Numerical Simulation of the Droplet Formation in a T-Junction Microchannel by a Level-Set Method

To satisfy the increasingly high demands in many applications of microfluidics, the size of the droplet needs accurate control. In this paper, a level-set method provides a useful method for studying the physical mechanism and potential mechanism of two-phase flow. A detailed three-dimensional numerical simulation of microfluidics was carried out to systematically study the generation of micro-droplets and the effective diameter of droplets with different control parameters such as the flow rate ratio, the continuous phase viscosity, the interfacial tension, and the contact angle. The effect of altering the pressure at the x coordinate of the main channel during the droplet formation was analysed. As the simulation results show, the above control parameters have a great influence on the formation of droplets and the size of the droplet. The effective droplet diameter increases when the flow rate ratio and the interfacial tension increase. It decreases when the continuous phase viscosity and the contact angle increase.

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Slug Formation Analysis of Liquid–Liquid Two-Phase Flow in T-Junction Microchannels

Journal of Thermal Science and Engineering Applications ◽

10.1115/1.4043385 ◽

2019 ◽

Vol 11 (5) ◽

Cited By ~ 10

Author(s):

Jin-yuan Qian ◽

Xiao-juan Li ◽

Zan Wu ◽

Zhi-jiang Jin ◽

Junhui Zhang ◽

...

Keyword(s):

Flow Rate ◽

Rate Ratio ◽

Two Phase Flow ◽

Continuous Phase ◽

Channel Width ◽

Flow Rate Ratio ◽

Width Ratio ◽

Phase Flow ◽

Channel Depth ◽

Two Phase

Slug flow is a common flow pattern in the liquid–liquid two-phase flow in microchannels. It is an ideal pattern for mass transfer enhancement. Many factors influence the slug formation such as the channel geometries (channel widths, channel depth), flow rates of the two phase, and physical properties. In this paper, in order to investigate the liquid–liquid two-phase slug formation in a T-junction microchannel quantitatively, the volume of fluid (VOF) method is adopted to simulate the whole slug formation process. With the validated model, the effects of the disperse phase channel width, channel depth, and two-phase flow rate ratio on slug formation frequency and slug size (slug volume and slug length) are analyzed with dimensionless parameters. Dimensionless parameters include the disperse-to-continuous phase channel width ratio, height-to-width ratio, and two-phase flow rate ratio. Results show that both the channel geometry and two-phase flow rate ratio have a significant influence on slug formation. Compared with the conventional slug formation stages, a new stage called the lag stage emerges when the disperse phase channel width decreases to half of the continuous phase channel width. When the channel depth decreases to one third of the continuous phase channel width, the flow patterns become unstable and vary with the two-phase flow rate ratio. Moreover, empirical correlations are proposed to predict the slug formation frequency. The correlation between slug formation frequency and slug volume is quantified.

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SIMULATIONS OF DROPLET FORMATION IN A T-JUNCTION MICRO-CHANNEL USING THE PHASE FIELD METHOD

International Journal of Computational Methods ◽

10.1142/s0219876213500965 ◽

2014 ◽

Vol 11 (04) ◽

pp. 1350096 ◽

Cited By ~ 2

Author(s):

L. L. WANG ◽

G. J. LI ◽

H. TIAN ◽

Y. H. YE

Keyword(s):

Contact Angle ◽

Flow Rate ◽

Capillary Number ◽

Rate Ratio ◽

Droplet Formation ◽

Field Method ◽

Leakage Rate ◽

Phase Field Method ◽

Flow Rate Ratio ◽

Micro Channel

Micro-fabrication techniques are developed rapidly because they offer numerous benefits for chemical and biological industries. Numerical simulations (based on incompressible Navier–Stokes equations) are presented of the two-phase flow in a cross-flowing T-junction micro-channel using the phase field method and the results are in agreement with experimental measurements. The leakage rate in the gap between the droplet and lower wall decreases during the droplet formation, the relationship between the leakage rate and the derivative of the up-stream droplet size is obtained, which is applicable when the droplet contacts with the lower wall on the wetted conditions or expands to the up-stream in the main channel. The droplet formation is related to several factors, including the capillary number, the contact angle, the flow rate ratio, and the micro-channel shape. The critical capillary number could distinguish between the squeezing and dripping regimes for the generation of different kinds of droplets. The simulations show that the critical capillary number is 0.012. Influence of those factors on the droplet length is related to the leakage rate. The leakage rate of the continuous phase decreases slowly as the flow rate ratio decreases or contact angle increases. In the squeezing regime, the leakage rate is weakly influenced by the contact angle at the small flow rate ratio and is different in three type micro-channels, the droplet length increases with the increase in contact angle which intensifies growth at the big flow rate ratio, and the longest droplet is obtained in the Y-junction micro-channel. In the dripping regime, at the big flow rate ratio the leakage rate is almost independent to the contact angle and micro-channel shape, and the droplet length also is same.

