CFD methodology for sedimentation tanks: The effect of secondary phase on fluid phase using DPM coupled calculations

Computational Fluid Dynamics (CFD) methods are employed in order to simulate the 3D hydrodynamics and flow behaviour in a sedimentation tank. Unlike most of the previous numerical investigations, in the present paper the momentum exchange between the primary and the secondary phase is taken into account, using a Lagrangian method (discrete phase model) with two-way coupled calculations. By computing particle trajectories the proposed numerical model can track the momentum gained or lost by the particle stream that follows that trajectory and these quantities can be incorporated in the subsequent continuous phase calculations. Thus, while the continuous phase always impacts the discrete phase, the effect of the discrete phase trajectories on the continuum can be incorporated. This interchange affects fluid velocity, especially in the case of large particles sizes, which have a greater relaxation time in relation to the characteristic time of the tank. The present investigation compares a series of numerical simulations for a sedimentation tank with varying particle diameters and volume fractions, in order to identify the influence of the secondary phase to the primary phase and vice-versa and the way that this influence affects the efficiency of the tank.