Experimental study of a single bubble motion in a liquid metal column exposed to a DC magnetic field

The motion of single Argon bubbles rising in the eutectic alloy GaInSn under the influence of a DC longitudinal magnetic field was examined. 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 = 2.4?10-13. The liquid metal was in a cylindrical container at rest. Bubble and liquid velocities were measured using Ultrasonic Doppler Velocimetry (UDV). The measured bubble terminal velocity showed oscillations indicating a zig-zag movement of ellipsoidal bubbles. Whereas for small bubbles (de ? 4.6 mm) an increase of the drag coefficient with increasing magnetic interaction parameter was observed, the application of the magnetic field reduces the drag coefficient of larger bubbles (de ? 5.4 mm). The measurements revealed a distinct electromagnetic damping of the bubble induced liquid velocity leading to more rectilinear bubble trajectories. Moreover, significant modifications of the bubble wake structure were observed. Raising of the magnetic field strength causes an enlargement of the eddies in the wake. The Strouhal number St decreases with increasing magnetic interaction parameter.