Experimental Verification And Simulation Study On The Effects Of Flow Field Structure And Operating Variables On The Performance Of PEM Fuel Cells

The flow field structure and operating variables of the proton exchange membrane fuel cell(PEMFC)significantly impact the fuel cell’s performance.To further understand the internal mass and heat transfer process of PEMFC,this paper uses the simulation calculation with experiment to study the effects of flow field structure design and operating variables on mass and heat transfer in PEMFC.The main research contents are as follows:Firstly,to improve the original bionic flow field based on the human superior mesenteric artery branch structure.A series of novel biomimetic flow fields(BIFFs)PEMFC models have been established and experimentally validated.The effect of the number of refined flow channels on the performance of BIFFs was studied and compared with a conventional serpentine flow field(CSFF)and a conventional parallel flow field(CPFF).The results show that the mass transfer loss,pressure drop,and parasitic power of BIFFs gradually decrease with the increase of the number of refined channels,and the pressure drop and parasitic power are far less than those of CPFF and CSFF.The current density and oxygen concentration distribution are more uniform,the drainage capacity is stronger,and the temperature distribution is more uniform.However,there are large low-performance areas inside CPFF,so the performance of BIFFs is higher than that of CPFF.Although the performance of BIFFs is lower than that of CSFF,the performance of BI-10(BIFF with ten refined flow channels)is very close to that of CSFF,and the heat dissipation capacity of BI-10 is higher than that of CSFF.Secondly,to optimize the operating conditions of BIFF,the PEMFC model of BI-10 was used to study the impact mechanism of different operating conditions(such as working pressure,inlet temperature,inlet relative humidity,and GDL porosity)on the performance and internal parameter distribution of PEMFC.The results show that changing operating conditions within a suitable range can improve the performance of fuel cells.Increasing the working pressure appropriately can increase the concentration of the reaction gas.Reducing the inlet temperature appropriately can increase the membrane water content and oxygen concentration.In areas with medium current density,increasing inlet humidity is beneficial to improving membrane water content and proton conductivity.In contrast,at high current density,appropriately reducing inlet humidity can reduce the accumulation of liquid water.Appropriately increasing the porosity of GDL can make it easier for the reaction gas to reach the interface and facilitate liquid water’s discharge.However,excessive increases in porosity,excessive gas supply,and excessive drainage can decrease membrane water content.Subsequently,the gas flow pattern is changed to enable the biomimetic flow field to be applied to the fuel cell stack.Taking BI-11(BIFF with 11 refined flow channels)as the research object,the effects of different gas flow patterns on its performance and internal parameter distribution were studied.The results show that when the inlet and outlet of BI-11 are set at the four corners of the fuel cell,one is the inlet and three are the outlet(i.e.,Case4),the output performance of the flow scheme is only slightly reduced compared to the original flow mode(i.e.,Case1).The current density and oxygen distribution of Case4 is relatively uniform.Although Case1 has better heat dissipation than Case4,the liquid water distribution of Case1 is greater than that of Case4.So Case4 can be used in the stack,and its performance is only 2.143% lower than Case1.Finally,to study the effect of different coolant flow patterns on the distribution of liquid water in PEMFC porous media,a water-cooled singlechannel PEMFC model was established.The results show that the uniformity of liquid water distribution is the best when the cathode gas flow and cathode cooling water co-flow,regardless of gas countercurrent or downstream flow.When the gas flow from the cathode and anode is countercurrent to the cooling water from the cathode,regardless of gas countercurrent or downstream flow,the uniformity of the liquid water distribution is the worst.The changes in the distribution of liquid water are closely related to relative humidity,temperature,membrane water transport,and current density.The more uniform the distribution of liquid water,the higher the peak current density within the PEM obtained and the better the output performance.