Directional emissivities of semi-transparent media Cases of dihedron, infinite cylinder and cone

Abstract

The apparent spectral directional and hemispherical emissivities of simply shaped semi-transparent media - parallel slab, sphere, dihedron, infinite cylinder, cone - are calculated by a ray-tracing technique. The proposed method is fairly general and adapted to several geometrical coordinate systems (absolute or local) according to the nature of the surface. It includes an accurate description of the physics of the radiative transfer in presence of multi-reflections and total reflection phenomena. Calculations are worked out for the two polarizations of the radiation. A close-form expression of the directional emissivity of an infinite cylinder is given which allows validation of the general method. A mapping of the hemispherical spectral emissivities is presented for the different examined cases. These results are applied to typical silicate glasses.