For the micro scale model, mathematical descriptions of solid surface topography and carbon fiber structure are established according to actual features of the components at the interface. Solid surface profile is modeled by the classic Greenwood & Willamson rough surface. Carbon paper is simulated by the random line network model based on the multi-layer construction. Contact pressure and resistance are calculated to generate the “mechanical-electrical” relation based on the Hertzian theory and statistical methods. In the micro model, the effects of carbon paper compression and internal fiber contact on contact resistance are given necessary attention, which are not considered in previous studies . For the macro scale model, the ECR of whole fuel cell is calculated based on the predicted “electrical-mechanical” constitution relation. First, channel configuration of widespread metallic BPP is described according to the forming process and measurement of channel configuration. Then, nonlinear contact pressure distribution is obtained based on the interface deformation characteristic and Winkler surface model. Finally, ECR considering the channel configuration is calculated based on the “electrical-mechanical” constitution relation from micro model.
Experiments of metallic BPP fabrication and ECR measurement are conducted to validate the multiscale numerical model. In the comparison, the model results show good agreement with the experimental results as shown in Fig.1 (b). During the experiments, the measurement results also show obvious dependence on the micro topography and channel configuration of the contacting BPP and GDL. Hence, influences of interface topography, material property, GDL deformation, and channel configuration are systematically studied based on the multiscale model. As shown in Fig.1 (c), it is found that lower ECR would be generated by reducing of surface roughness and softening of material, and significant increase occurs in ECR as the channel width decreases because of the growing contribution of channel gradient region. Size factor is proposed to evaluate the influence of various feature scale to the contact behavior in the fuel cell. Moreover, the assembly process of fuel cell could also be evaluated by the multiscale model.
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