Configurations and dynamics of single air/alcohol gas–liquid compound drops in vegetable oil

Gas–liquid compound drops can be used as a low energy liquid-in-liquid disperser, mixer and transporter in place of the energy intensive mechanical agitator. This paper presents an experimental investigation of single air/methanol and air/ethanol gas–liquid compound drops (alcohol-floated bubbles) in sunflower oil at room temperature. Dispersed methanol (ethanol) droplets rise and dissolve slowly in vegetable oil. The air bubbles can float such droplets and increase their rise velocities. The shape of alcohol droplet on the bubble surface was changed to be an alcohol film covering around the bubble and was continuously thrown into the sunflower oil in the form of a toroidal-shaped film, which increases a huge contact area between the alcohol and the oil. A double tube nozzle was used to inject the air bubble (internal tube) and the alcohols (external tube) into the oil. The images showing the configurations of the compound drops during their rise are shown and discussed. The experimental results of the rise velocity and the drag coefficient of the compound drops are presented and compared to those of the single air bubbles and the single alcohol droplets. Rise velocities and drag coefficients predicted by theory of immobile and mobile surface air bubble in sunflower oil are also included for comparison.