Nonlinear Viscoelastic Properties of Very Dilute Drag Reducing Polymer Solutions

Abstract

Viscous and elastic rheological properties of three very dilute solutions (100 to 500 parts per million) of a polyacrylamide in distilled water which exhibit drag reduction in turbulent flow were determined. Apparent viscosity and first normal stress difference functions were determined using a Weissenberg rheogoniometer over a shear rate range of approximately 10−2–1500 sec−1. In addition, transient response characteristics were determined using a specially designed transient rheometer modified for increased resolution. A relatively simple five‐parameter nonlinear integral constitutive equation which was consistent with all steady and unsteady measurements was used to correlate the data. For comparison, Carreau's seven‐parameter model B, which has previously been found to be appropriate for such solutions, was also evaluated for its ability to represent the observed data. Although capable of a precise representation of the steady shear and normal stress data, this model is incapable of qualitative representation of the transient response properties. The results indicate that, as expected, the viscous properties have less influence on the transient response than on the steady shear response.