Fractal model for the effective thermal conductivity of microporous layer

Abstract

Heat transfer in the fuel cells is generally limited by the effective thermal conductivity of the microporous layer (MPL). Due to the complexity of the microstructure and the difficulty of the test conditions, studies on the key parameters that affect the thermal conductivity of MPL is lacking. In this paper, we develop an analytical fractal model for the effective thermal conductivity of the MPL based on a lumped parametric model of the cube and a fractal particle chain model, and provide the contact ratio of the agglomerates using a 3D FIB-SEM reconstruction. The results indicate that the main factors affecting the thermal conductivity of MPL include the structural parameters, fractal dimension, and the thermal conductivity of the carbon particles and pores. The fractal characteristics of the MPL inhibit heat transfer rate and the pores act as a "thermal barrier wall" on the heat transfer path in the MPL. When the volume fraction of the MPL is 40 percent, the contact area ratio and fractal factor of the agglomerates are 0.351 and 0.84, respectively. In addition, this research will help to develop novel MPL structures with high thermal conductivity and improve simulation results for fuel cell temperatures.