| The gas diffusion layer is an important part of the Proton Exchange Membrane Fuel Cell(PEMFC)and is responsible for transporting the oxygen to the catalytic layer and discharging the liquid water generated by the reaction.However,if the liquid water generated in the catalytic layer is not discharged in a timely manner,it will lead to the accumulation of liquid water in the gas diffusion layer,which will lead to "flooding" and affect the life of the cell,therefore it is important to study the water transport in the gas diffusion layer.Firstly,based on the real carbon fiber structure of the gas diffusion layer,a threedimensional numerical model of the gas diffusion layer is reconstructed using a stochastic reconstruction method.The two-phase flow within the gas diffusion layer is investigated using the VOF model,and the effects of different thicknesses,different contact angles and different pressure drops on the liquid water transport performance are analyzed and assessed using the volume fraction of liquid water and the relative permeability of liquid water in the gas diffusion layer.The analysis revealed that thickness has a significant effect on the uniformity of liquid water transport,with the volume fraction of liquid water reaching equilibrium decreasing with increasing thickness and the effective permeability of liquid water decreasing with increasing saturation.Analysis of gas diffusion layers with different contact angles reveals that liquid water transport is more uniform when the contact angle is hydrophilic,while as the contact angle increases,the uniformity of liquid water transport diminishes,the volume fraction of liquid water reaching equilibrium decreases and the effective permeability decreases.In the analysis of the effect of different pressure drops on the transport performance of liquid water,it was found that as the pressure drop increases,it is easier to overcome the critical breakthrough pressure during the transport of liquid water,which indicates that increasing the pressure drop will be beneficial to the transport of liquid water.Based on the above numerical simulations,the effect of GDL thickness on fuel cell performance was further investigated.Physical and electrochemical tests were carried out using a spraying method to prepare samples with different thicknesses of GDL.The results showed that adjusting the thickness of the GDL had a greater effect on the pore size distribution,with a wider pore size distribution for a thickness of 240μm.In the electrochemical tests it was found that at 240 "μm" thickness the humidity showed a lower voltage loss and a higher ultimate current density at both 60% and 100%.Therefore,the gas diffusion layer with a thickness of 240μm has the best overall performance.Based on the numerical simulation study of the water transport process in the gas diffusion layer and the experimental study of the thickness of the gas diffusion layer,the structure of the gas diffusion layer is optimized and designed,and a new model of the gas diffusion layer with circular grooves is proposed and analyzed using the VOF model in comparison with the conventional gas diffusion layer and the gas diffusion layer with elliptical grooves,and the diffusion of liquid water is found through the study of the transport process and the diffusion of oxygen in terms of rate,the permeability of liquid water,etc.were evaluated and it was found that the gas diffusion layer structure with circular slots had the best drainage performance.Subsequently,numerical simulations using an electrochemical reaction model were carried out to investigate the gradient depth and arrangement distribution of the gas diffusion layer with circular slots.It can be found that this new gas diffusion layer structure facilitates the drainage of liquid water,reducing the possibility of flooding,and also facilitates the uniform distribution of oxygen,thus accelerating the rate of electrochemical reactions. |
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