A Computational Study of Drop Formation in an Axisymmetric Flow-Focusing Device

2006 ◽  
Author(s):  
Ismail Filiz ◽  
Metin Muradoglu
Keyword(s):  
Drop Size ◽  
Viscosity Ratio ◽  
Computational Study ◽  
Axisymmetric Flow ◽  
Front Tracking ◽  
Drop Formation ◽  
Flow Focusing ◽  
Outer Flow ◽  
Flow Rates ◽  
Creation Process

We investigate the formation and dynamics of drops computationally in an axisymetric geometry using a Front-Tracking/Finite-Difference (FT/FD) method. The effects of viscosity ratio between inner and outer liquids on the drop creation process and drop size distribution are examined. It is found that the viscosity ratio critically influences the drop formation process and the final drop distribution. We found that, for small viscosity ratios, i.e., 0.1 < λ < 0.5 drop size is about the size of the orifice and drop distribution is highly monodisperse. When viscosity ratio is increased, i.e., 0.5 < λ < 1 a smaller drop is created just after the main drop. For even higher viscosity ratios, the drop distribution is usually monodisperse but a satellite drop is created in some cases. The effect of the flow rates in the inner jet and the co flowing annulus are also studied. It is found that the drop size gets smaller as Qin / Qout is reduced while keeping the outer flow rate constant.

scholarly journals Controlling Shapes in a Coaxial Flow Focusing Microfluidic Device: Experiments and Theory

Micromachines ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 85
Author(s):  
Romen Rodriguez-Trujillo ◽  
Yu-Han Kim-Im ◽  
Aurora Hernandez-Machado
Keyword(s):  
Microfluidic Device ◽  
Soft Lithography ◽  
Flow Rate Ratio ◽  
Flow Focusing ◽  
Outer Flow ◽  
Flow Rates ◽  
Fluorescein Solution ◽  
Elliptical Section ◽  
Additional Water ◽  
And Control

A coaxial flow focusing PDMS (polydimethylsiloxane) microfluidic device has been designed and manufactured by soft lithography in order to experimentally study a miscible inner flow. We studied a coaxially focused inner flow (formed by an aqueous fluorescein solution) which was fully isolated from all microchannel surfaces by an additional water outer flow. Different flow rates were used to produce a variety of flow ratios and a 3D reconstruction of the cross-section was performed using confocal microscope images. The results showed an elliptical section of the coaxially focused inner flow that changes in shape depending on the flow rate ratio applied. We have also developed a mathematical model that allows us to predict and control the geometry of the coaxially focused inner flow.

Atomization of Liquids by Means of a Rotating Cup

1950 ◽  
Vol 17 (2) ◽  
pp. 145-153 ◽  
Author(s):  
J. O. Hinze ◽  
H. Milborn
Keyword(s):  
Working Conditions ◽  
Drop Size ◽  
Film Formation ◽  
Angular Speed ◽  
The State ◽  
Experimental Results ◽  
Drop Formation ◽  
Dimensionless Groups ◽  
Different Types ◽  
Centrifugal Action

Abstract Liquid, supplied through a stationary tube to the inner part of a rotating cup widening toward a brim, flows viscously in a thin layer toward this brim and is then flung off, all by centrifugal action. The flow within this layer and the disintegration phenomena occurring beyond the brim have been studied, experimentally as well as theoretically. A formula has been derived for the thickness and for the radial velocity of the liquid layer within the cup, which proved to agree reasonably well with experimental results. Three essentially different types of disintegration may take place around and beyond the edge of the cup designated, respectively, by: (a) the state of direct drop formation; (b) the state of ligament formation; and (c) the state of film formation. Which one of these is realized depends upon working conditions. Transition from state (a) into (b), or of state (b) into state (c) is promoted by an increased quantity of supply, an increased angular speed, a decreased diameter of the cup, an increased density, an increased viscosity, and a decreased surface tension of the liquid. The experimental results have been expressed in relationships between relevant dimensionless groups. For the state of ligament formation a semiempirical relationship has been derived between the number of ligaments and dimensionless groups determining the working conditions of the cup. Results of drop-size measurements made for the state of ligament formation as well as for the state of film formation show that atomization by mere rotation of the cup is much more uniform than commonly achieved with pressure atomizers.

