Effect of Fluid Properties on Droplet Generation in a Microfluidic T-Junction

2014 ◽  
Author(s):  
Katerina Loizou ◽  
Voon-Loong Wong ◽  
Wim Thielemans ◽  
Buddhika Hewakandamby
Keyword(s):  
Interfacial Tension ◽  
Scaling Laws ◽  
Viscosity Ratio ◽  
Continuous Phase ◽  
Generation Mechanism ◽  
Droplet Generation ◽  
Dispersed Phase ◽  
Supporting Evidence ◽  
Fluid Properties ◽  
Break Up

Over the last decade, significant work has been performed in an attempt to quantify the effect of different parameters such as flowrate, geometrical and fluid characteristics on the droplet break up mechanism in microfluidic T-Junctions. This demand is dictated by the need of tight control of the size and dispersity of the droplets generated in such geometries. Even though several researchers have investigated the effect of viscosity ratio on both the droplet break up mechanism as well as on the regime transition, fluid properties have not been included in most scaling laws. It is therefore evident that the contribution of fluid properties has not been quantified thoroughly. In the present work, the effect of fluid properties on the volume of droplets generated in a microfluidic T-junction is investigated. The main aim of this work is to examine the influence of viscosity of both the dispersed and continuous phase as well as the effect of interfacial tension on the size of droplet generated along with the break up mechanism. Three different oils have been utilised as continuous phase in this work to enable investigation of the effect of viscosity of the continuous phase with experiments performed at constant Capillary numbers. Various glycerol weight percentages have been employed to vary the viscosity of the dispersed phase fluid (water). Lastly, the effect of interfacial tension has been explored using two of the oils at constant μcUc (viscous force term). High speed imaging has been utilised to visualise and measure the volume of the resulting droplets. The viscosity ratio (viscosity of dispersed phase over viscosity of continuous phase) between the two phases appears to affect the droplet generation mechanism, especially for the highest viscosity ratio employed (mineral oil-water system) where the system behaves in a noticeably different way. Influence of interfacial tension is also noticeable even though less evident. In terms of the effect of viscosity of dispersed phase on the droplet generation a small difference on the volume of the droplets generated in olive oil glycerol systems is also reported. In an attempt to enumerate the effect of fluid properties on the droplet generation mechanism in a microfluidic T-junction, this paper will present supporting evidence in detail on the above and a comparison of the findings with the existing theories.

Optimization of Shear Driven Droplet Generation in a Microfluidic Device

2003 ◽  
Author(s):  
John Collins ◽  
Yung-Chieh Tan ◽  
Abraham P. Lee
Keyword(s):  
Interfacial Tension ◽  
Continuous Phase ◽  
Droplet Generation ◽  
Water Stream ◽  
Multiphysics Modeling ◽  
Flow Parameters ◽  
Fluid Properties ◽  
Novel Method ◽  
Oil Water ◽  
Dispersive Phase

Hydrophilic and lipophilic interfaces of fluids play an important role in the formation of droplets. A large collection of droplets constitutes emulsions of water dispersive phase into oil continuous phase. Since droplet generation forms the basis of the manufacturing of emulsion, great efforts have been made to understand the science, technological and industrial problems associated with the generation of droplets. This paper presents the optimization of a novel method of droplet generation [1] in a microchannel resulting from the laminar co-flow of water and oil in a T type channel. Water in oil droplets are formed with olive oil (interfacial tension 28mN/m, viscosity 84mPa/s, density 918Kg/m3). At the T-junction, the water stream sent through the middle channel is sheared and cut by the oil stream sent through the outer channel. Competition between interfacial tension and the Laplace pressure at the oil/water interface results in droplets of finite diameter. Fluid properties such as density, viscosity and surface tension and the flow parameters such as pressure, mass flow rate and velocity are varied at the inlets and outlets to optimize size, frequency and periodicity of droplets using CFD-ACE+, a multiphysics modeling tool (CFDRC, Huntsville, AL).

scholarly journals The liquid-liquid flow dynamics and droplet formation in a modified step T-junction Microchannel

2021 ◽  
Author(s):  
Jingwei Zhang ◽  
Si Da Ling ◽  
zhuo chen ◽  
Wenjun Ma ◽  
jianhong Xu
Keyword(s):  
Interfacial Tension ◽  
Surfactant Concentration ◽  
Continuous Phase ◽  
Flow Dynamics ◽  
Generation Mechanism ◽  
Droplet Generation ◽  
Phase Flow ◽  
Report Generation ◽  
Transition Stage ◽  
Abnormal Increase

