The effect of viscoelasticity on the jet break up and atomization of polymer solutions

The demand to control the jet break up and atomization of viscoelastic fluids necessitates an understanding of the influence of fluid rheology and viscoelasticity on these complex processes. Previous studies of jet break up and atomization of polymer solutions provide a myriad of qualitative observations of the effects of viscoelasticity. The work presented in this thesis differs from those previous studies in that we use a series of well-characterized polymer solutions, and that we measure and utilize the fluid relaxation time, the key viscoelastic parameter characterizing the onset of strain hardening, to quantify the jet break up and atomization processes.;This study probes the effect of viscoelasticity on two processes: the break up of a liquid jet driven by surface tension, and the complex atomization of liquid to produce spray. The jet break up study consists of two parts: jet break up by natural disturbances, and jet break up by forced disturbances. The processes of jet break up are characterized visually in terms of break up mechanism, break up length, and drop size distribution. Both imaging and diffraction techniques are used to characterize the size distributions of sprays produced by the atomization process.;Under natural disturbances, the final stage of disintegration of the liquid jets into drops is shown to be the most affected by viscoelasticity. Increasing viscoelasticity hinders the formation of satellite drops. Viscoelasticity gives rise to stable filaments, which not only delay the break up, but also produce tiny sub-main drops arising from a secondary instability on the filaments. These results confirm strain hardening as the key rheological behavior in jet break up.;The study of jet break up by a forced disturbance provides a technique for measuring the relaxation time of a strain-hardening fluid. The formation of satellite drops is investigated as a function of the fluid relaxation time and the disturbance parameters. The results demonstrate that the formation of satellite drops, which destroy the uniformity of drop sizes, can be controlled through the viscoelasticity of the fluid. A dimensionless group that captures the balance between the fluid relaxation time and the time scale of disturbance growth successfully describes the influence of viscoelasticity on the formation of satellite drops.;The atomization study shows that viscoelasticity increases the mean drop diameter and broadens the size distribution. Interestingly, the mean diameters of the viscoelastic sprays are proportional to the correlation developed for Newtonian fluids. While there are many correlations for Newtonian fluids that predict the mean diameter of the size distribution given the fluid properties and operating parameters, this is the first time the fluid relaxation time is incorporated into such drop size correlation.