Optimization And Research Of Radial Flow Field Of Circular Bipolar Plate In Proton Exchange Membrane Fuel Cell

In recent years,in order to cope with the pressure from the environmental pollution and the fossil fuel shortage,the governments and scientific research institutions around the world have payed more attention to study the clean and efficient energy technologies.Among large quantities of new energy technologies,the hydrogen energy has become the focus of attention due to its high efficiency and zero pollution.As the main method of the hydrogen energy utilization,the fuel cell not only can be used as the power source of transportation vehicles,but also can be used in the heat and power generation system.The research on the bipolar plate can significantly improve the fuel cell performance,which is significant to the commercialization.The optimization of the layout and structural parameter of flow fields has been the focus of the bipolar plate research.The proper flow channel layout and the structure parameter can help the reaction gas distribute to the MEA participating in the electrochemical reaction,which is helpful to the power density improvement.In addition,the produced water can be discharged from the flow channel efficiently ensuring the reliability of the fuel cell operation.The work in this thesis provides the theoretical support and the research experience for the future research on the structure design of the new flow channel for proton exchange membrane fuel cell.Firstly,the research status on the flow channel of the bipolar plate for PEMFC,especially the structural layout design of the flow fields on the bipolar plate and the related research on the shape and size of the cross section of the channel were investigated,and then a novel radial flow field of the circular bipolar plate for PEMFC was designed.Secondly,the main mathematical models used in the proton exchange membrane fuel cell modeling and simulation were constructed.The basic equations of fluid mechanics(mass conservation,momentum conservation,energy conservation and component conservation),Bulter-Volmer equation and current conservation equation,which are used to explain the electrochemical reactions and phenomena in the fuel cell,are included.Thirdly,the geometric models of the radial flow field of the circular bipolar plate for PEMFC and two conventional flow channels(the parallel channel and the serpentine channel)are built.The simulation calculation assumptions,boundary conditions and physical parameters used in the numerical simulation are introduced.The electrochemical performance of the three flow channels was compared.A test platform for PEMFC was built,and the single cells with the radial channel,the parallel channel and the serpentine channel was custom-made.The parameters of the simulation model are modified through experiments,and the accuracy and reliability of the model are guaranteed after verification.Finally,the three main geometrical parameters of the radial flow channel of the new PEMFC circular bipolar plate are studied,including the number of plates,the arrangement of the plates and the geometrical parameters of the channel cross section.In the process of studying the influence of the floor series on the performance of PEMFC,the radial flow fields with 4 floors,5 floors,6 floors and 7 floors are compared.It is found that the radial flow field with 5 floors can provide best electrochemical performances,greater limit current density and power density.The oxygen concentration distribution on the interface of the gas diffusion layer and the catalytic layer of the radial flow field with 4 and 5 floors is obviously better than the other two schemes.Although the distribution uniformity of water in the flow channels and the membrane of the scheme with 5 floors is not as good as that with 4 floors,it is the most reasonable scheme in the water content distribution in the membrane.In the study on the rib hole arranged at every floor,five different schemes(A-E)are made.By comparing different schemes,the C scheme performed best in the electrochemical properties(the limiting current densityand the maximum power density).Also,the mass transport capacity(the oxygen distribution in the interface of the cathode GDL/CL,the water content distribution in the cathode flow channels and membrane)of the radial flow field increased clearly.In the process of studying the influence of the geometry parameters of the channel cross section on the PEMFC performance,it was found that the rectangular channel with the channel aspect ratio of 1.5 to 1.75 could significantly improve the electrochemical performance of PEMFC,and had the best effect on the oxygen transport and product water discharge.