Flow-induced transition of compound droplet to composite microfiber in a channel with sudden contraction

Abstract

The deformation behavior and hydrodynamic stability of a three-dimensional Newtonian single-core compound droplet during flow in a channel with sudden contraction were studied by numerical modeling. This research was motivated by the quest for conditions of the steady transition of a compound droplet into a composite microfiber, whose core is stretched as much as the shell. With this aim, the dynamics and morphology evolution of the compound droplet were analyzed in detail as functions of capillary number, core-to-shell relative viscosities, interfacial tensions, and the relative initial core radius. It was found that the effective elongation of the core occurs either with a significant increase in the shell viscosity relative to the ambient fluid or with a decrease in the core viscosity with respect to the shell. In this case, as the composite droplet advances into the narrowing zone of the canal, it continues to stretch, becoming a bullet-shaped composite microfiber. A new mechanism of disintegration of the compound droplet was revealed, which is caused by the core destabilizing effect and manifests itself either with an increase in the relative core/shell interfacial tension or the relative core viscosity.