An Experimental Method of Measuring Spectral, Directional Emissivity of Various Materials and Joule Heating

Emissivity is an important parameter in calculating radiative cooling of a surface. In experiments at the NASA Ames hypervelocity ballistic range, one of the main errors indicated in temperature measurements is the uncertainty of emissivity for the materials under investigation. This thesis offers a method for measuring emissivity of materials at elevated temperatures at the University of Kentucky. A test specimen which consists of different sample materials under investigation and a blackbody cavity was heated in a furnace to an isothermal condition at known temperature. The emitted thermal radiation was measured and the comparison of sample and blackbody radiation yielded the desired emissivity. In addition to the furnace measurements, separate experiments were conducted in ambient air to determine how much irradiation is reflected back to the samples from the radiation shield used in the furnace to block undesired ambient radiation. Here, the sample heating was accomplished by applying a direct current across the samples. ANSYS simulations were performed to assist the design and analysis. Experiments were conducted in ambient air and a vacuum environment to verify these simulations