Numerical Simulation On Thermocapillary Convection Of High Prandtl Number Fluid Under Axial Gas Flow

Floating zone method(Floating zone method)is a kind of growth technology to make high quality crystal,which is considered to be one of the most promising method in space material preparation.Liquid bridge is a physical model to study growth process of floating zone.Under microgravity,surface tension gradient become a key factor that affect the quality of the material in floating zone crystal growth.Surface deformation is one of the most important factors that affect the thermocapillary convection,and surface deformation caused by the axial gas flow has aroused people's attention.At present,there are a small number of studies for cold liquid bridge,this paper focuses on surface deformation of non-isothermal liquid bridge by axial gas flow,which fills a domestic gap in this field.Firstly,this paper establish static liquid bridge model according to Young-Laplace equation under gravity,then physical and mathematical models for silicone oil liquid bridge surrounded by an annular gas channel are established.This paper adopts finite volume method to discrete controlling equations and boundary conditions,and simulates numericaliey the flow of the liquid bridge and the gas flow channel.The effects of gas flow velocity and direction on free surface and the flow pattern of isothermal and non-isothermal liquid bridge are analyzed.Fluent software(VOF and PISO algorithm)are selected for calculations and the N-S equation,and UDF programs are used to define dynamic contact angle.When the gas flow is directed against gravity,a pressure on free surface of liquid bridge with V=1(volume ratio)and t=1(aspect ratio)deviation promotes a bulging near the top and shrinkage near the bottom;when the gas stream is aligned with gravity,a pressure deviation promotes a shrinkage near the top and bulging near the bottom.The axial flow that just acting on the surface of liquid bridge causes sharp fluctuations of free surface.After 0.14s,the surface fluctuation which is less than 0.5?m reaches a steady state,with the increase of airflow velocity,the stable time will be delay relatively.For the free surface deformation,the maximum deformation usually appears in the bump or the pits,the deformation near the z=d/2 is always zero.There is thermocapillary convection in non-isothermal liquid bridge due to temperature difference,the axial gas flow along the opposite direction of gravity can suppress deformation of the free surface and interior thermocapillary convection,conversely,the axial gas flow along the direction of gravity will strengthen these.The greater gas flow velocity,the greater shearing force and the greater deformation of the free surface,so the axial velocity on the free surface becomes larger.The axial gas flow not only changes the shape and parameters of the free surface,but also affects flow and heat transfer in the liquid bridge.For isothermal liquid bridge,with the increase of gas flow velocity,the internal cell flows are violent,vortex center will be moved along the flow direction;for non-isothermal liquid bridges,the gas flow along the direction of thermocapillary convection will strengthen the cell flows,vortex center will be moved along the direction of thermocapillary convection,the gas flow along the opposite direction of thermocapillary convection will weaken the cell flows,vortex center will be moved along the opposite direction of thermocapillary convection.