Experimental investigation on effects of crystal and crucible rotation on thermal convection in a model Czochralski configuration

•Effects of crystal-crucible rotation on the flow is experimentally investigated.•Rotation rate dependence of critical condition for instability onset is exhibited.•The transition mechanism of flow pattern is analyzed.•Suppression effect of crucible rotation on the flow is certified.

A series of experiments are presented to understand the effects of crystal and crucible rotations on the thermal convection in a model Czochralski (Cz) configuration which consists of a crucible filled with the transparent 0.65 cSt silicone oil (Pr=6.7) and a model crystal. The thermal convection is induced by the temperature difference between the crucible sidewall and the crystal sidewall. The results show that the critical Rayleigh number for the onset of instability of thermal convection increases with the increase of the crystal rotation rate without the crucible rotation. When the crucible rotates, the critical Rayleigh number is higher than that with standing crucible at small crystal rotation rates. After the flow destabilizes, a three-dimensional oscillatory convection is characterized by traveling spoke patterns at small crystal rotation rates. With the increase of the crystal rotation rate, the azimuthal propagating velocity of the spoke pattern increases. Furthermore, the spoke pattern dims gradually and gives way to the wave pattern. The crystal rotation has a slight effect on the spoke number until the spoke pattern disappears. Compared with the shallow pool, the crystal rotation makes the flow more likely to be disturbed in the deeper pool. On the contrary, the crucible rotation is more conducive to suppressing the oscillatory flow in the deeper pool.