Directional spectral emittance of ceramic material - Comparison of theoretical prediction and experimental data

Abstract

Directional spectral emittance of absorbing and scattering isotherm ceramic (AUOs) is predicted using a radiative model based on the discrete ordinates method associated with the control volume technique to solve the radiative transfer equation. The extinction (Qc) and scattering (Qs) efficiencies and asymmetry factor (g) for radiation incident upon spherical particles of aluminum oxide are calculated from the Mie theory for a temperature range from 1200°C to 1700°C, the particle radius from 25um to 80um, and a range of wavelengths from 2um to Sum. These calculations are based on literature-based values of the complex index of refraction (n = n - ik) at high temperature for the monocrystral of sapphire (AI2O3). Independent scattering assumption is used. Directional spectral emittance is measured using direct radiometric technique. This new experimental device has been developed to minimize the temperature gradient inside the medium, and the overlap of the flux from the material and part of the flux from the heating source. This study aims at comparing the emittance of an isothermal medium of aluminum oxide consisting of a dispersion of spherical particles according to its porosity, grain size, and temperature. Directional spectral emittance determined theoretically is in good agreement with the experimental values.