Numerical Simulation of Particle Dispersion in Flow between Coaxial Cylinders under Unsteady Flow Conditions

Abstract

Two-dimensional numerical computations of unsteady flow of a suspension between two coaxial cylinders are performed. We investigate the dispersion characteristics based on a novel thixotropy model. The diameter of particles, solid volume fraction, and viscosity of dispersing media are set to 2.5 µm, 0.15, and 195 Pa·s, respectively. The shear rate is suddenly changed from 0.1 s^-1 to 1 s^-1. For model validation, the numerical results are compared with previously reported experimental results. The mean number of particles in a cluster increases slightly shortly after the shear rate change, reaches a maximum, and subsequently decreases, finally attaining a steady state at 40 s after the shear rate change. Our model better expresses the time variation of the dispersion characteristics than the previous model. After the validation, the effect of bonding energy on the time-variation characteristics is investigated. The bonding energy is varied as 2.7 × 10^-13, 2.7 × 10^-12, and 2.7×10^-11 J. We observe that the asymptotic values of the mean number of particles in a cluster depend on the bonding energy, but this relationship is not linear. From our results, we posit the existence of a certain critical bonding energy with regard to the dispersion characteristics.