Numerical Study on Droplet Formation in a Microchannel T-Junction Using the VOF Method

2010 ◽  
Author(s):  
Shobeir Aliasghar Zadeh ◽  
Rolf Radespiel
Keyword(s):  
Surface Tension ◽  
Flow Rate ◽  
Capillary Number ◽  
Numerical Study ◽  
Droplet Formation ◽  
Continuous Phase ◽  
Vof Method ◽  
Experimental Results ◽  
Glycerol Solution ◽  
Hexahedral Elements

The liquid-liquid two-phase flow in a T-junction was numerically investigated applying the VOF method and is compared with experimental results. The geometry was generated and meshed using the software Gridgen, and the corresponding equations for the CFD analysis were solved by using the commercial software Fluent (Fluent 12). The generated mesh consists of block-structured grids with hexahedral elements. Water-Glycerol solution (to-be-dispersed phase) and silicone oil (continuous phase) at room conditions are considered as fluids for this work. The effect of various parameters such as flow rate of the phases, width of the channel, viscosity and surface tension on the droplet formation are investigated and compared with available experimental results [1]. The breakup mechanism of droplets in various capillary-number regimes are explained. The numerical results of the length of the generated droplets as a function of the capillary number (varying the flow rate of the continuous phase) are in good agreement with the experimental values, which were measured using the same geometrical and physical properties. Further studies indicate that at a constant flow rate of the continuous phase, the droplet length rises strongly if the flow rate of the disperse phase increases, whereas the relative effects of the viscosity of the continuous phase, and the surface tension between phases on the length of droplets are moderate.

Numerical Study on Bubble Formation in a Microchannel Flow-Focusing Device Using the VOF Method

2011 ◽  
Author(s):  
Shobeir Aliasghar Zadeh ◽  
Rolf Radespiel
Keyword(s):  
Surface Tension ◽  
Disperse Phase ◽  
Flow Rate ◽  
Capillary Number ◽  
Bubble Formation ◽  
Continuous Phase ◽  
Glycerol Solution ◽  
Flow Focusing ◽  
Injection Angle ◽  
Bubble Length

The liquid-gas two-phase flow in a flow-focusing device are numerically investigated and the results are compared with experimental data. The geometries and the structured meshes were generated using the Gridgen software, while the computations were conducted with Fluent. N2 (disperse phase) and Water-Glycerol solution (continuous phase) at standard atmospheric conditions are considered as fluids. Based on dimensional analysis, the effects of various parameters such as the flow rates of both phases (effect of CQ = Qd/Qc), the viscosities of both phases (effect of the respective Reynolds number Re), the surface tension (effect of the capillary number) and the geometrical properties of the channel (channel width W and injection angle β) on the bubble formation and its length are compared to available experimental results. The break-up mechanism of the bubbles in various capillary regimes is explained. The computed length of the generated bubbles as a function of the capillary number (varying the flow rate of the continuous phase) are in good agreement with the experiments. Further studies indicate that at a constant flow rate of the continuous phase, the bubble length rises strongly as the flow rate of the disperse phase increases. In contrast, the relative effects of the viscosity and the surface tension on the length of the bubbles are moderate. The numerical results using various injection angles show that the bubble length increases, as the injection angle is raised from β = 45° to β = 90°.

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

2011 ◽  
Vol 9 (5) ◽  
pp. 1235-1256 ◽  
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.

Parametric Study of Droplet Formation and Characteristics Within Microfluidic Devices — A Case Study

2020 ◽  
Vol 12 (07) ◽  
pp. 2050077
Author(s):  
Seyedeh Sarah Salehi ◽  
Amir Shamloo ◽  
Siamak Kazemzadeh Hannani
Keyword(s):  
Interfacial Tension ◽  
Physical Properties ◽  
Flow Rate ◽  
Viscosity Ratio ◽  
Droplet Formation ◽  
Continuous Phase ◽  
Phase Flow ◽  
Phase Density ◽  
Size And Shape ◽  
The Impact

