Numerical optimization of the radial dependence of effective emissivity in blackbody cylindrical cavities

Abstract

The effective emissivity of a blackbody with cylindrical geometry has a definite radial dependence, at the bottom cavity, which is a function of the surface intrinsic emissivity, cavity geometry (L/D) and the temperature gradient along the cylinder walls.

The optimal use of large aperture blackbody cavities, particularly in thermal imager calibration applications or for the characterization of size-of-source effect of radiation thermometers for example, requires quite precise control of the thermal gradient, in order to achieve sources as uniform as possible in effective emissivity, over the complete aperture. In this paper, we present a numerical model in which the radial profile of effective emissivity is optimized, by means of the theoretical modification of the temperature gradients in a cylindrical diffuse cavity. The distribution functions of secondary absorption impacts are defined and the criteria for a suitable choice of experimentally realizable temperature gradients are presented, including the uncertainty analysis.