Evaluation on time variation of effective viscosity by ultrasonic spinning rheometry (Application to separating oil-water mixture)

Abstract

This paper evaluated measurement accuracy and precision of ultrasonic spinning rheometry (USR), which can evaluate rheological properties through equation of motion and velocity information captured by ultrasonic velocity profiler (UVP), in cases that assumptions of two-dimensional one-directional flow are not perfectly satisfied. Time variation of effective viscosity in separating oil-water mixture was examined by USR to demonstrate its applicability for both time-dependent rheological properties and multiphase media, which cannot be evaluated by conventional torque-type rheometers. Decrease in pseudoplasticity and effective viscosity of the media with time during separation of water droplets from the media accompanied by monotonic decrease in diameter and volume fraction of the droplets on the measurement line, was quantified. The time variations show the same trend with formula theoretically derived for evaluating emulsion viscosity, but the viscosity was estimated larger than the theory. An increase of effective volume fraction or non-equilibrium flow field may have increased the viscosity.