Numerical investigation of fluid property effects on formation dynamics of millimeter-scale compound droplets in a co-flowing device

Zhang, Taoxian; Zou, Xiong; Xu, Lan; Pan, Dawei; Huang, Weixing

doi:10.1016/j.ces.2020.116156

Cited by 23 publications

(13 citation statements)

References 29 publications

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“…Besides, the core of our numerical simulation is the VOF–CSF model, which is usually employed to track the interface evolution between two immiscible phases. In our previous work, the VOF–CSF model was also successfully applied to track the interface evolution under various conditions, which further validates the credibility of the VOF–CSF model used in our manuscript. ,, …”

Section: Methodssupporting

confidence: 78%

“…The volume of fluid–continuum surface force (VOF–CSF) method has been developed to simulate the droplet formation because of the advantage in capturing the interface evolution with a good mass conservation property . In the simulation, the continuity equation and Navier–Stokes equation need to be solved ∇ · U̅ = 0 ∂ ∂ t false( ρ U̅ false) + ∇ · false( ρ U̅ U̅ false) = − ∇ p + ∇ false[ μ ( ∇ U̅ + ∇ U̅ T ) false] + F̅ where U̅ is the velocity, p is the pressure, and t , ρ, and μ are the time, density, and viscosity, respectively.…”

Section: Methodsmentioning

confidence: 99%

“…The volume of fluid–continuum surface force (VOF–CSF) method has been developed to simulate the droplet formation because of the advantage in capturing the interface evolution with a good mass conservation property . In the simulation, the continuity equation and Navier–Stokes equation need to be solved where U̅ is the velocity, p is the pressure, and t , ρ, and μ are the time, density, and viscosity, respectively.…”

Section: Methodsmentioning

confidence: 99%

“…In our previous work, the VOF−CSF model was also successfully applied to track the interface evolution under various conditions, which further validates the credibility of the VOF−CSF model used in our manuscript. 38,41,42 3. RESULTS AND DISCUSSION…”

Section: Numerical Solutionmentioning

confidence: 99%

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Spontaneous Formation Mechanisms of Droplets in Step Emulsification

Zhang

Tao

et al. 2023

Ind. Eng. Chem. Res.

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Droplet step emulsification has been proven to possess the unique advantage of decoupling the flow parameters, which obviously contributes to the realization of the mass production of monodisperse droplets. However, a complete understanding of the dynamic characteristics underlying droplet spontaneous formation in step emulsification has not been fully revealed and remains a challenge because the channel confinement effect always results in the complexity in interface spatiotemporal evolution under various conditions. In this work, the spontaneous formation mechanisms of droplets in step emulsification are numerically investigated via a VOF–CSF model. The physics behind the two distinct flow patterns regarding dripping and jetting are deeply revealed based on the local flow field structures and pressure distribution, and it was found that in dripping, before final pinch-off of the neck, a finite time singularity usually exists, thus leading to infinite velocity and pressure inside the neck. However, in jetting, as the droplet steadily expands, the velocity and pressure inside the neck finally reach an equilibrium state. Besides, by taking multiple variables with a wide range into account, the flow pattern diagram and the prediction correlation of droplet size are established with several dimensionless numbers, exhibiting excellent universality. In particular, the force field characteristics previously undocumented for droplet step emulsification are also quantitatively clarified from a new perspective of momentum conservation. The results obtained in this study reveal the spontaneous formation mechanisms of droplets in step emulsification, thus providing theoretical guidance for precisely regulating the emulsification process.

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Section: Methodssupporting

confidence: 78%

Section: Methodsmentioning

confidence: 99%

“…The volume of fluid–continuum surface force (VOF–CSF) method has been developed to simulate the droplet formation because of the advantage in capturing the interface evolution with a good mass conservation property . In the simulation, the continuity equation and Navier–Stokes equation need to be solved where U̅ is the velocity, p is the pressure, and t , ρ, and μ are the time, density, and viscosity, respectively.…”

Section: Methodsmentioning

confidence: 99%

Section: Numerical Solutionmentioning

confidence: 99%

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Spontaneous Formation Mechanisms of Droplets in Step Emulsification

Zhang

Tao

et al. 2023

Ind. Eng. Chem. Res.

Self Cite

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show abstract

“…However, at a relative large diameter ratio between inner and outer jets, the evolution of inner and outer jets was almost synchronized, indicating a strong coupling manner between double interfaces. Apart from experimental investigation, numerical simulations are also widely utilized to study the dynamic behaviours of a coaxial jet (Liu et al 2017;Wang et al 2020;Zhang et al 2021). Numerical simulations can provide quantitative data such as the velocity field and pressure distribution of the jet, which are often difficult to measure in experiments.…”

Section: Introductionmentioning

confidence: 99%

Modulation of coaxial cone-jet instability in active co-flow focusing

Mu,

Qiao,

Ding

et al. 2023

J. Fluid Mech.

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The breakup of coaxial cone-jet interfaces to compound droplets in axisymmetric co-flow focusing (CFF) upon actuation is studied through numerical simulations. Due to the coupling effect of double interfaces, the response behaviours of coaxial cone-jet flow to actuation are more complex than those of a single-layered interface structure. Particularly, the coaxial jet presents totally different response modes between weak and strong interface coupling situations. In this work, the phase diagrams of response modes for coaxial jet breakup are depicted, considering the effect of perturbation frequency, amplitude and liquid flow rates. In particular, the breakup of a coaxial jet can be synchronized with actuation within a frequency range containing the natural breakup frequency, resulting in uniform compound droplets with a single core inside the shell, and the size of droplets can be adjusted by frequency. As the perturbation frequency exceeds the upper critical value, the external perturbation is unable to dominate the jet breakup, while below the lower critical frequency, the jet breaks up with multiple droplets generated in one period. The perturbation amplitude mainly affects the jet breakup length and also leads to the transition between different response modes. The coaxial cone upstream of the orifice can act as a buffer layer, regulating the perturbation amplitude of the coaxial jet downstream. The degree of buffering effect is affected by the perturbation frequency and amplitude. As the perturbation amplitude approaches unity, the decrease of perturbation frequency leads to the intermittent jet behaviour from the cone tip with a vibrating manner of the coaxial cone. Based on the linear instability analysis on the simplified single jet models for weak-coupled and strong-coupled jets, scaling analyses are carried out, which predict the jet breakup length and the natural frequency and critical frequency for the synchronized breakup. Finally, a strong pulse is added on the perturbation to produce compound droplets with a controllable number of cores. The present work provides valuable guidance for the practical application of on-demand compound droplet generation through active CFF.

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Numerical Simulation Study of Double-Emulsion Droplet Formation in a Co-flow Microchannel Capillary Device

et al. 2022

Transp Porous Med

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Numerical investigation of fluid property effects on formation dynamics of millimeter-scale compound droplets in a co-flowing device

Cited by 23 publications

References 29 publications

Spontaneous Formation Mechanisms of Droplets in Step Emulsification

Spontaneous Formation Mechanisms of Droplets in Step Emulsification

Modulation of coaxial cone-jet instability in active co-flow focusing

Numerical Simulation Study of Double-Emulsion Droplet Formation in a Co-flow Microchannel Capillary Device

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