In-plane Thermal Conductivity of Pem Fuel Cell Gas Diffusion Layers

Heat transfer through the gas diffusion layer (GDL) is a key process in the design and operation of a PEM fuel cell. The analysis of this process requires determination of the effective thermal conductivity. This transport property differs significantly in the through-plane and in-plane directions due to the anisotropic micro-structure of the GDL. In the present study, a novel test bed that allows the separation of in-plane effective thermal conductivity and thermal contact resistance in GDLs is described. Measurements are performed using Toray carbon paper TGP-H-120 samples for a range of PTFE content at a mean temperature of 65-70°C. The measurements are complemented by a compact analytical model that achieves good agreement with the experimental data. The in-plane effective thermal conductivity is found to be about 12 times higher than the through-plane conductivity and remains approximately constant, k ≈ 17.5 W/mK, over a wide range of PTFE content. NOMENCLATURE cross-sectional area of fluxmeters (m) cross-sectional area of GDL (m) radius of contact area between fibers (m) radius of the area covered by PTFE at contact points (m) thermal conductivity (W/mK) in-plane effective thermal conductivity of each cell, Fig. 3 (W/mK) , in-plane effective thermal conductivity of GDL (W/mK) , , in-plane effective thermal conductivity of GDL, no PTFE (W/mK) effective thermal conductivity based on the Parallel model (W/mK) thermal conductivity of PTFE (W/mK) thermal conductivity of carbon fiber (W/mK) length of GDL sample, distance between sample holders, Figs. 1, 3 (m) number of cells total number of GDL samples in the experiment number of fibers in each cell heat transfer rate (W) heat flux (W/m) cell thermal resistance (K/W) thermal resistance at sample ends (K/W) thermal resistance of fluxmeter (K/W) GDL thermal resistance (K/W) groove thermal resistance (K/W) total thermal resistance at each cell interface (K/W) summation of GDL and groove thermal resistance (K/W) thermal resistance of PTFE in contact regions of fibers (K/W) sample holder thermal resistance (K/W) total thermal resistance (K/W) thermal resistance of wooden block (K/W) fibers’ mean radius (m)