Instrumented test tube for rapid rheological behaviour of liquids estimation

Abstract

For very small shear rates, many liquids are Newtonian and one of the simplest method to evaluate their viscosity is the so-called “falling-ball method”. Classically, a ball falling in a large tube, is optically observed and evaluation of its fall time enables simple deduction of the velocity, leading to shear viscosity estimation. In this communication, the tracking of a falling ball was made in a test tube with high-frequency ultrasonic sensors in transmission configuration leading to apparent shear viscosity measurement for very small shear rates (<a few s−1). With the same device, an estimation of dynamic shear viscosity in high frequency domain (5 MHz) was also obtained with the ultrasonic velocity and attenuation evaluation. Thanks to the comparison of results obtained with our adaptation of the falling ball method and with ultrasonic waves, a global rheological behaviour can be deduced very rapidly, in a simple way, on the same experimental bench, for transparent or opaque liquids.