Effects of turbulence intensity on the shear detachment dynamics of bubble-particle

Abstract

Turbulence-induced bubble-particle detachment is a primary factor contributing to the low recovery rates of coarse particle flotation, garnering significant attention in recent years. Existing turbulence detachment theories predominantly categorize detachment mechanisms based on the motion characteristics of particles or bubbles, while overlooking the influence of shear flow fields at varying turbulence intensities on the stability of mineralized aggregates. The kinetic mechanisms underlying shear turbulence-induced detachment remain unclear. In this study, we investigate the detachment mechanism of particles and bubbles induced by shear turbulence using a custom-designed fluid channel. First, high-speed camera technology is employed to examine the dynamic detachment behavior of aggregates under different flow field intensities. Subsequently, particle image velocimetry (PIV) is utilized for in situ characterization and synchronized visualization of the flow field surrounding the bubble-particle detachment process. Results indicate that under the influence of the shear flow field, aggregate detachment occurs in three stages: bubble stretching and deformation, contact line sliding and contraction, and necking and rupture of the bubble. During the contact line sliding and contraction stage, a pattern of alternating contraction at the left and right contact points is observed. Furthermore, as the fluid velocity gradient increases, the detachment angle of the aggregates decreases, the detachment time increases, and the residual bubble size enlarges. Analysis of the flow field through PIV reveals that as fluid velocity within the channel increases, the flow transitions from stable laminar to complex, highly unstable turbulence, ultimately resulting in the formation of vortices of varying sizes and shapes around the particles. As turbulence intensity rises, the average flow field velocity and turbulence kinetic dissipation rate required for bubble-particle detachment in shear turbulence all increase. This study also finds a close correlation between the dynamic detachment behavior of aggregates and the vortex structures, whereby lateral vortices drive bubble deflection and the forward fluid shear force induces bubble detachment. The findings are expected to provide crucial theoretical guidance for understanding the kinetic mechanisms of bubble-particle detachment under shear turbulence.