Abstract
The apparent wall slip phenomenon is inevitably encountered in the standard rheological measurement for concentrated suspensions. It may significantly underestimate the apparent viscosity in the experiments. Previously we have proposed a slotted rotor design to reduce such effects. The objective of this study is to validate this design by conducting 3-D computational fluid dynamics (CFD) simulation and analyzing the velocity and shear stress fields in the double concentric cylinder rheometer with and without slotted rotor and the vane rheometer. Both shear thinning and yield stress fluids, modeled by a continuous viscosity constitutive equation, are considered in the simulations. The wall slip effects are taken into account using the wall slip length method. The results indicate that the double concentric cylinder rheometer equipped with a slotted rotor can measure the fluid properties with enhanced accuracy and less sensitivity to the wall slip velocity than a rheometer with a non-slotted rotor. The wall slip effects can be further reduced by either increasing the slot ratio or adding more slots to the rotor. Although the vane rheometer can reduce the wall slip effects too, it is only suitable for high shear thinning or high yield stress fluids due to the large end effects. As a conclusion, the use of a slotted rotor in the double concentric cylinder rheometer may significantly reduce both wall slip and end effects, making this design an excellent choice for rheological measurements.