scholarly journals Asymmetrical Induced Charge Electroosmotic Flow on a Herringbone Floating Electrode and Its Application in a Micromixer

Micromachines ◽  
2018 ◽  
Vol 9 (8) ◽  
pp. 391 ◽  
Author(s):  
Qingming Hu ◽  
Jianhua Guo ◽  
Zhongliang Cao ◽  
Hongyuan Jiang
Keyword(s):  
Electrode Surface ◽  
Slip Velocity ◽  
Fluid Velocity ◽  
Laminar Flows ◽  
Fluid Mixing ◽  
Electrode Pair ◽  
Great Opportunity ◽  
Mixing Performance ◽  
Induced Charge ◽  
Floating Electrode

Enhancing mixing is of significant importance in microfluidic devices characterized by laminar flows and low Reynolds numbers. An asymmetrical induced charge electroosmotic (ICEO) vortex pair generated on the herringbone floating electrode can disturb the interface of two-phase fluids and deliver the fluid transversely, which could be exploited to accomplish fluid mixing between two neighbouring fluids in a microscale system. Herein we present a micromixer based on an asymmetrical ICEO flow induced above the herringbone floating electrode array surface. We investigate the average transverse ICEO slip velocity on the Ridge/Vee/herringbone floating electrode and find that the microvortex generated on the herringbone electrode surface has good potential for mixing the miscible liquids in microfluidic systems. In addition, we explore the effect of applied frequencies and bulk conductivity on the slip velocity above the herringbone floating electrode surface. The high dependence of mixing performance on the floating electrode pair numbers is analysed simultaneously. Finally, we investigate systematically voltage intensity, applied frequencies, inlet fluid velocity and liquid conductivity on the mixing performance of the proposed device. The microfluidic micromixer put forward herein offers great opportunity for fluid mixing in the field of micro total analysis systems.

Numerical analysis of non-aligned inputs M-type micromixers with different shaped obstacles for biomedical applications

2021 ◽  
pp. 095440892110516
Author(s):  
Muhammad Irfan ◽  
Imran Shah ◽  
Usama M Niazi ◽  
Muhsin Ali ◽  
Sadaqat Ali ◽  
...  
Keyword(s):  
Structural Design ◽  
Biomedical Applications ◽  
Structural Changes ◽  
Nanoparticle Synthesis ◽  
Fluid Mixing ◽  
The Novel ◽  
Flow Conditions ◽  
Mixing Index ◽  
Mixing Performance ◽  
Passive Micromixer

Fluid mixing in lab-on-a-chip devices at laminar flow conditions result in a low mixing index. The reason is dominant diffusion over the convection process. The mixing index can be improved by certain changes in the micromixer structural design like introducing obstacles in the path of fluid flow. These obstacles will make dominant the advection process over the diffusion process. The main contribution of this work is based on proposing the novel hybrid type micromixer design for enhancing the mixing quality. Three non-aligned M-type and non-aligned M-type with obstacles passive type micromixers are analyzed by COMSOL5.5. These designs are hybrid types because different structural changes are combined in a single design for mixing improvement. First of all the straight non-aligned inlets, M-type passive micromixer (SMTM) is analyzed. It is observed that mixing performance is improved because of M-shaped mixing units and non-aligned inlets. This improvement is deemed to be not enough so different shaped obstacles are introduced in the micromixer design. These designs based on obstacles are named horizontal rectangular M-type micromixer, square M-type micromixer, and vertical rectangular M-type micromixer. The mixing index for SMTM, square M-type micromixer, horizontal rectangular M-type micromixer, and vertical rectangular M-type micromixer at Reynolds number Re = 60 is respectively given by 71.1%, 83.21%, 84.45%, and 89.99%. The mixing index of vertical rectangular M-type micromixer was 59.34% − 87.65% for Re = 0.5–100. Vertical rectangular M-type micromixer is concluded with the better-mixing capability design among the proposed ones. Based on these simulation results, the vertical rectangular M-type micromixer design can be utilized for mixing purposes in biomedical applications like nanoparticle synthesis and biomedical sample preparation for drug delivery.

scholarly journals Numerical Study of T-Shaped Micromixers with Vortex-Inducing Obstacles in the Inlet Channels

Micromachines ◽  
2020 ◽  
Vol 11 (12) ◽  
pp. 1122
Author(s):  
Chih-Yang Wu ◽  
Bing-Hao Lai
Keyword(s):  
Fluid Dynamics ◽  
Reynolds Number ◽  
Particle Tracking ◽  
Concentration Distribution ◽  
Numerical Study ◽  
Fluid Mixing ◽  
Sudden Increase ◽  
New Approach ◽  
Mixing Performance ◽  
Flow Modification

