A Planar Labyrinth Micromixer

2010 ◽  
Author(s):  
Jeremy T. Cogswell ◽  
Peng Li ◽  
Mohammad Faghri
Keyword(s):  
Soft Lithography ◽  
Lab On A Chip ◽  
Fluorescein Isothiocyanate ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Mixing Length ◽  
Two Fluids ◽  
Curved Channels ◽  
Passive Mixing ◽  
Important Challenge

Rapid mixing of two fluids in microchannels has posed an important challenge to the development of many integrated lab-on-a-chip systems. In this paper, we present a planar labyrinth micromixer (PLM) to achieve rapid and passive mixing by taking advantage of a synergistic combination of the Dean vortices in curved channels, a series of perturbation to the fluids from the sharp turns, and an expansion and contraction of the flow field via a circular chamber. The PLM is constructed in a single soft lithography step and the labyrinth has a footprint of 7.32 mm × 7.32 mm. Experiments using fluorescein isothiocyanate solutions and deionized water demonstrate that the design achieves fast and uniform mixing within 9.8 s to 32 ms for Reynolds numbers between 2.5 and 30. Compared to the mixing in the prevalent serpentine design, our design results in 38% and 79% improvements on the mixing efficiency at Re = 5 and Re = 30 respectively. An inverse relationship between mixing length and mass transfer Pe´clet number (Pe) is observed, which is superior to the logarithmic dependence of mixing length on Pe in chaotic mixers. Having a simple planar structure, the PLM can be easily integrated into lab-on-a-chip devices where passive mixing is needed.

scholarly journals A Computational Study on Mixing of Two-Phase Flow in Microchannels

2003 ◽  
Author(s):  
Farshid Bondar ◽  
Francine Battaglia
Keyword(s):  
Computational Study ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Mixing Index ◽  
Wave Type ◽  
Two Phase ◽  
Chaotic Flows ◽  
Two Fluids ◽  
Passive Mixing ◽  
Better Than

The passive mixing of water and alcohol, as two fluids with different densities, is carried out computationally in three-dimensional microchannels. Four designs of microchannels are considered to investigate the efficiency of mixing for Reynolds numbers ranging between 6 and 96. In a straight-type microchannel, mixing is very poor. In a square-wave-type microchannel, mixing is marginally better than the straight one. Mixing in the serpentine-type and twisted-type microchannels develops considerable better than the first two microchannels, especially at higher Reynolds numbers. However, in the twisted microchannel, the mixing index is substantially larger compared to the serpentine microchannel for the Reynolds number of 35. The higher mixing index implies the occurrence of spatially chaotic flows with a higher degree of chaos compared to the case of the serpentine microchannel. The results are compared quantitatively and qualitatively in Eulerian and Lagrangian frameworks and a correlation between Lagrangian chaos and Eulerian chaos is concluded.

A Microfluidic Mixer Fabricated From Compliant Thermoplastic Films

2008 ◽  
Vol 2 (1) ◽  
Author(s):  
N. Paya ◽  
T. Dankovic ◽  
A. Feinerman
Keyword(s):  
Reynolds Number ◽  
Lab On A Chip ◽  
Microfluidic Devices ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Minimal Amount ◽  
Microfluidic Mixer ◽  
Mixing Performance ◽  
Rapid Mixing ◽  
Microfluidic Flows

Mixing is often crucial to the operation of various microfluidic devices. And the most common objective is rapid mixing between two initially segregated fluid streams in a minimal amount of space. In microfluidic flows characterized by incompressibility and low Reynolds number, however, turbulence is almost entirely absent and mixing generally relies on diffusion. Therefore, based on the properties of the fluids involved, it can take impractically long to achieve high mixing efficiency in some cases. To resolve this problem, this paper demonstrates a novel compliant micromixer made of thermoplastic films for lab-on-a-chip applications. The microfluidic mixer utilizes self-rotation effects to achieve high mixing efficiency at Reynolds numbers below 100. In addition, a possible design is suggested for a thermoplastic voltage-actuated micromixer which can lead to even better mixing performance at Reynolds numbers below 1.

