Coalescence of small bubbles with surfactants

Lu, Jiakai; Corvalán, Carlos M.; Chew, Y.M. John; Huang, Jen‐Yi

doi:10.1016/j.ces.2018.11.002

Cited by 30 publications

(17 citation statements)

References 24 publications

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“…In the latter study, however, it is shown that the real wall shear in the simulation does not reach this estimated value but remains lower, causing the fluid, and the bubbles, to travel slower with respect to the present simulation, where the estimated wall shear is effectively reached. Additionally, the present computations Although not shown, good agreement was found in comparisons with the continuous and dispersed phase DNS-based results of Giusti et al [23] for Reτ = 150 upward and downward channel flows containing db = 220 μm bubbles that were one-way coupled to the flow.…”

supporting

confidence: 86%

“…However, in real life gas-liquid processes, bubbles constantly collide with each other. Depending on the size, velocity and interfacial chemistry, the bubbles may break-up or coalescence [23], changing the total number of bubbles in the flow and the bubble size distribution. These phenomena impact not only the fluid flow and turbulence field, but sometimes more importantly heat and mass transfer processes through the available interfacial area.…”

Section: Introductionmentioning

confidence: 99%

“…Most numerical studies [23,33,34] of microbubble coalescence have focused on surfactantladen flows and it is well known that tiny amounts of contaminants or surfactants can drastically modify the air-water interface behaviour [35]. Experimental results reveal that clean air bubbles coalesce within milliseconds, much faster than when contaminants are present.…”

Section: Introductionmentioning

confidence: 99%

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Simulation of Microbubble Dynamics in Turbulent Channel Flows

Zhai

Fairweather

Colombo

2020

Flow Turbulence Combust

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This work investigates microbubble dynamics in four-way (with coalescence) coupled microbubble-laden turbulent channel flows. Upward and downward flows of water at a shear Reynolds number of Reτ = 150 are predicted using direct numerical simulation (DNS).Microbubbles, assumed to be non-deformable and spherical, are injected into the water flow and tracked using a Lagrangian approach. One-way and two-way coupled predictions were successfully compared against other available DNS-based results and used to demonstrate different trends in bubble preferential motion, with bubbles pushed by the lift force towards the wall in upflow and towards the centre of the channel in downflow. Four-way coupled simulations with bubble coalescence clearly demonstrate that the presence of the bubbles, and collisions between them, have a non-negligible effect on the fluid phase. Analysis of bubble collision behaviour highlights that binary collisions most frequently occur at very small approach angles and with low relative approach velocities. Once a collision is detected, the occurrence of bubble coalescence is evaluated, with special attention given to the performance of different bubble coalescence models. The film drainage model returns a 100% coalescence efficiency, while on the other hand the energy model returns a 0% coalescence efficiency, with this large discrepancy requiring further investigation and model development. The knowledge gained from the present results on the mechanisms that underpin bubble collisions is of value to the further development of more advanced coalescence closure models.

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supporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Simulation of Microbubble Dynamics in Turbulent Channel Flows

Zhai

Fairweather

Colombo

2020

Flow Turbulence Combust

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“…Recently, the concepts of the hydrodynamic characteristics of dispersed particles in the continuous mobile phase have also been expanded. The phenomena of coalescence of dispersed particles, their transition into a continuous phase, and behavior on hydrophobic surfaces have been studied [30][31][32]. The practical significance of the research in this field is highlighted in previous studies by the need to develop oil-gas cleaning equipment [33], to design spray towers [34], and to improve the inertia-filtering separation process [35,36] with a highly developed interfacial surface.…”

Section: Literature Reviewmentioning

confidence: 99%

Identification of the Interfacial Surface in Separation of Two-Phase Multicomponent Systems

et al. 2020

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The area of the contact surface of phases is one of the main hydrodynamic indicators determining the separation and heat and mass transfer equipment calculations. Methods of evaluating this indicator in the separation of multicomponent two-phase systems were considered. It was established that the existing methods for determining the interfacial surface are empirical ones, therefore limited in their applications. Consequently, the use of the corresponding approaches is appropriate for certain technological equipment only. Due to the abovementioned reasons, the universal analytical formula for determining the interfacial surface was developed. The approach is based on both the deterministic and probabilistic mathematical models. The methodology was approved on the example of separation of two-phase systems considering the different fractional distribution of dispersed particles. It was proved that the area of the contact surface with an accuracy to a dimensionless ratio depends on the volume concentration of the dispersed phase and the volume of flow. The separate cases of evaluating the contact area ratio were considered for different laws of the fractional distribution of dispersed particles. As a result, the dependence on the identification of the abovementioned dimensionless ratio was proposed, as well as its limiting values were determined. Finally, a need for the introduction of the correction factor was substantiated and practically proved on the example of mass-transfer equipment.

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“…1 Therefore, the detailed study on the coalescence process will be valuable to help people to adjust and control the fluid particle size or interphase contact area in multiphase flow. Some investigations [1][2][3][4][5][6] used computational fluid dynamics (CFD) simulation (volume of fluid method, level-set method) to analyze the deformation, rupture and coalescence of fluid particles. Although the CFD simulation can describe the dynamics of droplets or bubbles, once the two fluid particles are in close contact, the simulation results are easy to show the non-physical characteristics, such as the numerical pseudo-coalescence of two bubbles.…”

Section: Introductionmentioning

confidence: 99%

Experiments and modeling of bubbles colliding head‐on in water

et al. 2021

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Experiments and modeling of head-on collision of a pair of bubbles driven by buoyancy in quiescent water are presented. The experiments showed that two bubbles after contacting for a few milliseconds may coalesce or bounce back depending on the collision velocity. As theoretical comparisons, the influence of velocity boundary conditions on the liquid film drainage and the characteristics of two film drainage models with the assumptions of "partially" and fully mobile interfaces under variablevelocity approach condition are studied. The "partially" mobile model is found to be easier to predict rebound case and longer drainage time, and could not obtain the drainage process where the film is thinned to the thickness below 10 −7 m at both low and relatively high Re. As a whole, the fully mobile model with variable-velocity approach shows more reasonable prediction results for the coalescence and rebound of bubbles in the ultrapure water.

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Coalescence of small bubbles with surfactants

Cited by 30 publications

References 24 publications

Simulation of Microbubble Dynamics in Turbulent Channel Flows

Simulation of Microbubble Dynamics in Turbulent Channel Flows

Identification of the Interfacial Surface in Separation of Two-Phase Multicomponent Systems

Experiments and modeling of bubbles colliding head‐on in water

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