Inertial focusing of spherical particles in rectangular microchannels over a wide range of Reynolds numbers

Lab on a Chip ◽  
2015 ◽  
Vol 15 (4) ◽  
pp. 1168-1177 ◽  
Author(s):  
Chao Liu ◽  
Guoqing Hu ◽  
Xingyu Jiang ◽  
Jiashu Sun
Keyword(s):  
Reynolds Numbers ◽  
Spherical Particles ◽  
Rectangular Microchannels ◽  
Inertial Focusing ◽  
Wide Range ◽  
Physical Insight ◽  
Insight Into

This work provides physical insight into the multiplex focusing of particles in rectangular microchannels with different geometries and Reynolds numbers.

Calculation of the primary trajectories of seeds and other particles in strong winds

1983 ◽  
Vol 219 (1215) ◽  
pp. 217-217
Keyword(s):  
Equations Of Motion ◽  
Aerodynamic Resistance ◽  
Reynolds Numbers ◽  
Spherical Particles ◽  
Spores And Pollen ◽  
General Terms ◽  
Wide Range ◽  
Strong Winds ◽  
Dispersal Distances ◽  
Enormous Number

The movement of variously dense spherical particles representing a variety of seeds, fruits, spores and pollen, and released from rest into arbitrary winds and a gravitational field is discussed in general terms that account in detail for changes in the quasi-static aerodynamic resistance to motion experienced by such particles during aerial flight. A hybrid analytical-empirical law is established which describes this resistance fairly accurately for particle Reynolds numbers in the range 0—60 000 and that allows for the numerical integration of the equations of motion so as to cover a very wide range of flight conditions. This makes possible the provision of a set of four-parameter universal range tables from which the dispersal distances for an enormous number of practical cases may be estimated. One particular case of particle movement in a region of pseudo-thermal convection is also discussed and this shows how a marked degree of deposition concentration may be induced in some circumstances by such a flow. Botanists and ecologists concerned with seed and particle dispersal in the environment may find the universal range tables of particular interest and use. This is because the tables obviate the need for the integration of the equations of motion when dealing with individual cases and permit an estimation of range purely on the basis of the specified quantities of particle size, density and altitude of release, atmospheric wind speed, density and viscosity, and the acceleration due to gravity.

scholarly journals Inertial focusing of finite-size particles in microchannels

2018 ◽  
Vol 840 ◽  
pp. 613-630 ◽  
Author(s):  
Evgeny S. Asmolov ◽  
Alexander L. Dubov ◽  
Tatiana V. Nizkaya ◽  
Jens Harting ◽  
Olga I. Vinogradova
Keyword(s):  
Lattice Boltzmann ◽  
Slip Velocity ◽  
Lift Force ◽  
Finite Size ◽  
Reynolds Numbers ◽  
Velocity Difference ◽  
Inertial Focusing ◽  
Inertial Migration ◽  
Lattice Boltzmann Simulations ◽  
Insight Into

At finite Reynolds numbers, $Re$, particles migrate across laminar flow streamlines to their equilibrium positions in microchannels. This migration is attributed to a lift force, and the balance between this lift and gravity determines the location of particles in channels. Here we demonstrate that velocity of finite-size particles located near a channel wall differs significantly from that of an undisturbed flow, and that their equilibrium position depends on this, referred to as slip velocity, difference. We then present theoretical arguments, which allow us to generalize expressions for a lift force, originally suggested for some limiting cases and $Re\ll 1$, to finite-size particles in a channel flow at $Re\leqslant 20$. Our theoretical model, validated by lattice Boltzmann simulations, provides considerable insight into inertial migration of finite-size particles in a microchannel and suggests some novel microfluidic approaches to separate them by size or density at a moderate $Re$.

