Multiphysics Field Numerical Simulation Of Proton Exchange Membrane Fuel Cell Stack

The development of a proton exchange membrane fuel cell stack model has attracted much attention for research because such stack model can help fuel cell developers to improve the design of fuel cell stacks,enabling the design of lower cost,better performance,and more efficient fuel cell stacks.However,due to the high computational cost and long calculation time,there are few fuel cell stack models that couple multiple physics.Most stack models to date only consider the fluid distribution of the fuel cell stack and ignore the complex problems of electrochemical and transport processes.The objective of this thesis is to develop a coupled fuel cell stack model that facilitates fast calculation and analysis to accurately predict fuel cell stack performance under various operating conditions.In the present study,multiphysics simulation software COMSOL Multiphysics 5.4 is employed to establish a two-dimensional geometric single cell model first.The single cell model includes sub-models such as secondary current distribution,concentrated mass transfer,Brinkman equation,PDE equation,laminar flow,and heat transfer.The single cell model was validated by comparing the simulation polarization curve with experimental data.A stack consisting of 50 cells was then constructed by connecting such single cells in series.For the problem of flow distribution in the stack,a flow network model was derived and implemented.The inlet velocities of gases was solved using MATLAB using the flow network model,and the results were applied to the stack model in an iterative manner to compute the distributions of gas,water and current density for Utype and Z-type stack configurations.The simulation results show that the distribution of the Z-type structure fuel cell stack is more uniform than the U-type fuel cell stack.Parametric study is carried out to determine the suitable coolant flow rate of the fuel cell stack.A more uniform temperature distribution is obtained by optimizing the cooling design.It is found that better cooling effect can be obtained when the direction of the coolant and the fuel flow are the same.Parametric studies show that increasing the porosity of the diffusion layer,the specific surface area of the catalytic layer,and the conductivity of the membrane are advantageous for the performance of the fuel cell stack.Furthermore,abnormal operating conditions such as a clogged unit cell the voltage and temperature distribution of a single fuel cell failure of a fuel cell stack,which has certain guiding significance for analyzing the fault and life of the fuel cell stack.To gain insights to the role of a stack behavior in a fuel cell system,a system model was built using AEMSim.By simulating the operation of the fuel cell stack under test conditions,data such as the output of the stack,the working conditions of the auxiliary components,and the fuel supply and consumption are obtained.The system model can provide guideline to the construction of the actual test platform and future purchase of test equipment.Furthermore,in the system model,the critical circuit can be optimized at any time,and simulation experiments can be performed on various scenarios assumed,thereby reducing design errors and shortening the design cycle.