A NUMERICAL STUDY OF EXTRUDATE SWELL IN VERY DILUTE POLYMER-SOLUTIONS REPRESENTED BY THE OLDROYD-B MODEL

The fluid flow analysis software package polyflow of the Université Catholique de Louvain (Ref. 1) has been used to make a parametric study of the swelling behaviour of a circular free jet of Oldroyd-B fluid. In particular, the effect of polymer concentration on the swell ratio has been investigated. The polymer concentration is represented by the 'viscosity fraction' β = ηm/(ηm + ηs), where ηs is the solvent viscosity and (ηm + ηs) is the total viscosity. The following chief conclusions have been drawn:. (i) Significant swelling can be observed in very dilute Oldroyd-B fluids (β < 0.2) despite the fact that the recoverable shear is small (of order 0.1). (ii) At a given value of the Weissenberg number, the swell ratio is sensitive to the polymer concentration when β is small, but relatively insensitive when β is large. The results qualitatively confirm a recent experimental study by Butler (Ref. 2). © 1990.