Simulation And Modeling Of Proton Exchange Membrane Fuel Cell For Vehicle Based On CFD Method

Proton exchange membrane fuel cell (PEMFC) is activated quickly at room temperature, low emission, high power density, has become recognized as a new alternative to the present power sources. Flow field plate is an important part in PEMFC, which has the important impacts not only on the performance of stack but also the costs of fuel cell, is a key obstacle to the wide application of fuel cell. But the detailed distributions of temperature, pressure, velocity, molar concentration and current density cannot be easily get by the experiment. Thus, The mathematical model is used to convey internal battery reaction process simulation study for the fuel cell flow field plates provide guidance to optimize the design and performance optimization.A CFD model is developed in this dissertation, including anode modeling and cathode modeling. The study emphasize particularly on the factors affecting the performance of fuel cells, the optimization design of flow field plates. Some of the simulation results are compared with experimental results.At first, a single-phase three-dimensional, steady-state temperature model for simulation of straight flow-field geometric structure on PEMFC, which including anode modeling and cathode modeling, is described to investigate the fluid flow, species transport and current density distribution in the respective subdomain. The studied domain consists of fluid channels, diffusion layers of anode and cathode. That transport phenomena occurred in the subdomain is described by the mass balances, momentum balances, materiel balances and current balances. Transports in the diffusion layers are described by a superposition of Maxwell-Stefan diffusion, and electrochemical kinetics for anodic methanol oxidation and catholic oxygen reduction are described by Tafel equation. The distribution ofconcentrations of reactants and the current density distribution have been calculated. The obtained results indicate that the gas velocity distribution is dominated in the flow field plate, and is close to zero in porous medium; the velocity in the middle of channel is not maximal; the maximal velocity leans to the interface between channel and diffusion layer; the velocity at the interface between channel and diffusion layer is not equal to zero; There is the smallest of anodic reactant mass fraction in the inlet of the anodic channel ,and the largest in the outlet near the catalyst layer. Oxygen mass fraction is the largest flow in the inlet and the smallest in the outlet near the catalyst layer. And the distribution of oxygen is opposite to the water distribution in the cathode. Current density distribution is symmetric in the reaction layer, and there is the maximum current density near the exit of a diffusion layer on both sides of the edge. Then, the study insists on the effect on the performance of fuel cells of the working condition (eg: temperature, pressure and humidity).Next,the model account for optimization design of the straight flow-field geometric structure of PEMFC, especially of the cathode, in order to make the distribution of reactant and resultant in PEMFC symmetrical and reasonable. The obtained results indicate, that with the increase of the proportion of the width of gas channel and ridge, the current density is increasing, and the performance of fuel cell is removing. When the range of the proportion of the width of gas channel and ridge is from three quarters to three and two thirds, that is to say the range of the width of gas channel from 0.3 to 0.55 millimeter, the performance of fuel cell is excellent respectively. Due to the performance of fuel cell, the facture of channel and the general geometric structure of fuel cell, it is reasonable to the range of the depth of channel from 0.3 to 0.4 millimeter.Finally, the performance experiment on PEMFC is developed to testify the validity of CFD model and simulation result. The obtained result indicate that the experimental results act in accord with the simulation results, and the range of relative error is from negative 10 percentage to plus 10 percentage. The CFD model can simulate the performance of fuel cell felicitously and will provide guidance to optimize the design and performance optimization.