Special Issue "Passive Micromixers"

A special issue of Micromachines (ISSN 2072-666X).

Deadline for manuscript submissions: closed (31 January 2018).

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Prof. Dr. Kwang-Yong Kim
E-Mail Website
Guest Editor
Department of Mechanical Engineering, Inha University, Incheon, 22212, Korea
Interests: micromixer; micro heat sink; fluid machinery; optimization; heat transfer
Special Issues and Collections in MDPI journals
Prof. Dr. Mubashshir A. Ansari
E-Mail Website
Guest Editor
Department of Mechanical Engineering, Aligarh Muslim University, Uttar Pradesh 202001, India
Interests: MEMS; microfluidics; micromixer; microparticle separation
Dr. Arshad Afzal
E-Mail Website
Guest Editor
Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Uttar Pradesh 208016, India
Interests: microfluidics; gas turbine cooling; surrogate modeling; thermal-fluid design optimization

Special Issue Information

Dear Colleagues,

Micro-total analysis systems and lab-on-a-chip platforms are widely used for sample preparation and analysis, drug delivery, and biological and chemical syntheses. Micromixer is an important component in these applications. Rapid and efficient mixing is a challenging task in the design and development of micromixers. The flow in micromixers is laminar, and, thus, the mixing is primarily dominated by diffusion. Recently, diverse techniques have been developed to promote mixing by enlarging the interfacial area between the fluids or by increasing the residential time of fluids in the micromixer. Based on their mixing mechanism, micromixers are classified into two types: Active and passive. Passive micromixers are easy to fabricate and generally use geometry modification to cause chaotic advection or lamination to promote the mixing of the fluid samples, unlike active micromixers which use moving parts or some external agitation/energy for the mixing. Many researchers have studied various geometries to design efficient passive micromixers. Recently, numerical optimization techniques based on computational fluid dynamic analysis have been proven to be efficient tools in the design of micromixers. The current Special Issue covers new mechanism, design, numerical and/or experimental mixing analysis, and design optimization of various passive micromixers.

Prof. Dr. Kwang-Yong Kim
Prof. Dr. Mubashshir A. Ansari
Dr. Arshad Afzal
Guest Editors

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Keywords

  • passive micromixer

  • micromixer design

  • analysis of mixing

  • design optimization

  • mixing mechanism

Published Papers (11 papers)

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Editorial

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Open AccessEditorial
Editorial for the Special Issue on Passive Micromixers
Micromachines 2018, 9(5), 250; https://doi.org/10.3390/mi9050250 - 21 May 2018
Viewed by 899
Abstract
Micromixers are important components of microfluidic systems [...] Full article
(This article belongs to the Special Issue Passive Micromixers)

