Dynamics of particle migration in channel flow of viscoelastic fluids

The migration of a sphere in the pressure-driven channel flow of a viscoelastic fluid is studied numerically. The effects of inertia, elasticity, shear-thinning viscosity, secondary flows and the blockage ratio are considered by conducting fully resolved direct numerical simulations over a wide range of parameters. In a Newtonian fluid in the presence of inertial effects, the particle moves away from the channel centreline. The elastic effects, however, drive the particle towards the channel centreline. The equilibrium position depends on the interplay between the elastic and inertial effects. Particle focusing at the centreline occurs in flows with strong elasticity and weak inertia. Both shear-thinning effects and secondary flows tend to move the particle away from the channel centreline. The effect is more pronounced as inertia and elasticity effects increase. A scaling analysis is used to explain these different effects. Besides the particle migration, particle-induced fluid transport and particle migration during flow start-up are also considered. Inertial effects, shear-thinning behaviour, and secondary flows are all found to enhance the effective fluid transport normal to the flow direction. Due to the oscillation in fluid velocity and strong normal stress differences that develop during flow start-up, the particle has a larger transient migration velocity, which may be potentially used to accelerate the particle focusing.

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Effects of Ionic Strength on Lateral Particle Migration in Shear-Thinning Xanthan Gum Solutions

Micromachines ◽

10.3390/mi10080535 ◽

2019 ◽

Vol 10 (8) ◽

pp. 535 ◽

Cited By ~ 2

Author(s):

Mira Cho ◽

Sun Ok Hong ◽

Seung Hak Lee ◽

Kyu Hyun ◽

Ju Min Kim

Keyword(s):

Ionic Strength ◽

Rheological Properties ◽

Viscoelastic Fluid ◽

Xanthan Gum ◽

Viscoelastic Fluids ◽

Shear Thinning ◽

Particle Migration ◽

Cell Counting ◽

Contour Length ◽

Wide Range

Viscoelastic fluids, including particulate systems, are found in various biological and industrial systems including blood flow, food, cosmetics, and electronic materials. Particles suspended in viscoelastic fluids such as polymer solutions migrate laterally, forming spatially segregated streams in pressure-driven flow. Viscoelastic particle migration was recently applied to microfluidic technologies including particle counting and sorting and the micromechanical measurement of living cells. Understanding the effects on equilibrium particle positions of rheological properties of suspending viscoelastic fluid is essential for designing microfluidic applications. It has been considered that the shear-thinning behavior of viscoelastic fluid is a critical factor in determining the equilibrium particle positions. This work presents the lateral particle migration in two different xanthan gum-based viscoelastic fluids with similar shear-thinning viscosities and the linear viscoelastic properties. The flexibility and contour length of the xanthan gum molecules were tuned by varying the ionic strength of the solvent. Particles suspended in flexible and short xanthan gum solution, dissolved at high ionic strength, migrated toward the corners in a square channel, whereas particles in the rigid and long xanthan gum solutions in deionized water migrated toward the centerline. This work suggests that the structural properties of polymer molecules play significant roles in determining the equilibrium positions in shear-thinning fluids, despite similar bulk rheological properties. The current results are expected to be used in a wide range of applications such as cell counting and sorting.

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Particle Focusing under Newtonian and Viscoelastic Flow in a Straight Rhombic Microchannel

Micromachines ◽

10.3390/mi11110998 ◽

2020 ◽

Vol 11 (11) ◽

pp. 998

Author(s):

Joo-Yong Kwon ◽

Taehoon Kim ◽

Jungwoo Kim ◽

Younghak Cho

Keyword(s):

Newtonian Fluid ◽

Microelectromechanical Systems ◽

Viscoelastic Fluids ◽

Newtonian Fluids ◽

Particle Migration ◽

Inertial Particles ◽

Cross Sectional ◽

Double Line ◽

Particle Focusing ◽

Wide Range

Particle behavior in viscoelastic fluids has attracted considerable attention in recent years. In viscoelastic fluids, as opposed to Newtonian fluids, particle focusing can be simply realized in a microchannel without any external forces or complex structures. In this study, a polydimethylsiloxane (PDMS) microchannel with a rhombic cross-sectional shape was fabricated to experimentally investigate the behavior of inertial and elasto-inertial particles. Particle migration and behavior in Newtonian and non-Newtonian fluids were compared with respect to the flow rate and particle size to investigate their effect on the particle focusing position and focusing width. The PDMS rhombic microchannel was fabricated using basic microelectromechanical systems (MEMS) processes. The experimental results showed that single-line particle focusing was formed along the centerline of the microchannel in the non-Newtonian fluid, unlike the double-line particle focusing in the Newtonian fluid over a wide range of flow rates. Numerical simulation using the same flow conditions as in the experiments revealed that the particles suspended in the channel tend to drift toward the center of the channel owing to the negative net force throughout the cross-sectional area. This supports the experimental observation that the viscoelastic fluid in the rhombic microchannel significantly influences particle migration toward the channel center without any external force owing to coupling between the inertia and elasticity.