The droplet generation mechanism in the step T-junction remains unknown, especially for the transition stage from dripping to jetting . In this work, the droplet generation mechanism was systematically investigated in a novel modified step T-junction. We found that under different fluid regimes, different factors take action. In dripping regime, the interfacial tension dominated the formation mechanism when the surfactant concentration was controlled below micelle concentration (CMC). In jetting regime, our experimental results showed that the influence of the surfactant concentration on the size of generated droplets was rather negligible while the phase ratio indeed determined such a parameter. In the dripping-jetting transition stage, an abnormal increase of droplet size was observed despite the increase of continuous phase flow. To the best for our knowledge, it is the first study to report generation mechanism in modified step T-junction from dripping to jetting regimes.

Phase Inversion in Two-Phase Liquid Systems

1992 ◽  
Vol 57 (7) ◽  
pp. 1419-1423
Author(s):  
Jindřich Weiss
Keyword(s):  
Interfacial Tension ◽  
Phase Inversion ◽  
Continuous Phase ◽  
Considerable Effect ◽  
Weak Dependence ◽  
Dispersed Phase ◽  
Two Phase ◽  
Liquid Systems ◽  
Phase Liquid

New data on critical holdups of dispersed phase were measured at which the phase inversion took place. The systems studied differed in the ratio of phase viscosities and interfacial tension. A weak dependence was found of critical holdups on the impeller revolutions and on the material contactor; on the contrary, a considerable effect of viscosity was found out as far as the viscosity of continuous phase exceeded that of dispersed phase.

Effect of Geometry on Droplet Generation in a Microfluidic T-Junction

2013 ◽  
Author(s):  
Katerina Loizou ◽  
Wim Thielemans ◽  
Buddhika N. Hewakandamby
Keyword(s):  
Aspect Ratio ◽  
Cross Section ◽  
Droplet Formation ◽  
Continuous Phase ◽  
Main Channel ◽  
Superficial Velocity ◽  
Droplet Generation ◽  
Dispersed Phase ◽  
Aspect Ratios ◽  
The Cross

The main aim of this study is to examine how the droplet formation in microfluidic T-junctions is influenced by the cross-section and aspect ratio of the microchannels. Several studies focusing on droplet formation in microfluidic devices have investigated the effect of geometry on droplet generation in terms of the ratio between the width of the main channel and the width of the side arm of the T-junction. However, the contribution of the aspect ratio and thus that of the cross-section on the mechanism of break up has not been examined thoroughly with most of the existing work performed in the squeezing regime. Two different microchannel geometries of varying aspect ratios are employed in an attempt to quantify the effect of the ratio between the width of the main channel and the height of the channel on droplet formation. As both height and width of microchannels affect the area on which shear stress acts deforming the dispersed phase fluid thread up to the limit of detaching a droplet, it is postulated that geometry and specifically cross-section of the main channel contribute on the droplet break-up mechanisms and should not be neglected. The above hypothesis is examined in detail, comparing the volume of generated microdroplets at constant flowrate ratios and superficial velocities of continuous phase in two microchannel systems of two different aspect ratios operating at dripping regime. High-speed imaging has been utilised to visualise and measure droplets formed at different flowrates corresponding to constant superficial velocities. Comparing volumes of generated droplets in the two geometries of area ratio near 1.5, a significant increase in volume is reported for the larger aspect ratio utilised, at all superficial velocities tested. As both superficial velocity of continuous phase and flowrate ratio are fixed, superficial velocity of dispersed phase varies. However this variation is not considered to be large enough to justify the significant increase in the droplet volume. Therefore it can be concluded that droplet generation is influenced by the aspect ratio and thus the cross-section of the main channel and its effect should not be depreciated. The paper will present supporting evidence in detail and a comparison of the findings with the existing theories which are mainly focused on the squeezing regime.

scholarly journals Drop formation in microfluidic cross-junction: jetting to dripping to jetting transition

2019 ◽  
Vol 23 (8) ◽  
Author(s):  
Nina M. Kovalchuk ◽  
Masanobu Sagisaka ◽  
Kasparas Steponavicius ◽  
Daniele Vigolo ◽  
Mark J. H. Simmons
Keyword(s):  
Interfacial Tension ◽  
Capillary Number ◽  
Continuous Phase ◽  
Flow Rate Ratio ◽  
Dispersed Phase ◽  
Flow Focusing ◽  
Jet Formation ◽  
Relative Contribution ◽  
Power Law Function ◽  
Dispersed Phases

