Experimental study of the oscillating bubble motion of a bubble chain in a gallium alloy under the influence of a horizontal magnetic field

• Oscillating motions of chain bubbles in gallium alloy are systematically evaluated • Oscillating motion is classified into five modes by the statistical evaluation • A horizontal MF dampens the oscillating motion of rising bubbles • Bubble oscillation mode depends on the MF strength and the bubble frequency • Bubble oscillation perpendicular to the horizontal MF occurs due to the wake A clear understanding of the dynamics of rising bubbles in liquid metals under a horizontal magnetic field (MF) is essential for improving the steelmaking processes. In this study, the motion of bubble chains rising in a gallium alloy was experimentally investigated using ultrasonic tomography. By systematically varying the inter-bubble distances, bubble diameters, and horizontal MF strengths, the combined effects of the wake caused by the leading bubbles and electromagnetic forces on the bubble motion are evaluated. The bubble oscillating motions in the chain bubbles are classified into five modes based on their magnitude and direction. Without the MF and at large inter-bubble distances, the bubbles exhibit random oscillations, whereas the application of a horizontal MF constrains their motion to two-dimensional planes depending on the MF strength. When the electromagnetic force becomes dominant, the bubbles rise nearly linearly. However, at small inter-bubble distances, anisotropic oscillations perpendicular to the MF direction appear, which are not observed in the case of single bubbles. Moreover, the anisotropy of bubble oscillation under a strong MF is more pronounced for larger bubble diameters than for small bubbles. Under these conditions, the motion directions of the bubbles become consistent, and successive bubbles rise along similar trajectories. These findings suggest that the motion of the trailing bubbles is influenced by the asymmetric wake vortices shed by the leading bubbles under horizontal MFs, resulting in differences in their rising trajectories. Our results provide valuable insights into the dynamics of bubbly flows in liquid metals under the influence of horizontal MFs.