Motion of single gas bubbles rising in a liquid metal exposed to a DC magnetic field

The motion of single Argon bubbles rising in the eutectic alloy GaInSn under the influence of a DC magnetic field was examined. The magnetic field lines were aligned either in longitudinal or in transverse direction. The magnetic field strength was chosen up to 0.3 T corresponding to magnetic interaction parameters N of 1.5. The experiments were carried out in the following parameter range: 2500 < Re < 5500, 2 < Eo < 7, Mo = 2.4e-13. The liquid metal was in a cylindrical container at rest. The Ultrasound Doppler Velocimetry (UDV) was applied to determine bubble and liquid velocities simultaneously. The measured bubble terminal velocity showed oscillations indicating a zig-zag movement of ellipsoidal bubbles. The measurements revealed a distinct electromagnetic damping of the bubble induced liquid velocity leading to more rectilinear bubble trajectories. Within the present interaction number range (N < 2), the applied magnetic field can either increase or decrease the bubble drag coefficient depending on the bubble size and the magnetic interaction parameter. Moreover, significant modifications of the bubble wake structure were observed. Raising of the magnetic field strength causes an enlargement of the eddy structures in the wake. In case of the longitudinal magnetic field the Strouhal number St decreases with increasing magnetic interaction parameter.