Experiments and modeling of bubbles colliding head-on in water

Experiments and modeling of head-on collision of a pair of bubbles driven by buoyancy in quiescent water are presented. The experiments showed that two bubbles after contacting for a few milliseconds may coalesce or bounce back depending on the collision velocity. As theoretical comparisons, the influence of velocity boundary conditions on the liquid film drainage and the characteristics of two film drainage models with the assumptions of “partially” and fully mobile interfaces under variable-velocity approach condition are studied. The “partially” mobile model is found to be easier to predict rebound case and longer drainage time, and could not obtain the drainage process where the film is thinned to the thickness below 10⁻⁷ m at both low and relatively high Re. As a whole, the fully mobile model with variable-velocity approach shows more reasonable prediction results for the coalescence and rebound of bubbles in the ultrapure water.