Microstructure development in concentrated suspensions in a spinning ball rheometer

Abstract

SUMMARYThe spinning ball rheometer has been proposed as a method to measure the microstructure e ect on the bulk rheological properties of concentrated suspensions. Recent experiments have shown that the measured extra torque on the spinning ball decreases as the radius of the spinning ball becomes comparable to the size of the suspended particle. We have performed a series of three-dimensional boundary element calculations of the rheometer geometry to probe the microstructure e ects that contribute to that apparent slip. We present a series of quasi-static results based on random initial conÿgurations as well as fully three-dimensional transient calculations, both of which are compared to the available experimental data. For the two cases, the apparent viscosity decreased as the size of the spinning ball decreased relative to the suspended particle. Comparison of the quasi-static and transient simulations indicates that the microstructure development is critical even at short times. In the transient calculations, the viscosity was observed to increase substantially relative to the torque based on the random initial conÿguration. Published in 2005 by John Wiley & Sons, Ltd.