Editorial

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2 pages, 161 KiB

Open AccessEditorial

Editorial for the Special Issue on Passive Micromixers

by Arshad Afzal, Mubashshir A. Ansari and Kwang-Yong Kim

Micromachines 2018, 9(5), 250; https://doi.org/10.3390/mi9050250 - 21 May 2018

Cited by 1 | Viewed by 2440

Abstract

Micromixers are important components of microfluidic systems [...] Full article

(This article belongs to the Special Issue Passive Micromixers)

Research

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28 pages, 11988 KiB

Open AccessArticle

Performance Analysis and Numerical Evaluation of Mixing in 3-D T-Shape Passive Micromixers

by Mahmut Burak Okuducu and Mustafa M. Aral

Micromachines 2018, 9(5), 210; https://doi.org/10.3390/mi9050210 - 28 Apr 2018

Cited by 24 | Viewed by 4885

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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14 pages, 6717 KiB

Open AccessArticle

Numerical and Experimental Study on Mixing Performances of Simple and Vortex Micro T-Mixers

by Mubashshir Ahmad Ansari, Kwang-Yong Kim and Sun Min Kim

Micromachines 2018, 9(5), 204; https://doi.org/10.3390/mi9050204 - 27 Apr 2018

Cited by 39 | Viewed by 5808

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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15 pages, 4089 KiB

Open AccessArticle

Topology Optimization of Passive Micromixers Based on Lagrangian Mapping Method

by Yuchen Guo, Yifan Xu, Yongbo Deng and Zhenyu Liu

Micromachines 2018, 9(3), 137; https://doi.org/10.3390/mi9030137 - 20 Mar 2018

Cited by 13 | Viewed by 3886

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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18 pages, 5300 KiB

Open AccessArticle

Multi-Objective Optimizations of a Serpentine Micromixer with Crossing Channels at Low and High Reynolds Numbers

by Wasim Raza, Sang-Bum Ma and Kwang-Yong Kim

Micromachines 2018, 9(3), 110; https://doi.org/10.3390/mi9030110 - 04 Mar 2018

Cited by 18 | Viewed by 3995

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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11 pages, 2654 KiB

Open AccessArticle

Mixing Enhancement in Serpentine Micromixers with a Non-Rectangular Cross-Section

by Joshua Clark, Miron Kaufman and Petru S. Fodor

Micromachines 2018, 9(3), 107; https://doi.org/10.3390/mi9030107 - 02 Mar 2018

Cited by 67 | Viewed by 6219

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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14 pages, 1635 KiB

Open AccessArticle

Optimization of Wavy-Channel Micromixer Geometry Using Taguchi Method

by Nita Solehati, Joonsoo Bae and Agus P. Sasmito

Micromachines 2018, 9(2), 70; https://doi.org/10.3390/mi9020070 - 06 Feb 2018

Cited by 13 | Viewed by 6159

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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7 pages, 2063 KiB

Open AccessArticle

3D Multi-Microchannel Helical Mixer Fabricated by Femtosecond Laser inside Fused Silica

by Chao Shan, Feng Chen, Qing Yang, Zhuangde Jiang and Xun Hou

Micromachines 2018, 9(1), 29; https://doi.org/10.3390/mi9010029 - 16 Jan 2018

Cited by 33 | Viewed by 4501

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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5177 KiB

Open AccessArticle

Analysis of Passive Mixing in a Serpentine Microchannel with Sinusoidal Side Walls

by Muhammad Usman Javaid, Taqi Ahmad Cheema and Cheol Woo Park

Micromachines 2018, 9(1), 8; https://doi.org/10.3390/mi9010008 - 28 Dec 2017

Cited by 41 | Viewed by 6953

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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9004 KiB

Open AccessArticle

A Numerical Research of Herringbone Passive Mixer at Low Reynold Number Regime

by Dongyang Wang, Dechun Ba, Kun Liu, Ming Hao, Yang Gao, Zhiyong Wu and Qi Mei

Micromachines 2017, 8(11), 325; https://doi.org/10.3390/mi8110325 - 31 Oct 2017

Cited by 12 | Viewed by 5830

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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10229 KiB

Open AccessReview

A Review on Micromixers

by Gaozhe Cai, Li Xue, Huilin Zhang and Jianhan Lin

Micromachines 2017, 8(9), 274; https://doi.org/10.3390/mi8090274 - 11 Sep 2017

Cited by 339 | Viewed by 19199

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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