Turbulence effect on the bubble-particle collision efficiency*

Understanding bubble-particle collisions is a crucial aspect of the flotation process. Here, we employed numerical methods to investigate the impact of turbulence on collision efficiency between a fully contaminated bubble and small inertial particles in a moderately turbulent flow. The bubble is represented by a rigid sphere moving at a constant velocity through homogeneous and isotropic turbulence at a Taylor Reynolds number of 32 and a bubble Reynolds number of 120, using the immersed boundary method to fully resolve the coupling between the bubble and the fluid. The small particles were modeled as point particles, and the particle Stokes number ranges from 0.01 to 5.2. We observe that collisions in the turbulent flow occurred for particles coming from a significantly wider region ahead of the bubble. This led to a remarkable enhancement in the collision efficiency of up to 100% compared to the results in the quiescent flow. Additionally, we found that the critical collision angle increased for all considered particle Stokes numbers due to turbulent fluctuation. To elucidate these findings, we proposed a statistical model based on turbulent sweeping which involves the results obtained in a quiescent flow. The model well predicts the collision probability in the incoming flow region. It turns out that the collision is enhanced by the turbulent fluctuation which temporarily enhances the velocity of fluid sweeping through the bubble, as well as the temporary bubble Reynolds number.