Optimal Design Of An Ejector For Anode Recirculation System In Proton Exchange Membrane Fuel Cell

Proton exchange membrane(PEM)fuel cell has many advantages,such as high efficiency,zero emission,low cost,simple structure,long life and easy modularization.It can achieve zero emission by replacing traditional internal combustion engines in automobile field,which has become one of the research hotspots in fuel cell field.The anode hydrogen fuel supply system is an important component in PEM fuel cell system.Traditional hydrogen fuel supply system mostly use burners or hydrogen circulating pumps,which has the shortcomings of low utilization rate of hydrogen fuel and high failure rate.To solve the above problems,this dissertation studies the anode gas circulation system based on ejector,and optimizes the ejector.It is great theoretical and practical value to improve the efficiency of PEM fuel cell system and realize energy saving and emission reduction.In this dissertation,the research status of PEM fuel cell anode gas circulation system based on ejector is introduced,and the principle of PEM fuel cell and three different anode hydrogen supply systems are briefly analyzed.On the premise of understanding the operating principle and advantages of the ejector,the anode recirculation system based on the ejector is studied.Secondly,A two-dimensional simulation model was established and compared with the turbulence model on the operating conditions.The second-order upwind algorithm,RNG k-? turbulence model and species transport model is selected to simulate the model at last.Then,the ejector design was optimized with the entrainment ratio as the optimization objective.According to the operating conditions of PEM fuel cell,the initial geometric parameters of ejector were determined.And the positions of mixing zone,diffuser and nozzle exit position were studied respectively.Through the analysis of the simulation results,the optimum length and convergence angle of the isobaric mixing zone,the length of the equal area mixing zone,and the optimum length and diffusion angle of the diffuser were obtained.After obtaining the above geometric parameters,the optimum ejector is designed for the operating conditions in this study.What's more,the pressure,temperature,velocity and component distribution of the fluid flow in the ejector are analyzed.Finally,combining with the operating conditions of the fuel cell in this dissertation,the relation between the diameter of the nozzle outlet,mixing chamber diameter on the efficiency of the ejector and PEM fuel cell system is studied.At the same time,the difference of efficiency between two anode hydrogen supply systems based on the hydrogen circulating pump and the ejector was quantitatively studied.The results show that the fuel cell system based on ejector has higher efficiency and fuel recirculation rate.