Control of Flow Field, Mass Transfer and Mixing Enhancement in T-Shaped Microchannels

2016 ◽  
Vol 33 (3) ◽  
pp. 387-394
Author(s):  
Y. Bazargan-Lari ◽  
S. Movahed ◽  
M. Mashhoodi
Keyword(s):  
Flow Field ◽  
Applied Voltage ◽  
Electroosmotic Flow ◽  
Microfluidic Devices ◽  
Mixing Efficiency ◽  
Mixing Enhancement ◽  
Field Mass ◽  
Control Of Flow ◽  
Micro Mixer ◽  
Two Fluid

AbstractA T-shaped microfluidic micro-mixer was designed to mix desired concentrations of two fluid streams and to prepare their homogenous mixture solution. A hydrostatic pressure gradient was induced in one of the branches of the system (mixing channel) by applying external electric field and generating electroosmotic flow in the two other branches of the system. The flow field and transferred mass into the mixing channel can be regulated by controlling the applied voltage of the system. In order to prepare more homogenous mixture solution, some obstacles were added to the mixing channel to induce perturbation in the flow field and enhance the mixing efficiency of the system. Numerical simulations were performed to show the correctness of the proposed mixing strategy and to investigate the influences of the applied voltage on the mixing efficiency and induced pressure flow in the mixing channel. A proposed design can be used as a guideline to control and enhance mixing efficiency, and consequently functionality, of different microfluidic devices.

Numerical Analysis of Micro-Mixing in Rough Microchannels

2011 ◽  
Vol 189-193 ◽  
pp. 1452-1455 ◽  
Author(s):  
Da Yong Yang
Keyword(s):  
Electroosmotic Flow ◽  
Roughness Element ◽  
Fluid Motion ◽  
Microfluidic Devices ◽  
Practical Significance ◽  
Mixing Efficiency ◽  
The Finite Element Method ◽  
Governing Equations ◽  
Design And Optimization ◽  
Control Fluid

Understanding the micro-mixing of electroosmotic flow is of both fundamental and practical significance for the design and optimization of various microfluidic devices to control fluid motion. In this paper, the governing equations of the micro-mixing in rough microchannels with rectangle surface roughness are solved using the finite element method and the effects of roughness height and space on mixing efficiency are investigated. The results indicate that the effects cannot be ignored and the mixing efficiency increases with the roughness element height and density.

Active Micromixers Based on Polarization Instability and Acoustic Streaming

2011 ◽  
Author(s):  
Nam-Trung Nguyen ◽  
Trung-Dung Luong ◽  
Oliver Ja¨nig
Keyword(s):  
Applied Voltage ◽  
Concentration Polarization ◽  
Acoustic Streaming ◽  
Mixing Efficiency ◽  
Strong Mixing ◽  
Mixing Enhancement ◽  
Square Root ◽  
Interdigitated Electrode ◽  
Active Mixer ◽  
Piezoelectric Substrate

This paper reports two pressure-driven high-throughput active micromixers. Mixing enhancement was achieved with applied external electrical and acoustic fields. In the first active mixer, nanoporous charge-selective Nafion membrane was used to achieve strong mixing vortices. These vortices are caused by electroconvection in the concentration polarization zone above the membrane. The required applied voltage is found to be propotional to the square root of the flow rate. In the second active mixer, surface acoustic wave lauched from an interdigitated electrode deposited on a piezoelectric substrate causes acoustic streaming and improves the mixing efficiency significantly. Surface wave with a frequency of 13 MHz was launched perpendicular to the flow. The mixing efficiency was observed to be proportional to the square of the applied voltage. Compared to conventional parallel electrodes, a focusing design of the interdigitated electrode leads to a better mixing efficiency.

Mixing Enhancement Induced by a Delta Wing in Supersonic Flows

2016 ◽  
Author(s):  
Wei Huang ◽  
Shi-bin Li ◽  
Li Yan ◽  
Jun Liu
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Delta Wing ◽  
Pressure Ratio ◽  
Mixing Efficiency ◽  
Mixing Enhancement ◽  
Mixing Process ◽  
Efficient Operation ◽  
Injection Flow ◽  
Transverse Injection

