Optimization Of Structural Parameters For Wide Working Conditions Of Ejector Based On Single-and Multi-factor Methods

The hydrogen supply cycle system is an important part of the proton exchange membrane fuel cell(PEMFC),and the ejector,as a key component of the hydrogen supply cycle system,has become a hot research topic due to its simple structure,no moving parts and no additional energy consumption.However,its narrow operating range and low entrainment ratio have affected its application to some extent.Therefore,in order to study the fluid flow characteristics inside the ejector and to improve the performance of the ejector.In this paper,the structural parameters and operating conditions of the ejector are mainly studied to improve the operating range of the ejector,and the main work and conclusions of this paper are as follows:(1)A CFD simulation model of the ejector was established,and the accuracy of the model established in this paper was verified by comparing with the previous experimental results,with a maximum error of only ±6.8%.(2)Three dimensionless structural parameters were constructed,and by varying the diameter of the nozzle throat and the values of the three dimensionless structural parameters,a single-factor analysis was conducted on these four structural parameters to study how the performance of the ejector is affected by the variation law of these parameters,and the optimal single-factor combination was derived.(3)An orthogonal analysis was used to investigate the magnitude of sensitivity and the optimal combination of parameters of the throat diameter and the three dimensionless structural parameters on the performance of the ejector when the fuel cell is left at different loading condition.(4)The objective of this paper is to extend the operating range of the ejector,and the optimal combination for a wide range of operating conditions is obtained in the multifactor analysis.After that,the optimized results of single-factor analysis and multi-factor analysis are compared,and it is proved that the multi-factor analysis improves the performance of the ejector better than the single-factor analysis.(5)Based on the optimal combination of structural parameters after the multi-factor optimization,the working conditions of the ejector are changed to study the effects of primary stream temperature and secondary stream temperature and humidity on the performance of the ejector,and the variation laws of the entrainment ratio and hydrogen cycle ratio under different working conditions of the ejector are summarized.The results show that the optimal combination of parameters of the ejector is obtained using both single-factor analysis and multi-factor analysis,and the operating range of the ejector after multi-factor optimization is 109.5% and 119.6% of the single-factor optimization and initial structure parameters,respectively,which proves that the multi-factor analysis based on multi-factor analysis is superior.Also the conclusion that the sensitivity of the ejector to the structural parameters is different under different fuel cell loading conditions is obtained in the multifactor analysis.At low stack current,the ejector performance is most affected by the nozzle throat diameter,and at high stack current,the ejector performance is most sensitive to the mixing chamber aspect ratio,but the ejector performance is better when the nozzle exit position is 0 for both low and high stack currents.The ejector performance showed an almost linear increase with increasing primary fluid temperature.A 60 K increase in primary flow temperature increased the secondary flow mass flow rate by 45.6%,11.6% and 6.5% when the stack current was 150 A,300 A and 450 A,respectively,proving a greater effect on low stack current with increasing temperature.The entrainment ratio increases with the increase of secondary stream temperature and humidity,but the hydrogen cycle ratio decreases significantly.The reason is that the mass fraction of water vapor in the secondary stream increases significantly with the increase of secondary stream temperature and humidity,and the water vapor has a larger molar mass,which in turn leads to the increase of entrainment ratio and the decrease of hydrogen cycle ratio.