Numerical Simulation Of Thermocapillary-buoyancy Convection In Encapsulated Liquid Bridge With Deformable Interfaces

Floating zone method is widely used in producing crystals. The thermocapillary convection induced by interface tension gradient becomes a prominent factor influencing the quality of materials under microgravity condition. Recent researches show that thermocapillary convection cannot be omitted even under earthgravity condition. The liquid encapsulation technology plays a very important role in reducing thermocapillary convection. The physical model of two immiscible coaxial liquid columns is researched being aimed at float zone technology of crystal growth and liquid encapsulation technology in the present paper. The results obtained can be applied directly to crystal growth procedure in the production of pure and high quality crystals.The physical and mathematical models of thermocapillary-buoyancy convection in two immiscible liquid layers are established. In order to obtain the free surface and the liquid-liquid interface deformation Runge-Kutta method is used to solve the Young-Laplace equation. Numerical simulation of thermocapillary-buoyancy convection in encapsulated liquid bridge is performed by employing primitive valuable method and finite volume method (FVM). The fluid of liquid bridge and liquid encapsulation are respectively FC-70 and KF-96. The distributions of temperature and velocity in encapsulated liquid bridge are then obtained and effects of a series of non-dimensional parameters on the thermocapillary-buoyancy convection are analyzed. Results show that:1) Both the free surface and the liquid-liquid interface are deformed under earthgravity condition. None of them is cylindrical. The deformation is affected by the geometrical dimension of the encapsulated liquid bridge and physical parameters of fluids.2) The buoyancy convection reduces the thermocapillary convection in the liquid encapsulation, so the impact of liquid encapsulation on the liquid bridge is weakened in this model.3) When the thickness of liquid encapsulation decreases, thermocapillary convection of the fluid in the liquid bridge becomes weaker. The thinner the liquid encapsulation is the greater the reduction of thermocapillary convection in the liquid bridge.4) The free surface and liquid-liquid interface deformation is becoming bigger with the increase of Ar. Meanwhile the thermocapillary convection in the liquid bridge is reducing.5) When Ma number increases, thermocapillary convection in the two liquid layers gets stronger. With the increase of Gr number, thermocapillary convection in the two liquid layers becomes weaker.