Computational Study on Estimating the Surface Heat Transfer Coefficient of Absorber Tube in Solar Parabolic Trough Collector

2013 ◽  
Vol 446-447 ◽  
pp. 1546-1551
Author(s):  
Harshit Saxena ◽  
Arpit Santoki ◽  
Nimish Awalgaonkar ◽  
Arpan Jivani ◽  
Ganni Gowtham ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Solar Radiation ◽  
Computational Study ◽  
Surface Heat ◽  
Parabolic Trough ◽  
Flow Rates ◽  
Surface Heat Transfer Coefficient ◽  
Mass Flow Rates ◽  
The Given

Solar Parabolic Trough collectors are commonly used to harness the solar power for power generating applications involving high temperatures. In the given paper study we have made use of the SolTrace software which uses the Monte Carlo algorithm for finding out the radiation received on the absorber tube of the collector. The computational study was performed taking into account the solar radiation received at Vellore city in India (12.92oN, 79.13oE) as on 16th February 2013. Further a 3D model of the absorber tube used in the parabolic trough collector was created and meshed with the help of the Ansys Gambit software. The absorber tube which we considered for our study is made up of Stainless Steel AISI 302 material. The meshed model so created was then exported to the Ansys Fluent 6.3 software and simulations were performed for different mass flow rates of the fluid. The fluid which we used in the computational analysis study is Therminol 55. The temperature differences for different mass flow rates of the liquid passing through the absorber tube were found out and based on the temperature rise contours plots so obtained, we have plotted the surface heat transfer coefficient for the absorber tube. We also found out the static temperature contour plot for the fluid flowing through the given absorber tube taking into account the heat flux acting on the absorber tube due to the hourly and daily average solar radiation.

scholarly journals Prediction of Droplet Production Speed by Measuring the Droplet Spacing Fluctuations in a Flow-Focusing Microdroplet Generator

Micromachines ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 812 ◽  
Author(s):  
Wen Zeng ◽  
Dong Xiang ◽  
Hai Fu
Keyword(s):  
Fluid Flow ◽  
Efficient Method ◽  
Immiscible Fluids ◽  
Droplet Generation ◽  
Flow Focusing ◽  
Flow Conditions ◽  
Flow Rates ◽  
Wide Range ◽  
Droplet Production ◽  
Monodisperse Droplets

In a flow-focusing microdroplet generator, by changing the flow rates of the two immiscible fluids, production speed can be increased from tens to thousands of droplets per second. However, because of the nonlinearity of the flow-focusing microdroplet generator, the production speed of droplets is difficult to quantitatively study for the typical flow-focusing geometry. In this paper, we demonstrate an efficient method that can precisely predict the droplet production speed for a wide range of fluid flow rates. While monodisperse droplets are formed in the flow-focusing microchannel, droplet spacing as a function of time was measured experimentally. We discovered that droplet spacing changes periodically with time during each process of droplet generation. By comparing the frequency of droplet spacing fluctuations with the droplet production speed, precise predictions of droplet production speed can be obtained for different flow conditions in the flow-focusing microdroplet generator.

Preparation of All-Trans-Retinoic Acid-Loaded mPEG-PLGA Nanoparticles Using Microfluidic Flow-Focusing Device for Controlled Drug Delivery

NANO ◽  
2020 ◽  
Vol 15 (08) ◽  
pp. 2050101
Author(s):  
Mojdeh Safari ◽  
Amir Amani ◽  
Tajudeen Adebileje ◽  
Jafar Ai ◽  
Seyed Mahdi Rezayat ◽  
...  
Keyword(s):  
Particle Size ◽  
Retinoic Acid ◽  
Plga Nanoparticles ◽  
Process Conditions ◽  
Flow Focusing ◽  
Flow Rates ◽  
Trans Retinoic Acid ◽  
All Trans Retinoic Acid ◽  
Microfluidic Flow ◽  
Minimum Particle Size

