Emissivities of diffuse cavities: Isothermal and nonisothermal cones and cylinders

Local, hemispherical, effective emissivities and integrated cavity emissivities have been computed for isothermal and nonisothermal diffuse conical and cylindrical cavities having lids with circular apertures. The local emissivities of the walls increase rapidly with decreasing aperture diameter and are moderately insensitive to the value of the lid emissivity. The integrated emissivity increases or decreases with the distance of the detector from the cavity; the direction of the change depends upon the cavity geometry. For a nonisothermal cavity, the effective spectral emissivity changes substantially with both wavelength and cavity temperature; consequently, it is in general significantly different from the effective total emissivity.