Flow instability driven by the combined temperature gradient and counter rotation of crucible and crystal in a liquid-encapsulated Czochralski configuration

摘要

The combined effects of temperature gradient and counter rotation of the crucible and crystal on the flow instability in a liquid-encapsulated Czochralski configuration are investigated through a series of direct numerical simulations. The two immiscible fluids of 5cSt silicone oil and HT-70 are considered in this work. Results show that the basic flow is in a steady state and is presented as rich flow structures depending on the rotation Reynolds numbers of the crucible and crystal. When the Marangoni number exceeds a threshold value, the unsteady multi-cellular structures are developed. The oscillatory flow behaves as fluctuation waves propagating from the crystal/fluid interface to the crucible sidewall. The amplitudes of the velocity and temperature fluctuations decrease with the increase of the crystal rotation rate, but increase with the crucible rotation rate. The critical conditions for the onset of the flow instability are obtained. The stability diagram indicates that the rotation of the crucible has a destabilizing effect on the flow, but the crystal rotation can depress the flow instability when the crystal rotation Reynolds number exceeds a certain value.