Periodic dripping dynamics in a co-flowing liquid-liquid system

Periodic dripping into air (the “leaky faucet” phenomenon) is now known and understood in detail, while the same problem for fluids dispersed into a second co-flowing immiscible liquid has received far less attention. Depending on the excitation mode of the fluid phases, distinctive oscillations in the dispersed fluid column lead to the formation of droplet groups. In this work, the impact of the velocity of the continuous phase, volume flow rate of the disperse phase, superimposed pressure oscillations of the dispersed phase, and the viscosity of the disperse phase on the drop formation dynamics in liquid-liquid systems is investigated. It is shown that different dripping modes correlate with certain flow conditions and that viscous damping controlled by the disperse fluid viscosity plays an important role in abating the flow-induced sequencing of drop detachment. A Capillary-number–Ohnesorge-number phase diagram is proposed to summarize the experimental results and to generalize periodic dripping dynami...