Abstract: Solid-liquid suspension characteristics for sinking and floating particles in a dual-impeller stirred tank are simulated numerically by using computational fluid dynamics(CFD). The multi-reference frame(MRF) method for treatment of impeller rotation and Euler-Euler two-fluid model based on the kinetics of granular are used in the simulation. Flow field and solid holdup distribution for sinking and floating particles in the agitated tank are predicted, and the effects of operating conditions on solid-liquid suspension are investigated. The numerical simulated liquid velocity distribution and flow pattern are good agreement with experimental data in literature. The simulated results indicated that solid-liquid suspension of sinking particles is quite different from that of floating particles. For sinking particles, solid holdup decreases along axial height as a whole, and the highest solid holdup is found in the centre of the bottom region. Local solid holdup in the centre of circulation loops, behind the blades and baffles was relatively low. Nevertheless, solid holdup distribution for floating particles is contrary to that of sinking particles as above-mentioned. The increase of impeller speed can cause local solid holdup in the centre of circulation loops decrease for sinking particle, while contrarily for floating particles. Decreasing solid content or smaller particles size is beneficial to the uniformity of solid-liquid suspension for the two types of particles. With increasing of particles content or particles size, sinking particles and floating particles are more prone to aggregate in the centre of bottom region and surface region, respectively.

Key words: sinking particles;floating particles;solid-liquid suspension;stirred tank;two-phase flow;numerical simulation