The coalescence of single drops at a plane liquid–liquid
interface has been studied both theoretically and experimentally.
Experiments were carried out with a wide range of drop size
using two and three component systems. The drops coalesced in a partial
manner and the drop size ratios between stages were determined. A
detailed examination is made of the rest-time distributions for each
stage of coalescence. Generally coalescence rest-times increased with
increase in size of drop and fall height of the primary drop. Reasonable
agreement between theory and experiment is approached for small drops.
Coalescence rest-times of large drops were considerably less than
predicted, presumably because of the deformation of the "trapped" film
and uneven drainage. The variables affecting the coalescence are
analysed and an empirical correlation is formulated to permit prediction
of coalescence rest-times.
Observations of the motion or the droplet fluid and the disturbed
interface were carried out using Schlieren photography. The way in
which wave disturbances at the interface can influence the coalescence
process is examined. It is shown that that such wave disturbances may
be responsible for the existence of the residence time distribution
observed in all single drop coalescence studies