Effect of internal radiative heat transfer on the convection in CZ oxide melt

A numerical study was carried out to investigate the effect of internal radiative heat transfer on the convection in the Czochralski oxide melt. Results were obtained for a wide range of the absorption coefficients of the melt. The flow and temperature fields showed a remarkable change with the variance in the absorption coefficient. In this study, we adopted two different kinds of boundary conditions for the radiative heat transfer at the melt surface, i.e., an opaque and a semitransparent diffuse gray surface, and for each case, the influence of Marangoni convection was investigated. The optical characteristic of the melt surface and the Marangoni effect greatly affected the convection and temperature field in the melt. When the surface was assumed to be semitransparent, in the range of a small absorption coefficient, the smaller the absorption coefficient was, the lesser the Marangoni effect became. This was caused by the disappearance of the temperature gradient at the melt surface, and consequently the flow became as weak as in the case without the Marangoni effect. These numerical results give a clue for discussion on the effect of internal radiative heat transfer in the melt of the Czochralski system.