Experimental Study on Single-Phase Gas Flow in Microtubes

2011 ◽  
Vol 133 (11) ◽  
Author(s):  
T. T. Zhang ◽  
L. Jia ◽  
C. W. Li ◽  
L. X. Yang ◽  
Y. Jaluria
Keyword(s):  
Heat Transfer ◽  
Gas Flow ◽  
Single Phase ◽  
Slip Flow ◽  
Experimental System ◽  
Flow Region ◽  
Flow And Heat Transfer ◽  
Wide Range ◽  
Physical Insight ◽  
Insight Into

An experimental system for single-phase gas flow in microtubes has been developed. The effects of viscous heating and compressibility on the flow and temperature field were studied for a wide range of governing parameters. Also, an analytical/numerical model of the flow was developed. Numerical results for the flow and heat transfer in the slip flow region were found to agree quite well with the experimental data, lending support to the model. The study provides greater physical insight into and understanding the effects of viscous dissipation and compressibility in microtube flow and the associated heat transfer. In addition, the combined experimental and numerical simulation approaches of the process can be used for control and optimization of systems based on microtube heat transfer.

NUMERICAL CHARACTERIZATION OF THE FLOW FIELD IN A FOUR-GENERATION AIRWAY

2008 ◽  
Vol 08 (01) ◽  
pp. 55-74 ◽  
Author(s):  
T. C. LAI ◽  
Y. S. MORSI ◽  
M. SINGH
Keyword(s):  
Reynolds Numbers ◽  
Bronchial Tree ◽  
Secondary Flows ◽  
Fourth Generation ◽  
Numerical Characterization ◽  
Wide Range ◽  
Symmetrical Model ◽  
Computational Fluid Dynamics Cfd ◽  
Insight Into

In this paper, various aspects of respiratory airflow generated from the branching network of tubes that make up the tracheal-bronchial tree are numerically analyzed using the computational fluid dynamics (CFD) package CFX. The model used is a four-generation airway that is geometrically similar to Weibel's symmetrical model. In the present analysis, two different models (in-plane and off-plane) are examined for a wide range of Reynolds numbers that correspond to human breathing conditions. The findings indicate that the secondary flow patterns generated become more significant as the flow passes from the trachea to the fourth-generation airway. Moreover, comparison between in-plane and off-plane models shows that the skewed velocity profiles and secondary flows for the in-plane model are more prominent than those for the off-plane one. In general, the model developed in this study is capable of providing an overall insight into the effect of fluid flow in multiple generations of the human upper respiratory airways.

Drag coefficient of a sphere in a non-stationary flow: new results

2007 ◽  
Vol 463 (2088) ◽  
pp. 3323-3345 ◽  
Author(s):  
G Jourdan ◽  
L Houas ◽  
O Igra ◽  
J.-L Estivalezes ◽  
C Devals ◽  
...  
Keyword(s):  
Drag Coefficient ◽  
Stationary Flow ◽  
Reynolds Numbers ◽  
Spherical Particles ◽  
Steady Flows ◽  
Two Phase ◽  
Spider Web ◽  
Wide Range ◽  
The Difference ◽  
Sphere Drag

The drag coefficient of a sphere placed in a non-stationary flow is studied experimentally over a wide range of Reynolds numbers in subsonic and supersonic flows. Experiments were conducted in a shock tube where the investigated balls were suspended, far from all the tube walls, on a very thin wire taken from a spider web. During each experiment, many shadowgraph photos were taken to enable an accurate construction of the sphere's trajectory. Based on the sphere's trajectory, its drag coefficient was evaluated. It was shown that a large difference exists between the sphere drag coefficient in steady and non-steady flows. In the investigated range of Reynolds numbers, the difference exceeds 50%. Based on the obtained results, a correlation for the non-stationary drag coefficient of a sphere is given. This correlation can be used safely in simulating two-phase flows composed of small spherical particles immersed in a gaseous medium.

