Drop Detachment from Liquid/Liquid Interfaces in Vortex-Induced Waves*

The dynamics of drop detachment from the interface during the pipe flow of two immiscible liquids are investigated experimentally and numerically. The experiments were carried out with 5 CST Silicone oil and tap water in a 26 mm ID pipe. We employ a transverse cylinder of 5.5mm diameter for generating vortex-induced waves in the stratified regime. It was found that as flow velocity increases in a stratified flow, the interface becomes wavy until eventually drops detach and entrain into the opposite phase; this marks the onset of the transition to dual continuous and then dispersed flows.  We observed that the wave crests or troughs deform to ligaments which elongate inside the other phase. The relative motion of the two phases stretches the ligament further until it becomes very thin and finally ruptures to form a droplet. We performed a parametric study to reveal the role of surface tension with numerical simulations.