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Local hemispherical effective emissivities and integrated cavity emissivities are computed for isothermal and nonisothermal diffuse double cones (a conical section joined to a conical frustum) with and without lids, and are compared with corresponding values for cylindrocones. The local emissivities increase and become more uniform with increasing taper of the frustum. They are also considerably higher when there is a lid. For cavities with the same conical section, length, and aperture, a lidded double cone is blacker than a lidded cylindrocone when the front half of the frustum is invisible, but less black otherwise. For double cones of the same length, diameter, and aperture, the best choice of cone and frustum angles depends upon the particular viewing conditions. The integrated cavity emissivities vary only slightly with the angles of cone and frustum when the frustum is relatively long, and the normal emissivity (for a small on-axis detector a large distance away) is higher than the hemispherical emissivity (for a detector that fills the cavity aperture). When the frustum is relatively short, all of these vary substantially with angle, and the hemispherical emissivity can be higher than the normal emissivity. There is a marked variation of both local and integrated emissivities with wavelength in nonisothermal double cones; e.g., for the particular cases illustrated, the normal spectral emissivities change by from 4% to 6% and the hemispherical spectral emissivities by from 17% to 20% between 0.3 and 1 μm for a 1% temperature variation at 1300 K. The amount of the change in these spectral emissivities also depends upon the geometry of the cavity.

Local, hemispherical, effective emissivities and integrated cavity emissivities are computed for isothermal and nonisothermal diffuse cylindro-cones (a cylindrical section of radius R_2 and length L_2 joined to a conical base of length L_1 and half-angle θ), with and without lids, and are compared with corresponding values for the limiting cases of right circular cones and cylinders. The local emissivities everywhere along the walls are considerably higher in a cylindro-cone with a lid than in a similar one without, and also increase rapidly with decreasing cone angle. They are considerably higher in a cylindro-cone than in a cone of length L_1 or in a cylinder of length L_2. On the other hand, for cavities of the same total length, the cylinder has the highest local emissivities except at and near the base, where the emissivity of the cone is highest. There is a regular transition between these two extremes through various intermediary cylindro-cones. The normal integrated cavity emissivities are higher than the hemispherical emissivities for cavities for which (L_1 + L_2)/2R_2 ≳ 0.8. The local and integrated spectral emissivities of nonisothermal cylindro-cones change markedly with wavelength and somewhat with cavity reference temperature. Approximate local emissivities for nonisothermal cylindro-cones can be obtained from corresponding isothermal ones in a simple manner, with useful accuracy.