In recent years, microfluidic devices present unique advantages for the development of a new generation of nanoparticle synthesis method compared to bulk methods. In this study, we report a microfluidic flow-focusing method for the production of all trans retinoic acid (ATRA)-loaded methoxy poly(ethylene glycol)-poly(lactide-coglycolide) (mPEG-PLGA) nanoparticles (NPs). Box–Behnken experimental design (BBD) was applied to optimize of formulation ingredients and process conditions with minimum particle size, maximum drug loading% (DL%) and encapsulation efficiency% (EE%). Polymer concentration, drug concentration and flow rates of solvent (S) and antisolvent (AS) were selected as independent variables. Based on optimization strategy, minimum particle size achieved shows average (SD) particle size of [Formula: see text][Formula: see text]nm with DL of [Formula: see text][Formula: see text]wt.% and EE of [Formula: see text][Formula: see text]wt.%, respectively. While maximum DL has been reported to be [Formula: see text][Formula: see text]wt.% with particle size of [Formula: see text][Formula: see text]nm and EE of [Formula: see text][Formula: see text]wt.%, respectively. Moreover, the results have shown that the AS/S ratio represents the most significant effect on particle size. Indeed, increasing the AS flow rate directly results in generating smaller particles. The AS/S ratio represents the least significant effect on DL%, such that, at fixed flow rates, higher DL was observed at high concentration of drug and lower concentration of polymer. In conclusion, optimization of the ATRA-loaded mPEG-PLGA NPs by BBD yielded in a favorable drug carrier for ATRA that could provide a new treatment modality for different malignancies.

scholarly journals Spray Drop Size and Velocity Measurements in a Swirl-Stabilized Combustor

1991 ◽  
Author(s):  
B. Chehroudi ◽  
M. Ghaffarpour
Keyword(s):  
Drop Size ◽  
Cone Angle ◽  
Hollow Cone ◽  
Flow Rates ◽  
Fuel Droplets ◽  
Radial Profiles ◽  
Fuel Nozzle ◽  
Pass Through ◽  
Yellow Region ◽  
Hollow Cone Spray

A pressure-swirl fuel nozzle generating a hollow-cone spray with nominal cone angle of 30 degrees is used in a swirl-stabilized combustor. The combustor is circular in cross section with swirl plate and fuel nozzle axes aligned and coinciding with the axis of the chamber. Kerosene is injected upward inside the chamber from the fuel nozzle. Separate swirl and dilution air flows are uniformly distributed into the chamber that pass through the honey comb flow straighteners and screens. Calculated swirl number of 1.5 is generated with the design swirl plate exit air velocity of 30 degrees with respect to the chamber axis. Effects of swirl and dilution air flow rates on the shape and stability of the flame are investigated. Stable and classical liquid fuel sheet disintegration zone exists close to the nozzle with no visible light followed by a luminous blue region and a mixed blue/yellow region that subsequently turns into yellow for most of the part in the flame. A Phase Doppler Particle Analyzer (PDPA) is used to measure drop size, mean and rms axial velocity for two cases of with and without combustion at six different axial locations from the nozzle. For the no-combustion case all air and fuel flow rates were kept at the same values as the combusting spray condition. Results for mean axial drop velocity profiles indicate widening of the spray due to combustion while the magnitudes of the peak velocities are slightly increased. No measurements inside the hollow-cone spray are possible due to burning of fuel droplets. Drop turbulence decreases due to combination of increase in gas kinematic viscosity and elimination of small drops at high temperatures. Sauter Mean Diameter (SMD) radial profiles at all axial locations increase with combustion due to preferential burning of small drops.

Parametric study of droplet size in an axisymmetric flow-focusing capillary device

2020 ◽  
Vol 28 (4) ◽  
pp. 1016-1022
Author(s):  
Mostafa Rahimi ◽  
Sajad Yazdanparast ◽  
Pouya Rezai
Keyword(s):  
Droplet Size ◽  
Parametric Study ◽  
Axisymmetric Flow ◽  
Flow Focusing

scholarly journals Microfluidic droplet generation based on non-embedded co-flow-focusing using 3D printed nozzle

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Adrien Dewandre ◽  
Javier Rivero-Rodriguez ◽  
Youen Vitry ◽  
Benjamin Sobac ◽  
Benoit Scheid
Keyword(s):  
Stokes Equations ◽  
Axisymmetric Flow ◽  
Droplet Generation ◽  
Droplet Radius ◽  
Planar Geometry ◽  
Flow Focusing ◽  
Glass Capillary ◽  
New Device ◽  
3D Printed ◽  
Droplet Generators

