Performance investigation of a multi-nozzle ejector for proton exchange membrane fuel cell system

Due to its merit of no consuming energy, no moving part, and less requiring space, and maintenance, the ejector is one of the most promising hydrogen recirculation devices for proton exchange membrane fuel cell (PEMFC) applications. However, the prominent problem is its poor adaptability of the conventional ejector to meet the power range requirements of the PEMFC system. Thus, a multi-nozzle ejector was investigated to widen the applicable power range of a PEMFC system. The designed multi-nozzle ejector consists of one central nozzle (CN) and two symmetrical nozzles (SNs). The CN mode is activated under low power conditions, while the SNs mode is switched to adapt high power conditions. A 3D computational fluid dynamics (CFD) model was established to simulate the performance of ejectors, and an experimental test bench was built to validate the accuracy of the CFD model. The results indicated that the mixing chamber diameter (D-m) and throat tilt angle of SNs (alpha(t)) have a significant effect on the entrainment performance. It was found that the multi-nozzle ejector can broaden the hydrogen supply range from 0.27 to 1.6 g/s (22-100 kW) with the optimal combination of aD(m)of 5.0 mm and alpha(t)of 8 degrees. Nevertheless, the hydrogen supply range is 0.48 to 1.6 g/s (37-100 kW) when using a conventional single-nozzle ejector with aD(m)of 5.0 mm. Moreover, the temperature, pressure, and relative humidity of the secondary flow have a great influence on the hydrogen entrainment ratio with the change of stack power.