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Applications of Biocatalysts for Sustainable Oxidation of Phenolic Pollutants: A Review

Sustainability ◽

10.3390/su13158620 ◽

2021 ◽

Vol 13 (15) ◽

pp. 8620

Author(s):

Sanaz Salehi ◽

Kourosh Abdollahi ◽

Reza Panahi ◽

Nejat Rahmanian ◽

Mozaffar Shakeri ◽

...

Keyword(s):

Phenolic Compounds ◽

Operating Conditions ◽

Phenolic Pollutants ◽

Petroleum Refinery Wastewater ◽

Start Up ◽

Low Concentrations ◽

Effective Removal ◽

Wide Range ◽

Loading Effects ◽

Spent Caustic

Phenol and its derivatives are hazardous, teratogenic and mutagenic, and have gained significant attention in recent years due to their high toxicity even at low concentrations. Phenolic compounds appear in petroleum refinery wastewater from several sources, such as the neutralized spent caustic waste streams, the tank water drain, the desalter effluent and the production unit. Therefore, effective treatments of such wastewaters are crucial. Conventional techniques used to treat these wastewaters pose several drawbacks, such as incomplete or low efficient removal of phenols. Recently, biocatalysts have attracted much attention for the sustainable and effective removal of toxic chemicals like phenols from wastewaters. The advantages of biocatalytic processes over the conventional treatment methods are their ability to operate over a wide range of operating conditions, low consumption of oxidants, simpler process control, and no delays or shock loading effects associated with the start-up/shutdown of the plant. Among different biocatalysts, oxidoreductases (i.e., tyrosinase, laccase and horseradish peroxidase) are known as green catalysts with massive potentialities to sustainably tackle phenolic contaminants of high concerns. Such enzymes mainly catalyze the o-hydroxylation of a broad spectrum of environmentally related contaminants into their corresponding o-diphenols. This review covers the latest advancement regarding the exploitation of these enzymes for sustainable oxidation of phenolic compounds in wastewater, and suggests a way forward.

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Focusing of Particles in a Microchannel with Laser Engraved Groove Arrays

Biosensors ◽

10.3390/bios11080263 ◽

2021 ◽

Vol 11 (8) ◽

pp. 263

Author(s):

Tianlong Zhang ◽

Yigang Shen ◽

Ryota Kiya ◽

Dian Anggraini ◽

Tao Tang ◽

...

Keyword(s):

Open Space ◽

Lateral Displacement ◽

Reynolds Numbers ◽

Secondary Flows ◽

Particle Sedimentation ◽

Nanoparticle Separation ◽

Wide Range ◽

Fs Laser ◽

Channel Bottom ◽

Myoblast Cells

Continuous microfluidic focusing of particles, both synthetic and biological, is significant for a wide range of applications in industry, biology and biomedicine. In this study, we demonstrate the focusing of particles in a microchannel embedded with glass grooves engraved by femtosecond pulse (fs) laser. Results showed that the laser-engraved microstructures were capable of directing polystyrene particles and mouse myoblast cells (C2C12) towards the center of the microchannel at low Reynolds numbers (Re < 1). Numerical simulation revealed that localized side-to-center secondary flows induced by grooves at the channel bottom play an essential role in particle lateral displacement. Additionally, the focusing performance proved to be dependent on the angle of grooves and the middle open space between the grooves based on both experiments and simulation. Particle sedimentation rate was found to critically influence the focusing of particles of different sizes. Taking advantage of the size-dependent particle lateral displacement, selective focusing of micrometer particles was demonstrated. This study systematically investigated continuous particle focusing in a groove-embedded microchannel. We expect that this device will be used for further applications, such as cell sensing and nanoparticle separation in biological and biomedical areas.

