Spectral emissivity of oxidized and roughened metal surfaces

Abstract

The effects of materials’ surface oxidation and roughness on spectral emissivity have been investigated for design improvement and effective thermal management of energy systems. Experiments confirm that both surface oxidation and surface roughness affect spectral emissivity with surface oxidation having a more dominant effect. The surface oxidation layer effect is substantial at low wavelengths, and the affected wavelength range widens as oxidation temperature and time are increased. Increasing surface roughness increases spectral emissivity independent of wavelength. To describe the experimental results, a computational model based on Kirchhoff’s Law is used. The dependence of optical constants on oxidation conditions were measured, and included in the computational model. Surface morphological characteristics for the roughened surfaces are described by multiple superimposed cosine function Fourier series. There is good agreement between computational predictions and experimental results.