Measurements of radiative properties of cellular ceramics at high temperatures

Abstract

The extinction coefficient and the single scattering albedo of selected cellular (reticulated) ceramics that are candidates for use in radiant burners were determined in the 1200-1400 K temperature range. Total radiation intensities leaving layers of the reticulated material heated to steady state in a tube furnace with two different boundary conditions were measured. An inverse radiation approach involving the two-flux approximation using a gray, isotropically scattering model was used to obtain the radiative properties from the measured intensities. Above an optical thickness of unity, this procedure was not sufficiently sensitive to yield the extinction coefficient. For such cases, the extinction coefficient was estimated from the geometric optics limit. The single scattering albedos varied from 0.68 to 0.88 with an uncertainty of ±7%, whereas the extinction coefficients varied from 81 to 270 m1 with an uncertainty of ±11%, depending on the number of pores per centimeter and the sample material. In the range of temperature investigation the variations in the radiation properties were not significant. Nomenclature b = backscattering fraction d = pore diameter, m / = forward scattering fraction fv = solid volume fraction / = intensity, W/m2-sr