Electromagnetic force in electric glass melting

Abstract

Electromagnetic effects occur in electrically heated glass melts. Sometimes this fact causes disadvantages but it also offers the chance to influence the glass flow beneficially. Α Lorentz force can be generated by a strong external magnetic field called "Fremdfeld" (foreign field). The Lorentz force in the "Eigenfeld" (eigenfield) that is caused by the magnetic field around the current density in the glass can be neglected. Α specific Lorentz force in the "Eigenfeld of the electrode" occurs in electric glass melting using rod electrodes and results from the magnetic field around these electrodes. The numeric JENA-HLX code was employed to calculate the current density distribution for complex voltages and the temperature-dependent electric conductivity. The magnetic field was built up according to the Biot-Savart law. Α first computer calculation shows that the Lorentz force will become the second driving force besides buoyancy near electrodes, provided electrode currents are about 800 Α or higher. Α second numeric trial dealt with a side-wall, a bottom and a top electrode in R-S-T connection. Here the most significant effect occurred at side-wall electrodes, where horizontal velocities increased. The third test was carried out to learn more about the Lorentz force in an electrically heated crucible. Here the most interesting effects were to observe when a Fremdfeld was applied to the electrically heated fluid. In modelling external horizontal and vertical magnetic fields, the resulting fluid flow depends on the mutual orientation and the phase shift between current density and magnetic field. For instance, the forced glass melt rotation around the electrodes is reversed if this phase shift changes from 0° to 180°. To sum up, the Lorentz force offers various opportunities to control the glass flow.