Theory of Radiative Heat Transfer between Closely Spaced Bodies

A general formalism is developed by means of which the radiative heat transfer between macroscopic bodies of arbitrary dispersive and absorptive dielectric properties can be evaluated. The general formalism is applied to the heat transfer across a vacuum gap between two identical semi-infinite bodies at different temperatures. The peculiarities arising when the gap width is of the order of, or smaller than, the dominant thermal radiation wavelengths are studied and quantitatively evaluated for the case of two metal bodies. The predicted strong increase with diminishing gap width is in qualitative agreement with experimental results.