scholarly journals Liquid–Liquid Flows with Non-Newtonian Dispersed Phase in a T-Junction Microchannel

Micromachines ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 335
Author(s):  
Anna Yagodnitsyna ◽  
Alexander Kovalev ◽  
Artur Bilsky
Keyword(s):  
Flow Pattern ◽  
Dynamic Viscosity ◽  
Slug Flow ◽  
Shear Thinning ◽  
Continuous Phase ◽  
Immiscible Liquid ◽  
Dispersed Phase ◽  
Effective Dynamic ◽  
Liquid Flows ◽  
Shear Thinning Fluid

Immiscible liquid–liquid flows in microchannels are used extensively in various chemical and biological lab-on-a-chip systems when it is very important to predict the expected flow pattern for a variety of fluids and channel geometries. Commonly, biological and other complex liquids express non-Newtonian properties in a dispersed phase. Features and behavior of such systems are not clear to date. In this paper, immiscible liquid–liquid flow in a T-shaped microchannel was studied by means of high-speed visualization, with an aim to reveal the shear-thinning effect on the flow patterns and slug-flow features. Three shear-thinning and three Newtonian fluids were used as dispersed phases, while Newtonian castor oil was a continuous phase. For the first time, the influence of the non-Newtonian dispersed phase on the transition from segmented to continuous flow is shown and quantitatively described. Flow-pattern maps were constructed using nondimensional complex We0.4·Oh0.6 depicting similarity in the continuous-to-segmented flow transition line. Using available experimental data, the proposed nondimensional complex is shown to be effectively applied for flow-pattern map construction when the continuous phase exhibits non-Newtonian properties as well. The models to evaluate an effective dynamic viscosity of a shear-thinning fluid are discussed. The most appropriate model of average-shear-rate estimation based on bulk velocity was chosen and applied to evaluate an effective dynamic viscosity of a shear-thinning fluid. For a slug flow, it was found that in the case of shear-thinning dispersed phase at low flow rates of both phases, a jetting regime of slug formation was established, leading to a dramatic increase in slug length.

Experimental Investigation of Flow-Induced Vibration in Gas/Shear-Thinning Liquid Flows in Vertical Pipe

2020 ◽  
Author(s):  
Ruinan Lin ◽  
Ke Wang ◽  
Qing Li ◽  
Narakorn Srinil ◽  
Fangjun Shi
Keyword(s):  
Newtonian Fluid ◽  
Industrial Process ◽  
Flow Region ◽  
Shear Thinning ◽  
Maximum Energy ◽  
Internal Diameter ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Liquid Flows ◽  
Shear Thinning Fluid

Abstract The non-Newtonian shear-thinning fluid widely exists in the industrial process and the rheology exerts a significant influence on the flow pattern transition and flow-induced vibration (FIV). However, studies on the rheology effect of the liquid phase in the vertical upward two-phase flows are quite lacking due to the complexity of non-Newtonian fluid properties. In the present study, the vertical upward gas/shear-thinning liquid flows experiments are conducted on a rigid acrylic pipe with an internal diameter of 20 mm. Three different Carboxymethyl Cellulose (CMC) solutions are used as the non-Newtonian fluid, aimed at capturing a two-phase flow regime transition including the vertical slug, churn and annular flows. The results indicate that the maximum energy spectral densities of vibration occur at the slug-to-churn flow transition boundary at low liquid velocities and the annular flow region under high liquid velocities, respectively. The effects of the rheology of the shear-thinning fluid in terms of the flow patterns and FIV are also presented and discussed.

