Dynamics of viscoelastic jets of polymeric liquid extrudate

Experimental observations are used to quantitatively describe purely elasti c instabilities in viscoelastic jets issuing from a capillary and an orific e. Beyond a critical value of the dimensionless flow rate, or Deborah numbe r, the flow becomes unstable and the purely elastic flow transition occurs. The instabilities result in free surface distortion in the form of vertica l stripes laid longitudinally along the axis of the jet. The stripes unifor mly spaced along the periphery of the jet are observed by photo-imaging mea surements for PIE-based Boger fluid. The critical conditions for the onset of surface distortions and spatio-temporal characteristics of the instabili ties are reported. Measurements of the extrudate swell are also conducted f or different values of capillary diameter to systematically examine the eff ect of geometry. (C) 1999 Elsevier Science B.V. All rights reserved.