Numerical investigation of an ejector for anode recirculation in proton exchange membrane fuel cell system

Two-dimensional axisymmetric ejector model neglects the non-axisymmetric flow properties in the ejector and may not apply well for the ejector with a side-branch secondary flow tube. In this study, a three-dimensional numerical model of an ejector for the anode recirculation in a proton exchange membrane fuel cell system is established. The renormalization group k-epsilon turbulent model is utilized in the ejector simulation. A side-branch secondary flow tube and a suction chamber are incorporated in the ejector model, and their effects are investigated. It is found that the ejector recirculation ratio representing the ejector performance increases significantly with the secondary flow tube inlet area; and as the secondary flow tube inlet area is fixed, the recirculation ratio is larger for the ejector design having smaller pressure in the suction chamber. The ejector recirculation ratio increases slightly with the secondary flow tube convergence and inclination angles, while it decreases fist and then increases with the suction chamber diameter. An optimization of the ejector geometric parameters is carried out using a sequential method. The effects of operating conditions on the ejector performance are also investigated. It is shown that both the relative humidity and temperature of the secondary flow influence the ejector selectivity, and more water vapor but less hydrogen is recirculated for both higher secondary flow humidity and temperature. (C) 2016 Elsevier Ltd. All rights reserved.