Design And Characteristic Research Of Hydrogen Ejector For Proton Exchange Membrane Fuel Cell

The hydrogen fuels of proton exchange membrane fuel cells(PEMFC)are general oversupply.So there are usually some unconsumed hydrogen at the anode exit.It can improve the fuel cell efficiency,effectively eliminate potential safety hazards and reduce air pollution to recycle hydrogen.Compared with conventional recovery systems such as compressor and hydrogen circulation pump,the ejector with mechanical structure not only can realize gas recovery and booster,but also reduce the extra power consumption.In this thesis,computational fluid dynamics(CFD)method and experimental method were combined to study the design and optimization of structure,performance and application of hydrogen ejector used in proton exchange membrane fuel cell,the main research content as follows:Firstly,based on the parameters of the PEMFC stack,the structure of the hydrogen ejector,involving the internal main section size and axial dimension,was designed and some of the structural parameters were obtained by empirical formula.At the same time,a two-dimensional numerical model of ejector symmetry surface was established to simulate and analyze the influence of the structural parameters which were calculated on the basis of empirical formulas(nozzle exit position,the constant-area mixing tube length,the constant-pressure mixing tube convergence angle,exit diameter and diffusion angle,the diameter of the ejected fluid inlet,convergence angle and inclination angle,the diameter of the nozzle outlet)on ejector ejector coefficients and optimized the structure.Secondly,based on the optimal structural parameters,a three-dimensional CFD model was established,and the internal gas flow and its performance were simulated.At the same time,the variation of its performance under different operating conditions(pressure,temperature,mass flow rate of working fluid,pressure,temperature,humidity of ejected fluid,and outlet pressure of mixed fluid)were studied.Then,the hydrogen ejector was machined and experimental scheme was designed.A performance test bench was set up to simulate the actual working conditions,and working performance was verified through experimental tests.Finally,the numerical simulation were performed to investigate the change in the internal flow rate of the fuel cells.And the performance of the fuel cell with changed mass flow rate was tested by the experiment,the application effect of hydrogen ejector was also achieved.At the same time,the influence of factors including gravity direction,number of micropores and micropore space of gas diffusion layer on the process of accumulated liquid water discharge were studied.The results show that the structural parameters of the ejector mainly affect the difference of pressure between the constant-pressure mixing chamber and ejected fluid,which affects the ejection coefficient of the ejector.Optimized ejectors have an 8.1% improvement in performance at design conditions.The experimental results about the performance of the hydrogen ejector under different operating conditions have been consistent with the simulation results.At the same time,the performance of the stack has been improved about 6% after the unconsumed hydrogen were recovered at the anode outlet of the stack by ejectors.