Microbubbles coalescence during transport in vertical channel flows

Asiagbe, KS; Fairweather, Michael; Njobuenwu, Derrick O.; Colombo, Marco

doi:10.1016/b978-0-444-64235-6.50016-4

Cited by 1 publication

(2 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Therefore, given the low relative velocity observed, which implies low-energy collisions, the 0% efficiency returned by the energy model is not entirely surprising. Asiagbe et al [56] employed large eddy simulation (LES) to examine air bubble collision and coalescence in water flows at Reτ = 150 with db = 220 μm bubbles using a similar film drainage coalescence model. In evaluating coalescence efficiency, the authors observed that, in the near-wall region, the bubbles experience shorter contact times.…”

Section: Bubble Coalescence Efficiency Analysismentioning

confidence: 99%

“…Similarly, Asiagbe et al [36], in considering a Reτ = 150 horizontal channel flow with db = 110 μm bubbles, observed an effectively 100% coalescence efficiency throughout the flow, with this attributed to the low flow Reynolds number. The work of Asiagbe et al [36,56] used a high resolution LES with 2.1 M nodes although, clearly, not all the velocity scales were resolved, with the smallest scaled modelled after filtering. The unresolved scales, particularly near the wall, will have some effect on the bubble motion, and may be responsible for the differences found between the DNS-and LES-based simulations.…”

Section: Bubble Coalescence Efficiency Analysismentioning

confidence: 99%

See 1 more Smart Citation

Simulation of Microbubble Dynamics in Turbulent Channel Flows

Zhai

Fairweather

Colombo

2020

Flow Turbulence Combust

View full text Add to dashboard Cite

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.

show abstract

Section: Bubble Coalescence Efficiency Analysismentioning

confidence: 99%