Use of a radiation diffusion model for determination of optical and thermal radiative properties of anisotropie silica fiber thermal insulation

Abstract

A radiation diffusion model is used to describe radiation transfer in highly scattering anisotropic semitransparent materials. The transmissivities of the sample disks of silica glass fiber thermal insulation of different thicknesses and orientations were measured. The samples were cut from the same insulation slab. The axis of material structure symmetry was parallel to the axis of samples in one case and perpendicular to it in the other case. The effective absorption coefficient and radiation diffusion coefficient were obtained for three wavelengths of a probing He-Ne laser, namely, 0.63, 1.15, and 3.39 µm. The spectral hemispherical absorptivity and biliemisperical reflectivity as a function of the thickness of the plane layer are calculated and presented.