Discrete ordinates solutions of the radiative transfer equation in two-and three-dimensional rectangular enclosures containing absorbing-emitting-scattering media have been obtained using S2, Se, Sg and Sg, approximations. Evaluation against exact analytical and numerical solutions show that while all of these approximations provide acceptable predictions of the radiation fluxes in twodimensional enclosures, use of the higher order (higher than S1,) approximations is not justified due to substantial increase in computational time and negligible improvement in the accuracy of the predictions. However, for three-dimensional enclosures, the 52 approximation is grossly in error. S1 S1) and S5, approximations predict wall heat fluxes and the temperatures of the medium accurately in these enclosures, but, once again, S4, approximation is shown to be adequate. A study of the sensitivity of the predicted net heat absorption by the walls to the dimensions of the system, and radiative properties of the medium and the surrounding walls, based on Fourier analysis technique, indicates that the predictions are more sensitive to the radiative properties than to the dimensions of the enclosure.
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