Measurement of Total Hemispherical Emissivity Using a Calorimetric Technique

Anapparatus has been designed to measure, using a calorimetric technique, the total hemispherical emissivity of opaque solid materials from −20 to 200◦C. The originality of the technique is the use of two samples and thermal guard rings in order to ensure one-dimensional heat flow in each sample and to reduce heat-loss corrections. Two temperatures are measured in each sample at two distances from the surface, and the surface temperature of each sample is linearly extrapolated. The mean total hemispherical emissivity of the two samples is calculated using a model that considers the main surfaces radiating in the chamber. Unwanted heat losses are evaluated and corrected. The facility design, model of calculation, evaluation of corrections, and uncertainty assessment are described. The measurement technique was validated by comparison to results from a study using another technique. The expanded uncertainty (k = 2) of the total hemispherical emissivity is between ±0.005 and ±0.03.