During the coalescence of a drop with a planar interface, a hole is generated by the rupture of a microscopic film between the drop and interface. An experimental study has been performed to investigate the time dependent behavior of the radius of the hole during coalescence. The study consisted of placing drops of various sizes and physical properties on a planar interface. The interface was made of two immiscible fluids which were also varied. The coalescence process was recorded from underneath the interface with the aid of a high speed digital camera and a prism. The experiment captured two separate processes, film rupture and the closing of the hole. During the film rupture, the hole radius demonstrated a power law time dependence. Results showed that while using an inertial time scale, the dimensionless time at which the dimensionless radius of the hole reached its maximum value was approximately constant for all drops. Moreover, all dimensionless drop rupture radii and times fit onto a single master curve and were independent of their physical properties. However during the closing of the hole, the dimensionless time and radii did not fit a master curve analogous to the hole rupture. This led to the conclusion that the opening and closing stages of drop coalescence transpire under two separate time scales.

An experimental study has been performed to establish the principal elements that govern drop coalescence. The study consisted of placing drops of various sizes and physical properties on a planar interface. The interface was made of two immiscible fluids which were also varied. The coalescence process was recorded with the aid of a high speed digital camera. The experimental portion of the project was aimed at capturing the time of coalescence and the size of the secondary drop that formed after coalescence had finished. Results of the experiments, when scaled properly, showed clear patterns with respect to inertial and viscous terms. Dimensional analysis indicated that Ohnesorge number, which compares viscous and inertial forces, had a strong influence on the behavior of drop coalescence. The ratio of secondary drop radius to primary drop radius, ri, was calculated to be approximately constant when Ohnesorge number was much smaller than unity. However, as Ohnesorge number approached unity from the lower bound, the value of ri decayed. No secondary drop was observed when Ohnesorge number was greater than unity. Dimensionless coalescence times confirmed this trend by being properly scaled with inertial time scales for small Ohnesorge number and preferring viscous time scales when Ohnesorge number was greater than unity.