Effect of Particle Size on the Rising Behavior of Particle-Laden Bubbles

Abstract

The rising behavior of bubbles, initially half and fully coated with glass beads of various sizes, was investigated. The bubble velocity, aspect ratio and oscillation periods were determined using high-speed photography and image analysis. In addition, the acting forces, drag modification factor and modified drag coefficient were calculated and interpreted. Results show that the aspect ratio oscillation of the rising bubbles is similar, irrespective of the attached particle size. As the particle size is increased, the rising bubbles have a lower velocity and aspect ratio amplitude, with the time from release to each aspect ratio peak increasing. Higher particle coverage is shown to decrease the bubble velocity and dampen the oscillations, reducing the number of aspect ratio peaks observed. The highest rise velocities correspond to the lowest aspect ratios and vice versa, whereas a constant aspect ratio yields a constant rise velocity, independent of the particle size. Force analysis shows that the particle drag modification factor increases with the increased particle size and is greatest for fully laden bubbles. The modified drag coefficient of particle-laden bubbles increases with the increased particle size, although it decreases with Reynolds number independent of the particle size. The drag force exerted by the particles plays a more dominant role in decreasing bubble velocities as the particle size increases. The results and interpretation produced a quantitative description of the behavior of rising particle-laden bubbles and the development of correlations will enhance the modeling of industrial applications.

Coalescence Dynamics of Particle-Laden Bubbles

“…Details of our experimental rig and the procedure for preparing nozzle-held particle-laden bubbles can be found elsewhere. 14,22 For experiments with particle-laden bubbles, two grams of silica particles were suspended in 250 mL 10 −3 mM tetradecyltrimethylammonium bromide (TTAB) solution in a perspex cell (50 mm × 50 mm × 125 mm). TTAB is a cationic surfactant composed of amphiphilic molecules and is able to adsorb on silica surfaces to increase particle hydrophobicity.…”

“…The size and position of bubbles generated in nozzles can be easily controlled with precision, making such an experimental setup suitable for investigating bubble coalescence, 19 bubble or droplet pinchoff, 20,21 and rising bubbles. 14,22 In this work, we carefully grew two bubbles of the same size from two steel nozzles positioned at the same height. The size of the bubbles was adjusted by varying the gas input volume using two microsyringe pumps (World Precision Instrument).…”

“…The size and position of bubbles generated in nozzles can be easily controlled with precision, making such an experimental setup suitable for investigating bubble coalescence, bubble or droplet pinch-off, , and rising bubbles. , …”

“…The surface tension of particle-laden interfaces also depends upon the particle-packing fraction at the interface. , A study on silica nanoparticle-stabilized foams revealed that particle hydrophobicity also plays a role in the properties of the interface . Microparticles, on the other hand, do not change the surface tension of a still interface because particles form a closely packed layer at the interface and the particle interactions are balanced.…”

The pinch-off dynamics of bubbles coated by microparticles

“…The energy barrier makes nanoparticles irreversibly adsorb on interfaces, whereas surfactants adsorb and desorb on a relatively fast timescale [18]. Microparticles, on the other hand, would settle out from a suspension, unless they attach to the airliquid interface, forming a close-packed structure at still interfaces [19,20,21].…”