To enhance fluid mixing, a new approach for inlet flow modification by adding vortex-inducing obstacles (VIOs) in the inlet channels of a T-shaped micromixer is proposed and investigated in this work. We use a commercial computational fluid dynamics code to calculate the pressure and the velocity vectors and, to reduce the numerical diffusion in high-Peclet-number flows, we employ the particle-tracking simulation with an approximation diffusion model to calculate the concentration distribution in the micromixers. The effects of geometric parameters, including the distance between the obstacles and the angle of attack of the obstacles, on the mixing performance of micromixers are studied. From the results, we can observe the following trends: (i) the stretched contact surface between different fluids caused by antisymmetric VIOs happens for the cases with the Reynolds number (Re) greater than or equal to 27 and the enhancement of mixing increases with the increase of Reynolds number gradually, and (ii) the onset of the engulfment flow happens at Re≈125 in the T-shaped mixer with symmetric VIOs or at Re≈140 in the standard planar T-shaped mixer and results in a sudden increase of the degree of mixing. The results indicate that the early initiation of transversal convection by either symmetric or antisymmetric VIOs can enhance fluid mixing at a relatively lower Re.

Evaluation of the Mixing Performance of the Micromixers With Grooved or Obstructed Channels

2008 ◽  
Vol 130 (7) ◽  
Author(s):  
Yeng-Yung Tsui ◽  
Ching-Shiang Yang ◽  
Chung-Ming Hsieh
Keyword(s):  
Vertical Plane ◽  
Pressure Head ◽  
Fluid Mixing ◽  
Mixing Performance ◽  
Large Pressure ◽  
Fluid Concentration ◽  
Speed Up ◽  
Periodic Configuration ◽  
The Cost ◽  
Good Agreement

The mixing flows in microchannels were examined using numerical methods. To speed up fluid mixing, it is essential to generate lateral transport of mass. In this study, the mixing flow is disrupted by either placing grooves or block obstacles on the walls of the channels. Since the grooves or the blocks appear in a periodic configuration, the velocity is solved only in a section of the channel. With the repeating cycle of flow velocity field, the fluid concentration can be calculated throughout the entire length of the channel. Good agreement with experiments in the mixing performance justifies the present methodology. Two different channel configurations are under consideration: grooved channels and obstructed channels. The results reveal that with straight grooves, a well organized vortex flow is formed in the vertical plane along the groove, which leads to a helical flow in the channel. The mixing performance can be enhanced by having grooves on both the top and the bottom walls arranged in a staggered manner, by which the transversal velocity is largely increased. It is seen that the strength of the secondary flow and, thus, the mixing can be improved by suitably choosing geometric parameters of the groove, such as the depth, the width, and the oblique angle. It is also shown that the efficient mixing for the staggered herringbone type groove is due to the fluid stratification caused by the exchange of position of the resulted counter-rotating vortices. As for the obstructed channels, the flows are in essence two dimensional. Very strong transversal velocity can be produced by narrowing down the flow passage in the channel. However, the efficient mixing is obtained at the cost of large pressure head loss.

Microfluidic mixing through oscillatory transverse perturbations

2018 ◽  
Vol 32 (12n13) ◽  
pp. 1840030 ◽  
Author(s):  
J. W. Wu ◽  
H. M. Xia ◽  
Y. Y. Zhang ◽  
P. Zhu
Keyword(s):  
Oscillatory Flow ◽  
Fluid Mixing ◽  
Mixing Enhancement ◽  
Constant Flow ◽  
Central Channel ◽  
Microfluidic Mixing ◽  
Mixing Performance ◽  
Side Channels ◽  
Fluidic Devices ◽  
High Fluid

Fluid mixing in miniaturized fluidic devices is a challenging task. In this work, the mixing enhancement through oscillatory transverse perturbations coupling with divergent circular chambers is studied. To simplify the design, an autonomous microfluidic oscillator is used to produce the oscillatory flow. It is then applied to four side-channels that intersect with a central channel of constant flow. The mixing performance is tested at high fluid viscosities of up to 16 cP. Results show that the oscillatory flow can cause strong transverse perturbations which effectively enhance the mixing. The influence of a fluidic capacitor in the central channel is also examined, which at low viscosities can intensify the perturbations and further improve the mixing.