Liquid-Liquid Flow Patterns in Microchannels

2017 ◽  
Author(s):  
Zhen Cao ◽  
Zan Wu ◽  
Mehdi Sattari Najafabadi ◽  
Bengt Sunden
Keyword(s):  
Aspect Ratio ◽  
Flow Pattern ◽  
Liquid Flow ◽  
Flow Patterns ◽  
Continuous Phase ◽  
Hydraulic Diameter ◽  
Intermittent Flow ◽  
Dimensionless Number ◽  
Dispersed Phase ◽  
Flow Pattern Map

In the present work, liquid-liquid flow patterns positioned 40 mm downstream the inlet of microchannels were experimentally investigated, including the effect of hydraulic diameter (Dh), liquid properties, aspect ratio of cross section (a) and inlet configuration. Deionized water, butanol, toluene and hexane were selected as probe fluids with water as the continuous phase. Cross-inlet microchannels of 200 μm * 200 μm (Dh = 200 μm), 400 μm * 400 μm (Dh = 400 μm), 600 μm * 600 μm (Dh = 600 μm) and 600 μm * 300 μm (Dh = 400 μm) as well as a T-inlet microchannel of 600 μm * 300 μm (Dh = 400 μm) were tested. For the tests in the microchannels of Dh = 600 μm and 400 μm, the superficial velocities of the dispersed phase and continuous phase varied between 0.3 mm/s and 12 mm/s and between 0.2 mm/s and 50 mm/s, while in the microchannel of Dh = 200 μm the superficial velocities of the dispersed phase and continuous phase ranged from 0.3 mm/s to 21 mm/s and from 0.2 mm/s to 150 mm/s. Annular flow, deformed interface flow, slug flow, intermittent flow, droplet and slug train flow and droplet flow were detected in the experiment. It shows that flow patterns depend on the hydraulic diameter, liquid properties, inlet configuration and aspect ratio significantly. Dimensionless analysis was employed to develop universal flow pattern maps regardless of the hydraulic diameter and liquid properties. It is indicated that an acceptable universal flow pattern map was derived based on the redefined dimensionless number Rei0.2 *Wei0.4, especially for the boundaries of the slug-droplet transitions, which are independent on the hydraulic diameter to some extent. The other dimensionless number Wei*Ohi worked rather effectively to develop a universal flow pattern map independent on liquid properties. The boundaries of the flow pattern transitions in different liquid-liquid flow almost overlap with each other.

Water-Oil Flow in Square Microchannels With a Crossed Junction

2018 ◽  
Author(s):  
Zhen Cao ◽  
Zan Wu ◽  
Jin-yuan Qian ◽  
Bengt Sunden
Keyword(s):  
Slug Flow ◽  
Annular Flow ◽  
Flow Patterns ◽  
Continuous Phase ◽  
High Flow ◽  
Low Flow ◽  
Dispersed Phase ◽  
Flow Rates ◽  
Droplet Flow ◽  
Oil Flow

In the present study, water-oil flow patterns and slug hydrodynamics were experimentally studied in square glass microchannels with various hydraulic diameters (Dh = 600 μm, 400 μm, 200 μm). The aqueous phase is the continuous phase while the organic phase is the dispersed phase. The ranges of flow rates of the continuous phase and the dispersed phase are 0–200 ml/h and 0–12 ml/h, 0–120 ml/h and 0–6 ml/h, and 0–60 ml/h and 0–2 ml/h in the microchannels with Dh = 600 μm, 400 μm and 200 μm, respectively. The results show that the hydraulic diameter has significant effects on flow patterns and three main flow patterns are observed, i.e., annular flow, slug flow and droplet flow. Generally, annular flow appeared at high flow rates of the dispersed phase and low flow rates of the continuous phase, while droplet flow appeared at low flow rates of the dispersed phase and high flow rates of the continuous phase. However, slug flow existed at comparable flow rates of the continuous and dispersed phases. A dimensionless analysis is carried out and a new dimensionless group including Weber number and Reynolds number is derived. The new defined dimensionless group performs well to develop a general flow pattern map. In addition, slug flow hydrodynamics are investigated as well in the present study, considering the slug length and slug velocity. Based on the present experimental results, a new scaling law is proposed to predict the slug length and it shows a good agreement with the experimental results. It has been widely reported that slug velocities depend linearly on the total flow rates of the two phases, which is consistent with the present study. The linear law provides a good prediction of the experimental slug velocities but different slopes are suggested in microchannels with different hydraulic diameters.