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Inertial focusing and zeta potential measurements of single-nanoparticles using octet-nanochannels

Lab on a Chip ◽

10.1039/d1lc00239b ◽

2021 ◽

Author(s):

Shohei Kishimoto ◽

Makusu Tsutsui ◽

Kazumichi Yokota ◽

Masateru Taniguchi

Keyword(s):

Zeta Potential ◽

Inertial Effects ◽

Inertial Focusing ◽

Particle Focusing ◽

Single Nanoparticle

Electrokinetics in octet nanochannels was demonstrated to enable particle focusing via inertial effects to accurate single-nanoparticle zeta-potential measurements.

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Theory to predict particle migration and margination in the pressure-driven channel flow of blood

Physical Review Fluids ◽

10.1103/physrevfluids.2.093102 ◽

2017 ◽

Vol 2 (9) ◽

Cited By ~ 27

Author(s):

Qin M. Qi ◽

Eric S. G. Shaqfeh

Keyword(s):

Channel Flow ◽

Particle Migration ◽

Pressure Driven

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Personality trait differences across types of entrepreneurs: a systematic literature review

Review of Managerial Science ◽

10.1007/s11846-021-00466-9 ◽

2021 ◽

Author(s):

Florentine U. Salmony ◽

Dominik K. Kanbach

Keyword(s):

Literature Review ◽

Personality Traits ◽

Systematic Literature Review ◽

Empirical Studies ◽

Academic Research ◽

Future Research ◽

Rural Farmers ◽

Start Up ◽

Wide Range ◽

Research Integration

AbstractThe personality traits that define entrepreneurs have been of significant interest to academic research for several decades. However, previous studies have used vastly different definitions of the term “entrepreneur”, meaning their subjects have ranged from rural farmers to tech-industry start-up founders. Consequently, most research has investigated disparate sub-types of entrepreneurs, which may not allow for inferences to be made regarding the general entrepreneurial population. Despite this, studies have frequently extrapolated results from narrow sub-types to entrepreneurs in general. This variation in entrepreneur samples reduces the comparability of empirical studies and calls into question the reviews that pool results without systematic differentiation between sub-types. The present study offers a novel account by differentiating between the definitions of “entrepreneur” used in studies on entrepreneurs’ personality traits. We conduct a systematic literature review across 95 studies from 1985 to 2020. We uncover three main themes across the previous studies. First, previous research applied a wide range of definitions of the term “entrepreneur”. Second, we identify several inconsistent findings across studies, which may at least partially be due to the use of heterogeneous entrepreneur samples. Third, the few studies that distinguished between various types of entrepreneurs revealed differences between them. Our systematic differentiation between entrepreneur sub-types and our research integration offer a novel perspective that has, to date, been widely neglected in academic research. Future research should use clearly defined entrepreneurial samples and conduct more systematic investigations into the differences between entrepreneur sub-types.

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Experimental Studies of Leading Edge Contouring Influence on Secondary Losses in Transonic Turbines

Volume 8: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2012-68497 ◽

2012 ◽

Cited By ~ 1

Author(s):

Ranjan Saha ◽

Jens Fridh ◽

Torsten Fransson ◽

Boris I. Mamaev ◽

Mats Annerfeldt

Keyword(s):

Gas Turbine ◽

Guide Vane ◽

Experimental Studies ◽

Three Dimensional ◽

Leading Edge ◽

Secondary Flows ◽

Noticeable Effect ◽

Flow Angle ◽

Wide Range ◽

Contour Plots

An experimental study of the hub leading edge contouring using fillets is performed in an annular sector cascade to observe the influence of secondary flows and aerodynamic losses. The investigated vane is a three dimensional gas turbine guide vane (geometrically similar) with a mid-span aspect ratio of 0.46. The measurements are carried out on the leading edge fillet and baseline cases using pneumatic probes. Significant precautions have been taken to increase the accuracy of the measurements. The investigations are performed for a wide range of operating exit Mach numbers from 0.5 to 0.9 at a design inlet flow angle of 90°. Data presented include the loading, fields of total pressures, exit flow angles, radial flow angles, as well as profile and secondary losses. The vane has a small profile loss of approximately 2.5% and secondary loss of about 1.1%. Contour plots of vorticity distributions and velocity vectors indicate there is a small influence of the vortex-structure in endwall regions when the leading edge fillet is used. Compared to the baseline case the loss for the filleted case is lower up to 13% of span and higher from 13% to 20% of the span for a reference condition with Mach no. of 0.9. For the filleted case, there is a small increase of turning up to 15% of the span and then a small decrease up to 35% of the span. Hence, there are no significant influences on the losses and turning for the filleted case. Results lead to the conclusion that one cannot expect a noticeable effect of leading edge contouring on the aerodynamic efficiency for the investigated 1st stage vane of a modern gas turbine.

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