Rheological Behavior and Flow Patterns Around Agitators in Polymer Solutions

Abstract

Flow patterns around agitators of varying design have been determined for the systems: polystyrene/styrene, polybutadiene/styrene, and (butadiene-styrene)-copolymer/styrene at several concentrations. Normal stress coefficients and shear viscosities have been determined in the same concentration range. Three regimes of flow are observed for most agitator types: (1) centrifugal force dominated at low concentrations, (2) vortex patterns or stagnant regions near the agitator of intermediate concentrations, (3) normal stress dominated at high concentrations. It is argued that this behavior may be represented by the dimensionless group Ψ10/2ρR2 where Ψ10 is the zero shear normal stress coefficient, R the radius of the agitator, and ρ the solution density. This is the ratio of viscoelastic to inertial forces. It is found that the transformations of regimes (1) to (2) and (2) to (3) occur in agitators of the same diameter at the same concentrations in any particular solution. The critical concentrations for different solutions correlates with the same value of Ψ1/2ρR2.