CFD investigation of macrobubble-fine oil droplets interactions near the air-water surface

The interaction between air bubbles and oil droplets is a key phenomenon in a range of industrial applications, particularly in flotation processes where fine dispersed oil droplets (diameter < 30 μm) are readily entrained into the air-water surface, primarily due to the hydrodynamic wake generated by rising bubbles. Based on the verified model of Computational Fluid Dynamics (CFD) integrated with the Volume of Fluid (VOF) multiphase approach and the discrete phase method (DPM), this paper investigated the dynamic interactions between a typical single macrobubble (10 mm) rising through a quiescent water and fine oil droplets (30 μm) near the air-water surface . Using high-resolution simulations at the bubble–droplet scale, the CFD-VOF-DPM model successfully captured the interaction dynamics between the bubble and oil droplets. The simulated rising macrobubble gradually transformed from an initial spherical shape to an elongated cap shape before bursting at the air-water surface. The simulations further revealed that approximately 55 % of the fine oil droplets were transported upward toward the water surface by the central jet flow generated in the bubble’s wake, while the remaining droplets were entrained within vortex structures in the wake flow. These entrained droplets were subsequently redirected downward and returned to the bulk liquid.