THE FLUID EFFECT ON THE EFFECTIVE ATTENUATION COEFFICIENT OF A FULLY SATURATED POROUS MEDIUM UNDER LASER RADIATION

We report the preliminary results of an experimental study on laser attenuation in a fluid-saturated porous medium. The objective is to access the influence of fluid properties on the effective spectral attenuation coefficient of a porous aluminum alloy matrix saturated with several fluids (i.e., mercury, air, water, and oil). We propose a simple theoretical model for the radiation-diffusion problem invoking Beerʹs law with an effective attenuation coefficient and an effective thermal conductivity. This model avoids the direct consideration of individual optical properties-of fluid and solid phases-and the difficulty in calculations involving the complex geometry of the porous medium. We determine the effective attenuation coefficient of the medium by matching the experimental data to numerical results from the theoretical model. We found evidence of a direct relationship between the attenuation coefficient and the effective Prandtl number of the medium, when the porous matrix is saturated with liquids (i.e., mercury, water, and oil). This relationship does not hold for the case of air saturating the matrix, due to distinct convective currents.