Study On The Flow And Heat Transfer Processes In A Liquid Bridge Under The Effect Of Surrounding Shear Gas Stream

In present industrial practice, the floating zone method is adopted to produce the high quality crystal. The scientific model used to simulate this method in practice is called liquid bridge. The surrounding shear gas stream and heat transfer on the interface are the important factors for the flow structure inside the liquid bridge. The studies on the mechanisms of governing the flow and heat transfer in the liquid bridge are particularly helpful for controlling the crystal growth and improving the quality of products.The present paper presents a mathematical model for the liquid bridge surrounded by an annular gas channel. The distributions of flow and temperature in the liquid bridge are discussed under diffenrent conditions by changing the controlling parameters such as the inlet vebcity, the temperature of the gas, the aspect ratio, and the volume of the liquid bridge. The governing equations are solved by the commercial CFD software FLUENT. Furthermore, the exchange of data on the liquid-gas interlace and the imposed thermocapillary force are implemented on the free surface by means of the user-defined function called UDF.In this paper, the effect of the different computational meshes on the numerical results is first investigated. The accuracy of results is improved obviously by densifying the near-wall and near-surface grids. In the suitable computational mesh, the problem is solved and several meaningful discoveries are obtained.1. In an isothermal liquid bridge under the effect of the surrounding shear gas stream, the distribution of velocity on the interface is in the shape of inverted "U", and a pair of symmetrical cell flows are generated, in which the vortex center is located at the intermediate height of liquid bridge. For a non-isothermal liquid bridge without surrounding shear gas stream, the distribution of velocity on the interface is in the shape "M", and a pair of symmetrical cell flows are generated, in which the vortex center is located at the hot corner.2. The ambient forced gas on the free surface has significant impacts on thermocapillary convection by the shear force and heat exchange effect. The exothermic effect of interface intensifies the thermocapillary convection. Conversely, the endothermic effect of interface weakens thermocapillary convection.When the direction of surrounding gas stream and the marangoni flow is same, the temperature of ambient gas is higher than that of the free surface. In the case of low gas velocity, the effect of heat transfer is more important than that of shearing force, and the surface flow is weakened. In the case of large gas velocity, the effect of heat transfer is smaller than that of shearing force, and the surface flow is enhenced. When the direction of surrounding gas stream and the marangoni flow is opposite, the shearing force and thermocapillary forces along the free surface compete with each other and there is a critical velocity of gas flow. When the gas velocity is lower than this value, the shearing force restrains the marangoni flow. When gas velocity is higher than this value, the cell flow driven by shearing force developed and become main volume returning cell at the vicinity of the cold disk.3. The shape of interface is determined by the voloume ratio and gravity level. Further, the different shapes of interface affect the distribution of surrounding gas shearing force, which results in the change of flow pattern inside the liquid bridge.