Investigation on the Droplet Formation Time With Xanthan Gum Solutions at a T-Junction

2012 ◽  
Author(s):  
Zhipeng Gu ◽  
Jong-Leng Liow ◽  
Guofeng Zhu
Keyword(s):  
Flow Rate ◽  
Xanthan Gum ◽  
Critical Concentration ◽  
Droplet Diameter ◽  
Droplet Formation ◽  
Continuous Phase ◽  
Formation Time ◽  
Drop Formation ◽  
Dispersed Phase ◽  
Phase Flow

Xanthan gum solutions with various concentrations were used as the dispersed phase to study the formation time for drop formation at a T-junction. Two critical concentrations (0.05 and 0.2 wt%) of xanthan gum solutions were observed resulting in three distinct regimes. The droplet diameter increased with increasing xanthan gum concentration within each regime but the transition through each critical concentration was accompanied by a significant reduction in the droplet size. Experimental results showed that the droplet formation time decreased exponentially with increasing continuous phase flow rate. It was also found that the formation time was reduced with increasing dispersed phase flow rate. Xanthan gum solutions with a higher concentration within each regime resulted in a longer formation time, and there was a decrease in the formation time at each critical concentration. The formation time consists of growth and breakup stages and the effect of xanthan gum concentration on each stage was examined.

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 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.

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 Holdup and characteristic velocity in a pulsed packed extraction column

2020 ◽  
Vol 9 (8) ◽  
pp. e674982543
Author(s):  
Jarlon Conceição da Costa ◽  
Luiz Mário Nelson de Góis ◽  
Silvana Mattedi e Silva
Keyword(s):  
Flow Rate ◽  
Water System ◽  
Continuous Phase ◽  
Liquid System ◽  
Operating Conditions ◽  
Extraction Column ◽  
Dispersed Phase ◽  
Internal Diameter ◽  
Phase Flow ◽  
Characteristic Velocity

The present work aims to evaluate the hydrodynamics of a pulsed packed extractor, with an internal diameter of 0.026m and a length of 1.0m, using the liquid butanol-water system. Thus, the basic parameters obtained for the hydrodynamic study of the extraction column in question as dispersed phase, slip velocity, characteristic velocity and flooding point. The methodology used in the work consisted of determining the holdup fraction of the dispersed phase, obtained through tests of simultaneous interruptions in the column feedings. The effects of frequency pulsation, dispersed phase flow rate and continuous phase flow rate investigated in the analysis of these parameters. New empirical correlations derived from the predictions of the parameters studied obtained in terms of operating variables and physical properties of the liquid system involved. The average absolute value of the relative error (AARE) was always below 5.6%. Good agreement between calculated and experimental results observed for all investigated operating conditions.

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.

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 Prediction Models of Droplet Characteristics Based on the Locally Convergent Configurations in PMMA Microchips

2021 ◽  
Vol 2097 (1) ◽  
pp. 012027
Author(s):  
Zhongxin Liu ◽  
Zhiliang Wang ◽  
Chao Wang ◽  
Jinsong Zhang
Keyword(s):  
Flow Rate ◽  
Relative Position ◽  
Prediction Models ◽  
Continuous Phase ◽  
Lubricating Oil ◽  
Flow Rate Ratio ◽  
Phase Flow ◽  
Exponential Relationship ◽  
Two Phase ◽  
Relationship Of

Abstract This paper novel designed the local convergence configuration in the coaxial channels to study the two-phase flow (lubricating oil (continuous phase, flow rate Q c)/deionized water (dispersed phase, flow rate Q d)). Two geometric control variables, the relative position (x) and tapering characteristics (α), had the different effects on the droplet formation. The increase of relative position x caused the higher frequency and finer droplets, and the increase of convergence angle α, took the opposite effects. The results indicated that the equivalent dimensionless droplet length Ld/Wout and the flow rate ratio Qd/Qc had an exponential relationship of about 1/2. Similarly, it was found that the dispersed droplets generating frequency and the two-phase capillary number, CaTP = uTPμc/σ, had an exponential relationship. The advantage of the convergent configurations in micro-channel was the size and efficiency of droplet generation was very favorable to be controlled by α and x.

