CFD Simulation of the Interaction Between a Macrobubble and a Dilute Dispersion of Oil Droplets in Quiescent Water

Wastewater generation is a growing concern in the preliminary treatment of heavy crude oil and tar sand. The separation of fine oil droplets from water by flotation is a critical process in the production of bitumen from tar sand. The flow structure from a high-resolution simulation of a single air macrobubble (>3 mm diameter) rising through water in the presence of a very dilute dispersion of mono-sized oil microdroplets (30 μm) under quiescent conditions is presented. A combined model of computational fluid dynamics (CFD), a volume of fluid (VOF) multiphase approach, and the discrete phase method (DPM) was developed to simulate bubble dynamics, the trajectories of the dispersed oil droplet, and the interaction between the air bubble and the oil droplet in quiescent water. The CFD–VOF–DPM combined model reproduced the interacting dynamics of the bubble and oil droplets in water at the bubble–droplet scale. With an extremely large diameter ratio between the bubble and the dispersed oil droplet, this model clearly demonstrated that the dominant mechanism for the interaction was the hydrodynamic capture of oil droplets in the wake of a rising air macrobubble. The entrainment of the oil droplets into the wake of the rising bubbles was strongly influenced by the bubble’s shape.