Expansion and Contraction of Capillary Jets of Viscoelastic Liquids

Abstract

The increase of diameter, or expansion which occurs when viscoelastic liquids are ejected into air from a capillary nozzle is investigated. For low ejection velocities the jet expands; the expansion reaches a maximum with increasing velocity then decreases; at high velocity the jet contracts. An analysis based upon the momentum equation for the jet shows the phenomenon to be dependent upon the Weber number, the rheological properties of the fluid, and the ratio of the tension in the jet to twice the kinetic energy of ejection. The origin of the tension is thought to lie in three different effects: a nonlinear normal stress developed in the capillary, a viscous normal stress developed outside the capillary as a result of relaxation of the original velocity profile in the capillary, and a normal stress developed outside the capillary as a result of elastic reaction to profile relaxation.