Search

A high DC magnetic field can be used to levitate liquid droplets in terrestrial conditions, as is known from experiments [1,2]. The DC magnetic levitation mechanism is considerably different from the AC case [3], where an intense turbulent flow is generated as a consequence of the rotational nature of the electromagnetic force. In DC magnetic levitation the force distribution is a potential function, which permits analytical solutions in particular cases [4]. The dynamic interactions of the flow with the oscillating interface, confined by the magnetic force, are analysed using a multi-physics numerical model for simulating the time dependent liquid metal and the magnetic field generated by currents in the coil system [5]. The numerical simulations demonstrate the possibility of levitating diamagnetic droplets in strictly controllable conditions permitting the material properties measurement from experimental observations.\ud \ud Two different coil arrangements are analysed using the numerical code to model the DC magnetic levitation of a water droplet. The levitation of liquid in controllable conditions is achievable but requires careful optimisation of the electromagnetic and gravity force balance. The fluid velocities, generated by the magnetic force modification due to the liquid surface oscillation in the strong gradient field, are small in magnitude and remain in the laminar regime.

The focus of this paper is to provide an insight into the complex nature of the flow fields that develop through the application of a magnetic field at different orientations to the direction of dendritic growth. Through the use of linear superposition and exploiting symmetry planes the results show that a variety of different flow fields can be achieved. Some of the features exhibited are a global circulation around the dendrite and circulations at the dendrite tips. How these circulations effect the morphology of the dendrite is investigated when the magnetic field is orientated in the (001) direction. Rotation of the preferential direction of growth and an increase in secondary branching are observed and are a consequence of circulations altering surface free energy. A qualitative agreement of these morphological changes is found between a full 3-dimensional model using a moving mesh and a 2-dimensional model using quasi 3-dimensional approximations.

It is well 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 the terrestrial conditions. The levitation confinement mechanism for large volumes of fluid is considerably different from the case of a small droplet where surface tension plays a key role in constraining the liquid outflow at the critical bottom point. The dynamic interaction between the oscillatory motion of the free surface and the effects of turbulent flow is analysed using a unified numerical model which describes the time dependent behaviour of the liquid metal and the magnetic field. The MHD modified k-omega turbulence model is used to describe the mixing and damping properties at smaller scales not resolved by the macro model. 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 the processing of reactive metals are discussed.