AbstractThe regimes of drop generation were studied in a Dolomite microfluidic device which combined both hydrodynamic and geometrical flow focusing over a broad range of flow rates. A series of aqueous dispersed phases were used with a viscosity ratio between continuous and dispersed phases of close to unity. Surfactants were added to alter the interfacial tension. It was shown that the transition from dripping to jetting is well described by the capillary numbers of both the dispersed and continuous phases. Only the jetting regime was observed if the capillary number of the dispersed phase was above a critical value, whereas at smaller values of this parameter a jetting → dripping → jetting transition was observed by increasing the capillary number of the continuous phase. The analysis performed has shown that the conditions for a dripping to jetting transition at moderate and large values of the capillary number of the continuous phase can be predicted theoretically by comparison of the characteristic time scales for drop pinch-off and jet growth, whereas the transition at small values cannot. It is suggested that this transition is geometry mediated and is a result of the interplay of jet confinement in the focusing part and a decrease of confinement following entry into the main channel. The flow fields inside the jet of the dispersed phase were qualitatively different for small and large values of the capillary number of the continuous phase revealing the relative contribution of the dispersed phase flow in jet formation. The volume of the drops formed in the jetting regime increased as a power law function of the flow rate ratio of the dispersed to continuous phase, independent of the interfacial tension.

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.

scholarly journals Influence on droplet formation in the presence of nanoparticles in a microfluidic T-junction

2012 ◽  
Vol 16 (5) ◽  
pp. 1429-1432
Author(s):  
Rui-Jin Wang ◽  
Zhi-Hua Li
Keyword(s):  
Interfacial Tension ◽  
Microfluidic Device ◽  
Droplet Formation ◽  
Continuous Phase ◽  
Liquid Interface ◽  
Dispersed Phase ◽  
Microscopic Mechanism ◽  
Formation Dynamics

The droplet formation in the presence of nanoparticles was studied in a T-shaped microfluidic device numerically. Nanoparticles in continuous phase did not influence droplet formation dynamics obviously. Contrarily, the presence of nanoparticles in dispersed phase will influence evidently droplet formation dynamics, the possible reason is that the accumulation of nanoparticles at the liquid-liquid interface would cause the variation of interfacial tension and the anisotropy of nanoparticles? movement at interface. Discussions on microscopic mechanism of droplet formation in the presence of nanoparticles were carried out.

scholarly journals Droplet Formation in a Cross-Junction Microfluidic Channel with Non-Newtonian Dispersed Phase

2021 ◽  
Vol 4 (1) ◽  
pp. 21
Author(s):  
Maryam Fatehifar ◽  
Alistair Revell ◽  
Masoud Jabbari
Keyword(s):  
Power Law ◽  
Flow Rate ◽  
Xanthan Gum ◽  
Real Life ◽  
Microfluidic Channel ◽  
Shear Thinning ◽  
Continuous Phase ◽  
Droplet Generation ◽  
Dispersed Phase ◽  
Generating Series

Microfluidics enables generating series of isolated droplets for high-throughput screening. As many biological/chemical solutions are of shear thinning non-Newtonian nature, we studied non-Newtonian droplet generation to improve the reliability of simulation results in real-life assays. We considered non-Newtonian power-law behaviour for Xanthan gum aqueous solution as the dispersed phase, and Newtonian canola oil as the continuous phase. Simulations were performed in OpenFOAM, using the inter foam solver and volume of fluid (VOF) method. A cross-junction geometry with each inlet and outlet channel height (H) and width (W) equal to 50 micrometers with slight contractions in the conjunctions was used to gain a better monodispersity. Following validation of the numerical setup, we conducted a series of tests to provide novel insight into this configuration. With a capillary number, of 0.01, dispersed phase to continuous phase flow-rate ratio of 0.05, and contact angle of 160°, simulations revealed that, by increasing the Xanthan gum concentration (0, 800, 1500, 2500 ppm) or, in other words, decreasing the n-flow behaviour index from 1 to 0.491, 0.389, and 0.302 in power-law model, (a) breakup of the dispersed phase thread occurred at 0.0365, 0.0430, 0.0440, and 0.0450 s; (b) the dimensionless width of the thread at the main channel entrance increased from 0 to 0.066, 0.096, and 0.16; and (c) the dimensionless droplet diameter decreased from 0.76 to 0.72, 0.68, and 0.67, respectively. Our next plan is to study effect of shear-thinning behaviour on droplet generation in different Ca and flow-rate ratios.