Quantitative Evaluation of Mixing Efficiency of Split-and-Recombine Mixing Method

2005 ◽  
Author(s):  
Osamu Hamanaka ◽  
Hiroharu Kato
Keyword(s):  
Secondary Flow ◽  
Quantitative Measure ◽  
Thin Layers ◽  
Mixing Efficiency ◽  
Abrupt Increase ◽  
Two Fluids ◽  
Fluid Analysis ◽  
Curved Channels ◽  
Split Point ◽  
Mixing Method

In this paper, we present the acceleration of mixing and chemical reaction by a split-and-recombine (SAR) mixing method quantitatively, which was performed by numerical computation using the heat fluid analysis software, Star-CD. The authors have newly defined the mixing efficiency, which is a quantitative measure of the mixing of two fluids. The calculated result of the mixing efficiency in SAR device with two different channel configurations, angled and curved channels, showed that the secondary flow is important in increasing mixing efficiency. The angled channel is more effective than the curved channel, because the secondary flow is much stronger in the angled channel. The abrupt increase in sectional area also increases mixing efficiency. The split angle at the split point in the SAR device also affects mixing efficiency, because the secondary flow becomes stronger with the split angle. The mixing efficiency was greater (about 1.3 times) with a split angle of 45 degrees than that with a split angle of 15 degrees. According to the above-mentioned results, the authors designed a three-successive-SAR device, whose mixing efficiency was approximately 7.5 times greater than that of straight channel. The present findings are different from the existing mixing increase concept of the SAR device, which produces many thin layers from two fluids.

Flow Pulsation and Geometry Effects on Mixing of Two Miscible Fluids in Microchannels

2014 ◽  
Vol 136 (12) ◽  
Author(s):  
Houssein Ammar ◽  
Ahmed Ould el Moctar ◽  
Bertrand Garnier ◽  
Hassan Peerhossaini
Keyword(s):  
Reynolds Number ◽  
Residence Time ◽  
Pure Water ◽  
Mixing Efficiency ◽  
Mixing Enhancement ◽  
Flow Pulsation ◽  
Mean Flow ◽  
Mixing Index ◽  
Two Fluids ◽  
Passive Mixing

Many microfluidic applications involve chemical reactions. Most often, the flow is predominantly laminar, and without active or passive mixing enhancement the reaction time can be extremely long compared to the residence time. In this work we demonstrate the merits of the combination of flow pulsation and geometrical characteristics in enhancing mixing efficiency in microchannels. Mixing was studied by introducing a mixing index based on the gray level observed in a heterogeneous flow of pure water and water colored by rhodamine B. The effects of the injection geometry at the microchannel inlet and the use of pulsed flows with average Reynolds numbers between 0.8 and 2 were studied experimentally and numerically. It appeared that the mixing index increases with the nondimensional residence time (τ), which is inversely proportional to the Reynolds number. In addition, we show that the mixing efficiency depends strongly on the geometry of the intersection between the two fluids. Better mixing was achieved with sharp corners (arrowhead and T intersections) in all cases investigated. In pulsed flow, the mixing efficiency is shown to depend strongly on the ratio (β) between the peak amplitude and the mean flow rate. Optimal conditions for mixing in the microchannels are summarized as a function of Reynolds number Re, the ratio β, and the geometries.

The Numerical Investigation of an Interdigital Micromixer With the Circular-Sector Obstacles

2009 ◽  
Author(s):  
Yan Feng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Surface Area ◽  
Molecular Diffusion ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Mixing Enhancement ◽  
Mixing Length ◽  
Circular Sector ◽  
Lateral Direction ◽  
Low Reynolds Numbers ◽  
Low Reynolds

In this paper, a passive interdigital micromixer with the circular-sector obstacles is proposed and the mixing performance is estimated by numerical simulation. The tested Reynolds numbers range from 0.01 to 10. Flow recirculation or vortices seems impossible to generate to enhance the mixing at such low Reynolds numbers. Hence, molecular diffusion is the dominant mixing mechanism. Based on the diffusion principle, enlarging the mixing length, reducing the diffusion length and increasing the surface area between species are major methods to obtain mixing enhancement. In order to achieve rapid mixing, shortening the mixing length is necessary. However, the reduced mixing length induces the decreased mixing time which the species take to mix. The circular-section obstacles are placed in the straight microchannels to enlarge the contact surface area between species. The flow path is distorted after passing the obstacles so that the real mixing length increases compared with traditional T-shape micromixers. Furthermore, flow advection takes a part role in mixing since the velocity direction is no longer perpendicular to diffusion direction. Different geometries and layouts of obstacles are analyzed for optimization. The results of optimal design show the worst mixing efficiency, around 50%, occurs at Re = 1. In order to improve the lower limitation of mixing efficiency, the duplicated layouts of obstacles in lateral direction with interdigital inlet are applied to reduce the diffusion path and increase the interface area so that the mixing efficiency could be enhanced. The results show that the mixing efficiency could achieve 85% at Re ≤ 1 with a low pressure drop of 100 Pa. It has the potential to be used in applications with low Reynolds numbers.

