Droplet formation in a flow focusing configuration: Effects of viscoelasticity

Abstract

We numerically investigate the effects of bulk fluid viscoelasticity on droplet formation and dynamics in an axisymmetric flow focusing configuration. Viscoelasticity is modeled using the finitely extensible nonlinear elastic-Chilcott-Rallison (FENE-CR) model. Extensive simulations are performed to examine droplet formation and breakup dynamics for a wide range of parameters including flow rate ratio, Weissenberg number, polymeric viscosity ratio, and extensibility parameter. It is found that these parameters have a significant influence on the droplet size and size distribution (dispersity). Three different regimes are observed in the sequence of squeezing, dripping, and jetting modes as the flow rate ratio is increased. It is also found that the viscoelasticity has a similar effect as decreasing flow rate ratio and acts to delay transition from squeezing to dripping and from dripping to jetting regimes. The strain-rate hardening occurs at a critical Weissenberg number resulting in an abrupt increase in droplet size and this effect is more pronounced as the polymeric viscosity ratio is increased.