Investigation of the critical flow velocity for detachment between various hydrophobic glass beads and bubbles in turbulent flow field

The critical flow velocity required to detach glass beads (soda-lime) of different hydrophobicity from bubbles was investigated. Using a home-made turbulence controlling system to observe the centrifugal motion of glass beads. The results indicated that different flow velocities were achieved by controlling the rotational speed. Different flow velocity indirectly affected the centrifugal acceleration when the centrifugal detachment of glass beads occurred. When the flow velocity exceeded the critical value, the different hydrophobic glass beads and bubble aggregates experienced centrifugal detachment force also reached the critical value. Due to the pinning effect, the more hydrophobic the glass beads attached to the bubbles, the more stable the aggregates formed. It was necessary to increase the flow velocity to enhance the centrifugal detachment force. The three-phase contact line (TPCL) between glass beads and bubbles rapidly slipped and contracted when attachment force was less than detachment force in centrifugal motion. Resulting in a noticeable necking phenomenon that completed the detachment. Meanwhile, the detachment behavior between glass beads and bubbles did not occur at specific locations, but rather randomly. It was depended on the size and strength of the vortex at that location, as well as the stability of attachment between bubbles and various glass beads.