Convection in a Czochralski crucible - Part 2: non-rotating crystal

We report on a convection experiment with a Pr=7 fluid. We study the instability of the now 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 DeltaT 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. (C) 2001 Elsevier Science B.V. All rights reserved.