Development Of Confocal Twin-nozzle Ejector For Anode Hydrogen Recirculation In Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cell(PEMFC)has broad development prospects due to its green and efficiency.As an important part of PEMFC,the hydrogen recirculation system is used to improve the utilization rate of hydrogen and improve the humidity inside the stack.The ejector-driven hydrogen circulation system has many advantages such as simple structure,small size,easy maintenance,no parasitic power,low noise,and so on.However,the narrow working range and difficult adjustment of the ejector,especially the poor ejection performance in the low power region,have become the bottleneck restricting the wide application of the ejector in the PEMFC system,and in-depth research is urgently needed.Aiming at the above problems,this thesis proposes a new type of confocal twin-nozzle ejector,which can work in different modes by controlling the nozzles to meet the requirements of anode gas recirculation under different working conditions of the PEMFC system,and effectively solves the problem of poor ejection performance in the low power region.The main contents of this thesis are as follows:(1)A design method for the confocal twin-nozzle ejector is proposed,and the geometric parameters of the ejector are determined.(2)A threedimensional numerical simulation model of the confocal twin-nozzle ejector is established,and the velocity streamlines distribution is used to visualize the flow characteristics of the internal fluid under the two working modes of the confocal twin-nozzle ejector,and reveal the internal fluid flow mechanism and working mechanism of the confocal twin-nozzle ejector.(3)The influence of the outlet pressure and supply hydrogen pressure on the performance of the confocal twin-nozzle ejector are analyzed,and two key geometric parameters of the diameter and length of the area mixing chamber are optimized.(4)Based on the actual working conditions of PEMFC,the logic control strategy of the confocal twin-nozzle ejector is proposed.(5)The influence of the water vapor content of the anode gas on the recirculation performance of the confocal twin-nozzle ejector is also studied.(6)An experimental test platform is built to analyze the performance of the confocal twin-nozzle ejector under different operating conditions,and verify the accuracy of the established numerical simulation model.The research results show that the proposed confocal twin-nozzle ejector can significantly improve the recirculation performance under low output power conditions.And through the logic control of the two working modes,it can provide a recirculation ratio greater than 0.89 for the PEMFC hydrogen recirculation system working in a wider power range of 17.90～84.00 kW with a suitable hydrogen supply pressure range of 250～700 kPa.The confocal twin-nozzle ejector proposed in this thesis provides an effective way to extend the working range of the ejector in the PEMFC hydrogen recirculation system and helps to promote the wide application of the ejector in fuel cells.