A model for the interaction of an oil droplet and a gas bubble rising in a quiescent liquid

Gas flotation for oily-water mixtures is common practice in many industrial cleanup applications. Gas bubbles (typically air) come into contact with dispersed oil drops, leading to compound drops (gas-filled oil drops) that rise faster. Although this process is widely used in the industry, the details of the interaction and the capture conditions are not well understood. Experiments were conducted considering different bubble and droplet sizes, as well as changing the viscosity of the surrounding liquid. The experiments demonstrated, that in most cases, the air bubble and oil drop did not coalesce but rather bounced off one another, resulting in a velocity jump of the oil droplet. A mathematical model was developed using these observations. A force balance of buoyancy, weight, drag, added mass, and a history force was used to predict the interaction process prior to and after the collision. The model presented offers new insight into both the application of droplet-bubble interactions as well as exploring bubble wake and fluid relaxation effects on an oil droplet.