The effect of crystal rotation direction on the thermal and velocity fields of a Czochralski system with a low Prandtl number melt

The purpose of this study is to understand the effect of crystal co- and counter-rotation on the thermal and velocity fields of a Czochralski (Cz) melt in a large crucible.The physical modeling of the Cz system was performed using Wood's metal, which has a similar Prandtl (Pr) number (=0.019) with Si melt and a low melting temperature (70 °C). The velocities and temperatures in a large crucible with 800 mm diameter were measured using an incorporated magnetic probe and thermocouples, respectively.The rate of crystal rotation affects the temperature and velocity fields. Without crystal rotation, the maximum thermal fluctuation region is located under the crystal due to buoyancy convection. With increasing crystal rotations rate, however, the maximum thermal fluctuation region migrates toward the crucible sidewall.When the rate of crystal counter-rotation is increased, the azimuthal velocities decrease and the thermal fluctuations are reduced at the edge of the crystal. With increasing crystal co-rotation rate, however, the azimuthal velocities increase considerably and the temperature fluctuations remain strongly at the edge of the crystal.The results of 3-D numerical simulations using the k–ε turbulent model are well in agreement with the experimental results.