Rising gas bubbles in a liquid metal under the influence of external magnetic fields

In the present paper we consider the impact of various external DC magnetic fields on the motion of a single bubble rising in a cylindrical column of stagnant liquid metal and the flow structure of a bubble plume, respectively. The ultrasound Doppler method (UDV) has been used to measure the velocity non-intrusively. The motion of single Argon bubbles rising in the eutectic alloy GaInSn under the influence of a DC vertical magnetic field was examined. The bubble terminal velocity showed oscillations indicating a zizag movement of ellipsoidal bubbles. The measurements revealed a distinct electromagnetic damping of the bubble induced liquid velocity leading to more rectilinear bubble trajectories. A global damping of the flow field was also observed if a vertical magnetic field has been imposed on a bubble plume. By contrast, a restructuring of the flow pattern being typical for a bubble plume was observed in the case of a horizontal magnetic field. The DC field gave rise to non-steady, non-isotropic and large-scale flow structures which was rather unknown until now and therefore not sufficiently considered for electromagnetic processing of materials.