| Proton exchange membrane fuel cell(PEMFC)is an ideal energy source in the 21 st century because of its high efficiency and low pollution.As a key component of PEMFC,the form of flow-field in bipolar plate and its electrochemical performance are the emphasis of research.In this paper,the working process of gas flow,water transfer,gas diffusion in porous media and electrochemical reaction in active region of PEMFC was studied.The main work and conclusions are as follows:(1)A three-dimensional,steady-state and constant-temperature PEMFC model is established based on the PEMFC electrochemical reaction theory.The numerical simulation and calculation of flow and mass transfer process in PEMFC monomer were carried out by using the multi-physical field direct coupling analysis software(COMSOL Multiphysics).(2)Under the same conditions and geometric parameters,the polarization curves of straight flow-field PEMFC are simulated and experimented,and the results are compared carefully.The result shows that the simulated polarization curve is same as the experimental result.This proves the accuracy of the model.(3)The numerical simulation of parallel flow-field,spiral flow-field,serpentine flow-field and multi-passes serpentine flow-field PEMFC is carried out and the hydrogen distribution in the anode diffusion layer,the pressure distribution in the anode flow-field,the gas distribution in the cathode diffusion layer,the water distribution in the cathode flow-field and the electrochemical characteristics were compared.The results show that: four kinds of PEMFC can guarantee better hydrogen distribution characteristics of anode diffusion layer when the anode inlet velocity is higher,however,when the anode inlet velocity increases continuously,only the hydrogen distribution characteristics of the spiral flow-field and themulti-passes serpentine flow-field PEMFC remain good;The anode pressure drop of the multi-passes serpentine flow-field PEMFC is most moderate,this ensures the required pressure drop for the gas distribution without increasing the burden on the external equipment due to the high pressure drop;The distribution of oxygen in the diffusion layer and and the drainage capacity of the multi-passes serpentine flow-field PEMFC is better than the other three kinds of PEMFC.(4)The performance changes of the serpentine flow-field PEMFC in different form(2,3,4,5-passes)of flow-field are compared and analyzed.The results show that: the inlet uniformity and drainage capacity of 5-passes flow-field PEMFC is better than the other three types of PEMFC;The current density and the maximum power density of the 5-channel serpentine channel PEMFC at the same potential are higher than the other three kinds of PEMFC;The current density at the same potential and the maximum power density of5-passes serpentine flow-filed PEMFC are higher than those of the other three kinds of PEMFC.(5)The effects of inlet velocity on oxygen distribution in PEMFC diffusion layer,water distribution in flow-filed and electrochemical performance of 5-passes serpentine flow-filed were studied by changing the inlet velocity of cathode.The results show that: The difference of oxygen concentration in the diffusion layer and the maximum water content in the channel decreases with the increase of inlet velocity.On the contrary,the average current density increases with the increase of inlet velocity.Each parameter tends to be stable when the velocity increases to a certain value,which indicates that the limited efficiency of electrocatalyst leads to a certain limit of electrochemical reaction after the increase of reactants(oxygen concentration),and finally tends to the chemical equilibrium state;According to the variation rule of each parameter with inlet velocity,the phase of parameter variation with inlet velocity can be divided into fast changing stages within the range of0.1m/s-0.4m/s,the steady change stage in the 0.4m/s~1.2m/s range and the slow change stage in the 1.2m/s~2.0m/s range.(6)When the cathode inlet velocity is 0.1m/s,the influence of different width-depth combination on its performance is investigated by changing the width and depth of the5-passes serpentine flow-field PEMFC.The results show that: For the concentrationdifference,the best size combination can be obtained when the size of width and depth are in the optimization range of 1.28 mm,1.9-2.0mm and 1.9-2.0mm respectively;For the water content,the best size combination can be obtained when the size of width and depth are in the optimization range of 1.32-1.40 mm and 1.9-2.0mm respectively;For the average current density,the best size combination can be obtained when the size of width and depth are in the optimization range of 1.36-1.40 mm and 1.9-2.0mm respectively. |
PDF Full Text Request