AbstractMost commercial microfluidic droplet generators rely on the planar flow-focusing configuration implemented in polymer or glass chips. The planar geometry, however, suffers from many limitations and drawbacks, such as the need of specific coatings or the use of dedicated surfactants, depending on the fluids in play. On the contrary, and thanks to their axisymmetric geometry, glass capillary-based droplet generators are a priori not fluid-dependent. Nevertheless, they have never reached the market because their assembly requires fastidious and not scalable fabrication techniques. Here we present a new device, called Raydrop, based on the alignment of two capillaries immersed in a pressurized chamber containing the continuous phase. The dispersed phase exits one of the capillaries through a 3D-printed nozzle placed in front of the extraction capillary for collecting the droplets. This non-embedded implementation of an axisymmetric flow-focusing is referred to non-embedded co-flow-focusing configuration. Experimental results demonstrate the universality of the device in terms of the variety of fluids that can be emulsified, as well as the range of droplet radii that can be obtained, without neither the need of surfactant nor coating. Additionally, numerical computations of the Navier-Stokes equations based on the quasi-steadiness assumption allow to provide an explanation to the underlying mechanism behind the drop formation and the mechanism of the dripping to jetting transition. Excellent predictions were also obtained for the droplet radius, as well as for the dripping-jetting transition, when varying the geometrical and fluid parameters, showing the ability of this configuration to enventually enhance the dripping regime. The monodispersity ensured by the dripping regime, the robustness of the fabrication technique, the optimization capabilities from the numerical modelling and the universality of the configuration confer to the Raydrop technology a very high potential in the race towards high-throughput droplet generation processes.

Limits of Parabolic Flow Theory in Microfluidic Particle Separation: A Computational Study

2013 ◽  
Author(s):  
Ryan S. Pawell ◽  
Tracie J. Barber ◽  
David W. Inglis ◽  
Robert A. Taylor
Keyword(s):  
Computational Study ◽  
Lateral Displacement ◽  
Particle Separation ◽  
Flow Profile ◽  
Flow Rates ◽  
Deterministic Lateral Displacement ◽  
Flow Development ◽  
Separation Threshold ◽  
Parabolic Flow ◽  
Size Based Separation

Microfluidic particle separation technologies are useful for enriching rare cell populations for academic and clinical purposes. In order to separate particles based on size, deterministic lateral displacement (DLD) arrays are designed assuming that the flow profile between posts is parabolic or shifted parabolic (depending on post geometry). The design process also assumes the shape of the normalized flow profile is speed-invariant. The work presented here shows flow profile shapes vary, in arrays with circular and triangular posts, from this assumption at practical flow rates (10 < Re < 100). The root-mean-square error (RMSE) of this assumption in the circular post arrays peaked at 0.144. The RMSE in the triangular post array peaked at 0.136. Flow development occurred more rapidly in circular post arrays when compared to triangular post arrays. Additionally, the changes in critical bumping diameter (DCB) the DLD design metric used to calculate the size-based separation threshold were examined for 10 different row shift fractions (FRS). These errors correspond to a DCB that varies as much as 11.7% in the circular post arrays and 15.1% in the triangular post arrays.

Drop Size and Velocity Measurements in an Electrostatically Produced Hydrocarbon Spray

1998 ◽  
Vol 120 (3) ◽  
pp. 580-585 ◽  
Author(s):  
J. S. Shrimpton ◽  
A. J. Yule
Keyword(s):  
Velocity Component ◽  
Drop Size ◽  
Average Diameter ◽  
Low Flow ◽  
Drop Diameter ◽  
Specific Charge ◽  
Velocity Measurements ◽  
Axial Velocity Component ◽  
Flow Rates ◽  
Injection Techniques

Liquid hydrocarbons are difficult to atomize electrostatically at practical flow rates due to their high resistivities and low concentration of charge carriers. However special “charge injection” techniques have been used in this investigation to produce combustible sprays of oils. An experimental investigation of the drop size and velocity distributions within a charged kerosine spray is presented, using a PDA system and photographic methods. Bimodal size distributions are found with a central core of larger drops or ligament formations near the nozzle surrounded by a sheath of smaller drops. Because of the bimodal character the concept of average diameter for the spray is difficult to apply so that there is little practical use defining a relationship between mean drop diameter and mean specific charge without a knowledge of a relationship between charge and size of individual drops. Examination of the velocity component distributions showed the processes which control the two-zone characteristics of the spray. The larger drops have a high inertia and were less deflected by the space charge force within the spray and it is argued that the larger drops possess a smaller specific charge compared with the smaller drops which reinforces the tendency for the large drops to remain along the spray centreline. For the smaller drops the converse is the case, to the extent that at low flow rates their trajectories have a negligible axial velocity component and recirculation toward the earthed injector body is observed.

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