Shape oscillation of microbubbles

•Experimental data on bubble oscillation were collected.•A simple, easily handled mathematical model of oscillatory motions was setup.•Expression for the amount of liquid that takes part in the oscillatory motions was derived.•Frequency and its dependence on the bubble size were evaluated.

Microbubbles – gas bubbles of diameter less than 1 mm – became currently of considerable importance for chemical and process engineering applications, mainly because of the recent discovery of an energetically efficient method of their generation with a fluidic oscillator in the gas supply into an aerator. The oscillation should be applied at the microbubble resonant conditions, about which there has been so far known very little. The key problem is the unknown and difficult to evaluate extent of the surrounding liquid that takes part in the microbubble oscillatory motions and represents the inertia term in the governing equation. The oscillation of microbubbles also influences their ascent, which is slow and puts them often into mutual proximity causing their conjunctions. Author evaluated basic data on oscillating microbubbles from high-speed camera frames and used them to setup a simple model, suitable for engineering design purposes.