Enhancement of Mixing in a Microchannel by Using AC-Electroosmotic Effect

2008 ◽  
Author(s):  
Yangyang Wang ◽  
Sangmo Kang ◽  
Yongkweon Suh
Keyword(s):  
Numerical Simulations ◽  
Chaotic Behavior ◽  
Electrode Array ◽  
Longitudinal Direction ◽  
Central Line ◽  
Transverse Flow ◽  
Electrode Pair ◽  
Mixing Performance ◽  
Commercial Code ◽  
Micro Mixer

This study has focused on optimizing the AC-electroosmotic micro-mixer, which is composed of a microchannel with an array of rectangular electrodes attached on the bottom wall. The electrode array is spatial-periodically arranged in pairs symmetric with respect to the longitudinal central line. An AC electrode field is applied to the electrodes, which drives the secondary transverse flow in a circulating cell mode near the electrodes. The main flow along the channel longitudinal direction plus this secondary transverse flow contribute to the stretching and folding of the fluid flow, that is the chaotic behavior, and thus to the enhancement of the fluid mixing. To design the better micro-mixer, numerical simulations have been performed by using a commercial code (CFX 10). In the simulations, the concept of mixing index is employed to evaluate the mixing performance as well as to optimize the size and spacing of each electrode in one pair. It is found that the optimum design of one electrode pair, which leads to the best mixing performance, is not simply harmonic one. When the length ratio of the two electrodes in a pair closes to 2:1, the best mixing effect can be attained. The flow pattern was visualized. Furthermore, the velocity field will be measured with a PTV technique to validate the numerical simulations.

Analytical Solution of Unsteady Casson Fluid Flow Through a Vertical Cylinder with Slip Velocity Effect

2021 ◽  
Vol 87 (1) ◽  
pp. 68-75
Author(s):  
Wan Faezah Wan Azmi ◽  
Ahmad Qushairi Mohamad ◽  
Lim Yeou Jiann ◽  
Sharidan Shafie
Keyword(s):  
Fluid Flow ◽  
Analytical Solution ◽  
Newtonian Fluid ◽  
Analytical Solutions ◽  
Slip Velocity ◽  
Fluid Velocity ◽  
Real Life ◽  
Casson Fluid ◽  
Flow Through ◽  
Velocity Effect

Casson fluid is a non-Newtonian fluid with its unique fluid behaviour because it behaves like an elastic solid or liquid at a certain condition. Recently, there are several studies on unsteady Casson fluid flow through a cylindrical tube have been done by some researchers because it is related with the real-life applications such as blood flow in vessel tube, chemical and oil flow in pipelines and others. Therefore, the main purpose of the present study is to obtain analytical solutions for unsteady flow of Casson fluid pass through a cylinder with slip velocity effect at the boundary condition. Dimensional governing equations are converted into dimensionless forms by using the appropriate dimensionless variables. Dimensionless parameters are obtained through dimensionless process such as Casson fluid parameters. Then, the dimensionless equations of velocity with the associated initial and boundary conditions are solved by using Laplace transform with respect to time variable and finite Hankel transform of zero order with respect to the radial coordinate. Analytical solutions of velocity profile are obtained. The obtained analytical result for velocity is plotted graphically by using Maple software. Based on the obtained result, it can be observed that increasing in Casson parameter, time and slip velocity will lead to increment in fluid velocity. Lastly, Newtonian fluid velocity is uniform from the boundary to the center of cylinder while Casson fluid velocity is decreased when approaching to the center of cylinder. The present result is validated when the obtained analytical solution of velocity is compared with published result and found in a good agreement.

scholarly journals Toward the Next Generation of Passive Micromixers: A Novel 3-D Design Approach

Micromachines ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 372
Author(s):  
Mahmut Burak Okuducu ◽  
Mustafa M. Aral
Keyword(s):  
Molecular Diffusion ◽  
Diffusion Constant ◽  
Interfacial Area ◽  
Laminar Flows ◽  
Fluid Mixing ◽  
Mixing Efficiency ◽  
Maximum Pressure ◽  
Small Diffusion ◽  
Passive Micromixer ◽  
Injection Type