The maximization of rapid fuel-air mixing is one of the essential issues for the efficient operation of scramjet engines. A delta wing with its height being 6mm is located ahead of the injector to enhance the mixing process between the injectant and air in the supersonic flow with the freestream Mach number being 3.75, and the influence of the distance between the delta wing and the injector on the mixing efficiency is evaluated numerically, as well as the effect of the jet-to-crossflow pressure ratio. At the same time, the predicted results obtained in the three-dimensional transverse injection flow field are compared with the available experimental data in the open literature, and the grid independency analysis is conducted as well. The obtained results show that the mixing efficiency increases with the decrease of the jet-to-crossflow pressure ratio, and this conclusion is consistent with that obtained in the transverse injection flow field. The predicted wall static pressure distributions show reasonable agreement with the experimental data, and the grid scale has only a slight impact on the predicted results. Further, it is observed that the mixing efficiency increase with the decrease of the distance between the delta wing and the injector, and the hydrogen penetrates deeper into the core flow when the distance is smaller. Accordingly, the plume area is larger. This illustrates that the transverse jet flow field is affected by the vortex generated by the delta wing, and the mixing process is enhanced. The maximum mixing efficiency at x = −350mm is nearly 0.84 in the range considered in this paper.

scholarly journals A Numerical Study of Sub-Millisecond Integrated Mix-and-Inject Microfluidic Devices for Sample Delivery at Synchrotron and XFELs

2021 ◽  
Vol 11 (8) ◽  
pp. 3404
Author(s):  
Majid Hejazian ◽  
Eugeniu Balaur ◽  
Brian Abbey
Keyword(s):  
Molecular Dynamics ◽  
Flow Rate ◽  
Numerical Study ◽  
Three Dimensional ◽  
Microfluidic Devices ◽  
Liquid Jets ◽  
Mixing Efficiency ◽  
X Ray Diffraction ◽  
Cross Sectional ◽  
Time Required

Microfluidic devices which integrate both rapid mixing and liquid jetting for sample delivery are an emerging solution for studying molecular dynamics via X-ray diffraction. Here we use finite element modelling to investigate the efficiency and time-resolution achievable using microfluidic mixers within the parameter range required for producing stable liquid jets. Three-dimensional simulations, validated by experimental data, are used to determine the velocity and concentration distribution within these devices. The results show that by adopting a serpentine geometry, it is possible to induce chaotic mixing, which effectively reduces the time required to achieve a homogeneous mixture for sample delivery. Further, we investigate the effect of flow rate and the mixer microchannel size on the mixing efficiency and minimum time required for complete mixing of the two solutions whilst maintaining a stable jet. In general, we find that the smaller the cross-sectional area of the mixer microchannel, the shorter the time needed to achieve homogeneous mixing for a given flow rate. The results of these simulations will form the basis for optimised designs enabling the study of molecular dynamics occurring on millisecond timescales using integrated mix-and-inject microfluidic devices.

Two-fluid electroosmotic flow in microchannels

2005 ◽  
Vol 284 (1) ◽  
pp. 306-314 ◽  
Author(s):  
Yandong Gao ◽  
Teck Neng Wong ◽  
Chun Yang ◽  
Kim Tiow Ooi
Keyword(s):  
Electroosmotic Flow ◽  
Two Fluid

scholarly journals Numerical Analysis of the Heterogeneity Effect on Electroosmotic Micromixers Based on the Standard Deviation of Concentration and Mixing Entropy Index

Micromachines ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1055
Author(s):  
Alireza Farahinia ◽  
Jafar Jamaati ◽  
Hamid Niazmand ◽  
Wenjun Zhang
Keyword(s):  
Reynolds Number ◽  
Zeta Potential ◽  
Electroosmotic Flow ◽  
Molecular Diffusion ◽  
Slip Surface ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Slip Coefficient ◽  
Mixing Rate ◽  
Heterogeneous Distribution

One approach to achieve a homogeneous mixture in microfluidic systems in the quickest time and shortest possible length is to employ electroosmotic flow characteristics with heterogeneous surface properties. Mixing using electroosmotic flow inside microchannels with homogeneous walls is done primarily under the influence of molecular diffusion, which is not strong enough to mix the fluids thoroughly. However, surface chemistry technology can help create desired patterns on microchannel walls to generate significant rotational currents and improve mixing efficiency remarkably. This study analyzes the function of a heterogeneous zeta-potential patch located on a microchannel wall in creating mixing inside a microchannel affected by electroosmotic flow and determines the optimal length to achieve the desired mixing rate. The approximate Helmholtz–Smoluchowski model is suggested to reduce computational costs and simplify the solving process. The results show that the heterogeneity length and location of the zeta-potential patch affect the final mixing proficiency. It was also observed that the slip coefficient on the wall has a more significant effect than the Reynolds number change on improving the mixing efficiency of electroosmotic micromixers, benefiting the heterogeneous distribution of zeta-potential. In addition, using a channel with a heterogeneous zeta-potential patch covered by a slip surface did not lead to an adequate mixing in low Reynolds numbers. Therefore, a homogeneous channel without any heterogeneity would be a priority in such a range of Reynolds numbers. However, increasing the Reynolds number and the presence of a slip coefficient on the heterogeneous channel wall enhances the mixing efficiency relative to the homogeneous one. It should be noted, though, that increasing the slip coefficient will make the mixing efficiency decrease sharply in any situation, especially in high Reynolds numbers.

