Numerical Simulation Of Liquid Water Transfer In Cathode Channel Of Proton Exchange Membrane Fuel Cells

Effective water management can improve the performance and durability of proton exchange membrane fuel cells,but inappropriate water management is easy to cause flooding and hinder the normal progress of chemical reactions.The transmission of liquid water in the cathode channel is one of the important contents of water management research.However,most of the relevant simulation studies simplify the micropores on the surface of gas diffusion layer(GDL)into a single circle at a fixed position,resulting in a large gap between the simulation results and the real working conditions of fuel cells.In this paper,the volume of fluid(VOF)model is used for computational fluid dynamics simulation to explore the effects of the number,location,shape,spacing and size of micropores on liquid water transport and gas-liquid two-phase flow model.The simulation results show that the interaction of two hole droplets in the U-shaped cathode channel leads to the rapid formation of bridge flow of liquid water,so the transmission speed is faster than that of single droplet.The droplet exudation from different positions on the GDL surface will be affected by different air currents.When the droplet exudation position is 15 mm away from the channel inlet,the water content in the simulated final channel is the least and the change of pressure drop is the least.Different micropore shapes lead to the droplets to be broken close to different channel walls.It takes a long time for the broken droplets to get close to the outer wall and a short time to get close to the inner wall.With the change of pore spacing in the range of 0.3-1.2mm,the double droplets show fusion,intermittent fusion and non fusion behavior.The influence of pore size on droplet motion is greater than that of pore spacing.When the pore size of the upstream micropore is larger,the downstream droplets are constantly swallowed by the upstream droplets.When the pore size of the downstream micropore is larger,the downstream droplets are broken first,and the upstream droplets are then fused with it.In this paper,the transmission of liquid water in U-shaped channel and straight channel is further studied,and the effects of channel shape on droplet growth cycle,average liquid water coverage on GDL surface and channel pressure drop are analyzed.The simulation results show that the airflow distribution at the bend in the U-shaped channel leads to the shortening of the movement of droplets,so the water removal effect is better than that in the straight channel,but at the same time,the pressure drop in the channel fluctuates greatly.It is also found that the slope angle at the bend of the channel has a certain diversion effect on the liquid water.The widening of the bend leads to a stronger effect of the air flow on the droplets,which minimizes the average liquid water coverage on the GDL surface and optimizes the water removal effect.