Study On The Structural Design And Two-phase Flow Of Serpentine Flow Channel And Gas Diffusion Layer Of Fuel Cell

Proton exchange membrane fuel cell(PEMFC)has attracted much attention due to its features of zero pollution,rapid response and high energy density.In the process of PEMFC reaction,the final product is only water.Gaseous water may condense into liquid water in the catalyst layer(CL).The liquid water passes through the gas diffusion layer(GDL),moves into the flow channel,and leaves the inside of fuel cell under the action of purge of reaction gas.If the liquid water cannot be efficiently and quickly discharged from the fuel cell,flooding can occur inside the cell.Excessive water in the cell not only blocks the flow of reactive gas,but also causes the rupture of the proton exchange membrane,affecting the service life of the fuel cell.Therefore,water management of fuel cells plays an important role in cell performance and service life.In this study,the movement of liquid droplets in the flow channel and the cross flow of liquid water in the GDL are studied by the VOF method.Based on the single serpentine flow channel and GDL commonly used in fuel cells,the structure is improved and optimized,and the related performance parameters of the GDL are calculated.The results show that when different sizes of rounded corners of channel are implemented,single droplets can be completely removed under both high speed and low speed airflow,with the rounded corner of 0.7 mm.The rounded corner of 0.7 mm can also realize continuous and even drainage under the condition of continuous flow from the water hole.In the GDL,liquid water is mainly transported by means of cross flow.Porosity,as an important structural parameter of the GDL,has important influence on the transport characteristic.GDL is assumed to be a homogeneous porous medium with a constant porosity in most studies.Based on the random parameter method for GDL microstructure reconstruction,through adjusting the value of each carbon fiber layer’s porosity,we respectively build GDLs without change of gradient and symmetric porosity distribution,having the low and high porosity gradient.With the average porosity of 0.7,using the VOF method,the effect of porosity gradient is studied on the cross flow in the GDL.The results show that the change of the porosity gradient can significantly influence the liquid flow rate and water saturation in the GDL.In addition,the porosity gradient distribution itself has a great influence on the GDL performance parameters,such as the effective diffusivity of oxygen,the effective thermal conductivity and effective conductivity.We select four different porosity values,set up four groups of model parameters on the through-plane direction and inplane direction in the simulation.It shows that the GDL performance parameters of the through-plane direction are sensitive to the gradient change of porosity,and decrease with the increase in porosity gradient;the performance parameters of the in-plane direction are insensitive to the porosity gradient variation.