Droplet-based microfluidics technologies hold great attention in a wide range of applications, including chemical analysis, drug screening, and food industries. This work aimed to describe the effects of different physical properties of the two immiscible phases on droplet formation in a flow-focusing microfluidic device and determining proper flow rates to form a droplet within the desired size range. A numerical model was developed to solve the governing equations of two-phase flow and the results were validated with previous experimental results. The results demonstrate different types of droplet formation regimes from dripping to jetting and different production rates of droplets as a consequence of the impact of each property on fluid flow, including the viscosity ratio, density, interfacial tension, and the flow rate ratio. Based on the results, flow rate, viscosity, and interfacial tension strongly affect the droplet formation regime as well as its size and shape. Droplet diameter increases by increasing the dispersed to continuous phase flow rate as well as the interfacial tension while it decreases by increasing the viscosity ratio and the continuous phase density. Moreover, the formation of satellite droplets was modeled, and the effect of interfacial tension, the viscosity of the dispersed phase and the continuous phase density were found to be important on the conditions that the satellite droplets are suppressed. Since the formation of the satellite droplets induces polydispersity in droplet size, this phenomenon is avoided. Collectively, choosing appropriate aqueous and oil phases with proper physical properties is crucial in forming monodisperse droplets with defined size and shape.

Numerical Study and Scale Analysis of Inner and Outer Diameters Prediction in Fabrication of Hollow Fiber Membranes for Nerve Regeneration

2008 ◽  
Author(s):  
Jun Yin ◽  
Nicole Coutris ◽  
Yong Huang
Keyword(s):  
Surface Tension ◽  
Hollow Fiber ◽  
Numerical Study ◽  
Hollow Fiber Membrane ◽  
Nerve Repair ◽  
Vof Method ◽  
Fiber Spinning ◽  
Fabrication Process ◽  
Scale Analysis ◽  
And Control

Recently the semi-permeable hollow fiber membrane (HFM) is finding promising applications in promoting axonal outgrowth for nerve repair and regeneration. It is of interest to model the phase inversion-based HFM fabrication process and control the fabricated HFM geometry. The effect of gravity and surface tension which is frequently ignored in general fiber spinning should be carefully addressed in HFM fabrication modeling. Both the volume of fluid (VOF) method and the scale analysis have been applied to appreciate the effect of gravity and surface tension on the HFM geometry profile. The VOF method-based simulation results reveal that both the gravity and/or surface tension significantly reduce the predicted radii/diameters, while the scale analysis reveals that the gravity or surface tension affects the HFM fabrication process dynamics. Both the approaches warrant the need of including the gravity and surface tension in HFM fabrication process modeling.

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

2014 ◽  
Vol 11 (04) ◽  
pp. 1350096 ◽  
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.

scholarly journals Parameters influencing the droplet formation in a focusing microfluidic channel

2021 ◽  
Vol 327 ◽  
pp. 05002
Author(s):  
Emil Grigorov ◽  
Jordan A. Denev ◽  
Boris Kirov ◽  
Vassil Galabov
Keyword(s):  
Present Model ◽  
Numerical Study ◽  
Microfluidic Channel ◽  
Droplet Formation ◽  
Continuous Phase ◽  
Second Step ◽  
A Value ◽  
Wide Range ◽  
Discrete Phase ◽  
Good Agreement

In the present work a detailed numerical study of the parameters influencing the droplet formation in a flow-focusing microfluidic device are made. First, an extensive verification of the simulations with data from the literature is carried out. Influence of parameters like viscosity and inflow velocity are compared with the results from literature showing a good agreement. Some differences are attributed to the different numerical techniques used: in the present work a pure volume-of-fluid method is used, while in the reference study this method is combined with the level-set method. As a second step of the verification of the present model, a comparison with experimental data from the literature was carried out which shows a very good agreement. After the verification was completed, eight new simulations are carried out covering a wide range of velocities of the continuous phase uc. In these simulations the velocity of the discrete phase ud remains unchanged. The variation of the continuous phase velocity reveals that with increasing the value of uc, respectively the value of the capillary number Ca, the droplet length reaches a point of saturation, i.e. a point where the droplet length does not decrease any more. For the present setup this saturation occurs for Ca > 0,03. On the other hand, when the velocity of the continuous phase goes towards very low values (Ca < 0,01 for the present setup), the droplet size increases significantly. Further, it was found that for increasing capillary numbers Ca above a value around 0,015 for water/oil and above 0,025 for water + 40% glycerol / oil systems, a transmission from the dripping towards the jetting regimes of droplet formation occurs. It was shown that when the viscosity of the continuous phase increases, higher total pressure jumps in the droplet occur, also leading to the formation of smaller droplets.

