Theoretical predictions of radiant transfer through long passages are shown to be quite sensitive to directional variation of radiation characteristics and to polarization of the radiation. With use of the Fresnel relations for specular reflection to find the amount and state of polarization of radiation reflected by dielectric and metallic walls, values of transmittance are calculated and tabulated for long passages of square and infinite slot cross sections with lengths of up to 30 times the lateral distance between walls. Differences in answers by factors up to 14 are shown to result from neglect of directional variation, polarization, and phase change in the reflection process. A simple, approximate analytical relation is presented to permit transmittance and integrated transmittance obtained for isothermal passage walls to be used to calculate transfer in passages with adiabatic or refractory walls.

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