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.

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 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.

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.

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.

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

2018 ◽  
Vol 71 (12) ◽  
pp. 957 ◽  
Author(s):  
Wenbo Han ◽  
Xueye Chen
Keyword(s):  
Numerical Simulation ◽  
Contact Angle ◽  
Interfacial Tension ◽  
Level Set Method ◽  
Level Set ◽  
Flow Rate ◽  
Rate Ratio ◽  
Continuous Phase ◽  
Flow Rate Ratio ◽  
Control Parameters

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.

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.

Two-Phase Flow Patterns in Microfluidic Cross-Shaped Junctions and Slug Hydrodynamics in the Dripping Regime

2017 ◽  
Author(s):  
Zan Wu ◽  
Zhen Cao ◽  
Bengt Sunden
Keyword(s):  
Flow Pattern ◽  
Capillary Number ◽  
Two Phase Flow ◽  
Flow Patterns ◽  
Continuous Phase ◽  
Flow Rate Ratio ◽  
Phase Flow ◽  
Two Phase ◽  
Viscous Shear ◽  
Fluid Properties

Flow patterns for water-butanol, water-toluene and water-hexane two-phase flows were visualized in the cross-shaped junctions of three square glass microchannels with hydraulic diameters of 200 μm, 400 μm and 600 μm. Typical flow pattern maps for water-butanol two-phase flow were developed based on Capillary number of the continuous phase and Weber number of the dispersed phase, and compared with a previous flow pattern map in the literature. Three main flow pattern groups were observed, including the tubing/threading regime group, the dripping regime and the jetting regime. The geometry confinement and fluid properties affected the viscous shear and interfacial tension forces and therefore their influence on flow pattern transitions was clarified. Besides, in the dripping regime, the dimensionless slug length can be scaled as a function of the flow rate ratio and the Capillary number of the continuous phase.

scholarly journals Chitosan microgels obtained by on-chip crosslinking reaction employing a microfluidic device

2014 ◽  
Vol 1 (1) ◽  
Author(s):  
Vanessa Zamora-Mora ◽  
Diego Velasco ◽  
Rebeca Hernández ◽  
Carmen Mijangos
Keyword(s):  
Sodium Tripolyphosphate ◽  
Mineral Oil ◽  
Continuous Phase ◽  
Crosslinking Reaction ◽  
Flow Focusing ◽  
Inlet Flow ◽  
Flow Rates ◽  
Dispersed Phases ◽  
On Chip ◽  
Average Size

AbstractIn the present work, we report on the preparation of microgels of chitosan crosslinked with sodium tripolyphosphate (TPP) employing the microfluidics technique (MF). To achieve this, several flow focusing geometries were designed and tested. As a first step, a two-inlet flow focusing geometry was employed to emulsify chitosan and the crosslinking reaction was carried out offchip. This procedure did not allow separating the resulting chitosan microgels due to an incomplete crosslinking reaction. A crosslinking reaction on-chip was studied as an alternative. A four-inlet flow focusing geometrywas designed in which three dispersed phases, chitosan 0.25% (w/v), TPP 0.05% (w/v) and acetic acid 1% (v/v) and an continuous phase mineral oil + Span 80 (3% w/v) were employed. The flow rates for the continuous phase were varied from 6.7 to 11.7 μL/min and chitosan microgels were successfully obtained with average diameters from 68 to 42 μm. The average size of the microgels outside the MF device decreased up to ~21% with respect to their size inside the MF device due to partial expulsion of water from the microgels when complete gelation occurred.

scholarly journals Influence of the Continuous and Dispersed Phases on the Symmetry of a Gas Turbine Air-Blast Atomizer

1990 ◽  
Vol 112 (1) ◽  
pp. 44-51 ◽  
Author(s):  
V. G. McDonell ◽  
G. S. Samuelsen
Keyword(s):  
Fuel Injection ◽  
Continuous Phase ◽  
Dispersed Phase ◽  
Volume Flux ◽  
Air Blast ◽  
Current Trends ◽  
Field Symmetry ◽  
Spray Field ◽  
Dispersed Phases ◽  
Radial Spread

Current trends in liquid-fueled practical combustion systems are leaving less tolerance for fuel injection deficiencies such as poor spray field symmetry. The present paper evaluates the symmetry of the flowfield produced by a practical airblast atomizer. Specifically, the influence of both the continuous phase and dispersed phase on the spray field symmetry is assessed. In the present case, asymmetry in volume flux is associated principally with disparities in the injection of the dispersed phase, which is manifested by a maldistribution of larger drops. Asymmetries observed in the continuous phase without the dispersed phase are reduced in magnitude by the presence of the dispersed phase, but still contribute to asymmetry in radial spread of the dispersed phase.

Sign in / Sign up

Export Citation Format

Share Document