scholarly journals Hydrodynamics of fluid around a collapsing bubble in the spark bubble droplet generation process

2014 ◽  
Vol 67 (3) ◽  
pp. 389-417 ◽  
Author(s):  
A. Dadvand ◽  
M. Dawoodian ◽  
B. C. Khoo
Keyword(s):  
Droplet Generation ◽  
Generation Process ◽  
Spark Bubble

scholarly journals Simulation and Validation of Droplet Generation Process for Revealing Three Design Constraints in Electrohydrodynamic Jet Printing

Micromachines ◽  
2019 ◽  
Vol 10 (2) ◽  
pp. 94 ◽  
Author(s):  
Yanqiao Pan ◽  
Liangcai Zeng
Keyword(s):  
Numerical Simulation ◽  
Simulation Model ◽  
High Performance ◽  
Droplet Generation ◽  
Generation Process ◽  
Design Constraints ◽  
Whole Process ◽  
Velocity Magnitude ◽  
Electrohydrodynamic Jet Printing ◽  
Jet Printing

Droplet generation process can directly affect process regulation and output performance of electrohydrodynamic jet (E-jet) printing in fabricating micro-to-nano scale functional structures. This paper proposes a numerical simulation model for whole process of droplet generation of E-jet printing based on the Taylor-Melcher leaky-dielectric model. The whole process of droplet generation is successfully simulated in one whole cycle, including Taylor cone generation, jet onset, jet break, and jet retraction. The feasibility and accuracy of the numerical simulation model is validated by a 30G stainless nozzle with inner diameter ~160 μm by E-jet printing experiments. Comparing numerical simulations and experimental results, period, velocity magnitude, four steps in an injection cycle, and shape of jet in each step are in good agreement. Further simulations are performed to reveal three design constraints against applied voltage, flow rate, and nozzle diameter, respectively. The established cone-jet numerical simulation model paves the way to investigate influences of process parameters and guide design of printheads for E-jet printing system with high performance in the future.

Algorithm for Detecting and Solving the Problem of Under-Filled Pointed Ends Based on 3D Printing Plastic Droplet Generation

2014 ◽  
Author(s):  
Jelena Prša ◽  
Franz Irlinger ◽  
Tim C. Lueth
Keyword(s):  
3D Printing ◽  
Droplet Generation ◽  
Generation Process ◽  
Critical Area ◽  
Final Shape ◽  
Angle Bisector ◽  
Critical Areas ◽  
3D Printed ◽  
Plastic Parts ◽  
Initial Geometry

In this paper the problem of under-filled pointed ends is introduced and mathematically defined. To tackle this problem, we present a new algorithm that detects and fills the critical areas, which arise at the 3D printed plastic parts. While printing the contours and/or infill lines, due to the limitations based on the width of the extruded material, narrow edges and pointed ends remain improperly filled. This eventually results in 3D printed objects with the final geometry that differs greatly from the initial geometry. This paper presents the fundamentals for solving the problem of 3D printing of geometries which contain narrow pointed ends. The critical area of the pointed ends is mathematically defined and, depending on the angle, the formulae for the calculation of under-filled and over-filled areas are given. The newly developed algorithm, based on the 3D Printing plastic droplet generation process, assures that the droplets of the repeating contours are placed at the edges of the contour-segments and by that minimises the potential under-fills. Furthermore, an additional number of droplets is defined, that are either printed in or removed from the under-filled areas in the angle bisector. The proposed algorithm is applied on parts, whose geometry describes pointed ends. The final 3D printed parts are very appealing and their shape resembles the original geometry more than the final shape of the parts without applying the algorithm.

Experimental Investigation of Geometrical Parameters for Gas-Liquid Droplet Generation in Flow-Focusing Configurations

2015 ◽  
Author(s):  
Pooyan Tirandazi ◽  
Carlos H. Hidrovo
Keyword(s):  
Flow Rate ◽  
Liquid Flow ◽  
Liquid Flow Rate ◽  
Liquid Droplet ◽  
Droplet Generation ◽  
Physical Parameters ◽  
Geometrical Parameters ◽  
Generation Process ◽  
Flow Focusing ◽  
Research Attention

