REFRACTIVE-INDEX EFFECTS ON TRANSIENT COOLING OF A SEMITRANSPARENT RADIATING LAYER

Refractive index effects are examined for transient tooling by radiation and conduction of a gray semitransparent layer. The layer is in a vacuum and so its heat loss is only by internal radiation leaving through its boundaries. Emission within the layer and energy reflected internally from its boundaries increase with the material refractive index. The reflected energy and heat conduction act to distribute energy across the layer and partially equalize the transient temperature distributions. For some conditions significant temperature gradients develop near the boundaries. The numerical solution method provides accurate transient temperature distributions in these regions so that the predicted radiative losses are not in error. An implicit finite difference procedure is used with nonuniform space and time increments. The integrals for the local radiative source in the energy equation are evaluated by Gaussian integration.