Stretching and Shearing of Immiscible Droplets in Laminar Flows

Droplet deformation in non-stagnant extensional flows is studied where a translating droplet undergoes deformation. A planar converging channel with bounding walls based on a hyperbolic equation was built and imposed a near constant extensional rate along the centerline of the channel in the streamwise direction. The deformation of a Silicone oil droplet is studied in this regime. To study shear influenced deformation, droplets were injected offset from the centerline where the strain rate tensor is strongly influenced by a shear component. Plots of drop draw ratio vs time showed that droplets with low initial Capillary number deformed and achieved a steady shape in the flow. Droplets with higher initial Capillary number experienced continuous deformation. From the instantaneous Capillary number of the droplet, and over many experiments, a heuristic inference of the critical Capillary number was made. These experiments, combined with a computational study, will aid in understanding non-stagnant extensional flows in channels as an analogue to commonly studied stagnant extensional flows in a four-roll mill.