Static and Dynamic Analysis of a NACA 0021 Airfoil Section at Low Reynolds Numbers Based on Experiments and Computational Fluid Dynamics

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
David Holst ◽  
Francesco Balduzzi ◽  
Alessandro Bianchini ◽  
Benjamin Church ◽  
Felix Wegner ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Pressure Coefficient ◽  
Reynolds Numbers ◽  
Technical Literature ◽  
Open Field Behavior ◽  
Static And Dynamic Analysis ◽  
Wide Range ◽  
Experimental Apparatus ◽  
Low Reynolds ◽  
Insight Into

The wind industry needs airfoil data for ranges of angle of attack (AoA) much wider than those of aviation applications, since large portions of the blades may operate in stalled conditions for a significant part of their lives. Vertical axis wind turbines (VAWTs) are even more affected by this need, since data sets across the full incidence range of 180 deg are necessary for a correct performance prediction at different tip-speed ratios. However, the relevant technical literature lacks data in deep and poststall regions for nearly every airfoil. Within this context, the present study shows experimental and numerical results for the well-known NACA 0021 airfoil, which is often used for Darrieus VAWT design. Experimental data were obtained through dedicated wind tunnel measurements of a NACA 0021 airfoil with surface pressure taps, which provided further insight into the pressure coefficient distribution across a wide range of AoAs. The measurements were conducted at two different Reynolds numbers (Re = 140 k and Re = 180 k): each experiment was performed multiple times to ensure repeatability. Dynamic AoA changes were also investigated at multiple reduced frequencies. Moreover, dedicated unsteady numerical simulations were carried out on the same airfoil shape to reproduce both the static polars of the airfoil and some relevant dynamic AoA variation cycles tested in the experiments. The solved flow field was then exploited both to get further insight into the flow mechanisms highlighted by the wind tunnel tests and to provide correction factors to discard the influence of the experimental apparatus, making experiments representative of open-field behavior. The present study is then thought to provide the scientific community with high quality, low-Reynolds airfoil data, which may enable in the near future a more effective design of Darrieus VAWTs.

scholarly journals Inertial Migration of Neutrally Buoyant Spherical Particles in Square Channels at Moderate and High Reynolds Numbers

Micromachines ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 198
Author(s):  
Yanfeng Gao ◽  
Pascale Magaud ◽  
Lucien Baldas ◽  
Yanping Wang
Keyword(s):  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Reynolds Numbers ◽  
Spherical Particles ◽  
Particle Volume ◽  
Inertial Focusing ◽  
Inertial Migration ◽  
High Reynolds Numbers ◽  
Micro Channels ◽  
High Reynolds

The inertial migration of particles in microchannel flows has been deeply investigated in the last two decades. In spite of numerous reports on the inertial focusing patterns in a square channel, the particle inertial focusing and longitudinal ordering processes remain unclear at high Reynolds numbers (>200) in square microchannels smaller than 100 µm in width. Thus, in this work, in situ visualization of particles flowing in square micro-channels at Reynolds numbers Re ranging from 5 to 280 has been conducted and their migration behaviors have been analyzed. The obtained results confirm that new equilibrium positions appear above a critical Re depending on the particle to channel size ratio and the particle volume fraction. It is also shown that, for a given channel length, an optimal Reynolds number can be identified, for which the ratio of particles located on equilibrium positions is maximal. Moreover, the longitudinal ordering process, i.e., the formation of trains of particles on equilibrium positions and the characterization of their length, has also been analyzed for the different flow conditions investigated in this study.

Calculation of the primary trajectories of seeds and other particles in strong winds

1983 ◽  
Vol 389 (1796) ◽  
pp. 15-66 ◽  
Keyword(s):  
Equations Of Motion ◽  
Aerodynamic Resistance ◽  
Reynolds Numbers ◽  
Spherical Particles ◽  
Spores And Pollen ◽  
General Terms ◽  
Wide Range ◽  
Strong Winds ◽  
Dispersal Distances ◽  
Enormous Number

The movement of variously dense spherical particles representing a variety of seeds, fruits, spores and pollen, released from rest into arbitrary winds and a gravitational field is discussed in general terms that account in detail for changes in the quasi-static aerodynamic resistance to motion experienced by such particles during aerial flight. A hybrid analytical-empirical law is established that describes this resistance fairly accurately for particle Reynolds numbers in the range 0-60000 and that allows for the numerical integration of the equations of motion so as to cover a very wide range of flight conditions. This makes possible the provision of a set of four-parameter universal range tables from which the dispersal distances for an enormous number of practical cases may be estimated. One particular case of particle movement in a region of pseudo-thermal convection is also discussed and this shows how a marked degree of deposition concentration may be induced in some circumstances by such a flow.

