Simultaneous measurement of normal spectral emissivity and temperature of materials with low thermal conductivity

Abstract

This study develops a measurement system and a method for measuring the normal spectral emissivity and temperature of low thermal conductivity materials at high temperatures. A self-design heating device using a synergistic heating treatment including a high-power laser and a radiation heating cavity is introduced, and a Fourier transform infrared spectrometer is utilized to measure the radiation signal of sample. Based on the temperature hypothesis model, which considers normal spectral emissivity keeps constant within small temperature difference less than 10.0 K, a method is proposed for realizing the inversion of normal spectral emissivity and temperature with the multispectral radiation signal. A genetic algorithm-based technique with big mutations is used to estimate the normal spectral emissivity and temperature of sample at high temperatures. The variation of blackbody radiation signals with the blackbody radiance is analyzed to verify the linearity for the detector of FTIR spectrometer. The apparent normal spectral emissivity of an alumina ceramic fiber is determined in the spectral range of 2.5–25.0 μm at 673–1273 K. Furthermore, the uniformity of temperature distribution on the sample surface and inside the sample is numerically evaluated. The standard uncertainty in the experiment at 1273 K is less than 4.0 % in the investigated bands.