Constant Viscosity Elastic Liquids

Abstract

The rheology of non‐shear thinning elastic fluids is re‐examined to clarify some of the misconceptions that exist in regard to their behavior. It is demonstrated that these fluids are no more than dilute solutions, constructed by dissolving a high molecular weight polymer solute in a highly viscous Newtonian solvent. Organic and inorganic systems can be constructed and there is no magic recipe. The highly elastic non‐shear thinning fluid systems represent a class of real fluid behavior entirely consistent with molecular theory for dilute solutions and with the Oldroyd B constitutive equation. It is shown that the Oldroyd B constitutive equation is far superior to the convected Maxwell model for predicting the dynamic and steady shear properties of these materials. However the Oldroyd B model fails at higher shear rates and may be completely inadequate for representing the extensional properties of such materials. The paper concludes with some squeeze film flow experimental data for constant viscosity elastic fluids in comparison to a theoretical prediction for Oldroyd B fluids by N. Phan‐Thien in this geometry. The predicted load reduction from Newtonian behavior as a result of fluid elasticity is confirmed by the experimental observations.