PNNL

Abstract

The shear strength of powders and slurries containing coarse particles using a vane impeller were examined as a function of vane size, vane immersion depth, container size, and interstitial fluid. Results show that for powders and concentrated slurry systems containing coarse particles, vane immersion depth and container diameter significantly impact the measured shear strength. An equation describing interparticle frictional and cohesive contributions to shear vane measurements was derived in an effort to describe experimental results. A Janssen stress distribution model for granular materials was the basis for this equation. The use of a Janssen stress distribution appears to explain the behavior of shear strength measurements at varying immersion depths with dry cohesionless glass beads, water saturated glass beads, and glass beads dispersed in a non-Newtonian matrix of kaolin clay slurry. The presence of the Janssen stress distribution can affect the interpretation of shear vane results. Rather than shear strength being a material property as is the case with flocculated colloid slurries and polymer solutions, shear strength becomes a process property where vane depth, container size, and container material can result in significant measurement variations. Such parameters should be considered before using the shear vane results on applications involving granular material components.