Flow Simulation In And Structure Improvement On Proton Exchange Membrane Fuel Cell Flow Channel

As a fuel,hydrogen has the advantages of product pollution-free and high energy density.It is a substitute for fossil fuel as automobile power source.Through proton exchange membrane fuel cell(PEMFC),hydrogen can be converted directly into electric energy continuously,stably and efficiently,so as to drive the automobile.At present,"water management" is one of the most important issues affecting the working stability and energy conversion efficiency of PEMFC.In this paper,the optimization of proton exchange membrane fuel cell flow channel was studied by numerical simulation,the motion state of the liquid droplets in the flow channel is used to judge whether the corresponding flow channel geometry and other parameters are conducive to the elimination of liquid water.Firstly,the gas-liquid two-phase flow process in the cathode flow channel of PEMFC was modeled,and reasonable assumptions were made based on the flow conditions in the flow channel to simplify the mathematical model.In this paper,VOF method is adopted to track the interface between gas phase and liquid phase in the flow process to obtain the position and morphology of liquid droplets.The accuracy of the mathematical model was verified by comparing with the simulation results of another scholar.A hexahedral structured grid was made for the physical model,and the appropriate grid density was determined by grid independence verification.Secondly,this paper further studies the influence of the thickness of the hydrophilic thin plate placed in the flow channel on the effect of water removal for the serpentine flow field with large flow resistance.The increase of sheet thickness is not conducive to the removal of liquid water on the surface of GDL(gas diffusion layer),and the pressure drop in the flow channel increases due to the obstruction of the thin plate to the flow.Compared with the conventional channel,the placement of thin plate is favorable for the removal of liquid water on the surface of GDL.When the droplet leaves the surfaces of the thin plate,the larger contact angle of the thin plate surfaces will result in greater flow loss and significantly increase flow pressure drop.When the height of the sheet increases from 0.7mm to 1mm,it is unfavorable to promote the process of droplet detachment from the GDL wall,also increases the flow pressure drop.Finally,in order to solve the problem of uneven pressure drop and material distribution between adjacent flow channels in parallel flow field,a new flow channel structure was proposed,in which an oblique baffle was added in the passage along the flow direction.The results show that the baffle in the new flow channel can accelerate the discharge process of liquid water through its own structural characteristics and surface hydrophilic characteristics.The discharge process of liquid water is not sensitive to the change of the length of baffle along the flow direction.In the vertical direction,the increase of the height of the baffle from the middle position is not conducive to the removal of liquid water.Although the average pressure drop in the flow channel decreases by about 25% with the increase of the baffle height,the liquid water on the GDL wall cannot detach from the baffle surface in time.At the same time,the increase of baffle height will also lead to a significant decrease in the flow rate over the baffle,which is not conducive to the diffusion of gas to the GDL porous layer.Increasing the inlet velocity can promote the velocity of liquid water on each surface,but also lead to a large increase in the flow pressure drop.