Droplet Formation by Dripping at Micro T-Junction in Liquid-Liquid Mixing

2010 ◽  
Author(s):  
Sujin Yeom ◽  
Sang Yong Lee
Keyword(s):  
Disperse Phase ◽  
Drag Force ◽  
Flow Rate ◽  
Shear Force ◽  
Growth Stage ◽  
Droplet Formation ◽  
Continuous Phase ◽  
Main Channel ◽  
Interfacial Shear ◽  
Two Phases

In the present work, the phenomenon of droplet formation by dripping at a micro T-junction in liquid-liquid mixing was studied experimentally. The drop formation process consisted of three stages: the X-Y growth, X growth, and the detachment stages. In the X-Y growth stage, the bulged part of the disperse phase grows both in X (parallel to the main channel) and Y (lateral to the main channel) directions. The X-Y growth stage is followed by the X growth stage where the bulged part grows only in the main channel direction. Subsequently, in the detachment stage, the drag force exerted by the continuous phase becomes larger than the surface tension force between the two phases and the bulged part is finally separated into a droplet with regular intervals through a rapid necking process. Droplet sizes were estimated from the drop generation frequency and the flow rate of the disperse phase, and were also confirmed by direct measurements through photography. The sizes of the micro droplets generally decrease with the larger flow rate of the continuous phase or with a smaller flow rate of the disperse phase. This is due to the increase of the interfacial shear force between the two phases through the increase in the relative velocity. The droplet size also decreases with increase of the viscosity of the either phase. This again is due to the increase of the interfacial shear force (and hence the drag force) between the phases when the viscosity of either phase becomes large. The measured drop sizes will serve as a set of the benchmarking data for the development of a droplet detachment model in the dripping mode at micro T-junctions.

scholarly journals Water cooled micro-hole cellular structure as a heat dissipation media: An experimental and numerical study

2020 ◽  
Vol 24 (2 Part A) ◽  
pp. 683-692 ◽  
Author(s):  
Hussain Tariq ◽  
Ahmad Shoukat ◽  
Muhammad Anwar ◽  
Asif Israr ◽  
Hafiz Ali
Keyword(s):  
Flow Rate ◽  
Cellular Structure ◽  
Heat Dissipation ◽  
Numerical Study ◽  
Volumetric Flow Rate ◽  
Experimental Results ◽  
Heat Sinks ◽  
Base Temperature ◽  
Micro Hole ◽  
Alumina Nanofluid

Thermal performance of micro-hole cellular structure using water as a cool?ing fluid was investigated through CFD and then numerical results were validated with the experimental results. The minimum base temperature for the micro-hole cellular structure was found to be 29.7?C and 32.3?C numerically and experimentally, respectively, with volumetric flow rate of 0.000034 m3/s (2 Lpm) at a heating power of 345 W. Numerical values of the base temperature are in close agreement with experimental results with an error of 8.75%. Previously, the base temperatures of heat sinks using alumina nanofluid with 1% of volumetric concentration and water with volumetric flow rate of 0.000017 m3/s (1 Lpm) have been reported to be 43.9?C and 40.5?C, respectively.

scholarly journals Experimental Studies of Droplet Formation Process and Length for Liquid–Liquid Two-Phase Flows in a Microchannel

Energies ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1341
Author(s):  
Li Lei ◽  
Yuting Zhao ◽  
Wukai Chen ◽  
Huiling Li ◽  
Xinyu Wang ◽  
...  
Keyword(s):  
Formation Mechanism ◽  
Flow Rate ◽  
Volume Flow Rate ◽  
Scaling Law ◽  
Experimental Studies ◽  
Droplet Formation ◽  
Continuous Phase ◽  
Volume Flow ◽  
Dispersed Phase ◽  
Two Phase

In this study, changes in the droplet formation mechanism and the law of droplet length in a two-phase liquid–liquid system in 400 × 400 μm standard T-junction microchannels were experimentally studied using a high-speed camera. The study investigated the effects of various dispersed phase viscosities, various continuous phase viscosities, and two-phase flow parameters on droplet length. Two basic flow patterns were observed: slug flow dominated by the squeezing mechanism, and droplet flow dominated by the shear mechanism. The dispersed phase viscosity had almost no effect on droplet length. However, the droplet length decreased with increasing continuous phase viscosity, increasing volume flow rate in the continuous phase, and the continuous-phase capillary number Cac. Droplet length also increased with increasing volume flow rate in the dispersed phase and with the volume flow rate ratio. Based on the droplet formation mechanism, a scaling law governing slug and droplet length was proposed and achieved a good fit with experimental data.

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

Inventions ◽  
2018 ◽  
Vol 3 (3) ◽  
pp. 54 ◽  
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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