Chunfeng Zhou, Pengtao Yue & James J. Feng
Phys. Fluids 18, 092105 (2006)
Abstract - This work is motivated by recent
experimental development of microfluidic flow-focusing devices that
produce highly monodisperse simple or compound drops. Using finite
elements with adaptive meshing in a diffuse-interface framework, we
simulate the breakup of simple and compound jets in co-flowing
conditions, and explore the flow regimes that prevail in different
parameter ranges. Moreover, we investigate the effects of
viscoelasticity on interface rupture and drop pinch-off. The formation
of simple drops exhibits a dripping regime at relatively low flow rates
and a jetting regime at higher flow rates. In both regimes, drops form
because of the combined effects of capillary instability and viscous
drag. The drop size increases with the flow rate of the inner fluid and
decreases with that of the outer fluid. Viscoelasticity in the drop
phase increases the drop size in the dripping regime but decreases it
in the jetting regime. The formation of compound drops is a delicate
process that takes place in a narrow window of flow and rheological
parameters. Encapsulation of the inner drop depends critically on
coordination of capillary waves on the inner and outer interfaces.