Investigation of regimes during partial/complete coalescence of a liquid drop on a liquid pool

The coalescence dynamics of a liquid drop on a liquid pool are investigated, considering either air or another liquid as a surrounding fluid. Numerical simulations are performed over a wide range of dimensionless parameters to investigate the subtle interplay of different forces on the partial coalescence and complete coalescence regimes. Our comprehensive study reveals that these two regimes can be demarcated into three sub-regimes depending on the coalescence stage: (i) first-stage partial coalescence, (ii) second-stage complete coalescence, and (iii) first-stage complete coalescence. This rarity classification of the coalescence process is illustrated as a function of the controlling dimensionless numbers in the phase diagrams. To gain quantitative insights into the coalescence dynamics, the hydrodynamic variances associated with this parametric analysis are examined in terms of kinetics of the neck radius and the apex height of the drop, ratio of the daughter drop to mother drop diameter, and the pinch-off time.