GENERAL

In heat transfer, there are three different modes conduction, convection, and radiation. We have included conduction and convection in the Navier-Stokes system of equations discussed in the previous chapters. Radiative heat transfer is another mode of heat transfer to be examined in this chapter. Heat transfer by radiation occurs in many engineering applications of nonparticipating and participating media. In this chapter, we study this subject as a separate mode of heat transfer first and then as a combined mode integrated into other modes.

In nonparticipating media, conduction and convection are absent. Here we are concerned with view factors, radiative boundary conditions, and radiative heat transfer in absorbing, emitting, and scattering media. Radiative heat transfer is associated with the radiative heat flux which involves integrals with respect to the wavelength, solid angle, and optical depth. The governing equation for radiative heat transfer, then, takes the form of integrodifferential equations. This aspect of the radiative heat transfer is unique and requires a special computational treatment.

Participating media combines the radiative heat transfer with conduction and/or convection. The most significant feature in the combined mode heat transfer is the fact that the radiative heat flux is always three-dimensional, even if the computational domain is chosen to be one- or two-dimensional. For this reason, special mathematical formulations and computational schemes must be developed. We discuss this subject in Sections 24.2.4 and 24.3.3.

For the sake of completeness and future reference, some basic definitions and formulas in radiative heat transfer are summarized below.