Optimization of the Directional Emission from V-Groove and Rectangular Cavities

Abstract

Specially designed cavities are known to produce directional emissivities that have large variations with direction. Surfaces with large variations in radiative properties offer a means of controlling radiative exchange between surfaces. In this paper a measure of the directionality, or degree of focusing, is defined. Possible combinations of directionality and hemispherical emissivity are identified. Two limiting cases for the directional emissivity are discussed which provide collimation of emitted energy in directions which graze and are normal to the cavity opening area, respectively. For a given strength of emission these idealized situations provide maximum focusing of the emission pattern. A V-groove and a rectangular groove are selected as cavities which provide directional emissivities that approach the characteristics of the two limiting cases. Hemispherical emissivity and directionality results for both cavities are presented. Geometries and surface properties of both cavities are optimized to produce maximum focusing of emitted energy. Comparisons are made among the emission characteristics of the V-groove, rectangular groove, and the two idealized limiting cases.