An Analytical-Experimental Study for the Determination of the Effective Thermal Conductivity of High Porosity Fibrous Foams

Abstract

In this paper, we present a comprehensive analysis for estimating the effective thermal conductivity of high porosity fibrous foams. Commercially available fibrous foams form a complex array of interconnected fibers with an irregular lump of metal at the intersection of two fibers. In our theoretical analysis, we represent this structure by a model consisting of two-dimensional hexagonal arrays where the fibers form the sides of the hexagons. The lump is taken into account by considering a square, hexagonal or circular blob of metal at the intersection. The analysis shows that the effective thermal conductivity of the foam depends strongly on the porosity and the ratio of the cross-sections of the fiber and the intersection. It has no systematic dependence on pore density. Further, the choice of the geometric configuration of the intersection affects the estimate of the effective thermal conductivity. Experimental data with aluminum and Reticulated Vitreous Carbon (RVC) foams, using air and water as fluid media are used to validate the analytical predictions. Finally, the experimental results are used to arrive at a simple, closed-form empirical correlation for estimating the effective thermal conductivity in terms of the porosity, and the solid and fluid conductivities.