Parallel-plate Rheometer Calibration Using Oil and Computer Simulation

Fluid flow patterns in traditional rotational rheometers are generally well known and rheological parameters such as viscosity can be easily calculated from experimental data of single phase fluids and analytical solutions of the patterns. However, when the fluid is a suspension, where some of the particles are as large as 2 mm in diameter, these rheometers need to be modified. The distance between the shearing planes needs to be increased, which necessitates additional physical confinement of the fluid. This causes the flow pattern to be not analytically soluble leading to an inability to correctly compute the viscosity. This paper presents a modified parallel plate rheometer, and proposes means of calibration using standard oils and numerical simulation of the flow. A lattice Boltzmann method was used to simulate the flow in the modified rheometer, thus using an accurate numerical solution in place of the intractable analytical solution. The simulations reproduced experimental results by taking into account the actual rheometer geometry. The numerical simulations showed that small changes in the rheometer design can have a significant impact on how the rheological data should be extracted from the experimental results.