Numerical Simulation And Experimental Study Of Operating Process Of Proton Exchange Membrane Fuel Cell(PEMFC)

Proton exchange membrane fuel cell(PEMFC)is a kind of efficient energy conversion device which can convert chemical energy into electrical energy directly.Water is the main chemical reaction product of this process.This device can achieve zero pollution truly and be considered to be the most likely source of power for replacing traditional internal combustion engines in the future.However,before the large-scale commercialization of fuel cells,it still faces challenges in terms of performance,durability and start-up,and these characteristics are greatly affected by the gas,water and heat management of the fuel cells.Therefore,in order to understand the heat and mass transfer process in the whole system,this paper based on the test system of fuel cell and developed experimental research on the impact of different operating conditions on fuel cell performance.Furthermore,the process of heat and mass transfer in the fuel cell is investigated by simulation and calculation method.The main research contents in this paper are as follow:Firstly,based on the fuel cell experiment platform,the research about the influence of different back pressure,intake gas temperature and relative humidity on the performance and start-up procedure of the single fuel cell has been carried out.The results show that the fuel cell performance can be optimized by the nonlinear coordinated control of intake gas temperature and back pressure.The enhancement of back pressure and relative humidity also can improve the performance of fuel cell,while the excessive high relative humidity will lead to a decrease in starting stability.Secondly,based on the simulation calculation method of FLUENT,the research on simulation calculation of working process of PEMFC has been developed and the law of effect of different operating voltage,parallel flows and opposite flows of hydrogen on product water,temperature distribution and performance has been analyzed.The results show that the parallel flows and opposite flows have little effect on the location of high water content,both of them appear at the air outlet.However,the parallel flows and opposite flows of hydrogen have great effect on the distribution of temperature and current density,and their distributions are related to the size of load.The difference in performance between parallel flows and opposite flows is small under medium or low loads,while the difference is greater under high loads,and the performance of parallel flows is the best.Thirdly,the process of liquid water transfer inside fuel cell stack has been simulated and the effect of different porosities of gas diffusion layers(GDL),operating pressure and operating temperature on the product water,temperature and performance differences of each cell product has been analyzed.The results show that the performance of the stack increases with the increase of GDL porosity under the same load.However,under the medium load,the effect of GDL porosity on the performance and temperature of each cell increases.As the increasing of operating pressure,the performance has been improved and the distribution of water content,temperature and current density is more uniform.Appropriate operating temperature can promote the improvement of performance,while the differences of temperature,water content and current density among each cell are greatly.Excessive high or low operating temperature will lead to the decrease of performance.Finally,the effects of fuel cells with Z-type and U-type cooling flow channel on the working process has been simulated and calculated.The influence of different cooling methods on the performance,product water and temperature distribution of each cell in the stack has also been analyzed.The results show that the performance of Z-type stack is better than U-type stack,and the distribution of current density and water content is more uniform.However,the temperature of Z-type stack is lower when air cooling is used,and the current density of each cell is different greatly.In conclusion,in this paper,experimental test,theoretical analysis and numerical simulation are used to study the working process of fuel cell,and the rules influence of different operating conditions on the water,heat distribution and performance of fuel cell are analyzed.These research results play a guiding role in improving the performance of the fuel cell and have a reference value for the development of engineering applications.