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Title: The behavior of rising bubbles covered by particles
Author: Wang, Peipei
ISNI:       0000 0001 2445 1138
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2019
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Bubble-particle aggregates play a dominant role in separation processes such as froth flotation. Previous studies on individual rising bubble motion have mainly focused on gas-liquid two-phase systems and there has been no systematic investigation on the influence of particles on the rising behavior of particle-laden bubbles. In this project, clear visualization of the behavior of bubble-particle aggregates is achieved by using capillaries to generate bubbles of controlled size in a transparent experimental rig, which are released after attachment of particles is achieved. The pendant drop model was used and fitted to the edge points of the bubbles to calculate their particle surface coverage. High-speed photography and image analysis techniques were used to record and analyze the hydrodynamics of rising bubbles in terms of velocity and aspect ratio. The influence of particle coverage and particle size on the behavior of rising bubbles was studied. In addition, the buoyancy force, drag force as well as the mass force on the particles and bubbles were calculated and interpreted. Results show that with the increase of particle coverage or attached particle size, the aspect ratio oscillation patterns of the rising bubbles are similar and the high frequency oscillation periods do not change significantly. This indicates that the capillary wave caused by surface tension does not change, it is the hydrodynamic force that differentiates bubble motion. With the increase of particle size or coverage, the rising bubbles show a lower velocity as well as a damped aspect ratio oscillation. Particles attached on the bubbles decrease the bubble acceleration, and this acceleration is inversely correlated to the bubble aspect ratio and its change. The highest rising velocities correspond to the lowest aspect ratios and vice versa, independently of the particle size or coverage. A particle drag modification factor, which quantifies the drag influence of particles on bubble velocity, was identified from force analysis. A modified drag coefficient for uncoated and particle-laden bubbles was introduced, which allows, for the first time, to predict the behavior of rising particle-laden bubbles in gas-liquid-solid systems. The results and interpretation produced a quantitative description of the behavior of rising particle-laden bubbles and the development of correlations that can be used to inform the modelling of industrial applications such as pulp phase phenomena in froth flotation.
Supervisor: Brito-Parada, Pablo ; Cilliers, Jan Sponsor: Imperial College London ; IOM3 (Institute of Materials, Minerals and Mining) Bosworth Smith Trust
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral