Convection in a Czochralski crucible-Part2: rotating crystal

摘要

ew report on a convection experiment with a Pr=7 fluid. We study the instability of the flow driven by thermal buoyant convection, thermocapillary convection and forced convection due to crystal rotation. Flow visualization and thermocouple measurements are performed. A transition to oscillatory convection is found when the crystal dummy is rotated at a rate above some threshold value f~c. F~c was found to increase linearly with the temperature difference △T between the crystal dummy and the crucible but f~c was found to be independent of the fluid depth H in the crucible. A strong influence of the meniscus geometry on f~c was found. We report critical parameters for the transition to time- dependent flow and oscillation frequencies. The flow patterns under stable and unstable conditions are described. The unstable flow resembles a baroclinic instability which has been discussed before by other authors for such systems.