Passive micromixers are miniaturized instruments that are used to mix fluids in microfluidic systems. In microchannels, combination of laminar flows and small diffusion constants of mixing liquids produce a difficult mixing environment. In particular, in very low Reynolds number flows, e.g., Re < 10, diffusive mixing cannot be promoted unless a large interfacial area is formed between the fluids to be mixed. Therefore, the mixing distance increases substantially due to a slow diffusion process that governs fluid mixing. In this article, a novel 3-D passive micromixer design is developed to improve fluid mixing over a short distance. Computational Fluid Dynamics (CFD) simulations are used to investigate the performance of the micromixer numerically. The circular-shaped fluid overlapping (CSFO) micromixer design proposed is examined in several fluid flow, diffusivity, and injection conditions. The outcomes show that the CSFO geometry develops a large interfacial area between the fluid bodies. Thus, fluid mixing is accelerated in vertical and/or horizontal directions depending on the injection type applied. For the smallest molecular diffusion constant tested, the CSFO micromixer design provides more than 90% mixing efficiency in a distance between 260 and 470 µm. The maximum pressure drop in the micromixer is found to be less than 1.4 kPa in the highest flow conditioned examined.

On the longitudinal dispersion of dye whose concentration varies harmonically with time

1973 ◽  
Vol 58 (4) ◽  
pp. 657-667 ◽  
Author(s):  
P. C. Chatwin
Keyword(s):  
Harmonic Function ◽  
Cross Section ◽  
Fluid Velocity ◽  
Laminar Flows ◽  
Longitudinal Dispersion ◽  
Low Frequencies ◽  
High Frequencies ◽  
Downstream Distance ◽  
Concentration Pattern ◽  
Discharge Velocity

In recent years many problems concerned with the dispersion of a passive contaminant along pipes and channels have been investigated, and this paper is concerned with one such problem which arises in diverse applications. This is the study of the longitudinal dispersion of a contaminant whose concentration is prescribed as a harmonic function of time at one cross-section. On the basis of physical arguments and of detailed calculations for two laminar flows it is shown that for high frequencies the concentration pattern is transported downstream at the maximum fluid velocity but that for low frequencies it is transported at the discharge velocity, and that the fluctuations in concentration decay to zero in a much shorter downstream distance for high frequencies than for low frequencies. It is shown further that at high frequencies the concentration is exponentially small except near the places where the fluid velocity attains its maximum, whereas for low frequencies the variation in concentration over the cross-section is small. Some of these conclusions are compared with those made by others, and the agreement is in general satisfactory.

Numerical treatment for solving a model of non-Newtonian Casson fluid flow over an extensible sheet based on maritime field

2021 ◽  
pp. 2150078
Author(s):  
Nourhan I. Ghoneim
Keyword(s):  
Fluid Flow ◽  
Finite Difference ◽  
Mixed Convection ◽  
Numerical Solution ◽  
Slip Velocity ◽  
Fluid Velocity ◽  
Internal Heat ◽  
Casson Fluid ◽  
Flow And Heat Transfer ◽  
Improved Technique

A numerical solution for steady-state, incompressible, laminar Casson fluid flow and heat transfer in the combined region of a boundary layer is presented for the case of mixed convection and slip velocity. Before introducing the present technique of non-Newtonian Casson model, reviewing the literature has been carefully performed, an improved technique for this model is studied, which has not been previously reported. The presented analysis involves the harness of a magnetic field, viscous dissipation, internal heat generation/absorption and the slip velocity. Finite difference method (FDM) has been used to get an accurate and complete numerical solution. In this novel study, it is proved by means of a finite difference technique, that the velocity and the thermal field may be influenced with the presence of mixed convection phenomenon. The results show that both the fluid velocity and temperature may be predicted from the values of the controlling parameters. Finally, the graphical output reveals that the fluid velocity is diminished by strengthening both the Hartman number and the Casson parameter while the reverse characteristics are observed for the Grashof number.

On the advection of spherical and non-spherical particles in a non-uniform flow

1990 ◽  
Vol 333 (1631) ◽  
pp. 289-307 ◽  
Keyword(s):  
Settling Velocity ◽  
Fluid Velocity ◽  
Added Mass ◽  
Laminar Flows ◽  
Chaotic Advection ◽  
Spherical Particles ◽  
Inertial Effects ◽  
Gravitational Settling ◽  
Regular Motion ◽  
Velocity Gradients

Small spherical particles when introduced into a non-uniform or unsteady flow are usually subject to inertial effects, either of the particle mass or of the fluid added-mass, and the gravitational settling. Small non-spherical particles, even when inertial effects are negligible, turn in response to the local fluid velocity gradients and the settling velocity of a particle varies with its orientation. These features are distinct from the response of lagrangian elements which simply move with the local fluid velocity. In this paper these different responses for small, stokesian particles are considered for some example non-uniform laminar flows. It is noted that this added feature may lead to chaotic particle motion where the motion of lagrangian elements is regular, and conversely regular motion where there is chaotic advection of lagrangian elements.

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