Keywords: magnetic levitation, liquid metal processing, computational fluid dynamics, magnetohydrodynamics, free surface, high frequency electric current.

It is known from experiments and industrial applications of cold crucible melting that an intense AC magnetic field can be used to levitate large volumes of liquid metal in terrestrial conditions [1,2]. The levitation confinement mechanism for large volumes of fluid is considerably different from the case of a small droplet where the surface tension plays a key role in constraining the liquid outflow at the critical bottom point. Full levitation of a large mass of liquid metal is achievable when the electromagnetic force generates a strong tangential flow along the surface which is directed away from the bottom stagnation point. The bottom confinement is dynamic in nature and requires careful optimisation of the electromagnetic field distribution.

The dynamic interaction of the turbulent flow with the oscillating interface, confined by the magnetic force, is analysed using the unified numerical model SPHINX which describes the time dependent behaviour of the liquid metal and the magnetic field [3]. The k-omega turbulence model, modified by the presence of the magnetic field [4], is used to describe mixing and damping properties at smaller scales unresolved by the macro model.

Two independent numerical codes are used to model (and validate) the high frequency AC magnetic field. The full three-dimensional solution using the finite element package COMSOL shows that the electromagnetic field in the liquid metal is approximately axisymmetric, and is largely unaffected by the presence of the copper crucible segmented structure. While this is true, the presence of the segments significantly reduces the overall energy efficiency. The integral equation based SPHINX code permits high frequency solutions and accounts for dynamical adjustment of the free surface.

The numerical multiphysics simulations suggest that it is possible to levitate a few kilograms of liquid metal in a cold crucible without requiring mechanical support from the container walls. Possible applications to processing of reactive metals are discussed.

1

T. Toh, H. Yamamura, H. Kondo, M. Wakoh, Sh. Shimasaki, S. Taniguchi, "Kinetics Evaluation of Inclusions Removal During Levitation Melting of Steel in Cold Crucible", ISIJ International, 47(11), 1625-1632, 2007. doi:10.2355/isijinternational.47.1625

2

H. Tadano, M. Fujita, T. Take, K. Nagamatsu, A. Fukuzawa, "Levitational Melting of Several Kilograms of Metal with a Cold Crucible", IEEE Trans. Magn., 30(6), 4740-4742, 1994. doi:10.1109/20.334207

3

V. Bojarevics, K. Pericleous, "Modelling Electromagnetically Levitated Liquid Droplet Oscillations", ISIJ International, 43(6), 890-898, 2003. doi:10.2355/isijinternational.43.890

4

O. Widlund, "Modelling of magnetohydrodynamic turbulence", Ph.D. Thesis, Royal Institute of Technology, Stockholm, Sweden, 2000.

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £125 +P&P)