Surface oscillations of electromagnetically levitated viscous metal droplets

Abstract

We investigate the oscillation spectrum of electromagnetically levitated metal droplets. In the case of electromagnetic levitation, gravity is compensated by a Lorentz force, which is generated by an external current. The oscillation spectrum contains information about the thermophysical properties of the liquid metal, namely surface tension and viscosity. For a correct interpretation of these spectra the influence of the external forces on the frequencies and the damping of the surface waves must be well understood. The external forces deform the droplet, so that the static equilibrium shape is aspherical. For a perfect conductor the effect of the Lorentz force and gravity on the oscillation spectrum is calculated for an arbitrary magnetic field and arbitrary values of the viscosity. The high Reynolds number limit is evaluated. Explicit results are obtained for a linear magnetic field, which describes the experimental situation well.