8 - Radiant Energy Exchange

Abstract

This chapter discusses radiant energy exchange. There are many important processes for which absorption and emission are negligible except at phase interfaces, and as terrestrial radiant energy exchange is always quasi-steady, the specific intensity equation can be simplified. In treating the problem of radiant energy exchange between black bodies, it is convenient to define a view factor, Fu. The view factor can be defined as the fraction or radiant energy leaving the ith surface, which is incident upon the jth surface. Often the view factor is denoted by Fi=jor FAi→Aj to clearly indicate that the radiant energy is emitted by the ith surface and is incident upon the jth surface. One can solve some simple gray body exchange problems without matrix methods if one employs what is known as the method of successive reflections. Even though the method has limited application, it provides a very nice picture of the radiant energy exchange process, and as such it can serve to strengthen one's understanding of radiant heat transfer.