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Flotation process is a multi‐phase and multi‐scale complex flow system, in which hydrodynamics plays an indispensable role. In recent years, computational fluid dynamics (CFD) numerical simulation has gradually become a powerful tool for studying flotation. In this review, the theories of CFD numerical simulation in flotation research were reviewed, involving various turbulence models and multi‐phase flow simulation approaches. An attempt has been made to analyze and discuss the characteristics and applicability of different turbulence models and multi‐phase flow simulation approaches in flotation researches in detail. The CFD simulation of two commonly used flotation devices, that is, mechanically agitated flotation machine and flotation column, has been reviewed in detail. The detailed principles, operation, and hydrodynamic of flotation devices were discussed from the viewpoint of CFD. The advances made in CFD simulation for studying flotation process, including particle suspension, bubble dispersion, particle–bubble collision, attachment, and detachment subprocesses have been critically analyzed. Focused analysis was given on the influence mechanism of turbulence on the particle–bubble interactions. Finally, the gaps in the available literature are discussed and potential research directions are also proposed. [ABSTRACT FROM AUTHOR]

The jet microbubble generator is often used to produce bubbles in flotation equipment, which generates microbubbles by self‐absorbing or inflating. Bubble behavior is a dominant factor in froth flotation, and its velocity, size, and distribution greatly affect flotation performance. However, the asymmetry distribution of the pressure, bubble velocity, and gas holdup in generator with single inlet probably causes eccentric wear to the equipment. Therefore, in this study, using particle image velocimetry (PIV), high‐speed dynamic camera, and computational fluid dynamics (CFD) technology, the bubble behaviors in the jet microbubble generators with single inlet and double inlet was studied. The results show that under air flux of 0.4 L/min, the change of bubble diameter (D32) in two generators is obvious, reducing by 5.97% and 3.77% under circulation water flux of 1.5 and 2.5 m3/h, respectively. Comparing the influence of circulating water fluxes, the double‐inlet structure can reduce the bubble diameter more effectively. The maximum turbulent dissipation rate in the throat section of the generator with double inlet is greater than 120, while it is less than 100 in single‐inlet structure. For bubbles in generator with double inlet, velocity difference in radial direction reduces to 0.03 m/s and is more symmetrical. Meanwhile, the double‐inlet generator can also optimize the uniformity gas holdup distribution, which is beneficial to increase the collision probability of flotation and reduce the abrasion of microbubble generator. [ABSTRACT FROM AUTHOR]

This paper aims to obtain a better heat transfer performance by using vortex generators with different structures in the square channel. To compare the flow pattern of three different vortex generators, the stream‐wise velocity profile, the visualized Q‐criterion, and the stream‐wise vorticity flux distribution were used to obtain the flow structures in detail. The heat transfer performance was quantified by the Nusselt number (Nu) and compared for the different vortex generators. It was found that the concave structure vortex generator has a better heat transfer performance with an increase of about 11.07% for average Nu. This is because the concave vortex generator induces a more complex hydraulic dynamic flow structure due to its two counter rotating vortex pairs in the square channel. Furthermore, the distance from the lower counter rotating vortex pairs to the wall is significantly decreased by the restraint from the upper counter rotating vortex pairs. This can help disturb the thermal boundary layer and improve the heat transfer performance. [ABSTRACT FROM AUTHOR]

Abstract: A cyclonic–static microbubble flotation column (FCSMC) operates under multiple flow regimes, which significantly improves recovery and selectivity. To understand the flow behavior and separation in an FCSMC, unsteady gas–fluid flow numerical simulations are performed. The computational fluid dynamics model is validated against the particle image velocimetry measurements applied to a lab‐scale FCSMC. Hydrodynamic features and qualitative mineralization characteristics are studied. Global analysis reveals that an FCSMC operates under plug flow, swirling flow, and jet and pipe flow regimes along the pulp flow direction, through which the flow velocity, gas holdup, and turbulence gradually increase. This gradual intensification should overcome the mineral's decreased floatability over time. Local hydrodynamic and separation analyses indicate that the gas and liquid in the column unit move axially in opposite directions with very‐low velocities, which results in countercurrent collisions, a low recovery capacity and high selectivity. In the cyclone unit, both phases rotate clockwise with high tangential, low radial, and axial velocities. Both axial and radial velocities of the gas and liquid have different magnitudes and opposite directions, which indicates the countercurrent collisions in the axial and radial directions. The density‐based separation of tailings and surface flotation of middling takes place in this zone. In the pipe unit, the flow velocity, gas holdup, and turbulence are the highest of the entire FCSMC. Minerals with the lowest floatability are recovered in this zone, but the selectivity is low. Overall, the presence of multiple flow regimes allows the integration of multiple mineralization steps in one column and provides conditions for overcoming the decreased mineral floatability over flotation time, improving both mineralization and selectivity. [ABSTRACT FROM AUTHOR]

