The influence of Marangoni effect on flow and deformation of an electromagnetically levitated molten droplet under static magnetic fields

The influence of Marangoni effect on electromagnetically levitated molten droplet under a static magnetic field is investigated by a series of numerical simulations based on Arbitrary Lagrangian-Eulerian method. Firstly the motions and dynamic deformation as well as flow and temperature fields of droplet without Marangoni effect are calculated under various static magnetic fields, then Marangoni effect is introduced and clear comparisons are conducted. The results show that the static magnetic field could dynamically suppress the oscillation and enhance the levitation stability of molten droplet. With the increase of magnetic field intensity, the oscillation amplitude of droplet is decreased and the dynamic deformation during the oscillation is reduced. When the droplet eventually achieves the equilibrium position, the deformation can also be reduced by static magnetic field. Meanwhile the convection inside molten droplet is suppressed and the temperature difference grows, creating a suiting situation for Marangoni effect. The influence of Marangoni effect on behaviors of molten droplet can be divided into two aspects. On one hand, when the static magnetic field is less than 2T, considering of Marangoni effect will dynamically enlarge the deformation due to the linear decrease of surface tension. But further increasing of magnetic field, the shape difference between cases with and without Marangoni effect gets minished gradually because of the strong suppression effect of magnetic field on droplet deformation. On the other hand, when static magnetic field is over 2T, the Marangoni effect would produce a new vortex near the equatorial surface of droplet. With the increasing of magnetic field, firstly the maximum velocity area shifts into zones near the free surface due to the competition between electromagnetic force and thermocapillary force. Then it returns to the free surface and on this occasion, the flow near the equatorial areas is totally dominated by thermocapillary force. Undoubtedly, the Marangoni effect plays an important role in electromagnetic levitation process and it is necessary to take the Marangoni effect into consideration in future numerical simulations for precise prediction of droplet behavior. (C) 2016 Elsevier Ltd. All rights reserved.