Important Parameters in Drop Coalescence at Planar Surfaces

Abstract

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 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, Oh, 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 Oh was much smaller than unity. However, as Oh approached unity from the lower bound, the value of ri decayed. No secondary drop was observed when Oh was greater than unity. Normalized 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.