Three-dimensional Numerical Simulation Of Coupled Thermal-solutal Capillary Convection Of A Binary Mixture In An Annular Pool

Capillary convection is a common phenomenon existing in many industrial processes,such as crystal growth,welding and alloy solidification etc.Especially in the process of binary crystal preparation,the coupled thermal-solutal capillary convection driven by temperature and concentration gradients has a great impact on the quality of crystal products.At present,most researches focus on discussing the coupled thermal-solutal capillary convection of liquid layer with horizontal temperature and concentration gradients and adiabatic free surface.There are lack of further researches on the coupled thermal-solutal capillary convection of a binary mixture with Soret effect in a shallow annular pool with nondiabetic surface.Therefore,based on the process of binary crystal growth,a series of three-dimensional numerical simulations were performed to investigate the coupled thermal-solutal capillary convection of a binary mixture with Soret effect in a shallow annular pool heated from below.The effects of the strength of heat diffusion on the surface,aspect ratios and Soret effect on the characteristics of basic flow,the critical condition for flow transition and the flow pattern transition were discussed,the following conclusions were obtained.(1)When the buoyancy is neglected,the axisymmetric steady flow,the hydrotheral waves and the chaos flow appears orderly with the increase of thermal capillary Reynolds number.When the flow is unsteady,the concentration fluctuation is similar to the temperature fluctuation.However,the dimensionless fluctuation amplitude of the concentration is relatively weak.When the buoyancy exsits,the critical thermal capillary Reynolds number for the flow destabilization becomes larger and the critical oscillation frequency decreases,so the stability of capillary convection is enhanced.And the three-dimensional oscillatory flow appears near the outer wall due to the Rayleigh-Bénard instability.(2)When the strength of heat diffusion on the surface increases,the the strength of the capillary convection becomes stronger,and the critical thermal capillary Reynolds number and the critical oscillation frequency for the flow destabilization decrease.The wave number decreases obviously with the increase of the thermal capillary Reynolds number when the free surface is adiabatic,while the wave number doesn't change obviously with the thermal capillary Reynolds number when the surface is nonadiabatic.Furthermore,the oscillation frequency increases with the increase of the thermal capillary Reynolds number at any Biot number.(3)When the aspect ratio increases,the strength of the capillary convection on the surface become weaker,however,the flow of the whole annular pool becomes stronger because of the enhanced bouyancy.The critical thermal capillary Reynolds number and the critical oscillation frequency for the flow destabilization decrease with the increase of the aspect ratio.At the same time,the wave number of the hydrothermal waves decreases and the diversities of flow partern decrease.And the three-dimensional steady structure can be observed in deeper annular pool.(4)Compared with the pure thermocapillary-bouyancy flow,the Soret effect of the binary mixture enhances the flow.And the critical thermal capillary Reynolds number for the flow destabilization becomes smaller but the the critical oscillation frequency becomes larger.Meanwhile,because the Soret effect of toluene/n-hexane mixture is very weak,the Soret effect changes the nondimensional fundamental oscillation only,but has little effect on the flow pattern transition.