Effect Of Rotation On Thermal-solutal Capillary Convection Of Binary Fluid Mixture In A Czochralski Configuration

The Czochralski?Cz?method is one of the most common crystal growth technology,which can rapidly produce large scale crystals and easy control the crystal growth direction.The driving forces of melt flow include thermal capillary,solute capillary forces,centrifugal and Coriolis forces during the binary crystal growth process.Due to the interaction of these driving forces,the flows are very complex.Such complex flows driven by the combined forces greatly affect the growth quality of binary crystals and make the crystal growth process difficult to be controlled.Therefore,this paper presents a series of three-dimensional numerical simulations on the complex convection in a Cz configuration filled with Ge-Si melt,and mainly discuss the influences of rotation and capillary ratio on the flow structures and evolutions.The purpose of this work is to reveal the physical essence of flow transition and the mechanism of flow instability.The main works and results are as follows:Firstly,the numerical simulations of the complex convection driven by the multiple driving forces in a Czochralski model are carried out.The results show that the flow is two-dimensional steady basic flow when the driving forces are small.The main forms of flow structures are the single vortex cell rotating clockwise or counter-clockwise and the multi-vortex cell.The structure and direction of vortex cell are closely related to the combination of driving forces on different scales.Secondly,the flow stability diagram and the evolution of flow patterns for the different rotation rates and capillary ratio are obtained.With the increase of driving forces,the two-dimensional steady flow transits into three-dimensional oscillatory flow.At some certain range of rotation rate,the rotation of crystal and/or crucible can suppress the flow instability.When the capillary ratio is-0.2,the basic flow evolves into the spoke patterns.When the crystal rotates only,the critical thermal capillary Reynolds number of flow transition(Re_T,cri)increases firstly and then decreases with the increasing disk rotation rate.When the crucible rotates only,Re_T,cri increases with the increase of crucible rotation rate.When the crystal and crucible rotate together,the melt flow will undergo two type transitions.For the special case of -1 capillary ratio,the thermal and solutal capillary forces are equal and opposite.Comparing with cases of capillary ratio equal -0.2,the flow instabilities are enhanced.Finally,a large number of flow patterns on the free surface are obtained by numerical simulations.For the condition of capillary ratio equal-0.2,the rotating waves appear in the melt layer when the disk rotation effect is dominant.When the thermal-solutal capillary effect is dominant,the spoke patterns appear on the free surface and the spokes become skewed due to the rotation effect.When the capillary ratio is-1,various types of flow patterns appear on the free surface at different crystal or crucible rotation rates with the increasing Re_T,which are rosebud-like patterns,spoke patterns,hydrosolutal waves,annular waves propagating in radial direction,spiral-like waves and rotating waves.For counter rotating of crystal and crucible,the coexistence of hydrosolutal and spiral waves travelling in opposite directions are presented.