Editorial

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Editorial for the Special Issue on Micromachines for Non-Newtonian Microfluidics

by Lanju Mei and Shizhi Qian

Micromachines 2022, 13(6), 906; https://doi.org/10.3390/mi13060906 - 08 Jun 2022

Cited by 1 | Viewed by 1231

Microfluidics has seen a remarkable growth over the past few decades, with its extensive applications in engineering, medicine, biology, chemistry, etc [...] Full article

(This article belongs to the Special Issue Non-Newtonian Microfluidics)

Research

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10 pages, 2044 KiB

Open AccessArticle

The Effects of Viscoelasticity on Droplet Migration on Surfaces with Wettability Gradients

by Ying Jun Ren and Sang Woo Joo

Micromachines 2022, 13(5), 729; https://doi.org/10.3390/mi13050729 - 30 Apr 2022

Cited by 5 | Viewed by 1427

Abstract

A finite-volume method based on the OpenFOAM is used to numerically study the factors affecting the migration of viscoelastic droplets on rigid surfaces with wettability gradients. Parameters investigated include droplet size, relaxation time, solvent viscosity, and polymer viscosity of the liquid comprising droplets. [...] Read more.

A finite-volume method based on the OpenFOAM is used to numerically study the factors affecting the migration of viscoelastic droplets on rigid surfaces with wettability gradients. Parameters investigated include droplet size, relaxation time, solvent viscosity, and polymer viscosity of the liquid comprising droplets. The wettability gradient is imposed numerically by assuming a linear change in the contact angle along the substrate. As reported previously for Newtonian droplets, the wettability gradient induces spontaneous migration from hydrophobic to hydrophilic region on the substrate. The migration of viscoelastic droplets reveals the increase in the migration speed and distance with the increase in the Weissenberg number. The increase in droplet size also shows the increase in both the migration speed and distance. The increase in polymer viscosity exhibits the increase in migration speed but the decrease in migration distance. Full article

(This article belongs to the Special Issue Non-Newtonian Microfluidics)

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12 pages, 2536 KiB

Open AccessArticle

The Effect of Surface Wettability on Viscoelastic Droplet Dynamics under Electric Fields

by Bo Sen Wei and Sang Woo Joo

Micromachines 2022, 13(4), 580; https://doi.org/10.3390/mi13040580 - 07 Apr 2022

Cited by 4 | Viewed by 2139

Abstract

The effects of surface wettability and viscoelasticity on the dynamics of liquid droplets under an electric field are studied experimentally. A needle-plate electrode system is used as the power source to polarize a dielectric plate by the corona discharge emitted at the needle [...] Read more.

The effects of surface wettability and viscoelasticity on the dynamics of liquid droplets under an electric field are studied experimentally. A needle-plate electrode system is used as the power source to polarize a dielectric plate by the corona discharge emitted at the needle electrode, creating a new type of steerable electric field realized. The dynamics of droplets between the dielectric plate and a conductive substrate include three different phenomena: equilibrium to a stationary shape on substrates with higher wettability, deformation to form a bridge between the top acrylic plate and take-off on the substrates with lower wettability. Viscoelastic droplets differ from water in the liquid bridge and takeoff phenomena in that thin liquid filaments appear in viscoelastic droplets, not observed for Newtonian droplets. The equilibrated droplet exhibits more pronounced heights for Newtonian droplets compared to viscoelastic droplets, with a decrease in height with the increase in the concentration of the elastic constituent in the aqueous solution. In the take-off phenomenon, the time required for the droplet to contact the upper plate decreases with the concentration of the elastic constituent increases. It is also found that the critical voltage required for the take-off phenomenon to occur decreases as the elasticity increases. Full article

(This article belongs to the Special Issue Non-Newtonian Microfluidics)

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21 pages, 7601 KiB

Open AccessArticle

Calculation of Effective Thermal Conductivity for Human Skin Using the Fractal Monte Carlo Method

by Guillermo Rojas-Altamirano, René O. Vargas, Juan P. Escandón, Rubén Mil-Martínez and Alan Rojas-Montero

Micromachines 2022, 13(3), 424; https://doi.org/10.3390/mi13030424 - 10 Mar 2022

Cited by 10 | Viewed by 2778

Abstract

In this work, an effective thermal conductivity (ETC) for living tissues, which directly affects the energy transport process, is determined. The fractal scaling and Monte Carlo methods are used to describe the tissue as a porous medium, and blood is considered a Newtonian [...] Read more.