Research

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Open AccessArticle
Performance Analysis and Numerical Evaluation of Mixing in 3-D T-Shape Passive Micromixers
Micromachines 2018, 9(5), 210; https://doi.org/10.3390/mi9050210 - 28 Apr 2018
Cited by 13 | Viewed by 1742
Abstract
In micromixer devices, laminar characteristics of the flow domain and small diffusion constants of the fluid samples that are mixed characterize the mixing process. The advection dominant flow and transport processes that develop in these devices not only create significant challenges for numerical [...] Read more.
In micromixer devices, laminar characteristics of the flow domain and small diffusion constants of the fluid samples that are mixed characterize the mixing process. The advection dominant flow and transport processes that develop in these devices not only create significant challenges for numerical solution of the problem, but they are also the source of numerical errors which may lead to confusing performance evaluations that are reported in the literature. In this study, the finite volume method (FVM) and finite element method (FEM) are used to characterize these errors and critical issues in numerical performance evaluations are highlighted. In this study, we used numerical methods to evaluate the mixing characteristics of a typical T-shape passive micromixer for several flow and transport parameters using both FEM and FVM, although the numerical procedures described are also equally applicable to other geometric designs as well. The outcome of the study shows that the type of stabilization technique used in FEM is very important and should be documented and reported. Otherwise, erroneous mixing performance may be reported since the added artificial diffusion may significantly affect the mixing performance in the device. Similarly, when FVM methods are used, numerical diffusion errors may become important for certain unstructured discretization techniques that are used in the idealization of the solution domain. This point needs to be also analyzed and reported when FVM is used in performance evaluation of micromixer devices. The focus of this study is not on improving the mixing performance of micromixers. Instead, we highlight the bench scale characteristics of the solutions and the mixing evaluation procedures used when FVM and FEM are employed. Full article
(This article belongs to the Special Issue Passive Micromixers)
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Open AccessArticle
Numerical and Experimental Study on Mixing Performances of Simple and Vortex Micro T-Mixers
Micromachines 2018, 9(5), 204; https://doi.org/10.3390/mi9050204 - 27 Apr 2018
Cited by 19 | Viewed by 2242
Abstract
Vortex flow increases the interface area of fluid streams by stretching along with providing continuous stirring action to the fluids in micromixers. In this study, experimental and numerical analyses on a design of micromixer that creates vortex flow were carried out, and the [...] Read more.
Vortex flow increases the interface area of fluid streams by stretching along with providing continuous stirring action to the fluids in micromixers. In this study, experimental and numerical analyses on a design of micromixer that creates vortex flow were carried out, and the mixing performance was compared with a simple micro T-mixer. In the vortex micro T-mixer, the height of the inlet channels is half of the height of the main mixing channel. The inlet channel connects to the main mixing channel (micromixer) at the one end at an offset position in a fashion that creates vortex flow. In the simple micro T-mixer, the height of the inlet channels is equal to the height of the channel after connection (main mixing channel). Mixing of fluids and flow field have been analyzed for Reynolds numbers in a range from 1–80. The study has been further extended to planar serpentine microchannels, which were combined with a simple and a vortex T-junction, to evaluate and verify their mixing performances. The mixing performance of the vortex T-mixer is higher than the simple T-mixer and significantly increases with the Reynolds number. The design is promising for efficiently increasing mixing simply at the T-junction and can be applied to all micromixers. Full article
(This article belongs to the Special Issue Passive Micromixers)
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Open AccessArticle
Topology Optimization of Passive Micromixers Based on Lagrangian Mapping Method
Micromachines 2018, 9(3), 137; https://doi.org/10.3390/mi9030137 - 20 Mar 2018
Cited by 8 | Viewed by 1688
Abstract
This paper presents an optimization-based design method of passive micromixers for immiscible fluids, which means that the Peclet number infinitely large. Based on topology optimization method, an optimization model is constructed to find the optimal layout of the passive micromixers. Being different from [...] Read more.
This paper presents an optimization-based design method of passive micromixers for immiscible fluids, which means that the Peclet number infinitely large. Based on topology optimization method, an optimization model is constructed to find the optimal layout of the passive micromixers. Being different from the topology optimization methods with Eulerian description of the convection-diffusion dynamics, this proposed method considers the extreme case, where the mixing is dominated completely by the convection with negligible diffusion. In this method, the mixing dynamics is modeled by the mapping method, a Lagrangian description that can deal with the case with convection-dominance. Several numerical examples have been presented to demonstrate the validity of the proposed method. Full article
(This article belongs to the Special Issue Passive Micromixers)
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Open AccessArticle
Multi-Objective Optimizations of a Serpentine Micromixer with Crossing Channels at Low and High Reynolds Numbers
Micromachines 2018, 9(3), 110; https://doi.org/10.3390/mi9030110 - 04 Mar 2018
Cited by 9 | Viewed by 1843
