(371g) Computational Study of Solids Mixing in Flotation Cells Using CFD-DEM Simulations

Basavarajappa, M., University of Utah
Miskovic, S., University of Utah

In the present work, computational fluid dynamics (CFD) and discrete element method (DEM) have been coupled to study transport and mixing of discrete solid phase (quartz particles) in flotation cells. The off bottom suspension and subsequent homogenization of solid particles in the bulk fluid crucially depends on the impeller-stator design, impeller speed, off bottom clearance, and physical properties of particles. The turbulence level and distribution of turbulent kinetic energy (k) determines the extent of solid phase mixing and level of homogenization in the flow. At relatively high solids loading, inter-particle collisions become important and have to be modeled to accurately describe the flow. In the CFD-DEM approach, fluid motion is modeled using CFD, and solid particle motion and their interactions are simulated by DEM. During the coupling process, particle locations and velocities are updated in the CFD solver after a small time step and forces on the particles due to fluid motion are calculated. From the CFD solver, the forces on the particles are used in DEM to calculate new particle locations and velocities. The turbulence in the fluid phase is modeled by using Reynolds averaged Navier Stokes (RANS) based k-ε model. The contact model used in DEM is non-linear Hertz-Mindlin model – a soft sphere approach.

Particle size of 500 and 2000 µm at low solids loading (< 5%) are considered and the resulting solid flow dynamics are investigated. Modulation of turbulence due to preferential concentration in the case of smaller particles, and generation of wakes and their interaction for larger particles are also investigated. Furthermore, the turbulent zone close to the impeller in the presence of particles is fully characterized. Finally, the importance of stator in dispersing solid particles is additionally studied. This work represents a first attempt to model complex liquid-particle flows inside of flotation cells by using CFD-DEM method.