In this work, an effective thermal conductivity (ETC) for living tissues, which directly affects the energy transport process, is determined. The fractal scaling and Monte Carlo methods are used to describe the tissue as a porous medium, and blood is considered a Newtonian and non-Newtonian fluid for comparative and analytical purposes. The effect of the principal variables—such as fractal dimensions

D_{T}

and

D_{f}

, porosity, and the power-law index, n—on the temperature profiles as a function of time and tissue depth, for one- and three-layer tissues, besides temperature distribution, are presented. ETC was improved by considering high tissue porosity, low tortuosity, and shear-thinning fluids. In three-layer tissues with different porosities, perfusion with a non-Newtonian fluid contributes to the understanding of the heat transfer process in some parts of the human body. Full article

(This article belongs to the Special Issue Non-Newtonian Microfluidics)

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26 pages, 5932 KiB

Open AccessArticle

Transient Two-Layer Electroosmotic Flow and Heat Transfer of Power-Law Nanofluids in a Microchannel

by Shuyan Deng and Tan Xiao

Micromachines 2022, 13(3), 405; https://doi.org/10.3390/mi13030405 - 01 Mar 2022

Cited by 7 | Viewed by 2270

Abstract

To achieve the optimum use and efficient thermal management of two-layer electroosmosis pumping systems in microdevices, this paper studies the transient hydrodynamical features in two-layer electroosmotic flow of power-law nanofluids in a slit microchannel and the corresponding heat transfer characteristics in the presence [...] Read more.

To achieve the optimum use and efficient thermal management of two-layer electroosmosis pumping systems in microdevices, this paper studies the transient hydrodynamical features in two-layer electroosmotic flow of power-law nanofluids in a slit microchannel and the corresponding heat transfer characteristics in the presence of viscous dissipation. The governing equations are established based on the Cauchy momentum equation, continuity equation, energy equation, and power-law nanofluid model, which are analytically solved in the limiting case of two-layer Newtonian fluid flow by means of Laplace transform and numerically solved for two-layer power-law nanofluid fluid flow. The transient mechanism of adopting conducting power-law nanofluid as a pumping force and that of pumping nonconducting power-law nanofluid are both discussed by presenting the two-layer velocity, flow rates, temperature, and Nusselt number at different power-law rheology, nanoparticle volume fraction, electrokinetic width and Brinkman number. The results demonstrate that shear thinning conducting nanofluid represents a promising tool to drive nonconducting samples, especially samples with shear thickening features. The increase in nanoparticle volume fraction promotes heat transfer performance, and the shear thickening feature of conducting nanofluid tends to suppress the effects of viscous dissipation and electrokinetic width on heat transfer. Full article

(This article belongs to the Special Issue Non-Newtonian Microfluidics)

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15 pages, 4759 KiB

Open AccessArticle

Viscoelastic Particle Focusing and Separation in a Spiral Channel

by Haidong Feng, Alexander R. Jafek, Bonan Wang, Hayden Brady, Jules J. Magda and Bruce K. Gale

Micromachines 2022, 13(3), 361; https://doi.org/10.3390/mi13030361 - 25 Feb 2022

Cited by 11 | Viewed by 2407

Abstract

As one type of non-Newtonian fluid, viscoelastic fluids exhibit unique properties that contribute to particle lateral migration in confined microfluidic channels, leading to opportunities for particle manipulation and separation. In this paper, particle focusing in viscoelastic flow is studied in a wide range [...] Read more.

As one type of non-Newtonian fluid, viscoelastic fluids exhibit unique properties that contribute to particle lateral migration in confined microfluidic channels, leading to opportunities for particle manipulation and separation. In this paper, particle focusing in viscoelastic flow is studied in a wide range of polyethylene glycol (PEO) concentrations in aqueous solutions. Polystyrene beads with diameters from 3 to 20 μm are tested, and the variation of particle focusing position is explained by the coeffects of inertial flow, viscoelastic flow, and Dean flow. We showed that particle focusing position can be predicted by analyzing the force balance in the microchannel, and that particle separation resolution can be improved in viscoelastic flows. Full article

(This article belongs to the Special Issue Non-Newtonian Microfluidics)

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17 pages, 2834 KiB

Open AccessArticle

Dynamics of Tri-Hybrid Nanoparticles in the Rheology of Pseudo-Plastic Liquid with Dufour and Soret Effects

by Enran Hou, Fuzhang Wang, Umar Nazir, Muhammad Sohail, Noman Jabbar and Phatiphat Thounthong

Micromachines 2022, 13(2), 201; https://doi.org/10.3390/mi13020201 - 27 Jan 2022

Cited by 43 | Viewed by 2414

Abstract

The rheology of different materials at the micro and macro levels is an area of great interest to many researchers, due to its important physical significance. Past experimental studies have proved the efficiency of the utilization of nanoparticles in different mechanisms for the [...] Read more.