Bubble behaviors in the gas-liquid and lab-scale cyclonic-static micro-bubble flotation column (FCSMC) were investigated and optimized. By particle image velocimetry and charge-coupled device camera, bubble velocity and migration under low and high gas holdup conditions were measured. The particle image velocimetry measurement under low gas holdup shows that the swirling was significantly stronger than the rising in the near-axis area, and it declined as height increased. The central region contained high gas holdup and velocity. The bubble distribution under high gas holdup revealed that, in the column flotation unit, when water circulation rate ( qw) increased, gas concentration moves toward the bottom. An excessively high qw drove gas downward and even caused the gas to be pulled into the pump. When aeration rate ( qg) increased, the radial distribution improved but was not significant. If qg was excessive, the gas amount increased toward the top due to reflux when the rising bubbles met the free surface. Specifically, the greater bubble concentration in central region was observed under most test conditions. Additionally, an elongated 'air column' existed along the central axis and became more obvious with a high qw. The cyclonic inverted cone structure resulted in the gas gathering toward the center and the air column phenomena that deteriorate bubble mineralization. A non-uniform filling method was proposed to optimize the flow field. Filling with non-uniform sieve plates was proved to be more effective on bubble distribution equalization, air column inhabitation and non-axial velocity decreasing. These results provide the basis for structure optimization and process regulation of cyclonic-static micro-bubble flotation column. © 2016 Curtin University of Technology and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Cyclonic-Static Micro-bubble Flotation Column (CSMFC) has been widely used in fine mineral separation. The micro-bubble generator, as a key unit of this flotation column, is used to produce micro-bubble which designed based on the principle of gas liquid jet pump. Unlike the other jet pump, the performance of micro-bubble generator not only focuses on the air suction volume flow rate, but also includes the size and distribution of bubbles. In this paper, the performance of bubble generator is studied both experimentally and numerically. Three-dimensional numerical simulations employing the Eulerian two-phase flow model and S-N drag model by Fluent 14.0 software is carried out. The experimental and Computational Fluid Dynamics results, of air volume flow rate, match closely with each other. The maximum relative error between experiment and numerical simulation is smaller than 7.6%. Then these numerical models are utilized in simulating the 3D flow field of micro-bubble generator with different nozzle-to-throat spacing. Thirteen sets of simulations were conducted to explore the influence of the dimensionless nozzle-to-throat spacing (0-3) on air volume flow rate, bubble diameter and distribution. The results demonstrate that the performance of bubble generator is optimal when the dimensionless nozzle-to-throat spacing is over 1.25-2.5 while the water volume flow rate is fixed to 50m3/h. In this range, the bigger air suction volume flow rate, the smaller bubble diameter and higher bubble distribution uniformity index, which are beneficial for fine minerals flotation, were obtained. [ABSTRACT FROM AUTHOR]

Cyclonic‐static microbubble flotation column (FCSMC) is a sorting equipment for micro fine‐grained minerals. The column height is an important factor affecting the flotation efficiency, which will directly affect the flow field and separation performance. In this study, particle image velocimetry measurement on single phase of lab‐scale FCSMC with diameter D of 0.1 m was tested to verify the accuracy of the turbulent model used in computational fluid dynamics simulation. Then the FCSMC with different upper column and lower column height were simulated and analyzed. Results show that the axial velocity and tangential velocity play a major role in FCSMC. With the increasing of the upper column height, both tangential velocity and centrifugal intensity decrease, which help to get a static environment for column flotation unit. But too high upper column height will affect the separation of the cyclone flotation unit due to small centrifugal intensity. When the lower column height‐to‐diameter ratio H2/D increases from 1 to 4, it has no obvious effect on column flotation unit, but does effect on the flow field of the cyclone flotation unit. As the lower column height increases, the upward overflow is more prominent and the region becomes larger. Peculiarly, tangential velocity is large under too small lower column height, like H2/D = 1, but is bad for the separation of large size tailings due to low distance and great suction. Within the scope of this study, the lower column height range is more suitable for H2/D = 2–3. [ABSTRACT FROM AUTHOR]