Experimental study on the motion behavior of multi-sized bubbles in a continuous casting mold

A 1:3 scaled water model experimental system was established based on the similarity principle. High-speed cameras and particle image velocimetry were employed to capture bubble images, and ImageJ was used for image processing to extract bubble trajectories, size distribution, and gas volume fraction. The motion behavior of multi-sized bubbles in the continuous casting mold was systematically investigated. The experimental results indicate that the casting speed, flow rate, mold size, and slag layer all have significant effects on the movement and distribution patterns of multi-sized bubble-like flows within the mold. First, small bubbles exhibit a distinct fan-shaped flow pattern, whereas large bubbles remain confined near the submerged entry nozzle, rising almost vertically. Both casting speed and gas flow rate influence the strength of the upper recirculating flow, which in turn affects the spatial distribution and movement behavior of bubbles. Moreover, the width of the mold influences bubble trajectories by altering the jet impingement area. As the mold width increases from 1050 to 1750 mm, the trajectories of small bubbles gradually evolve into a fan-shaped flow. Consequently, fewer bubbles follow the downward flow into the deeper region of the mold, and the gas volume fraction decreases from 6.52% to 4.26%. In addition, due to its inherent viscous resistance and surface tension, the slag significantly suppresses the gas–liquid two-phase flow. As the slag thickness increases from 0 to 2 cm, the rising velocity of bubbles decreases, and the overall gas volume fraction drops from 5.29% to 2.62%.