QUANTIFYING AIR ATOMIZATION OF VISCOELASTIC FLUIDS THROUGH FLUID RELAXATION TIMES

The industrial need to control the atomization of non-Newtonian fluids necessitates an understanding of the influence of fluid rheology and different viscoelastic properties on this complex process. Previous studies of atomization of a pertinent class of non-Newtonian fluids—polymer solutions—provide a wealth of qualitative observations of the effects of viscoelasticity but are often hindered by the inability to decouple different types of non-Newtonian behavior. Here we use a series of well-characterized polymer solutions whose non-Newtonian behavior are dominated by extensional hardening and utilize a fluid relaxation time τ—the key viscoelastic parameter characterizing the onset of extensional hardening—to quantify the atomization process. The model fluids are sprayed via an air atomizer, and the drop size distributions are measured using a diffraction-based size analyzer. The atomization study shows that viscoelasticity increases the mean drop diameter and broadens the size distribution. We incorporate fluid relaxation time into a drop size correlation that predicts the Sauter mean diameter.