Aggregation in mixing tanks - the role of inter-particle forces

We study aggregation of equally-sized spherical particles under mildly turbulent flow conditions (Reynolds numbers in the range 4000–8000) in a mixing tank through numerical simulation. The dynamics of the liquid flow is solved in terms of the volume-averaged Navier-Stokes equations by an extended lattice-Boltzmann method on a fixed uniform cubic grid. The particle dynamics is updated through applying Newton's second law to each particle. The simulations include a two-parameter model for the attractive force between the particles that causes aggregation. The dynamics of solids and liquid are two-way coupled through a mapping procedure. An overall solids volume fraction of 10% has been investigated. The level of aggregation of particles in the mixing tank mainly depends on the strength of the attractive force and on the impeller-based Reynolds number, not so much on the distance over which the aggregative force is active. A higher Reynolds number leads to less aggregation.