Experimental study on the flow instability of a binary mixture driven by rotation and surface-tension gradient in a shallow Czochralski configuration

A series of experiments have been conducted on the flow instability of a binary mixture driven by the combined surface-tension gradient and rotations of the crystal and crucible in a shallow Czochralski configuration with the aspect ratio and radius ratio of 0.043 and 0.5 respectively. The working fluid was the n-decane/n-hexane mixture with an initial mass fraction of 50%. The results indicate that the hydrothermal waves (HTWs) instability appears when the thermal capillary Reynolds number exceeds a critical value. Furthermore, the critical thermal capillary Reynolds number increases at first, then decreases with the increase of the crystal or crucible rotation rate. At the combined crystal and crucible rotation, it decreases first, and then almost maintains a constant value with the increase of the crystal rotation rate. The Soret effect in the binary mixture makes the flow more unstable than that in the pure fluid. The propagating direction of the HTWs is the same as the crucible rotation direction at the beginning, and then influenced by the crystal rotation with the increase of the crystal rotation rate at a small thermal capillary Reynolds number. In addition, the propagation angle of the HTWs is greatly affected by rotations.