Abstract
In order to maximize the mixing performance of a micromixer with an integrated three-dimensional serpentine and split-and-recombination configuration, multi-objective optimizations were performed at two different Reynolds numbers, 1 and 120, based on numerical simulation. Numerical analyses of fluid flow and mixing in the [...] Read more.
In order to maximize the mixing performance of a micromixer with an integrated three-dimensional serpentine and split-and-recombination configuration, multi-objective optimizations were performed at two different Reynolds numbers, 1 and 120, based on numerical simulation. Numerical analyses of fluid flow and mixing in the micromixer were performed using three-dimensional Navier-Stokes equations and convection-diffusion equation. Three dimensionless design variables that were related to the geometry of the micromixer were selected as design variables for optimization. Mixing index at the exit and pressure drop through the micromixer were employed as two objective functions. A parametric study was carried out to explore the effects of the design variables on the objective functions. Latin hypercube sampling method as a design-of-experiment technique has been used to select design points in the design space. Surrogate modeling of the objective functions was performed by using radial basis neural network. Concave Pareto-optimal curves comprising of Pareto-optimal solutions that represents the trade-off between the objective functions were obtained using a multi-objective genetic algorithm at Re = 1 and 120. Through the optimizations, maximum enhancements of 18.8% and 6.0% in mixing index were achieved at Re = 1 and 120, respectively. Full article
(This article belongs to the Special Issue Passive Micromixers)
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Open AccessArticle
Mixing Enhancement in Serpentine Micromixers with a Non-Rectangular Cross-Section
Micromachines 2018, 9(3), 107; https://doi.org/10.3390/mi9030107 - 02 Mar 2018
Cited by 28 | Viewed by 2227
Abstract
In this numerical study, a new type of serpentine micromixer involving mixing units with a non-rectangular cross-section is investigated. Similar to other serpentine/spiral shaped micromixers, the design exploits the formation of transversal vortices (Dean flows) in pressure-driven systems, associated with the centrifugal forces [...] Read more.
In this numerical study, a new type of serpentine micromixer involving mixing units with a non-rectangular cross-section is investigated. Similar to other serpentine/spiral shaped micromixers, the design exploits the formation of transversal vortices (Dean flows) in pressure-driven systems, associated with the centrifugal forces experienced by the fluid as it is confined to move along curved geometries. In contrast with other previous designs, though, the use of non-rectangular cross-sections that change orientation between mixing units is exploited to control the center of rotation of the transversal flows formed. The associated extensional flows that thus develop between the mixing segments complement the existent rotational flows, leading to a more complex fluid motion. The fluid flow characteristics and associated mixing are determined numerically from computational solutions to Navier–Stokes equations and the concentration-diffusion equation. It is found that the performance of the investigated mixers exceeds that of simple serpentine channels with a more consistent behavior at low and high Reynolds numbers. An analysis of the mixing quality using an entropic mixing index indicates that maximum mixing can be achieved at Reynolds numbers as small as 20 in less than four serpentine mixing units. Full article
(This article belongs to the Special Issue Passive Micromixers)
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Open AccessArticle
Optimization of Wavy-Channel Micromixer Geometry Using Taguchi Method
Micromachines 2018, 9(2), 70; https://doi.org/10.3390/mi9020070 - 06 Feb 2018
Cited by 6 | Viewed by 2094
Abstract
The micro-mixer has been widely used in mixing processes for chemical and pharmaceutical industries. We introduced an improved and easy to manufacture micro-mixer design utilizing the wavy structure micro-channel T-junction which can be easily manufactured using a simple stamping method. Here, we aim [...] Read more.
The micro-mixer has been widely used in mixing processes for chemical and pharmaceutical industries. We introduced an improved and easy to manufacture micro-mixer design utilizing the wavy structure micro-channel T-junction which can be easily manufactured using a simple stamping method. Here, we aim to optimize the geometrical parameters, i.e., wavy frequency, wavy amplitude, and width and height of the micro channel by utilizing the robust Taguchi statistical method with regards to the mixing performance (mixing index), pumping power and figure of merit (FoM). The interaction of each design parameter is evaluated. The results indicate that high mixing performance is not always associated with high FoM due to higher pumping power. Higher wavy frequency and amplitude is required for good mixing performance; however, this is not the case for pumping power due to an increase in Darcy friction loss. Finally, the advantages and limitations of the designs and objective functions are discussed in the light of present numerical results. Full article
(This article belongs to the Special Issue Passive Micromixers)
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Open AccessArticle
3D Multi-Microchannel Helical Mixer Fabricated by Femtosecond Laser inside Fused Silica
Micromachines 2018, 9(1), 29; https://doi.org/10.3390/mi9010029 - 16 Jan 2018
Cited by 21 | Viewed by 2078
Abstract
Three-dimensional (3D) multi-microchannel mixers can meet the requirements of different combinations according to actual needs. Rapid and simple creation of 3D multi-microchannel mixers in a “lab-on-a-chip” platform is a significant challenge in micromachining. In order to realize the complex mixing functions of microfluidic [...] Read more.
