Transient Coupled Heat Transfer Inside a Scattering Medium with Graded Refractive Index

摘要

Transient heat transfer of coupled radiation and conduction within a semitransparent parallel plane slab of absorbing-emitting-scattering gray medium with graded index is investigated. The refractive index of the medium varies continuously along the slab thickness, and both boundary surfaces are specular and semitransparent. The medium is discretized into a number of sublayers with a constant refractive index in each, in which the radiative transfer is numerically simulated using a multilayer radiative transfer model. The multilayer model is developed using a ray-tracing method based on a zonal method. Comparison of present results with previous research shows excellent agreement, which helps to verify the validity of the multilayer radiative transfer model of a medium with a graded refractive index. Effects of optical thickness, scattering albedo, and gradient of refractive index on transient thermal behavior are examined for a medium with nonlinear refractive index distributions. It is found that temperature peaks also appear in the inner regions of a graded refractive index medium with two semitransparent surfaces subjected to external radiation even though there is no convection cooling on the surfaces and the absorbing coefficient (or extinction coefficient) is spatially uniform in the medium.