The interaction of an oil droplet and a gas bubble rising in a quiescent fluid

Gas flotation for oily-water mixtures is common practice in many industrial cleanup applications. To better understand the process, experiments were conducted considering interacting pairs of 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 an oil droplet velocity enhancement. A mathematical model was developed to capture the droplet dynamics by incorporating the effect of the bubble-induced field, which is in good agreement with the experimental measurements. A force balance of buoyancy, weight, drag, added mass, and a bubble velocity-induced force was used to predict the interaction process prior to and after the collision. The present work offers new insights into understanding droplet-bubble interactions that can help design novel applications for the removal of oil droplets suspended in water.