Three-dimensional (3D) multi-microchannel mixers can meet the requirements of different combinations according to actual needs. Rapid and simple creation of 3D multi-microchannel mixers in a “lab-on-a-chip” platform is a significant challenge in micromachining. In order to realize the complex mixing functions of microfluidic chips, we fabricated two kinds of complex structure micromixers for multiple substance mixes simultaneously, separately, and in proper order. The 3D multi-microchannel mixers are fabricated by femtosecond laser wet etch technology inside fused silica. The 3D multi-microchannel helical mixers have desirable uniformity and consistency, which will greatly expand their utility and scope of application. Full article
(This article belongs to the Special Issue Passive Micromixers)
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Open AccessArticle
Analysis of Passive Mixing in a Serpentine Microchannel with Sinusoidal Side Walls
Micromachines 2018, 9(1), 8; https://doi.org/10.3390/mi9010008 - 28 Dec 2017
Cited by 17 | Viewed by 2993
Abstract
Sample mixing is difficult in microfluidic devices because of laminar flow. Micromixers are designed to ensure the optimal use of miniaturized devices. The present study aims to design a chaotic-advection-based passive micromixer with enhanced mixing efficiency. A serpentine-shaped microchannel with sinusoidal side walls [...] Read more.
Sample mixing is difficult in microfluidic devices because of laminar flow. Micromixers are designed to ensure the optimal use of miniaturized devices. The present study aims to design a chaotic-advection-based passive micromixer with enhanced mixing efficiency. A serpentine-shaped microchannel with sinusoidal side walls was designed, and three cases, with amplitude to wavelength (A/λ) ratios of 0.1, 0.15, and 0.2 were investigated. Numerical simulations were conducted using the Navier–Stokes equations, to determine the flow field. The flow was then coupled with the convection–diffusion equation to obtain the species concentration distribution. The mixing performance of sinusoidal walled channels was compared with that of a simple serpentine channel for Reynolds numbers ranging from 0.1 to 50. Secondary flows were observed at high Reynolds numbers that mixed the fluid streams. These flows were dominant in the proposed sinusoidal walled channels, thereby showing better mixing performance than the simple serpentine channel at similar or less mixing cost. Higher mixing efficiency was obtained by increasing the A/λ ratio. Full article
(This article belongs to the Special Issue Passive Micromixers)
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Open AccessArticle
A Numerical Research of Herringbone Passive Mixer at Low Reynold Number Regime
Micromachines 2017, 8(11), 325; https://doi.org/10.3390/mi8110325 - 31 Oct 2017
Cited by 7 | Viewed by 2498
Abstract
Passive mixing based on microfluidics has won its popularity for its unique advantage, including easier operation, more efficient mixing performance and higher access to high integrity. The time-scale and performance of mixing process are usually characterized by mixing quality, which has been remarkably [...] Read more.
Passive mixing based on microfluidics has won its popularity for its unique advantage, including easier operation, more efficient mixing performance and higher access to high integrity. The time-scale and performance of mixing process are usually characterized by mixing quality, which has been remarkably improved due to the introduction of chaos theory into passive micro mixers. In this paper, we focus on the research of mixing phenomenon at extremely low Reynold number (Re) regime in a chaotic herringbone mixer. Three-dimensional (3D) modeling has been carried out using computational fluid dynamics (CFD) method, to simulate the chaos-enhanced advection diffusion process. Static mixing processes using pressure driven and electric field driven modes are investigated. Based on the simulation results, the effects of flow field and herringbone pattern are theoretically studied and compared. Both in pressure driven flow and electro-osmotic flow (EOF), the mixing performance is improved with a lower flow rate. Moreover, it is noted that with a same total flow rate, mixing performance is better in EOF than pressure driven flow, which is mainly due to the difference in flow field distribution of pressure driven flow and EOF. Full article
(This article belongs to the Special Issue Passive Micromixers)
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Review

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Open AccessReview
A Review on Micromixers
Micromachines 2017, 8(9), 274; https://doi.org/10.3390/mi8090274 - 11 Sep 2017
Cited by 135 | Viewed by 5779
Abstract
Microfluidic devices have attracted increasing attention in the fields of biomedical diagnostics, food safety control, environmental protection, and animal epidemic prevention. Micromixing has a considerable impact on the efficiency and sensitivity of microfluidic devices. This work reviews recent advances on the passive and [...] Read more.
Microfluidic devices have attracted increasing attention in the fields of biomedical diagnostics, food safety control, environmental protection, and animal epidemic prevention. Micromixing has a considerable impact on the efficiency and sensitivity of microfluidic devices. This work reviews recent advances on the passive and active micromixers for the development of various microfluidic chips. Recently reported active micromixers driven by pressure fields, electrical fields, sound fields, magnetic fields, and thermal fields, etc. and passive micromixers, which owned two-dimensional obstacles, unbalanced collisions, spiral and convergence-divergence structures or three-dimensional lamination and spiral structures, were summarized and discussed. The future trends for micromixers to combine with 3D printing and paper channel were brought forth as well. Full article
(This article belongs to the Special Issue Passive Micromixers)
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