Magnetohydrodynamics of insulating spheres
J. W. Haverkort, T. W. J. Peeters

A widespread notion in the field of ‘ideal’ magnetohydrodynamics describing highly conducting fluids there can be no electrical charge accumulation. Any nonzero charge will quickly redistribute over a short enough time-scale to be irrelevant. One can however easily show that in the presence of a magnetic field Lorentz forces can act to sustain a finite charge density, see equation 3.  This charge and the associated electric field have a distinct influence on the current distribution and the resulting forces on non-conducting inclusions and bubbles in a conducting fluid as shown in the above picture and explained in the paper.

In the industrial processing of metals, magnetic fields are often used to stir or break liquid metals, calm free surfaces, influence turbulence properties and remove unwanted inclusions.

Even though bubbles and solid inclusions in liquid metals may not conduct electricity themselves, because the surrounding metal does, some interesting magnetohydrodynamic effects arise, like the electromagnetic Archimedes force, and electromagnetically induced drag.

In a continuous caster, liquid steel enters a mold and slowly turns into a solid slab. Under the influence of unwanted flow patterns small bubbles or inclusions can be trapped into the steel, forming elongated ‘blowholes’ after rolling the steel slabs. To suppress unwanted liquid steel flows enormous electromagnets fully surrounding the casting mold. Currents induced by the flow though this magnetic field generate Lorentz forces that brake the flows.

Through computer simulations we discovered a new effect on gas bubbles in the submerged entry nozzle of a continuous caster. We show that, depending on the shape of the magnetic field, the so-called electromagnetic Archimedes force can force  Argon bubbles radially outwards. This effect may be used improving the anti-clogging capacity of gas.

Magnetohydrodynamic Effects on Insulating Bubbles and Inclusions in the Continuous Casting of Steel
J. W. Haverkort and T. Peeters