Validity of One-Dimensional Radiative Transfer in Participating Media

For radiative transfer through an absorbing, scattering medium with planar geometry, the validity of the one-dimensional assumption is examined. Using the generalized zonal with Monte Carlo method as a solver, exact numerical solutions are generated to identify conditions under which the one-dimensional assumption is valid. Specifically, for the predictions of transmissivity and reflectivity for a collimated or diffuse energy beam through a planar slab, numerical data are presented to show that a medium aspect ratio (ratio of the width to the thickness) of five or more is a necessary but not sufficient condition for the data to agree with the one-dimensional result. The implication of this condition on the utilization of the one-dimensional radiative transfer assumption in some practical engineering problems such as pipe flow and thermal insulation is discussed.