Microchannel Emulsification Devices for Generating Highly Uniform Droplets

2009 ◽  
Author(s):  
Isao Kobayashi ◽  
Mitsutoshi Nakajima
Keyword(s):  
Droplet Size ◽  
Large Scale ◽  
Continuous Phase ◽  
Droplet Generation ◽  
High Tech ◽  
Dispersed Phase ◽  
Scale Production ◽  
Crystal Silicon ◽  
Uniform Droplets ◽  
Highly Uniform

Monodisperse emulsions consisting of uniform droplets have received a great deal of attentions over the past decade due to their high-tech applications, e.g., monodisperse microparticles as spacers for electronic devices and monodisperse micro-carriers for drug delivery systems (DDS). Our group proposed microchannel (MC) emulsification, which enables generating highly uniform droplets with the smallest coefficient of variation of below 5% using MC arrays of unique geometry. The resultant droplet size can be precisely controlled by MC geometry. Droplet generation for MC emulsification is very mild and does not require any external shear stress; a dispersed phase that passed through MCs is transformed spontaneously into uniform droplets inside a continuous-phase domain. The aim of this paper is to present recent developments in MC emulsification devices, particularly focusing on straight-through MC arrays consisting of uniform straight-through holes for large-scale production of monodisperse emulsions. A straight-through MC array device of a standard 24 × 24-mm size was made of single-crystal silicon, and a straight-through MC array consisting of numerous MCs was positioned within a 10 × 10-mm central region of the device. We initially designed symmetric straight-through MCs with circular and oblong sections. Highly uniform droplets with average sizes of 4 to 100 μm were generated using oblong straight-through MCs. The simulation results using CFD (computational fluid dynamics) agreed well with the experimental results and provided useful information, such as the movement of the oil-water interface around the MC outlet during droplet generation. Below the critical value of the dispersed phase flux, monodisperse emulsions were produced via suitable oblong straight-through MCs, with droplet size and size distribution independent of the flux value. The development of asymmetric straight-through MC arrays consisting of numerous pairs of microslots and circular MCs improved the productivity of highly uniform droplets and stability during droplet generation.

Computational Investigation of Microdroplet Formation in a Crossflow Membrane Emulsification Process

2011 ◽  
Author(s):  
Manabendra Pathak
Keyword(s):  
Surface Tension ◽  
Flow Rate ◽  
Viscosity Ratio ◽  
Period Doubling ◽  
Continuous Phase ◽  
Inertia Force ◽  
Dispersed Phase ◽  
Phase Flow ◽  
Membrane Emulsification ◽  
Emulsification Process

Monodisperse microdroplets are formed, when a liquid is injected through a micropore into another immiscible liquid. Depending on the relative flow between the two phases, droplets may form in quiescent, coflowing and crossflowing environment. The dispersions of one phase liquid in another crossflowing liquid are observed in liquid emulsification process and the system has been used extensively in microfluidic devices to produce monodisperse microdroplets with controllable size. Liquid emulsions are widely used in food, cosmetics, pharmaceutics and polymer industries. In the present work, microdroplet formation in a crossflow membrane emulsification process has been investigated computationally using VOF/finite volume method. The full transient simulation has been carried out starting from the injection of dispersed phase to breakup into drops for different values of dispersed phase and continuous phase flow rate, surface tension and viscosity ratio of both the phases. Depending upon the values of the both phases, the droplet formation process shows the dripping and jetting behavior. The qualitative features of the two regimes and their transition have been correlated with different non-dimensional numbers such as Capillary number, Weber number and viscosity ratio of the two phase liquids. Some interesting nonlinear behavior such as period doubling been observed near the transition between the dripping and jetting regimes has. The topological characteristics of dripping, jetting and transition regimes in membrane emulsification have been observed different than in the cases of T-junction emulsification and flow focusing emulsification. Two ways of dripping to jetting transition have been observed, one with the increasing dispersed phase flow rate at constant continuous phase flow rate and other way is reducing the surface tension at constant dispersed phase flow rate. The effect of inertia force has been observed negligible for high value of surface tension and significant for lower surface tension value.

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