Measurements of Temperature and Emissivity Distributions on a High-Temperature Surface Using an Auxiliary Light Source Method

Abstract

A method to simultaneously measure two-dimensional temperature and emissivity distributions on high-temperature diffuse surfaces is developed using an auxiliary light source. The high-temperature diffuse surface is irradiated from the hemispherical space with the auxiliary light source switched “on” or “off.” Two images of the effective radiation intensity are obtained in quick succession for the two states to determine the temperature and emissivity distributions. The measurement method and uncertainty models show that the effect of the unknown emissivity on the accuracy of the temperature field measurement can be eliminated. The optical pyrometer is a color charge coupled device (CCD) sensor with a quartz lamp array used as the auxiliary light source to illustrate the measurement method. An oxidized W–Ni–Fe alloy sample is heated at high temperatures of 600–1000 °C by a 700 W induction-heating device. The distributions of the effective radiation intensities from the sample surface during the “on” and “off” states of the lamp array are measured in the three color channels (R, G, and B channels) to calculate the temperature and emissivity distributions. The temperature measurement uncertainties are less than 4 °C for a temperature range of 600–900 °C. The temperature measurements are experimentally validated by the thermocouple method only with a small temperature difference. The emissivities calculated from the three color channels are very close with a range of 0.855–0.957. The relative uncertainties in the emissivities for channels R and G are less than 2.0%, while the relative uncertainty for channel B data was higher at 2.8% and 7.5% due to lower measurement signals in channel B. This analysis may provide a useful method for measuring the temperatures of high-temperature diffuse surfaces by successfully compensating for the effects of unknown or changing emissivities.