Numerical Analysis of Junction Point Pressure during Droplet Formation in Y-Junction Microchannel

2013 ◽  
Vol 481 ◽  
pp. 241-246
Author(s):  
Zhao Miao Liu ◽  
Li Kun Liu
Keyword(s):  
Numerical Simulation ◽  
Three Dimensional ◽  
Droplet Formation ◽  
Continuous Phase ◽  
Contact Angles ◽  
Junction Point ◽  
Dispersed Phase ◽  
Wetting Property ◽  
Point Pressure ◽  
Pressure Changes

Junction point pressure changes during droplet formation in Y-junction microchannels with differed Y-angles, wetting property and capillary number of the liquid by using a three dimensional numerical simulation. The pressure of the junction point fluctuates throughout the droplet formation process, and it can be used to depict exactly and directly different stages of droplet in microchannels. And the pressure of junctions with different Y-angles of microchannel, different contact angles of dispersed phase with the surface, and different capillary numbers of continuous phase could thus be investigated via the droplet formation mechanism.

scholarly journals Experimental Study on the Effect of Locally Convergent Configurations on the Flow Pattern in PMMA Microchips

2021 ◽  
Vol 2097 (1) ◽  
pp. 012006
Author(s):  
Jinsong Zhang ◽  
Zhongxin Liu ◽  
Chao Wang ◽  
Zhiliang Wang
Keyword(s):  
Flow Rate ◽  
Rectangular Cross Section ◽  
Continuous Phase ◽  
Lubricating Oil ◽  
Phase Flow ◽  
Two Phase ◽  
Convergence Angle ◽  
Syringe Needle ◽  
Micro Flow ◽  
Two Parameters

Abstract The geometries of micro-channel play a key role in forming of digital droplets, and can be real-time or effective controlling methodologies. Local convergence regions are designed in the rectangular cross-section channels on PMMA microchips, in which two-phase coaxial jets are introduced by inserting a syringe needle. The two-phase flow (lubricating oil (continuous phase, flow rate Q c)/deionized water (dispersed phase, flow rate Q d)) is considered. Two geometric control variables, the relative position (needle displacement x) and tapering characteristics (convergence angle α), are naturally adopted to discribe such geometry configurations. The micro-flow under the change of these two parameters is mainly studied in this paper. Four kinds of characteristic flow patterns, namely, sausages, slug, dripping and jetting, are found in the experiment, and their occurring parameters and developing dynamic characteristics are discussed. The experiment shows that the increase of inner needle displacement x can produce higher frequency and finer droplets, which is in consistent with our previous results obtained in round tube experiments and simulations. While increasing the convergence angle α, contrarily, takes opposite effects.

Numerical Simulation of Micro-Droplet Formation in a Coflowing Liquid Using Front Tracking Method

2006 ◽  
Author(s):  
Jinsong Hua ◽  
Jing Lou ◽  
Baili Zhang
Keyword(s):  
Front Tracking ◽  
Droplet Formation ◽  
Continuous Phase ◽  
Tension Force ◽  
Drop Formation ◽  
Interface Tension ◽  
Flowing Fluid ◽  
Tracking Method ◽  
Front Tracking Method ◽  
Flowing System

Micro-droplets can be formed when a disperse liquid is injected via a needle nozzle into another immiscible co-flowing fluid. The mode of droplet formation depends on many factors such as liquid flow rates of the inner disperse phase and outer continuous phase, liquid viscosity, nozzle dimensions, interface tension force, etc. In this paper, the drop formation in a co-flowing system is simulated numerically using front tracking method to investigate the drop formation mechanism, which is very critical in the design of micro-fluidic devices for generating micro-droplets in a controllable manner. One set of Navier-Stokes equations for both liquid phases are solved numerically on a fixed Eulerian two-dimensional cylindrical coordinate mesh to account for the flow dynamics, and the front tracking method is applied to track the movement of the interface between the two immiscible liquids as well as the surface tension force. In this set of governing equations for modeling, the effects of flow inertial, capillary, viscous, and gravitational forces are all accounted to explore the droplet formation modes and dynamics in co-flowing system. The simulations reasonably predict the process of droplet formation in the co-flowing liquid. In addition, the effects of the continuous phase flow speed, viscosity and the interface tension force on droplet formation are investigated.

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