Investigation of The Thermocapillary Flow in A Liquid Bridge subject to A Non-uniform Rotating Magnetic Field
The effect of an external non-uniform rotating magnetic field (RMF) on the thermocapillary flow in a liquid bridge under microgravity is studied numerically. The thermocapillary flow subject to a non-uniform RMF (7mT, 25Hz) is investigated over a range of Marangoni numbers (15-40). The results indicate that, in comparison with the thermocapillary flow without the magnetic field, the maximum tangential velocity is greatly enhanced and the maximum axial velocity is reduced significantly due to the effect of the non-uniform RMF. As a consequence, the thermocapillary flow remains steady and approximately axisymmetric under the effect of the non-uniform RMF. These results demonstrate that a non-uniform RMF can be used as an effective method to control the thermocapillary flow.
Marangoni flow in half-zone liquid bridge of molten tin under ramped temperature difference
Abstract A long-run numerical simulation was carried out on a realistic half-zone liquid bridge model of molten tin, which is identical to JAXA's (former NASDA) liquid bridge experiment apparatus. Using the time-dependent temperature difference imposed on both ends of supporting iron rods, the simulation numerically reproduces the experiment for a time period of 3100 s and enables the study of the two-step bifurcation behavior of Marangoni flow. The present study also evaluates the effect of heating velocity on the bifurcations of the Marangoni flow and indicates that the case with a higher heating velocity gives larger critical Marangoni numbers. Moreover, in this study, we investigate the cause of the second critical Marangoni number and critical frequency disagreement between the experimental results and numerical results, and indicate that the second critical Marangoni number determined through free surface temperature oscillations in the experiment may not correspond to the exact onset of oscillatory Marangoni flow.
Effect of axisymmetric magnetic fields on radial dopant segregation of floating-zone silicon growth in a mirror furnace
The effect of axisymmetric magnetic fields on radial dopant segregation of floating-zone silicon growth in a mirror furnace is studied through computer simulation. The mirror furnace is modeled by a point lamp model, and the magnetic fields are generated by wire coils carrying different currents. Heat and mass transfer, fluid flow, melt/solid interfaces, and the free surface are solved globally by a robust finite-volume/Newton's method. Both axial and cusp fields are considered. It is observed that the magnetic fields suppress the convection in the core region effectively, and squeeze the thermocapillary flow toward the free surface. However, due to poor mixing in the core region, large radial segregation is induced by strong magnetic fields, particularly by the cusp field. With a higher heat input, multiple steady states are also observed in weak magnetic fields.