Numerical simulations of wall contact angle effects on droplet size during step emulsification

Wang, Meng; Kong, Chuang; Liang, Qisen; Zhao, Jiajun; Wen, Maolin; Xu, Zhongbin; Ruan, Xiangyan

doi:10.1039/c8ra06837b

Cited by 24 publications

(18 citation statements)

References 27 publications

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“…Numerous research has benefited from the VOF method to simulate multiphase flows. It has been proved to be suitable for incompressible two-phase flows as it guarantees the conservation of mass [28][29][30]. The governing equations, namely continuity and momentum, should be solved simultaneously for the whole flow field:…”

Section: Governing Equationsmentioning

confidence: 99%

Non-Newtonian Droplet Generation in a Cross-Junction Microfluidic Channel

2021

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A two-dimensional CFD model based on volume-of-fluid (VOF) is introduced to examine droplet generation in a cross-junction microfluidic using an open-source software, OpenFOAM together with an interFoam solver. Non-Newtonian power-law droplets in Newtonian liquid is numerically studied and its effect on droplet size and detachment time in three different regimes, i.e., squeezing, dripping and jetting, are investigated. To understand the droplet formation mechanism, the shear-thinning behaviour was enhanced by increasing the polymer concentrations in the dispersed phase. It is observed that by choosing a shear-dependent fluid, droplet size decreases compared to Newtonian fluids while detachment time increases due to higher apparent viscosity. Moreover, the rheological parameters—n and K in the power-law model—impose a considerable effect on the droplet size and detachment time, especially in the dripping and jetting regimes. Those parameters also have the potential to change the formation regime if the capillary number (Ca) is high enough. This work extends the understanding of non-Newtonian droplet formation in microfluidics to control the droplet characteristics in applications involving shear-thinning polymeric solutions.

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Section: Governing Equationsmentioning

confidence: 99%

Non-Newtonian Droplet Generation in a Cross-Junction Microfluidic Channel

2021

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“…As a widely used simulation method, 20,24,25 the volume of uid (VOF) is employed in our simulations to track the interface between phases based on the volume fraction a within individual grid cells. The continuity equation and Navier-Stokes equation are used to solve the transport equation to dene the ow eld.…”

Section: Methodsmentioning

confidence: 99%

“…20 An enormous amount of research reveals that the viscosity ratio l and ow rate ratio Q of the dispersed phase to continuous phase, surface tension between the two phases, and contact angle have signicant inuences on droplet generation. [21][22][23][24] Whereas the ratio of surface to volume is high, the interaction between solid wall and uids can signicantly affect droplet generation 25,26 and many researchers have found that the geometry of the Tjunction is a crucial factor in droplet formation. 27,28 For the interaction between uid and wall, most researchers employed the contact angle to represent the wetting property in two-phase ow.…”

Section: Introductionmentioning

confidence: 99%

Effects of wall velocity slip on droplet generation in microfluidic T-junctions

Song

et al. 2019

RSC Adv.

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“…They are droplet generation by co-flowing streams, , droplet generation by stretching or elongation shearing streams, and droplet formation in cross-flowing streams. − Droplet generation in cross-flowing streams or droplet formation in a T-junction is one of the widely used techniques due to its geometric simplicity, less power requirement, and better control over droplet size. ,− In this technique, a dispersed-phase fluid is perpendicularly intercepted by a continuous-phase fluid flowing through a main channel, and the droplets are generated by shearing action of the continuous phase. The pressure difference across the interface of two immiscible fluids and the drag force imparted by the continuous phase influence the formation and evolution of the droplet inside the main channel.…”

Section: Introductionmentioning

confidence: 99%

“…10,13−15 In this technique, a dispersed-phase fluid is perpendicularly intercepted by a continuous-phase fluid flowing through a main channel, and the droplets are generated by shearing action of the continuous phase. The pressure difference across the interface of two immiscible fluids and the drag force imparted by the continuous phase influence the formation and evolution of the droplet 16 inside the main channel.…”

Section: Introductionmentioning

confidence: 99%

Pressure Transient during Wettability-Mediated Droplet Formation in a Microfluidic T-Junction

Kumar

Pathak

2020

Ind. Eng. Chem. Res.

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Droplet formation in a microfluidic T-junction is observed in enormous applications. Uniformity in droplet size and its stability are two crucial parameters, which are needed for a myriad of applications. As the dispersed and continuous phases interact near the junction point of the channel, flow instabilities arise due to unbalanced conditions of different forces acting on the droplet. These instabilities result in fluctuating pressure, which further affects the droplet formation process. In the present work, pressure characteristics during droplet formation from highly viscous fluids in a microfluidic T-junction have been investigated for different operating conditions. Both numerical and analytical models have been developed to predict the pressure characteristics during different stages of the droplet formulation, and comparison of results is presented. Further, an experimental investigation is performed for validating the present numerical model. Excellent agreement has been observed between the numerical and experimental results. The effects of wettability of the channel wall and a high viscosity ratio on pressure characteristics have been investigated. Pressure decreases with an increase in contact angle or hydrophobicity of the channel wall, whereas the frequency of the pressure fluctuation increases with an increase in contact angle. The amplitude of pressure fluctuation decreases with an increase in viscosity of the dispersed phase, while the frequency of the fluctuations increases. The frequency of the pressure fluctuation coincides with the frequency of the droplet formation. At a high capillary number, pressure is characterized by low amplitude and high frequency (LAHF) fluctuations, whereas at a low capillary number, pressure is characterized by high amplitude and low frequency (HALF) fluctuations.

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Numerical simulations of wall contact angle effects on droplet size during step emulsification

Abstract: A study on the effects of wall contact angle makes it more flexible to predict and control the size of droplets generated in step emulsification.

Cited by 24 publications

References 27 publications

Non-Newtonian Droplet Generation in a Cross-Junction Microfluidic Channel

Non-Newtonian Droplet Generation in a Cross-Junction Microfluidic Channel

Effects of wall velocity slip on droplet generation in microfluidic T-junctions

Pressure Transient during Wettability-Mediated Droplet Formation in a Microfluidic T-Junction

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