Evaluation Method for the Three-dimensional Behavior of Bubbles in a Liquid Metal under Horizontal Magnetic Field Using Ultrasonic Tomography

To improve the quality of steel production, it is important to understand the behavior of bubbles rising in a liquid metal under a horizontal magnetic field (MF). However, such behavior has not been fully experimentally evaluated because of the limitations of existing experimental methods. In this study, a two cross-sectional ultrasonic tomography (UT) method was developed and used to measure the 3D motion of bubbles in a cylindrical container with an inner diameter of 50 mm. We conducted UT measurements alternately at the upper and lower measurement cross-sections of the container using the developed method, with a measurement interval of 2 ms in each cross-section. The applicability of this system was evaluated by measuring the 3D behavior of bubbles in a gallium alloy under different MF strengths. When no MF was applied or the MF strength was lower, the directions of the velocity vectors were randomly distributed. However, they aligned in the direction of the flow channel with an increase in the MF strength. With an increase in the flow rate, that is, as the distance between the bubbles decreased, the velocity oscillations of the bubbles perpendicular to the MF direction were greater than those parallel to the MF direction at higher MF strengths. Consequently, the distribution of the bubble-passing positions at the cross-section was slightly more spread in the direction perpendicular to the MF than in the parallel direction. These results demonstrate the effectiveness of the developed method in evaluating the 3D behavior of rising bubbles in a liquid metal.