Little attention has been paid to the geometrical parameters of Gas Diffusion Layers (GDLs), as many researchers have reported the GDL transport properties, like thermal conductivity, as a function of only one parameter; porosity. In this paper, a statistical unit cell approach is presented for estimation of the thermal conductivity on the basis of measured geometrical data such as the angles and also the distance between fibers (aspect ratio) and fiber diameter. The dependency of the thermal conductivity on each of these parameters is considered to obtain the best GDL structure. It is discussed, for the first time in this paper, that the parameter of the aspect ratio can usually be as important as porosity, and the traditional thought that a porous media with higher porosity has a lower thermal conductivity cannot always be correct. It is also concluded that the maximum thermal conductivity of a GDL is not a function of the aspect ratio and fiber diameter and only dependent on porosity and fiber angle. In general, the geometrical concepts and the optically measured data presented in this paper can be employed for estimation of other GDL transport properties such as permeability.

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