The rheology of different materials at the micro and macro levels is an area of great interest to many researchers, due to its important physical significance. Past experimental studies have proved the efficiency of the utilization of nanoparticles in different mechanisms for the purpose of boosting the heat transportation rate. The purpose of this study is to investigate heat and mass transport in a pseudo-plastic model past over a stretched porous surface in the presence of the Soret and Dufour effects. The involvement of tri-hybrid nanoparticles was incorporated into the pseudo-plastic model to enhance the heat transfer rate, and the transport problem of thermal energy and solute mechanisms was modelled considering the heat generation/absorption and the chemical reaction. Furthermore, traditional Fourier and Fick’s laws were engaged in the thermal and solute transportation. The physical model was developed upon Cartesian coordinates, and boundary layer theory was utilized in the simplification of the modelled problem, which appears in the form of coupled partial differential equations systems (PDEs). The modelled PDEs were transformed into corresponding ordinary differential equations systems (ODEs) by engaging the appropriate similarity transformation, and the converted ODEs were solved numerically via a Finite Element Procedure (FEP). The obtained solution was plotted against numerous emerging parameters. In addition, a grid independent survey is presented. We recorded that the temperature of the tri-hybrid nanoparticles was significantly higher than the fluid temperature. Augmenting the values of the Dufour number had a similar comportment on the fluid temperature and concentration. The fluid temperature increased against a higher estimation of the heat generation parameter and the Eckert numbers. The impacts of the buoyancy force parameter and the porosity parameter were quite opposite on the fluid velocity. Full article

(This article belongs to the Special Issue Non-Newtonian Microfluidics)

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18 pages, 2852 KiB

Open AccessArticle

Computational Assessment of Thermal and Solute Mechanisms in Carreau–Yasuda Hybrid Nanoparticles Involving Soret and Dufour Effects over Porous Surface

by Enran Hou, Fuzhang Wang, Essam Roshdy El-Zahar, Umar Nazir and Muhammad Sohail

Micromachines 2021, 12(11), 1302; https://doi.org/10.3390/mi12111302 - 23 Oct 2021

Cited by 8 | Viewed by 1313

Abstract

Engineers, scientists and mathematicians are greatly concerned about the thermal stability/instability of any physical system. Current contemplation discusses the role of the Soret and Dufour effects in hydro-magnetized Carreau–Yasuda liquid passed over a permeable stretched surface. Several important effects were considered while modelling [...] Read more.

Engineers, scientists and mathematicians are greatly concerned about the thermal stability/instability of any physical system. Current contemplation discusses the role of the Soret and Dufour effects in hydro-magnetized Carreau–Yasuda liquid passed over a permeable stretched surface. Several important effects were considered while modelling the thermal transport, including Joule heating, viscous dissipation, and heat generation/absorption. Mass transportation is presented in the presence of a chemical reaction. Different nanoparticle types were mixed in the Carreau–Yasuda liquid in order to study thermal performance. Initially, governing laws were modelled in the form of PDEs. Suitable transformation was engaged for conversion into ODEs and then the resulting ODEs were handled via FEM (Finite Element Method). Grid independent analysis was performed to determine the effectiveness of the chosen methodology. Several important physical effects were explored by augmenting the values of the influential parameters. Heat and mass transfer rates were computed against different parameters and discussed in detail. Full article

(This article belongs to the Special Issue Non-Newtonian Microfluidics)

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10 pages, 8866 KiB

Open AccessArticle

Flow Direction-Dependent Elastic Instability in a Symmetry-Breaking Microchannel

by Wu Zhang, Zihuang Wang, Meng Zhang, Jiahan Lin, Weiqian Chen, Yuhong Hu and Shuzhou Li

Micromachines 2021, 12(10), 1139; https://doi.org/10.3390/mi12101139 - 23 Sep 2021

Cited by 1 | Viewed by 1467

Abstract

This paper reports flow direction-dependent elastic instability in a symmetry-breaking microchannel. The microchannel consisted of a square chamber and a nozzle structure. A viscoelastic polyacrylamide solution was used for the instability demonstration. The instability was realized as the viscoelastic flow became asymmetric and [...] Read more.