Three regimes of inertial focusing for spherical particles suspended in circular tube flows

2019 ◽  
Vol 871 ◽  
pp. 952-969 ◽  
Author(s):  
Saki Nakayama ◽  
Hiroshi Yamashita ◽  
Takuya Yabu ◽  
Tomoaki Itano ◽  
Masako Sugihara-Seki
Keyword(s):  
Circular Tube ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Tube Diameter ◽  
Spherical Particles ◽  
Immersed Boundary ◽  
Cross Sectional ◽  
Inertial Focusing ◽  
Critical Reynolds Numbers ◽  
The Cross

An experimental and numerical study on the inertial focusing of neutrally buoyant spherical particles suspended in laminar circular tube flows was performed at Reynolds numbers ($Re$) ranging from 100 to 1000 for particle-to-tube diameter ratios of ${\sim}0.1$. In the experiments, we measured the cross-sectional distribution of particles in dilute suspensions flowing through circular tubes several hundreds of micrometres in diameter. In the cross-section located at 1000 times the tube diameter from the tube inlet, all particles were highly concentrated on one annulus or two annuli, depending on $Re$. At low $Re$, the particles were focused on the so-called Segré–Silberberg (SS) annulus, in accordance with previous studies (regime (A)). At higher $Re$, two particle focusing annuli appeared, with the outer annulus corresponding to the SS annulus (regime (B)). We call the annulus closer to the tube centre ‘the inner annulus’, although this term was used by Matas et al. (J. Fluid Mech., vol. 515, 2004, pp. 171–195) for a significantly broader annulus which included the transient accumulation of particles observed in regime (A). At even higher $Re$, particles were focused on the inner annulus (regime (C)), indicating that the radial position of the SS annulus is no longer a stable equilibrium position. These experimental results were confirmed by a numerical simulation based on the immersed boundary method. The results of this study also indicate that the critical Reynolds numbers between two neighbouring regimes decrease with the increase of the particle-to-tube diameter ratio.

Static and Dynamic Analysis of a NACA 0021 Airfoil Section at Low Reynolds Numbers Based on Experiments and CFD

2018 ◽  
Author(s):  
Francesco Balduzzi ◽  
Alessandro Bianchini ◽  
Giovanni Ferrara ◽  
David Holst ◽  
Benjamin Church ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Pressure Coefficient ◽  
Vertical Axis ◽  
Reynolds Numbers ◽  
Technical Literature ◽  
Static And Dynamic Analysis ◽  
Wide Range ◽  
Experimental Apparatus ◽  
Low Reynolds ◽  
Insight Into

The wind industry needs airfoil data for ranges of Angle of Attack (AoA) much wider than those of aviation applications, since large portions of the blades may operate in stalled conditions for a significant part of their lives. Vertical axis wind turbines (VAWTs) are even more affected by this need, since data sets across the full incidence range of 180 degree are necessary for a correct performance prediction at different tip-speed ratios. However, the relevant technical literature lacks data in deep and post stall regions for nearly every airfoil. Within this context, the present study shows experimental and numerical results for the well-known NACA 0021 airfoil, which is often used for Darrieus VAWT design. Experimental data were obtained through dedicated wind tunnel measurements of a NACA 0021 airfoil with surface pressure taps, which provided further insight into the pressure coefficient distribution across a wide range of AoAs. The measurements were conducted at two different Reynolds numbers (Re = 140k and Re = 180k): each experiment was performed multiple times to ensure repeatability. Dynamic AoA changes were also investigated at multiple reduced frequencies. Moreover, dedicated unsteady numerical simulations were carried out on the same airfoil shape to reproduce both the static polars of the airfoil and some relevant dynamic AoA variation cycles tested in the experiments. The solved flow field was then exploited both to get further insight into the flow mechanisms highlighted by the wind tunnel tests and to provide correction factors to discard the influence of the experimental apparatus, making experiments representative of open-field behaviour. The present study is then thought to provide the scientific community with high quality, low-Reynolds airfoil data, which may enable in the near future a more effective design of Darrieus VAWTs.

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