Uncertainty analysis of steady-state calorimetric emissivity measurements

Abstract

Determining the accuracy and uncertainty in total hemispherical emissivity data is important in the uncertainty quantification of predictive models using radiant heat transfer. Very High Temperatures Reactors (VHTR) are intended to passively remove decay from fission products by the emissive power of the structural materials and ultimately the reactor pressure vessel into the surroundings. By removing this decay heat, the reactor and its fuel will remain intact. Total hemispherical emissivity data must be obtained for specific materials with specific surface conditions. The goal of this dissertation is to determine the uncertainty on previously experimental data on the emissivity of VHTR materials using a calorimetric emissometer constructed according to ASTM C835-06. An additional purpose is to provide a model for which the uncertainty in other ASTM C835-06 designs, or similar calorimetric emissometers, can be evaluated. This is achieved by using an uncertainty analysis described by the JCGM 100:2008: Evaluation of measurement data -- Guide to the expression to the uncertainty in measurement, or GUM. A thorough examination of the calorimeter design and experimental procedure is given to identify and characterize errors in the measurement of raw data and calculation of total hemispherical emissivity. Uncertainty is reported for select cases to demonstrate the minimum and maximum values.