Measurements of the directional spectral emissivity based on a radiation heating source with alternating spectral distributions

Abstract

A method was developed to simultaneously measure the directional spectral emissivity and the temperature of samples with diffuse surfaces at high temperatures using a radiation heating source with alternating spectral distributions and multiple wavelength measurements. The method avoids the need for direct measurements of the sample surface temperature to determine the spectral emissivity. The inverse problem for the spectral emissivity and the temperature of a sample irradiated by a simulated radiation source was analyzed numerically to illustrate the excellent solution accuracy of the measurement method for various noise levels and spectral emissivities in the near-infrared spectra. The solution uncertainties for the spectral emissivity and temperature were smaller for the sample with a larger spectral emissivity. Measurements with a 99.9% purity graphite sample irradiated by a quartz lamp array as the radiation heating source verified the applicability of the method. The spectral emissivities and temperatures of the graphite sample were calculated using the Levenberg–Marquardt algorithm for two heating conditions with alternating spectral distributions and 30 wavelengths in the spectral range of 1.15–1.60μm. The uncertainties in the spectral emissivity and temperature were very small. The method is useful for accurately measuring the sample spectral emissivity without direct temperature measurements at high temperatures.