Experimental study about gas-liquid metal two-phase flows under the influence of 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 about 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 single bubble wake. Within the whole present parameter range, the bubble Strouhal number was decreased in the longitudinal magnetic field while increased in the transverse magnetic field. On the other hand, the bubble drag coefficient was found to be increased or decreased depending on the bubble size and the magnetic interaction parameter.
In a next step the gas flow rate was increased leading to the formation of weak bubble plumes. The interest was mainly focused on the effect of both longitudinal and transverse magnetic fields on the global flow structure in the container. The UDV results revealed that the velocity field of the liquid phase was completely reorganized by the external DC magnetic field. The magnetic field application does not result exclusively in a plain damping of the recirculating flow. Especially in the case of a transverse magnetic field new flow pattern were observed in both planes parallel and perpendicular to the magnetic field lines. The tendency was found to align and elongate the flow structures along the magnetic field direction. Magnetic damping effects become important with increasing magnetic field strength.