Over the last few years considerable research attention has been directed towards droplet-based microfluidic devices because of their numerous applications in chemical and biological fields, to name a few. Specifically, gas-liquid droplet systems are of great importance for applications in which a gaseous phase is required instead of a second liquid phase. In this paper we experimentally investigate the manipulation of water droplets in flow-focusing configurations using a high inertial air stream. Compared to a T-junction geometry, the flow-focusing geometry provides the injection of highly inertial air on both sides of the droplet generation region, producing a more consistent droplet generation process in this type of gas-liquid microfluidic system. For this study, we changed the width of the liquid channel, the air flow rate, and the liquid flow rate in order to experimentally investigate their effects on the flow regime and generation frequency. The interactions of different geometrical and physical parameters produce three distinct flow regimes in the gas-liquid flow rate space (co-flow, jetting, and dripping). The controlled size and generation rate of droplets in this scheme provide the capability for precise and oil-free delivery of discrete microliter volumes of fluid.

SIZE-CONTROLLED DROPLET GENERATION IN A MICROFLUIDIC DEVICE FOR RARE DNA AMPLIFICATION BY OPTIMIZING ITS EFFECTIVE PARAMETERS

2018 ◽  
Vol 18 (01) ◽  
pp. 1850002 ◽  
Author(s):  
ALI LASHKARIPOUR ◽  
ALI ABOUEI MEHRIZI ◽  
MASOUD GOHARIMANESH ◽  
MOHAMMADREZA RASOULI ◽  
SAJAD RAZAVI BAZAZ
Keyword(s):  
Single Molecule ◽  
Dominant Role ◽  
Dna Amplification ◽  
Microfluidic Devices ◽  
Sample Volume ◽  
Droplet Generation ◽  
Droplet Radius ◽  
Generation Process ◽  
Effective Parameters ◽  
Precise Control

Versatility and portability of microfluidic devices play a dominant role in their widespread use by researchers. Droplet-based microfluidic devices have been extensively used due to their precise control over sample volume, and ease of manipulating and addressing each droplet on demand. Droplet-based polymerase chain reaction (PCR) devices are particularly desirable in single DNA amplification. If the droplets are small enough to contain only one DNA molecule, single molecule amplification becomes possible, which can be advantageous in several cases such as early cancer detection. In this work, flow-focusing microfluidic droplet generation’s parameters are numerically investigated and optimized for generating the smallest droplet possible, while considering fabrication limits. Taguchi design of experiment method is used to study the effects of key parameters in droplet generation. By exploiting this approach, a droplet with a radius of 111[Formula: see text]nm is generated using a 3[Formula: see text][Formula: see text]m orifice. Since the governing physics of the droplet generation process is not totally understood yet, by means of analysis of variance (ANOVA) analysis, a generalized linear model (GLM) is proposed to predict the droplet radius, given the values of eight major parameters affecting the droplet size. The proposed model shows a correlation of 95.3% and 64.95% for droplets of radius greater than and lower than 5[Formula: see text][Formula: see text]m, respectively. Finally, the source of this variation of behavior in different size scales is identified.

An Investigation on Mechanism of Droplet Generation in High Inertial Gaseous Flow

2019 ◽  
Author(s):  
Xinyu Yao ◽  
Zhenyu Liu ◽  
Huiying Wu
Keyword(s):  
Gas Flow ◽  
Channel Wall ◽  
Droplet Generation ◽  
Generation Process ◽  
Visualization Experiment ◽  
Gas System ◽  
Inertial Flow ◽  
Detachment Time ◽  
Water Gas ◽  
Droplet Detachment

Abstract Droplet generation involving high inertial gas flow in a T-junction microchannel was experimentally and numerically studied in this work. The effect of high inertial flow on the water droplet generation was investigated based on the obtained results. At various gas Reynold (Re) numbers and liquid Capillary (Ca) numbers, the unique flow regime mapping including squeezing, dripping and jetting was observed. It was found that stable aqueous droplets are generated in the squeezing and dripping flow regimes. Visualization experiment shows that the morphology of droplets generated in the water-gas system is different from that in the traditional water-oil system. As the Re number increases or the Ca number decreases, the droplet length decreases. Increasing both Re number and Ca number can increase the detachment frequency. Based on the 3D VOF simulations, the droplet attachment to one of the channel wall during the pinch-off period and the rebound of liquid phase after droplet detachment was observed. Droplet size, detachment time and droplet generation frequency were then analyzed for the droplet generation. The dominant detachment mechanism during the whole droplet generation process was also discussed in this work.