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Lattice Boltzmann Simulation of Droplet Generation in a Microfluidic Cross-Junction

Communications in Computational Physics ◽

10.4208/cicp.231009.101110s ◽

2011 ◽

Vol 9 (5) ◽

pp. 1235-1256 ◽

Cited By ~ 19

Author(s):

Haihu Liu ◽

Yonghao Zhang

Keyword(s):

Droplet Size ◽

Flow Rate ◽

Lattice Boltzmann ◽

Capillary Number ◽

Rate Ratio ◽

Viscosity Ratio ◽

Droplet Formation ◽

Continuous Phase ◽

Viscous Force ◽

Flow Rate Ratio

AbstractUsing the lattice Boltzmann multiphase model, numerical simulations have been performed to understand the dynamics of droplet formation in a microfluidic cross-junction. The influence of capillary number, flow rate ratio, viscosity ratio, and viscosity of the continuous phase on droplet formation has been systematically studied over a wide range of capillary numbers. Two different regimes, namely the squeezinglike regime and the dripping regime, are clearly identified with the transition occurring at a critical capillary number Cacr. Generally, large flow rate ratio is expected to produce big droplets, while increasing capillary number will reduce droplet size. In the squeezing-like regime (Ca ≤ Cacr), droplet breakup process is dominated by the squeezing pressure and the viscous force; while in the dripping regime (Ca ≤ Cacr), the viscous force is dominant and the droplet size becomes independent of the flow rate ratio as the capillary number increases. In addition, the droplet size weakly depends on the viscosity ratio in both regimes and decreases when the viscosity of the continuous phase increases. Finally, a scaling law is established to predict the droplet size.

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Drop formation in cross-junction micro-channel, using lattice Boltzmann method

Thermal Science ◽

10.2298/tsci160322230f ◽

2018 ◽

Vol 22 (2) ◽

pp. 909-919 ◽

Cited By ~ 1

Author(s):

Kayvan Fallah ◽

Moahammad Rahni ◽

Alireza Mohammadzadeh ◽

Mohammad Najafi

Keyword(s):

Contact Angle ◽

Lattice Boltzmann Method ◽

Flow Rate ◽

Lattice Boltzmann ◽

Rate Ratio ◽

Viscosity Ratio ◽

Flow Rate Ratio ◽

Drop Formation ◽

Micro Channels ◽

Boltzmann Method

Drop formation in cross-junction micro-channels is numerically studied using the lattice Boltzmann method with pseudo-potential model. To verify the simulation, the results are compared to previous numerical and experimental data. Furthermore, the effects of capillary number, flow rate ratio, contact angle, and viscosity ratio on the flow patterns, drop length, and interval between drops are investigated and highlighted. The results show that the drop forming process has different regimes, namely, jetting, drop, and squeezing regimes. Also, it is shown that increasing in the flow rate ratio in the squeezing regime causes increment in drop length and decrement in drops interval distance. On the other hand, the drops length and the interval between the generated drops increase as contact angle increases. Also, the drop length and distance between drops is solely affected by viscosity ratio.

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Examining the Effect of Flow Rate Ratio on Droplet Generation and Regime Transition in a Microfluidic T-Junction at Constant Capillary Numbers

Inventions ◽

10.3390/inventions3030054 ◽

2018 ◽

Vol 3 (3) ◽

pp. 54 ◽

Cited By ~ 4

Author(s):

Katerina Loizou ◽

Voon-Loong Wong ◽

Buddhika Hewakandamby

Keyword(s):

Transition Region ◽

Flow Rate ◽

Capillary Number ◽

Rate Ratio ◽

Continuous Phase ◽

Flow Rate Ratio ◽

Phase Flow ◽

Regime Transition ◽

Droplet Volume ◽

Rate Ratios

The focus of this work is to examine the effect of flow rate ratio (quotient of the dispersed phase flow rate over the continuous phase flow rate) on a regime transition from squeezing to dripping at constant capillary numbers. The effect of the flow rate ratio on the volume of droplets generated in a microfluidic T-junction is discussed, and a new scaling law to estimate their volume is proposed. Existing work on a regime transition reported by several researchers focuses on the effect of the capillary number on regime transition, and the results that are presented in this paper advance the current understanding by indicating that the flow rate ratio is another parameter that dictates regime transition. In this paper, the transition between squeezing and dripping regimes is reported at constant capillary numbers, with a transition region identified between squeezing and dripping regimes. Dripping is observed at lower flow rate ratios and squeezing at higher flow rate ratios, with a transition region between the two regimes at flow rate ratios between 1 and 2. This is presented in a flow regime map that is constructed based on the observed mechanism. A scaling model is proposed to characterise droplet volume in terms of flow rate ratio and capillary number. The effect of flow rate ratio on the non-dimensional droplet volume is presented, and lastly, the droplet volume is expressed in terms of a range of parameters, such as the viscosity ratio between the dispersed and the continuous phase, capillary number, and the geometrical characteristics of the channels.

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Numerical Simulation of Three-Fluid Stratified Flow Using the Level-Set Method

International Journal of Computational Methods ◽

10.1142/s021987621650033x ◽

2016 ◽

Vol 13 (06) ◽

pp. 1650033 ◽

Cited By ~ 1

Author(s):

H. Y. Li ◽

Y. F. Yap ◽

J. Lou ◽

Z. Shang

Keyword(s):

Pressure Gradient ◽

Level Set Method ◽

Level Set ◽

Flow Rate ◽

Volumetric Flow Rate ◽

Stratified Flow ◽

Reduction Factor ◽

Flow Rate Ratio ◽

Fully Developed Flow ◽

Entry Length

Laminar three-fluid stratified flow which involves two different moving interfaces is numerically investigated in a two-dimensional domain in this paper. These interfaces are captured using the level-set method via two level-set functions. The effects of various parameters including Froude number Fr and Weber number We as well as the initial locations of the two interfaces on the evolution of the two interfaces are investigated. It is found that the decrease of We number increases the entry length. For a given volumetric flow rate ratio, the interfacial location at fully developed flow is identical irrespective of the Froude and Weber numbers as well as the initial interfacial location at the inlet. The interfacial locations for fully developed flow show distinct behaviors under different flow rate ratios and viscosity ratios. Increase of volumetric flow rate and viscosity for any one of the fluids increases the pressure drop in the channel. The study of pressure gradient reduction factor (PGRF) shows that it is possible to achieve pressure gradient reduction by introducing less viscous fluids in the transportation of a more viscous fluid.

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