Abstract
More than a century after Max Planck's 1906 book Theorie der Wärmestrahlung, alternative expressions for the entropy flux as related to thermal black-body radiation under non-equilibrium conditions are still controversially discussed in the scientific literature. In this paper, we consider the radiative heat exchange between two planar black bodies of different temperatures. Solely by exploiting the Second Law, it is shown that the mathematical formula for the related non-equilibrium entropy flux can uniquely be inferred from the Stefan–Boltzmann law, without taking advantage of the statistical Planck distribution. Expressions for the entropy production at the emitting surfaces are derived and an effective temperature associated with the radiation between the two bodies is suggested.
© de Gruyter 2011
