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

We report on a convection experiment with a Pr=7 fluid. We study the instab ility of the now driven by thermal buoyant convection, thermocapillary conv ection and forced convection due to crystal rotation. Flow visualization an d thermocouple measurements are performed. A transition to oscillatory conv ection is found when the crystal dummy is rotated at a rate above some thre shold 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 f ound to be independent of the fluid depth H in the crucible. A strong influ ence of the meniscus geometry on f(C) was found. We report critical paramet ers for the transition to time-dependent flow and oscillation frequencies. The flow patterns under stable and unstable conditions are described. The u nstable flow resembles a baroclinic instability which has been discussed be fore by other authors for such systems. (C) 2001 Elsevier Science B.V. All rights reserved.