Determining collision efficiency in multi-bubble-particle systems in presence of turbulence

Bubble-particle collision efficiency in the existing flotation literature is determined in a single bubble-particle system assuming an ideal flow field in absence of any turbulence which does not fully represent reality of the actual flotation systems. To address this knowledge gap, in this study, we numerically computed collision efficiency in a multi-bubble-particle system (particle diameter dP = 30 µm, bubble diameter dB = 1 mm) using a two-way coupled Eulerian-Lagrangian 3D computational fluid dynamics model with different solids concentrations (0.385 %–3.080 %) at turbulence intensities (Ti = 0 %–20 %). Collision efficiency of multiple particles with a single central bubble was determined in presence of different configurations of neighbouring bubbles. Two simplified multi-bubble configurations – monolayer and multilayer comprising different number of bubbles/layer, were investigated. It was noted that side-by-side collisions in monolayer configuration did not occur because particles did not have sufficient time and kinetic energy to migrate to a surrounding bubble. On contrary, in multilayer configurations, particles traversing around a leading bubble had a chance to get entrained in the rear wake and collide with a trailing bubble which resulted in higher collision efficiency compared to monolayer configurations. Modelling showed that bulk energy dissipation rate increased with number of bubbles per layer, number of bubble layers, turbulence intensity and solids concentration. For the lowest and highest solids concentration, the optimal collision efficiency occurred at Ti = 20 %, while for the intermediate solid concentration, it occurred at Ti between 4 % and 11 %. In all cases, collision efficiency increased with the energy dissipation rate.