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DNS using CLSVOF method of single micro-bubble breakup and dynamics in flow focusing

Abstract

Numerical simulations are performed to investigate the breakup of air bubble in flow focusing configuration; the CLSVOF (coupled level set with volume of fluid) method is employed to track the interface, which allows a better identification of the liquid–gas interface via a function called level set. The CFD simulations showed that the velocity ratio, the interfacial tension, the outer channel diameter, the continuous phase viscosity, the orifice width and length play an important role in the determination of the air bubble’s size and shape. However, at low capillary number, increasing the flow velocity ratio gives a smaller bubble size in shorter time, while the increase in interfacial tension leads to a bigger bubble. Moreover, the carrier fluid is found to slightly affect the bubbling mechanism, while the smallest bubbles were obtained with the smallest orifice size. In addition, three breakup regimes are observed in this device: disc-bubble (DB), elongated bubble (EB) and the slug bubble (SB) regime flows. This work also demonstrates that the CLSVOF is an effective method to simulate the bubbles breakup in flow focusing geometry. In addition, a comparison of our computational simulations with available experimental results reveals reasonably good agreement.

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Abbreviations

F:

Frequency (Hz)

U:

Velocity (m/s)

n:

Unit vector normal to the interface

κ:

Curvature of the interface

F:

The surface tension force

D:

Diameter (mm)

μ:

Dynamic viscosity (kg/m.s)

a:

Phase fraction (%)

σ:

The surface tension coefficient (N/m)

t:

Time (s)

W:

Width

L:

Length

γ:

Velocity ratio

FF:

Flow focusing

CFD:

Computational fluid dynamics

D:

Diameter/width

ρ:

Density (kg/m3)

Q:

Flow rate

(BBT):

The bubble breakup time

DNS:

Direct numerical simulation

VOF:

Volume of fluid method

LBM:

Lattice Boltzmann

LS:

Level set

CLSVOF:

Coupled LS with VOF method

SDS:

Surfactant sodium dodecyl sulphate

Atm:

Atmosphere

O:

Oil

Out:

Outer channel

W:

Water

d:

Dispersed phase

c:

Continuous phase

w:

Width

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Acknowledgement

The author would like to acknowledge the valuable comments and suggestions of the reviewers, which has improved the quality of this paper.

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Correspondence to Tawfiq Chekifi.

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Chekifi, T., Boukraa, M. & Aissani, M. DNS using CLSVOF method of single micro-bubble breakup and dynamics in flow focusing. J Vis 24, 519–530 (2021). https://doi.org/10.1007/s12650-020-00715-1

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  • DOI: https://doi.org/10.1007/s12650-020-00715-1

Keywords

  • Bubbling
  • Multiphase flow
  • CLSVOF
  • CFD and flow focusing