A novel computerized viscometer/rheometer

Abstract

An innovative, Couette-type viscometer/rheometer was developed, designed, and fabricated with the main objective being to measure viscosity and elastic properties of low-viscous, non-Newtonian, and visco-elastic fluids, like dilute polymer solutions. The goal was to simplify and improve some existing drawbacks of commercial instruments employing several novel design solutions, particularly with regard to instrument precision and sensitivity. With a single pair of cylinders and a torsion bar stiffness of 0.116 Nm/rad, viscosities from 0.5 to 50 000 cP (centi-Poise) in a shear-rate range from 1 to 200 s−1, and oscillatory tests from 0.1 to 10 Hz, could be measured. The transducers’ electronic signals are handled by a software, developed in C language, and an IBM-PC compatible computer with a data acquisition board. The innovative design solutions (use of a cruciform torsion bar, optoelectronics sensors, and a novel alignment procedure) have improved the critical instrument performance and reduced the number and cost of components, customarily used in commercial viscometers/rheometers. The overall steady shear-rate calibration was performed using the standard-viscosity fluids of 51 and 445 cP. Initial results show high precision (around 4%), particularly at higher velocities. The oscillatory testing was performed by measuring the phase shift between the stress and strain for viscoelastic fluids and for the limiting case of a standard Newtonian fluid. The novel design has proved efficient and with potential for further improvements.