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 Modeling the motion of a Taylor bubble in a microchannel through a shear-thinning fluid

2021 ◽  
Vol 312 ◽  
pp. 05006
Author(s):  
Andrea Aquino ◽  
Davide Picchi ◽  
Pietro Poesio
Keyword(s):  
Shear Thinning ◽  
Current Theory ◽  
Continuous Phase ◽  
Bubble Velocity ◽  
Recent Theory ◽  
Taylor Bubble ◽  
Lubrication Film ◽  
Shear Thinning Fluids ◽  
Validity Range ◽  
Shear Thinning Fluid

Applications of multiphase flows in microchannels as chemical and biological reactors and cooling systems for microelectronic devices typically present liquid slugs alternated with bubbles of elongated shape, the Taylor bubbles. These occupy almost entirely the cross-section of the channel and present a hemispherical front and a liquid layer, the lubrication film, which separates the gas from the tube wall. The Taylor bubble perturbs the surrounding fluids activating many transport mechanisms in the proximity of the gas-liquid interface; therefore, the bubble motion significantly influences the heat and mass transfer rates. Although many works deeply investigate the bubble hydrodynamics in Newtonian fluids, the knowledge about the relation between bubble hydrodynamics and rheological properties is insufficient, and studies where the continuous phase exhibits a shear-thinning behavior are missing. Our numerical analysis tries to fill this gap by investigating the motion of a Taylor bubble in a non-Newtonian shear-thinning fluid, modeled by the Carreau viscosity model. First, we validate the results against the Newtonian case and a recent theory for shear-thinning fluids (Picchi et al., Journal of Fluid Mechanics, 2021, 918). Then, we investigate the bubble hydrodynamics far from the validity range of the current models. Finally, we study the scaling of the bubble velocity and lubrication film thickness, extending the current theory to shear-thinning fluids.

scholarly journals Generation and Dynamics of Janus Droplets in Shear-Thinning Fluid Flow in a Double Y-Type Microchannel

Micromachines ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 149
Author(s):  
Fan Bai ◽  
Hongna Zhang ◽  
Xiaobin Li ◽  
Fengchen Li ◽  
Sang Woo Joo
Keyword(s):  
Surface Tension ◽  
Formation Mechanism ◽  
Computational Study ◽  
Shear Thinning ◽  
Droplet Formation ◽  
Continuous Phase ◽  
Viscous Force ◽  
Rheological Parameters ◽  
Janus Droplet ◽  
Shear Thinning Fluid

Droplets composed of two different materials, or Janus droplets, have diverse applications, including microfluidic digital laboratory systems, DNA chips, and self-assembly systems. A three-dimensional computational study of Janus droplet formation in a double Y-type microfluidic device filled with a shear-thinning fluid is performed by using the multiphaseInterDyMFoam solver of the OpenFOAM, based on a finite-volume method. The bi-phase volume-of-fluid method is adopted to track the interface with an adaptive dynamic mesh refinement for moving interfaces. The formation of Janus droplets in the shear-thinning fluid is characterized in five different states of tubbing, jetting, intermediate, dripping and unstable dripping in a multiphase microsystem under various flow conditions. The formation mechanism of Janus droplets is understood by analyzing the influencing factors, including the flow rates of the continuous phase and of the dispersed phase, surface tension, and non-Newtonian rheological parameters. Studies have found that the formation of the Janus droplets and their sizes are related to the flow rate at the inlet under low capillary numbers. The rheological parameters of shear-thinning fluid have a significant impact on the size of Janus droplets and their formation mechanism. As the apparent viscosity increases, the frequency of Janus droplet formation increases, while the droplet volume decreases. Compared with Newtonian fluid, the Janus droplet is more readily generated in shear-thinning fluid due to the interlay of diminishing viscous force, surface tension, and pressure drop.

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.

Capillary pressure, osmotic pressure and bubble contact areas in foams

Soft Matter ◽  
2021 ◽  
Author(s):  
Reinhard Höhler ◽  
Jordan Seknagi ◽  
Andrew Kraynik
Keyword(s):  
Osmotic Pressure ◽  
Capillary Pressure ◽  
Continuous Phase ◽  
Dispersed Phase ◽  
Average Pressure ◽  
Contact Areas ◽  
The Difference

The capillary pressure of foams and emulsions is the difference between the average pressure in the dispersed phase and the pressure in the continuous phase.

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