Numerical investigation of fluid property effects on formation dynamics of millimeter-scale compound droplets in a co-flowing device

Abstract Effects of fluid property on the formation of millimeter-scale compound droplets in a co-flowing device were systematically investigated via a simulation method using the VOF-CSF model. The simulation shows that compound droplets are formed in three regimes, namely, dripping regime, transition regime, and jetting regime. Increasing the flow rate or viscosity of outer fluid cause flow regime to convert from dripping to jetting, and the diameter of droplet significantly decreases. However the effects of inner fluid viscosity on formation dynamics always appear various, where the breakup mode of core droplet can be significantly changed, but the influences on its geometric dimensions can be ignored. In addition, the effects of internal and external interface tension are also further discussed. Finally, a dimensionless number ξ is proposed to predict the flow regimes of compound droplets formation. The results could provide theoretical guidance for controllably preparing monodisperse millimeter-scale compound droplets with specific size.