A critical review on turbulent collision frequency/efficiency models in flotation: Unravelling the path from general coagulation to flotation

“…For additional details, we refer the reader to the reviews on the topic (e.g. Nguyen et al 2016;Hassanzadeh et al 2018;Kostoglou, Karapantsios & Oikonomidou 2020b). Note that here and in the following we use subscripts i = b, p to denote bubbles and heavy particles, respectively.…”

Section: Modelling Approaches For Bubble-particle Collisions In Turbu...mentioning

confidence: 99%

Bubble–particle collisions in turbulence: insights from point-particle simulations

Chan

Krug

2023

J. Fluid Mech.

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Bubble–particle collisions in turbulence are central to a variety of processes such as froth flotation. Despite their importance, details of the collision process have not received much attention yet. This is compounded by the sometimes counter-intuitive behaviour of bubbles and particles in turbulence, as exemplified by the fact that they segregate in space. Although bubble–particle relative behaviour is fundamentally different from that of identical particles, the existing theoretical models are nearly all extensions of theories for particle–particle collisions in turbulence. The adequacy of these theories has yet to be assessed as appropriate data remain scarce to date. In this investigation, we study the geometric collision rate by means of direct numerical simulations of bubble–particle collisions in homogeneous isotropic turbulence using the point-particle approach over a range of the relevant parameters, including the Stokes and Reynolds numbers. We analyse the spatial distribution of bubble and particles, and quantify to what extent their segregation reduces the collision rate. This effect is countered by increased approach velocities for bubble–particle compared to monodisperse pairs, which we relate to the difference in how bubbles and particles respond to fluid accelerations. We found that in the investigated parameter range, these collision statistics are not altered significantly by the inclusion of a lift force or different drag parametrisations, or when assuming infinite particle density. Furthermore, we critically examine existing models and discuss inconsistencies therein that contribute to the discrepancy.

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“…The dynamics of particles settling in a fluid are a complex topic that still poses many open questions. They are relevant in both natural and industrial phenomena such as cloud formation in the atmosphere [1], volcanic ash propagation [2], transmission of pathogens [3], surface coating [4] or mineral ore processing [5]. Particles can either be released in an externally forced flow or in a fluid at rest.…”

Section: Introductionmentioning

confidence: 99%

Settling of localized particle plumes in a quiescent water tank

Zürner

Toupoint²,

Souza³

et al. 2023

Phys. Rev. Fluids

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The fall or rise of inertial particles plumes in an initially quiescent fluid is ubiquitous in natural and industrial processes. Disentangling the influence of the numerous parameters of these systems on the plume velocity is thus a major issue. Moreover, understanding the energy transfer between the two phases and the structure of induced flow is another very relevant question. A specific experiment has been designed to tackle these problems. A continuous plume of inertial particles released above the center of a still water tank generates a large-scale recirculation flow. The present experimental study investigates the stationary settling dynamics and induced flow properties using various particle populations with particle-to-fluid density ratios from 3.8 to 14.3, Archimedes numbers 4 to 580 and mass fractions 10 −6 to 10 −3 , revealing an unexplored region of the parameter space. The fluid and particle velocities are measured simultaneously by two cameras, utilizing optical filtering and image post-processing. It is found that the settling in the laboratory frame generally follows the terminal velocity predicted using the Schiller-Naumann drag. The particle velocity relative to the surrounding fluid is unaffected by the particle mass fraction and always hindered due to the kinetic energy transferred to the fluid. This transfer of energy is most effective for low Archimedes numbers. All modifications of the settling behavior due to the particle mass fraction are caused by the back-reaction of the induced flow on the particles, no direct particle-particle interactions are observed.

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A critical review on turbulent collision frequency/efficiency models in flotation: Unravelling the path from general coagulation to flotation

Cited by 22 publications

References 99 publications

Hydrodynamic characterisation of flotation impeller designs using Positron Emission Particle Tracking (PEPT)

Hydrodynamic characterisation of flotation impeller designs using Positron Emission Particle Tracking (PEPT)

Bubble–particle collisions in turbulence: insights from point-particle simulations

Settling of localized particle plumes in a quiescent water tank

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