Simulation of Two Designs of Micro-Mixers With Enhanced Advection Mechanisms

2011 ◽  
Author(s):  
S. A. Kazemi ◽  
M. Passandideh-Fard ◽  
J. Esmaeelpanah
Keyword(s):  
Numerical Study ◽  
Control Volume ◽  
Numerical Technique ◽  
Chaotic Advection ◽  
Mixing Efficiency ◽  
Mixing Length ◽  
Surface Development ◽  
Mixer Design ◽  
Gas Liquid Flow ◽  
Micro Mixer

In this paper, a numerical study of two new designs of passive micro-mixers based on chaotic advection is presented. The advection phenomenon in a T-shaped micro-mixer is enhanced using a segmented gas-liquid flow; and a peripheral/axial mixing mechanism. The simulations are performed for two non-reactive miscible gases: oxygen and methanol. The numerical model employed for this study is based on the solution of the physical governing equations namely the continuity, momentum, species transport and an equation to track the free surface development. The equations are discretized using a control volume numerical technique. The distribution of the species concentration within the domain is calculated based on which a mixing intensity factor is introduced. This factor is then used as a criterion for the mixing length. In the first micro-mixer design with a drop injection mechanism for a typical condition, the mixing length is reduced by nearly 15%. Compared to that of a simple T-shaped micro-mixer with the same flow rates, the two gases interface area is increased in axisymmetric micro-mixer leading to an increase of the mixing efficiency and a reduction of the mixing length. Also, the effects of the baffles height and span on the mixing efficiency and length in axisymmetric micro-mixer are studied. Having baffles in the channel can substantially decrease the mixing length.

Chaotic Electroosmotic Flow

2002 ◽  
Author(s):  
Shizhi Qian ◽  
Haim H. Bau
Keyword(s):  
Zeta Potential ◽  
Electroosmotic Flow ◽  
Analytic Solution ◽  
Microfluidic Devices ◽  
Chaotic Advection ◽  
Uniform Electric Field ◽  
Periodic Modulation ◽  
Chaotic Flows ◽  
Zeta Potentials ◽  
Series Convergence

Two dimensional, time-independent and time-dependent electroosmotic flows driven by a uniform electric field in rectangular cavities with uniform and non-uniform zeta potential distributions along the cavities’ walls are investigated theoretically. The time-independent flow fields are computed with the aid of Fourier series. The series’ convergence is accelerated so that highly accurate solutions are obtained with just a few (<10) terms in the series. The analytic solution is used to compute flow patterns for various distributions of the zeta potential along the cavities’ boundaries. It is demonstrated that by time-wise periodic modulation of the zeta potentials, one can induce chaotic advection in the cavities. Such chaotic flows may be used to stir and mix fluids in microfluidic devices.

Density Distribution in Stagnation Region of Saffman Equation for Dusty Gas

2002 ◽  
Author(s):  
Kazuhiro Tsuboi
Keyword(s):  
Flow Field ◽  
Particle Density ◽  
Stokes Number ◽  
The Body ◽  
Particle Flow ◽  
Particle Phase ◽  
Primary Interest ◽  
Stagnation Region ◽  
Two Fluid ◽  
Good Agreement

We investigate the behaviour of flow field around an obstacle placed in uniform particle flow based on two-fluid Saffman equation. Particle density in the vicinity of the front stagnation point is, in particular, the primary interest in the present study. In the case of small Stokes number, in which particle impingement does not occur, there exists the exact solution of the flow field of particle phase is obtained. Perturbed solution is also obtained in the reciprocal of Stokes number when Stokes number is large enough. Comparison between numerical results and these solutions shows good agreement and the peak of particle density appears near the threshold of partide impingement to the body surface.

Sign in / Sign up

Export Citation Format

Share Document