Experimental investigation on the effect of crystal and crucible rotation on thermocapillary convection in a Czochralski configuration

Experimental investigation is conducted to understand the effects of crystal and crucible rotations on the thermocapillary convection in a Czochralski configuration. A transparent fluid (0.65cSt silicone oil with Pr = 6.7) is contained in a cylindrical model crucible with the inner diameter of 92 mm and the depth of 2 mm. A copper disc with the diameter of 46 mm is used to simulate the crystal. The rotation rates of the crystal and crucible are 0 ∼ ± 60 rpm and 0 ∼ ± 1 rpm, respectively. Results indicate that there is a transition from stable axisymmetric flow to a three-dimensional oscillatory flow with the increase of the thermocapillary Reynolds number. The critical thermocapillary Reynolds number for the flow pattern transition decreases with the increase of the crystal rotation rate, and it is greater for the crystal-crucible co-rotation, compared to the counter-rotation. When the crystal rotation rate is small, the thermocapillary force is dominant, and the oscillatory flow behaves as the hydrothermal waves. The crystal rotation has only a slight effect on the wave number and propagation angle of the hydrothermal waves. At a high crystal rotation rate, the hydrothermal waves will transit to rotating waves. The temperature fluctuation of the hydrothermal waves is suppressed by the crucible rotation.