Evaluation of high shear viscosity data from jet and concentric cylinder viscometers

Abstract

This work compares and evaluates viscosity data obtained on similar fluids by two widely accepted high shear techniques. Both the jet and concentric cylinder viscometers are useful high shear methods. The major limitation of the jet viscometer is an inability to distinguish quantitatively between energy losses in laminar flow and those due to capillary geometry and experimental conditions. For example, the jet viscometer gives minima in viscosity-shear rate correlations which are difficult to treat. These minima are not found in concentric cylinder viscometer data for the same and similar fluids. The apparent viscosity increase at high shear in the jet may be due to factors other thanReynold's turbulence, as previously supposed. This effect may be due to molecular relaxation phenomena in certain cases. The jet viscometer might thus be used to evaluate molecular relaxation and/or other phenomena contributing to this effect. For a variety of systems, the concentric cylinder viscometer gives significantly smaller temporary viscosity losses due to shear than do the jet viscometer data. These comparisons are made using the maximum jet shear rate at the capillary wall. The differences are, of course, larger if average shear rates are used to compare the data. It is concluded that the jet viscometer results tend to be erroneous. This is possibly due to capillary end effects or problems with kinetic energy corrections.