Extensional flow behaviour of dilute polymer solutions after simple shear flow

Abstract

The flow behaviour of dilute polymer solutions in a die flow is affected by the stress history of the fluid. In this work the influence of pre-shearing on an extensional die flow of dilute polymer solutions was studied; in certain situations an increase in viscosity was observed. The flow behaviour of Newtonian fluids, on the other hand, was not at all affected by the pre-shearing. For the dilute polymer solutions an increase of the viscosity in flow through the die was found when a critical wall shear stress was exceeded. The critical wall shear stress found in these studies was of the same order of magnitude as that in pipe flow corresponding to the onset of drag reduction. This suggests that the same mechanism is effective in both cases.