scholarly journals Flexible Piezoelectric Drop-On-Demand Droplet Generation

2017 ◽  
Author(s):  
Norbert Riefler ◽  
Thomas Wriedt ◽  
Udo Fritsching
Keyword(s):  
Pressure Wave ◽  
Droplet Generation ◽  
Pulse Excitation ◽  
Generation Process ◽  
Two Phase ◽  
On Demand ◽  
Drop On Demand ◽  
Order Of Magnitude ◽  
Droplet Sizes ◽  
Phase Fluid

The size of droplets generated by piezoelectric drop-on-demand (DOD) droplet generators can be varied to a cer-tain degree within one order of magnitude. This variation means that the droplet size is not solely determined by the nozzle diameter, and the droplet generation process is not restricted to drops extruded through a nozzle in conven- tional operation. By varying the electronic driving pulse, different droplet sizes can be obtained. To investigate the interaction of piezoelectric pulse excitation and the finally produced droplets, different approaches are applied. A comparison of a modal analysis of a pure piezo based on mechanical admittance calculations proofs the usability of electrical impedance measurements. This kind of measurements are then compared to finite-element simulations of a coupled piezo system – one as actuator, the other as pressure sensor – to extend the usable methods with the result that the fluid is of minor influence on the modal frequencies. Last, two phase fluid flow simulations with consequent pressure wave evaluations of the fluid show different pressure wave frequency specta than the modalanalysis.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4846

Effect of Intersection Angle and Wettability on Droplet Generation in Microfluidic Flow-Focusing Device

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Saima Iqbal ◽  
Shazia Bashir ◽  
Muhammad Ahsan ◽  
Muhammad Bashir ◽  
Saad Shoukat
Keyword(s):  
Contact Angle ◽  
Droplet Breakup ◽  
Droplet Generation ◽  
Maximum Diameter ◽  
Generation Process ◽  
Flow Focusing ◽  
Intersection Angle ◽  
Droplet Shape ◽  
Vof Model ◽  
Microfluidic Flow

Abstract This article investigates the dynamics of droplet generation process in a microfluidic flow-focusing device under the effect of geometry altered by the intersection angle (φ), which the flanking inlets make with central inlet and wall wettability quantified by the contact angle (θ) using volume of fluid (VOF) model. These parameters have been found to alter the droplet shape and size greatly. The effect of intersection angles has been examined for φ = 15 deg, 30 deg, 45 deg, 60 deg, 90 deg, and 120 deg for generating size-controlled droplets. It was predicted that the diameter of droplet increased with the increase in intersection angle (φ = 15 deg, 30 deg, 45 deg, 60 deg, 90 deg, and 120 deg) and the maximum diameter has been generated at φ = 90. In addition, the wetting characteristics (hydrophilic to hydrophobic) have been studied numerically in detail by changing the contact angle of the dispersed phase with the channel wall ranging from 90 deg to 180 deg. It was indicated that the droplets of rectangular shape are formed in hydrophilic channel by completely wetting the wall when θ ≤ 90 deg. They transform their shape to slightly oval form with the increase in contact angle and start acquiring spherical shape when the channel becomes hydrophobic. Furthermore, Parameters such as dimensionless droplet diameter, droplet shape, and droplet breakup time have also been investigated extensively for flowrate ratios Q = 0.125, 0.25, 0.5, and 1, in order to optimize the microfluidic device.

Modeling of Droplet Generation by a Modified T-Junction Device Using COMSOL

2014 ◽  
Vol 705 ◽  
pp. 112-116 ◽  
Author(s):  
Lei Lei ◽  
Hong Bo Zhang ◽  
Donald J. Bergstrom ◽  
Bing Zhang ◽  
Wen Jun Zhang
Keyword(s):  
Numerical Study ◽  
Cross Flow ◽  
Droplet Generation ◽  
Comsol Multiphysics ◽  
Generation Process ◽  
Flow Conditions ◽  
Key Factors ◽  
Flow Rates ◽  
Junction Device ◽  
Simulation Results

This paper presents a numerical study of the formation of droplets in a novel two-dimensional T-junction device by using a commercial CFD package: COMSOL Multiphysics. Numerical simulations were carried out for different flow conditions. Different flow rates lead to four regimes: continuous flow, droplet generation, detached, and stalled. The capillary number of the cross-flow turns out to be the key factors in the droplet generation process. The simulation results are validated by comparison to the existing experimental data.

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