Numerical And Optimization Analysis Of Hydrogen Ejector For Anode Recirculation In PEMFC System

With the purpose of improving the efficiency and reducing the response time at an increased power demand,hydrogen fuel which stoichiometric ratio is greater than 1 is supposed to be supplied for the fuel cell,giving rise to some unconsumed hydrogen.It is of great value to improve the fuel cell efficiency and reduce the air pollution by recycling the unconsumed hydrogen.In comparison with compressor,the ejector recirculation system is an ideal scheme.In this study,a 3D numerical model of an ejector for the anode recirculation in a proton exchange membrane fuel cell(PEMFC)system is established based on CFD procedure,which reflects the flow situation of the secondary flow exactly.The ejector performance represented by the recirculation ratio is simulated under various ejector geometric and operating parameters.Firstly,multiple ejector geometric parameters are investigated and optimized using the ejector model,including the secondary flow tube inlet diameter,convergence and inclination angles,the suction chamber diameter,the constant-pressure mixing tube length and convergence angle,the constant-area mixing tube length,and the diffuser length and angle.Then,effects of operating conditions on the ejector performance are carried out based on the optimum ejector design,including the mass flow rate of primary flow,humidity and temperature of secondary flow.Finally,the ejector designing scheme comes to a conclusion.It is found that the ejector recirculation ratio is increased 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 geometric design having smaller pressure in the suction chamber.The optimum ejector design exists for a specific PEMFC stack operating current,and the optimum PEMFC stack operating current also exists for a specific ejector.The relative humidity and temperature of the secondary flow influence the ejector selectivity,and more water vapor but less hydrogen is recirculated at both higher secondary flow humidity and temperature,and vice versa.