Effect of turbulence dispersion on bubble-particle collision efficiency

In this study, bubble-particle collision efficiency in a single-bubble system (bubble diameter ∼ 1 mm) for different turbulence intensity (Ti ∼ 4% − 20%) and various particle size (diameter ∼ 30 to 100 µm) were theoretically studied by injecting particles on a stationary bubble. A critical distance for particle injection upstream of the bubble was analytically determined ensuring no distortion of the flow streamlines at the particle release location. To quantify the turbulence collision efficiency, an analytical turbulence dispersion (TD) model was proposed. This model was also compared with a 3D computational fluid dynamics (CFD) model incorporating a random walk momentum exchange model. A statistical parameter, 90%-collision radius was introduced to represent effective particle releasing radius, which was shown to increase with the turbulence intensity and particle diameter. A threshold turbulence intensity of 7% was noted below which the analytical model agreed well with the CFD model, however, above this threshold, the analytical model was found to overestimate the collision efficiency and underestimate the 90%-collision radius. The CFD model demonstrated that with increasing turbulence intensity, energy dissipation rate in the system also increased and particles showed more stochastic pattern in their trajectories. A force analysis showed that larger diameter particles approaching the bubble experienced higher horizontal deflections in the higher turbulence intensity cases due to larger inertial forces acting on them, however such effect was not apparent farther downstream of the bubble.