Modelling of light propagation in porous media: Application to a volumetric solar receiver with porous structure

Abstract

In this work the propagation of light in porous media is modelled by using the Monte Carlo ray tracing (MCRT) method. The porous media is composed of a solid matrix with homogeneous porous material and isotropic properties, and the boundary of the medium is characterized through a diffuse albedo. The Henyey-Greenstein (HG) phase function is used to model the scattering inside the porous media. The model is validated by comparing the results of diffuse reflectance and transmittance with the corresponding values of a long slab geometry and finite thickness present in literature. Then the model is used to determine the absorption of solar radiation in a porous volumetric solar receiver coupled to a solar concentration system. The effect of the incidence angle, optical thickness, asymmetry factor of the phase function and wall properties on the solar radiation absorption is studied. Using a parabolic dish as concentration system coupled to a cylindrical receiver (concentration factor of 500) as test case, a peak of absorbed solar radiation of 156 MW m−3 and absorption efficiency of 91.35% was obtained, by using an asymmetry factor of 0.4 and extinction coefficient of 1 1/cm.