This paper reports flow direction-dependent elastic instability in a symmetry-breaking microchannel. The microchannel consisted of a square chamber and a nozzle structure. A viscoelastic polyacrylamide solution was used for the instability demonstration. The instability was realized as the viscoelastic flow became asymmetric and unsteady in the microchannel when the flow exceeded a critical Weissenberg number. The critical Weissenberg number was found to be different for the forward-directed flow and the backward-directed flow in the microchannel. Full article

(This article belongs to the Special Issue Non-Newtonian Microfluidics)

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15 pages, 2709 KiB

Open AccessArticle

Significant Involvement of Double Diffusion Theories on Viscoelastic Fluid Comprising Variable Thermophysical Properties

by Muhammad Sohail, Umar Nazir, Omar Bazighifan, Rami Ahmad El-Nabulsi, Mahmoud M. Selim, Hussam Alrabaiah and Phatiphat Thounthong

Micromachines 2021, 12(8), 951; https://doi.org/10.3390/mi12080951 - 12 Aug 2021

Cited by 27 | Viewed by 1634

Abstract

This report examines the heat and mass transfer in three-dimensional second grade non-Newtonian fluid in the presence of a variable magnetic field. Heat transfer is presented with the involvement of thermal relaxation time and variable thermal conductivity. The generalized theory for mass flux [...] Read more.

This report examines the heat and mass transfer in three-dimensional second grade non-Newtonian fluid in the presence of a variable magnetic field. Heat transfer is presented with the involvement of thermal relaxation time and variable thermal conductivity. The generalized theory for mass flux with variable mass diffusion coefficient is considered in the transport of species. The conservation laws are modeled in simplified form via boundary layer theory which results as a system of coupled non-linear partial differential equations. Group similarity analysis is engaged for the conversion of derived conservation laws in the form of highly non-linear ordinary differential equations. The solution is obtained vial optimal homotopy procedure (OHP). The convergence of the scheme is shown through error analysis. The obtained solution is displayed through graphs and tables for different influential parameters. Full article

(This article belongs to the Special Issue Non-Newtonian Microfluidics)

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20 pages, 59988 KiB

Open AccessArticle

Entropy Generation Analysis and Radiated Heat Transfer in MHD (Al₂O₃-Cu/Water) Hybrid Nanofluid Flow

by Nabeela Parveen, Muhammad Awais, Saeed Ehsan Awan, Wasim Ullah Khan, Yigang He and Muhammad Yousaf Malik

Micromachines 2021, 12(8), 887; https://doi.org/10.3390/mi12080887 - 27 Jul 2021

Cited by 20 | Viewed by 1960

Abstract

This research concerns the heat transfer and entropy generation analysis in the MHD axisymmetric flow of Al₂O₃-Cu/H₂O hybrid nanofluid. The magnetic induction effect is considered for large magnetic Reynolds number. The influences of thermal radiations, viscous dissipation [...] Read more.

This research concerns the heat transfer and entropy generation analysis in the MHD axisymmetric flow of Al₂O₃-Cu/H₂O hybrid nanofluid. The magnetic induction effect is considered for large magnetic Reynolds number. The influences of thermal radiations, viscous dissipation and convective temperature conditions over flow are studied. The problem is modeled using boundary layer theory, Maxwell’s equations and Fourier’s conduction law along with defined physical factors. Similarity transformations are utilized for model simplification which is analytically solved with the homotopy analysis method. The h-curves up to 20th order for solutions establishes the stability and convergence of the adopted computational method. Rheological impacts of involved parameters on flow variables and entropy generation number are demonstrated via graphs and tables. The study reveals that entropy in system of hybrid nanofluid affected by magnetic induction declines for β while it enhances for Bi, R and λ. Moreover, heat transfer rate elevates for large Bi with convective conditions at surface. Full article

(This article belongs to the Special Issue Non-Newtonian Microfluidics)

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14 pages, 6476 KiB

Open AccessArticle

Numerical Analysis of Thermal Radiative Maxwell Nanofluid Flow Over-Stretching Porous Rotating Disk

by Shuang-Shuang Zhou, Muhammad Bilal, Muhammad Altaf Khan and Taseer Muhammad

Micromachines 2021, 12(5), 540; https://doi.org/10.3390/mi12050540 - 10 May 2021

Cited by 45 | Viewed by 2658

Abstract

The fluid flow over a rotating disk is critically important due to its application in a broad spectrum of industries and engineering and scientific fields. In this article, the traditional swirling flow of Von Karman is optimized for Maxwell fluid over a porous [...] Read more.

