Elektromagnetisches Abstützen von Flüssigmetall-Tropfen
The dynamic behavior of liquid metal drops submitted to a high-frequency magnetic field is investigated experimentally. The motivation for the present study comes from electron beam evaporation. In this innovative coating technology, it is favorable that the free surface of the evaporating melt forms a dome-type shape that is held only by electromagnetic pressure. The pressure is generated by a ring-like inductor fed by a high-frequency electrical current. Such an arrangement shows a much higher thermodynamic efficiency than the present technique of evaporation from water-cooled crucibles as convective heat losses are minimized. However, the stability of such free surfaces is the most important problem and stability control is crucial for success.Using Galinstan as the liquid metal to be tested during the experiments, we place a certain volume of liquid metal on the glass plate. A ring-like inductor fed by an alternating electrical current generates the magnetic field. The surface contour of the drop is observed using a high-speed camera system. The data are analyzed by utilizing image processing methods.In the experiment, we vary the inductor current I, the drop volume V and the current frequency f up to 300kHz. Upon increasing the inductor current within the range 0A < I < Icrit, we first observe a static axisymmetric squeezing. However, when the inductor current exceeds a certain critical value, i.e. I > Icrit, these symmetric states become unstable to azimuthal waves. The amplitude, mode number, and oscillation frequency of the observed waves depend strongly on the control parameters.