The importance of internal radiation in glass melts is well known. Because glass is a semitransparent medium, radiation must be taken into account in the fluid itself. The Rosseland approximation is a practical model that can be used for realistic 3D simulations. The correction leads to a modification of the apparent conductivity of the material. The so-called Fourier conductivity of the glass is modified by a third-order polynomial correction that models radiation in a semitransparent fluid [29].

If you can afford the computational expense, you will achieve more accurate results by defining an internal radiation sub-task rather than applying the Rosseland approximation. See Internal Radiation for details. Note that the Rosseland approximation should not be invoked for boundaries of a domain in which an internal radiation sub-task is defined.