The fluid flow over a rotating disk is critically important due to its application in a broad spectrum of industries and engineering and scientific fields. In this article, the traditional swirling flow of Von Karman is optimized for Maxwell fluid over a porous spinning disc with a consistent suction/injection effect. Buongiorno’s model, which incorporates the effect of both thermophoresis and Brownian motion, describes the Maxwell nanofluid nature. The dimensionless system of ordinary differential equations (ODEs) has been diminished from the system of modeled equations through a proper transformation framework. Which is numerically computed with the bvp4c method and for validity purposes, the results are compared with the RK4 technique. The effect of mathematical abstractions on velocity, energy, concentration, and magnetic power is sketched and debated. It is perceived that the mass transmission significantly rises with the thermophoresis parameter, while the velocities in angular and radial directions are reducing with enlarging of the viscosity parameter. Further, the influences of thermal radiation

Rd

and Brownian motion parameters are particularly more valuable to enhance fluid temperature. The fluid velocity is reduced by the action of suction effects. The suction effect grips the fluid particles towards the pores of the disk, which causes the momentum boundary layer reduction. Full article

(This article belongs to the Special Issue Non-Newtonian Microfluidics)

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11 pages, 30983 KiB

Open AccessArticle

Electroosmotic Mixing of Non-Newtonian Fluid in a Microchannel with Obstacles and Zeta Potential Heterogeneity

by Lanju Mei, Defu Cui, Jiayue Shen, Diganta Dutta, Willie Brown, Lei Zhang and Ibibia K. Dabipi

Micromachines 2021, 12(4), 431; https://doi.org/10.3390/mi12040431 - 14 Apr 2021

Cited by 14 | Viewed by 2048

Abstract

This paper investigates the electroosmotic micromixing of non-Newtonian fluid in a microchannel with wall-mounted obstacles and surface potential heterogeneity on the obstacle surface. In the numerical simulation, the full model consisting of the Navier–Stokes equations and the Poisson–Nernst–Plank equations are solved for the [...] Read more.

This paper investigates the electroosmotic micromixing of non-Newtonian fluid in a microchannel with wall-mounted obstacles and surface potential heterogeneity on the obstacle surface. In the numerical simulation, the full model consisting of the Navier–Stokes equations and the Poisson–Nernst–Plank equations are solved for the electroosmotic fluid field, ion transport, and electric field, and the power law model is used to characterize the rheological behavior of the aqueous solution. The mixing performance is investigated under different parameters, such as electric double layer thickness, flow behavior index, obstacle surface zeta potential, obstacle dimension. Due to the zeta potential heterogeneity at the obstacle surface, vortical flow is formed near the obstacle surface, which can significantly improve the mixing efficiency. The results show that, the mixing efficiency can be improved by increasing the obstacle surface zeta potential, the flow behavior index, the obstacle height, the EDL thickness. Full article

(This article belongs to the Special Issue Non-Newtonian Microfluidics)

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28 pages, 17867 KiB

Open AccessArticle

Electroosmotic Flow of Viscoelastic Fluid through a Constriction Microchannel

by Jianyu Ji, Shizhi Qian and Zhaohui Liu

Micromachines 2021, 12(4), 417; https://doi.org/10.3390/mi12040417 - 09 Apr 2021

Cited by 24 | Viewed by 3787

Abstract

Electroosmotic flow (EOF) has been widely used in various biochemical microfluidic applications, many of which use viscoelastic non-Newtonian fluid. This study numerically investigates the EOF of viscoelastic fluid through a 10:1 constriction microfluidic channel connecting two reservoirs on either side. The flow is [...] Read more.

Electroosmotic flow (EOF) has been widely used in various biochemical microfluidic applications, many of which use viscoelastic non-Newtonian fluid. This study numerically investigates the EOF of viscoelastic fluid through a 10:1 constriction microfluidic channel connecting two reservoirs on either side. The flow is modelled by the Oldroyd-B (OB) model coupled with the Poisson–Boltzmann model. EOF of polyacrylamide (PAA) solution is studied as a function of the PAA concentration and the applied electric field. In contrast to steady EOF of Newtonian fluid, the EOF of PAA solution becomes unstable when the applied electric field (PAA concentration) exceeds a critical value for a fixed PAA concentration (electric field), and vortices form at the upstream of the constriction. EOF velocity of viscoelastic fluid becomes spatially and temporally dependent, and the velocity at the exit of the constriction microchannel is much higher than that at its entrance, which is in qualitative agreement with experimental observation from the literature. Under the same apparent viscosity, the time-averaged velocity of the viscoelastic fluid is lower than that of the Newtonian fluid. Full article

(This article belongs to the Special Issue Non-Newtonian Microfluidics)

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17 pages, 5085 KiB

Open AccessArticle

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

by Fan Bai, Hongna Zhang, Xiaobin Li, Fengchen Li and Sang Woo Joo

Micromachines 2021, 12(2), 149; https://doi.org/10.3390/mi12020149 - 03 Feb 2021

Cited by 8 | Viewed by 2529

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Non-Newtonian Microfluidics)

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