Droplet Formation from Particulate Suspensions

Abstract

This work presents an experimental study of the formation of pendant droplets of a liquid suspension of non-colloidal, neutrally buoyant, solid particles from a circular orifice into a second liquid phase. The length of the liquid thread at break-off (L) and the diameter of the resulting droplet (D) are examined for various particle volume fractions (φ), ratios of spherical particle diameter to orifice diameter (Dp/d), and flow rate (Q). While no obvious trends were observed for the thread length of the forming drop as the particle concentration of the suspension was increased, structures much different from those in droplet formation from pure liquids were observed near the bifurcation point. Specifically, the particles where observed to be swept out of the necking region of the liquid thread both toward the fluid remaining at the exit of the capillary and down into the forming droplet. At higher particle concentrations this movement of the particles out of the neck created spindle-like structures near both ends of the neck and pinch-off was observed to occur much further away from the surface of the droplet than is the case for pure liquids.