Numerical Modeling And Performance Study Of Radial Flow Field Of Circular Bipolar Plate For Proton Exchange Membrane Fuel Cell

With the gradual warming of global climate and the gradual shortage of energy,hydrogen energy,as a clean secondary energy,has attracted more and more attention and is known as the“ultimate energy” in the 21 st century.Proton exchange membrane fuel cell(PEMFC)is an efficient energy conversion device that directly converts hydrogen chemical energy into electrical energy.With the advantages including fast start-up at low temperature,zero pollution,light weight,high specific power and specific energy,PEMFC has been widely used in space station,military,automobile,distributed power generation and other fields.Bipolar plate is an important part of PEMFC,which is used to connect the single cells in the stack,distribute reaction gas evenly,collect and export current,and block fuel and oxidant.Its performance depends on the flow field structure.At present,the common parallel flow field is prone to flooding because of its low pressure drop;The serpentine flow field has a long intake path,which leads to a large pressure drop and a very large parasitic energy loss;Toyota's 3D flow field has good performance,but the complex structure is difficult to make.Because the flow field of bipolar plate has a significant impact on the performance of fuel cell,it is of great significance to study the new flow field.Based on the existing flow field structures,a radial flow field model of circular bipolar plate is proposed.The reaction gas diffuses from the center to the circumference,its intake path is short and its drainage is good.The performance of radial flow field is analyzed by the method of numerical simulation and experimental verification,and the influence of bipolar plate of radial flow field on the performance of PEMFC is studied.the mathematical model for calculation and simulation of PEMFC is established.The governing equations of the model mainly include mass conservation equation,momentum conservation equation,energy conservation equation,component conservation equation,current conservation equation,electrochemical equation and liquid water formation and transmission equation.The model is simplified by the model assumption and setting boundary conditions and model parameters,and finally a reasonable PEMFC mathematical model is obtained.A new type of radial flow field is constructed,which has the drainage characteristics of serpentine flow field and the flow distribution characteristics of parallel flow field.Its variable cross-section channel structure and regular arrangement of ribs further improve the diffusion mass transfer efficiency and gas distribution uniformity.Based on COMSOL multi-physical field simulation software,a PEMFC calculation domain including cathode channel,cathode catalytic layer,cathode gas diffusion layer,proton exchange membrane,anode catalytic layer,anode gas diffusion layer and anode channel is established.The optimization of new flow field design is realized by the numerical analysis of radial flow field with different channel depth,channel and rib width.Radial flow field of R-?,R-? and R-? with different channel and rib width are established.The results show that the design of R-? can obtain higher limiting current density and maximum power density,and its gas distribution uniformity and drainage capacity are better.Sixteen groups of R-? and R-? with different cathode channel depths are established,respectively.The results show that the depth of the cathode channel has an important influence on the oxygen concentration distribution and drainage capacity of the radial flow field.When the channel depth of R-? and R-? is 2 mm and 1.5 mm respectively,the water concentration is the lowest,and the channel depth of R-? and R-? is 1.5 mm and1.5 mm respectively,the uniformity of oxygen concentration distribution is the best.Based on the above optimization of the radial flow field,R-? is taken as the research object,and the performance comparison parameter benchmark of different flow field is established,and the simulation analysis of the new radial flow field and several typical traditional flow fields of PEMFC is carried out.The results show that under the same working voltage,the current density of PEMFC with different flow fields are as follows: radial flow field > 4-way multi-serpentine flow field > spiral flow field > single serpentine flow field >parallel flow field,and the maximum power density shows the same rule.Under the working voltage of 0.65 V,the performance comparison of PEMFC in different flow fields shows that,the drainage capacity and mass transfer capacity of radial flow field design are superior toother flow fields.The pressure drop of the radial channel is 39.82 Pa,which is close to that of parallel channel.Its parasitic energy loss is very small,which is beneficial to improve the efficiency of the cell.Based on the fuel cell test systems,taking the parallel flow field as the experimental object,the polarization curve of the simulation value of the parallel field is compared with the experimental value to verify the reliability of the selected mathematical model.A feasible visualization experiment scheme is designed and presented,which can be used to study the formation and transmission of liquid water in PEMFC with radial flow field.