Calibration of modified parallel-plate rheometer through calibrated oil and lattice Boltzmann simulation

Fluid flow patterns in traditional rotational rheometers are generally well known so that rheological parameters such as viscosity can be easily calculated from experimental data of single phase fluids and analytical solutions of the flow patterns. However, when the fluid is a suspension, where some of the particles are as large as 2 mm in diameter, these rheometers may need to be modified. The distance between the shearing planes needs to be increased, which necessitates additional physical confinement of the fluid. The inclusion of a confining wall makes current analytical solutions inapplicable here. This paper presents the analysis of a modified parallel plate rheometer for measuring cement mortar and propose a methodology for 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.