An Experimental Study of Droplet Deformation and Breakup in Pressure‐Driven Flows through Converging and Uniform Channels

Abstract

A transparent channel was constructed of Plexiglas and droplets of known volume were injected into the reservoir upstream of the channel, through which a suspending medium (i.e., continuous phase) was pumped at a constant flow rate. The deformation patterns of the droplets were recorded on still and movie films as they approached the die entrance and passed through the fully developed region of the channel. The suspending fluids were glycerin as Newtonian medium, and aqueous solutions of polyacrylamide (Separan AP30) at various concentrations (0.6, 2.0, 4.0, and 6.0 wt %) as viscoelastic medium. Droplets were formed of both viscoelastic and Newtonian fluids. For the viscoelastic droplets, polyisobutylene dissolved in decalin (0.6, 2.0, 6.0, and 10.0 wt %) was used, and for Newtonian droplets, low molecular weight polybutene (Indopols L50 and H25) was used. It was observed that at wall shear rates of a suspending medium below a certain critical value, the droplets, initially spherical when upstream in the reservoir, elongated very much at the die entrance and then recoiled somewhat in the fully developed region downstream of the channel. However, at wall shear rates of a suspending medium higher than a certain critical value, a deformed droplet broke up into smaller droplets. The phenomenon of breakup of viscoelastic droplets was observed as being somewhat different from that of Newtonian droplets. Independent measurements were taken of the rheological properties and interfacial tension of the fluids tested, and were used to explain the deformation and breakup phenomenon of the liquid droplets.