Surface Roughness Effects on Radiant Energy Interchange

Radiant interchange between opaque interacting surfaces is formulated for unequal temperature adjoint plates with a one-dimensional surface roughness profile. Rough surface bidirectional reflectance and directional emittance depend on material emittance, roughness element slope, and roughness element specularity. Numerical solution to simultaneous integral equations governing the dimensionless radiant intensities lead to local and overall absorption factors for selected values of the influencing parameters. Absorption factor results show a strong dependence on surface roughness and indicate that roughness effects are more important in the evaluation of radiant interchange than radiant heat loss. Absorption factor values differing by a factor of two to four are commonly observed for identical emittance materials as a result of roughness. The diffuse emission-diffuse reflection property model employing rough surface apparent hemispherical emittance gave the closest agreement to rough surface absorption factor results. Simple property model results, however, were often significantly in error.