Chaotic mixing in electromagnetically controlled thermal convection of glass melt

A numerical investigation has been carried out to study the mixing behavior of electromagnetically controlled thermal convection of glass melt in a cylindrical crucible. Thermal convection caused by the internal heating of the glass melt is controlled by an external magnetic field applied along the axis of the crucible. Unlike in thermal convection without and with steady external magnetic fields, Lagrangian particle motion exhibits chaotic behavior in an oscillating magnetic field. The present study shows that the asymmetric thermal field caused by the gravitational body force is rotated in the clockwise and anticlockwise directions alternatively by the Lorentz force imposed by the oscillating magnetic field. As the magnetic field varies sinusoidally with time, the flow field undergoes periodic reorientation causing repeated stretching and folding of the material lines resulting in better mixing in the glass melt. The degree of mixing increases with the period of oscillation till it reaches a maximum and subsequently decreases with further increase in the period. A decline in the mixing performance is observed with increase in the magnetic field strength for a given period of oscillation. This is on account of the fact that the Lorentz forces try to nullify the asymmetry created by the gravitational body forces. The computational results presented here will be useful for developing better glass homogenization systems.