Study of solid-gas-suspensions used for direct absorption of concentrated solar radiation

Abstract

Suspensions of solid particles of the appropriate diameter in gases have interesting selective absorption properties, as they absorb solar radiation, whereas the emmissivity in the IR range is low. For the numerical evaluation of the important factors governing this absorption, the absorption cross section obtained by Mie Theory was substituted in Beer-Lambert relation for different conditions. For a given concentration and optical depth, the absorption was found to be dependent on the imaginary part, n 2, of the complex index of refraction, n = n 1 − in 2, of the material used. It is also dependent on the size of the particle d (represented by the diameter in case of spherical particles). For solar spectrum (0,2–3 μ) and spherical particles, the recommended values are n 2 ⋍ 0,6 and d = 0.5 μ. These values may be satisfied by spherical particles of graphite.