejector, while the traditional ejector cannot work. In addition, the fluctuation of the primary flow pressure of the novel structured ejector (565-700 kPa) is smaller than that of the traditional ejector (118-700 kPa) and the twin-nozzle ejector (236-700 kPa) as the stack power varies from 17.9 kW to 84 kW, which indicates that the fuel cell system with novel structured ejector can work more stable and reliably.