Numerical Investigation and Geometric Parameterization of Lamination Inlet of Passive Micromixer

2010 ◽  
Author(s):  
Yanfeng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Mixing Length ◽  
Straight Channel ◽  
Interface Area ◽  
Mixing Performance ◽  
Passive Micromixer ◽  
Two Parameters ◽  
Parallel Type

A lamination inlet is proposed and optimized in this paper. The perpendicular incoming fluids are applied instead of parallel type. The total mixing length is fixed at 3.2 mm and the depth of channel is fixed at 0.1 mm. The tested Reynolds number is calculated at the entrance of downstream straight channel. The tested Reynolds numbers range from 5 to 200. The perpendicular incoming type enhances the mass-convection and enlarges the interface area. Two parameters, the radius of holes (R) and the distance between two holes (D1), are selected to achieve the optimization. Numerical simulation is used to estimate the mixing performance and flow characteristics. The results show that the vortices are generated in the microchannel. The interface becomes irregular. In order to evaluate the mixing improvement, the parallel lamination is also simulated. The comparison shows that the perpendicular inlet type has better mixing efficiency than the parallel lamination type. This inlet type could be connected with certain mixing element to achieve the applications in biochemistry.

Numerical Investigations of a Passive Micromixer Based on Minkowski Fractal Principle

2019 ◽  
Vol 18 (2) ◽  
Author(s):  
Yao Chen ◽  
Xueye Chen
Keyword(s):  
Pressure Drop ◽  
Flow Direction ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Numerical Investigations ◽  
Two Fluids ◽  
Chaotic Convection ◽  
Passive Micromixer ◽  
Minkowski Fractal ◽  
Obstacle Height

Abstract This paper is mainly to study the mixing efficiency and pressure drop of the Minkowski fractal obstacle micromixers. The mixing efficiency of primary Minkowski fractal obstacle (PMFO) micromixer and secondary Minkowski fractal obstacle (SMFO) micromixer are compared at five kinds of Reynolds numbers. With the increase of obstacle height and the decrease of distance, the chaotic convection in the microchannel is enhanced. Especially at obstacle height (h) = 0.2 mm, obstacle distance (D) = 0.15 mm, and Re = 100, the vortex caused by the Minkowski fractal obstacle structure is more obvious. In addition, vortex phenomenon increases the contact area of two fluids and enhances chaotic convection. It shows that the flow direction of the fluid in the microchannel varies significantly.

Two Fluid Mixing in a Micromixer with Helical Channels and Grooved Surfaces

2013 ◽  
Vol 284-287 ◽  
pp. 2096-2101
Author(s):  
Ya Hui Hu ◽  
Farn Shiun Hwu ◽  
Kao Hui Lin
Keyword(s):  
Pure Water ◽  
Reynolds Numbers ◽  
Acetone Solution ◽  
Mixing Efficiency ◽  
Inspection Method ◽  
Two Fluids ◽  
Biomedical Diagnosis ◽  
Passive Micromixer ◽  
Image Inspection ◽  
Helical Channels

The mixing behavior of two fluids in a passive micromixer with a Y-type inlet and helical fluid channels with herringbone grooves etched into the bottom was studied in a numerical simulation and experiments. The mixing of the pure water and acetone solution prepared with different Reynolds numbers and acetone concentrations was investigated. An image inspection method using the variance in contrast of the image gray level as the measurement parameter was adopted to calculate the mixing efficiency distribution. Inspection results show that the mixing efficiency decreased with the increase in the concentration of the acetone solution, although the mixing efficiency around the outlet reached to a value of 90%, even when the Reynolds numbers of the fluids were as low as Re = 1, and the best efficiency achieved for the case of Re = 10 was over 98%. The results show that it should be possible to apply the proposed micromixer in the field of biomedical diagnosis.

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.

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