AN ASSESSMENT OF A ROLLING-BALL VISCOMETER FOR STUDYING NON-NEWTONIAN FLUIDS

This paper assesses the potential value of a rolling-ball viscometry method for studying opaque non-Newtonian fluids under ambient conditions. In the apparatus described an ultrasonic technique is used to monitor continuously the rolling velocity of a ball in an inclined tube filled with fluid. A relationship to enable the approximate calculation of the equivalent shear rate imposed by the rolling ball is proposed. The computed drag forces on the ball have been used to quantify the rheological characteristics of typical Bingham and power-law fluids. Experimental results produced for bentonite dispersions (Bingham-plastic fluids) and Polyox solutions (power-law fluids), obtained from the rolling-ball rheometer, have been compared with those obtained from a Bohlin VOR Rheometer. The self-consistency between the corresponding data sets is good, confirming the applicability of the rolling-ball method for studying rheologically complex fluids and the accuracy of the first-order estimate of the equivalent shear rate. The intrinsic simplicity of the construction of the rolling-ball viscometer provides the basis for the construction of a robust and accurate device for studying the rheology of fluids at high pressures and temperatures.