Study On The Diffusion Layer Based On Fractal Theory And Its Influence On The Performance Of μDMFC

The components of μDMFC were assembled under a certain package pressure.The diffusion layer of porous structure was most susceptible to deformation due to the packaging pressure,and its porosity and diffusivity would also change the battery performance.Based on the fractal theory and the numerical simulation method,the change of the diffusion layer caused by the package pressure and the effect on the performance were studied.Through the understanding of the fuel cell working process,the function of the components in the work was understood and the transport path of the reactant and the reaction product was analyzed.Combined with the FLUENT software PEM fuel cell module,the mathematical model of fuel cell was analyzed,and the foundation of the later study on the performance of fuel cell was laid.Based on the micromorphology of carbon fiber,the physical parameters and structural parameters of carbon fiber were determined.Based on DIGIMAT-MF and homogenization theory and the elastic modulus of compression direction,the anisotropic physical parameters of diffusion layer were obtained.Based on the DIGIMAT-FE,using randomly generated method to construct the structure of carbon paper,established different porosity carbon paper micro structure of 3D model.According to the micro structure characteristics of diffusion layer,the definition of fractal scale was made for its diameter and number of pores and capillary bend channel,and its fractal dimension measurement method was also analyzed.By obtaining fluid flow path on the cross section of carbon paper,analysis the relationship of porosity and the curve fractal dimension based on the data processed of box counting method,and the curve fractal dimension coefficient was obtained after data processing.Similarly,through the image obtained with different porosity carbon diffusion layer,analysis the relationship of porosity and pore area fractal dimension based on the differential box counting method,and the pore area fractal dimension coefficient was obtained after data processing.The static simulation of the diffusion layer which defined as isotropic material and anisotropic material was carried out.It is showed that the deformation of the diffusion layer was more accurate when it was defined as anisotropic material.Based on the diffusion layer as an anisotropic material condition,by comparing the deformation of diffusion layer under different packing pressure,the law of packaging pressure influence on the deformation of diffusion layer was obtained,and law of influence of diffusion layer deformation on its diffusivity and permeability was studied.A single channel fuel cell model based on diffusion layer deformation was established.The influence of transmission parameters caused by packaging pressure on battery performance is studied by numerical simulation.