Bubble breakup and size evolution in turbulent vortex flow

Abstract

The size of bubbles exerts a significant impact on flotation efficiency. In the fine particle flotation system, small-sized bubbles are required to facilitate efficient collision and adhesion between fine particles and bubbles. This study employs numerical simulation of single-bubble breakup and high-speed dynamic camera experiments to investigate the mechanism of bubble breakup within the vortex generator and the effect of differently structured vortex tubes on bubble size reduction. The results indicate that the mechanisms facilitating bubble breakup in different regions of the vortex mineralization tube. These include the continuous low-energy vortex effects in the recirculation zone behind the vortex generator, strong strain rates and turbulent kinetic energy at the boundary between the return zone and the main flow region, and the shear obstruction effects on the wall near the vortex generator. Among the tested structures, the rectangular vortex generator exhibits the optimal performance in promoting bubble breakup. At the circulation flow rate of 0.21 m³ /h, the size of bubbles after passing through the rectangular vortex mineralization tube is 31 % of that after passing through a smooth tube. This is attributed to the fact that the rectangular vortex mineralization tube has the highest volume-averaged turbulent kinetic energy, while a continuous low-vorticity vortex region exists behind the vortex generator. This study demonstrates that bubble breakup can be promoted by increasing turbulent kinetic energy and creating local low-vorticity regions, thereby providing a reference for reducing bubble size in flotation processes.