Exchange of Thermal Radiation Between Surfaces Separated by Transparent Medium
Radiation heat exchange between two black surfaces depends on the shape and size of the bodies, relative position, and distance between them while the radiation exchange between gray bodies also depends on their emissivity. For calculation of the radiation exchange between two black surfaces, basic integral equation of the shape factor has been derived which represents the fraction of the total radiation emitted by a surface intercepted by other surface. Salient features of the shape factor have been presented and a number of illustrative examples on calculation of the shape factor for different systems have been given. Radiation exchange between gray bodies is a complex process. Electrical analogy-based method is given to solve such problems wherein the actual system is reduced to an equivalent electric network. Concept of radiation shield, which reduces the radiation heat transfer from a body by placing a thin opaque partition between the surfaces, has been explained in Sect. 11.9. In the end of the chapter, the Newton’s law of cooling is presented.