Flow Channel Design And Cold Start Simulation For Proton Exchange Membrane Fuel Cells

With the development of science and technology,the demand for energy is getting bigger and bigger,and along with the increasing attention to environmental protection,hydrogen energy will be the most valued and potential new energy source,which is regarded as the "ultimate energy source of the 21st century".Proton exchange membrane fuel cells are the clean power source of the 21st century due to their high energy efficiency,clean and pollution-free,and no noise pollution,etc.They can be used in automobiles,aviation,drones,ships,etc.The difficulty of hydrothermal management in PEMFC is one of the main reasons for the low market share of vehicles powered by PEMFC.During the normal operation phase,concentration polarization and water inundation are easily generated.During the cold start phase,the water generated inside the cell will freeze in the porous media area,which not only affects the overall output performance of the cell,but also damages the porous media inside the cell and shortens the service life of the fuel cell.Therefore,avoiding cathode concentration polarization and water flooding with improving cold start performance is crucial.In this paper,a cathode-side the sugar gourd type channel is designed,and a three-dimensional multiphase multi-physics field coupled flow channel simulation model is established based on this flow channel.The distribution of parameters such as velocity,temperature,oxygen concentration and water content in sugar gourd type channel was analyzed by simulation calculation.Based on this flow channel,a threedimensional multi-phase and multi-physical field coupled cold start-up model was established.The performance of sugar gourd type channel and traditional straight channel in cold start-up was compared and analyzed,and the influence of cathode catalytic layer thickness,porosity and convective heat transfer coefficient on cold startup was explored.The main research contents of this paper are as follows:(1)In the flow channel simulation analysis,the processes of water formation,transport and phase change are considered,and reasonable assumptions are made on the flow channel analysis model to establish the momentum,energy,component,charge,mass,and liquid water transport equations inside the proton exchange membrane fuel cell.In the simulation analysis of cold start,the process of ice formation,water transport and phase transformation in the film are considered based on the flow channel model,and the unsteady term is added to establish the multi-phase and multi-physical field unsteady cold start model.(2)A three-dimensional multiphase single-cell single-channel simulation computational model is established in FLUENT,and the grid-independence and model validation are performed.The electrochemical reactions occur in the catalytic layer on the cathode side,and the transport of the gas stream occurs in the flow channel as well as in the porous media region.The influence of the sugar gourd type channel on the velocity field at the cathode side and the distribution of oxygen concentration,liquid water and temperature at the interface between the catalytic layer and the diffusion layer at the cathode side are studied by simulation.It was found that the use of the sugar gourd type channel increased the velocity of the gas stream in the y-direction,enhanced the removal of liquid water,and resulted in a more uniform temperature distribution at the interface between the cathode catalytic layer and the diffusion layer.In conclusion,the heat and mass transfer capability of the proton exchange membrane fuel cell was enhanced,and the current density was increased by about 8%.(3)A three-dimensional multiphase multiphysics field single-cell single-channel cold-start simulation computational model was developed in COMSOL,and the gridindependence and model validation were performed.The effect of flow channel changes on the temperature,ice volume fraction and water content distribution during cold start was investigated by the cold start model.It is found that the temperature rises faster,and the distribution of ice volume fraction and oxygen concentration is more uniform during the cold start of the sugar gourd type channel.The effects of cathode catalytic layer thickness and porosity on the cold start performance were investigated by a cold start model.It was found that a thicker cathode catalytic layer and a larger porosity contribute to the cold start performance.The influence of different surface heat transfer coefficients on cold start was also studied.It is found that the smaller the heat transfer coefficient of the outer surface of the fuel cell,the smoother the cold start and the faster the temperature rise.