Simulation of orientation of fibre particles in a stirred tank and its influential factors

Abstract

Different from spherical particles, orientation is an important property of fibre particles. It influences processing and utilizing of the irregular particles. In this paper, orientation distribution of fibre particles under different conditions in a turbulent stirred tank is simulated. The influences of virtual mass force and aspect ratio of fibre particles on the orientation are studied. The simulation is performed in a standard baffled tank stirred by a six-blade Rushton turbine impeller. Two-fluid model is employed to simulate the turbulent solid-liquid two-phase flow with fibre particles of different sizes and concentrations in the stirred tank. A novel method, which employs the rigid particle rotation equation directly, is presented for simulation of the orientation of fibre particles. Simulation results show that the inclusion of virtual mass force in the momentum equation changes the orientations. The effects of virtual mass force vary in different regions. Near the impeller blades, the influence of virtual mass force on orientation is nearly negligible at the center region. While near the wall of the tank, the orientation presents obvious difference with and without virtual mass force. The orientation of fibre particles varies with the aspect ratio. In the impeller discharging region, the orientations vary little with the aspect ratio in the center. Far from the center, the orientation decreases with the aspect ratio above the impeller and increases with the aspect ratio below the impeller. The inclusion of virtual mass force is unnecessary for spheres. However, for particles of irregular shape, especially those with different orientations, the presence of virtual mass force and aspect ratio can have significant effect on orientations.