Experimental study and visualization of the particle–bubble collision process

In the present study, an experimental approach is developed to study collisions of particles with a fixed air bubble. An air bubble with a diameter of 5.5 mm in deionized water is created, plastic particles (with diameters of 1.5, 2, and 2.5 mm) are released at different heights from the bubble surface, and their collisions with the bubble surface are studied. The results show that the particle size significantly affects the particle velocity and sliding time on the bubble surface. As the particle diameter increases, its sliding velocity on the bubble surface increases, and the particles are detached quickly from the bubble surface. The effects of the drag, capillary, pressure, weight, and buoyancy forces acting on the particles during the attachment-detachment on the bubble surface are also studied. The results show that the particle stays attached if the capillary force is dominant. The effects of the three-phase contact line on the capillary and pressure forces are also analyzed. A modified Bond number is proposed to check the attachment-detachment regimes.