Special Issue "Optimization of Microfluidic Devices"

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

Deadline for manuscript submissions: closed (15 November 2019).

Special Issue Editor

Prof. Dr. Kwang-Yong Kim
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

Special Issue Information

Dear Colleagues,

Performance of most microfluidic devices depends strongly on the geometric shape of flow channels. Thus, shape optimization of microchannels is required to improve the performance of microfluidic devices. Recently, computational fluid dynamics (CFD) has been widely used in the analyses of fluid flow, mixing, and chemical reactions in microfluidic devices. In addition, design optimization using 3D CFD and optimization techniques has become an efficient tool for the design of microfluidic devices, owing to the development of computers. Most microfluidic problems involve multiple conflicting design objectives. For example, the degree of mixing and pressure drop can be two objectives of a micromixer design. A popular approach to multi-objective optimization is optimization using multi-objective evolutionary algorithms (MOEAs), where multiple trade-off solutions for the objectives are determined. The latest MOEAs include Pareto evolutionary algorithms, Pareto archived evolutionary strategies, and an elitist non-dominated sorting genetic algorithm. Multi-objective problems yield many solutions, which are known as Pareto-optimal solutions. These Pareto optimal solutions can be used to analyze trade-offs among designs. The current Special Issue covers applications of design optimization to various microfluidic devices.

Prof. Kwang-Yong Kim
Guest Editor

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Keywords

  • Optimization
  • Microfluidic device
  • Computational fluid dynamics
  • Multi-objective optimization

Published Papers (16 papers)

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Research

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Open AccessArticle
Design Applicable 3D Microfluidic Functional Units Using 2D Topology Optimization with Length Scale Constraints
Micromachines 2020, 11(6), 613; https://doi.org/10.3390/mi11060613 - 24 Jun 2020
Viewed by 586
Abstract
Due to the limits of computational time and computer memory, topology optimization problems involving fluidic flow frequently use simplified 2D models. Extruded versions of the 2D optimized results typically comprise the 3D designs to be fabricated. In practice, the depth of the fabricated [...] Read more.
Due to the limits of computational time and computer memory, topology optimization problems involving fluidic flow frequently use simplified 2D models. Extruded versions of the 2D optimized results typically comprise the 3D designs to be fabricated. In practice, the depth of the fabricated flow channels is finite; the limited flow depth together with the no-slip condition potentially make the fluidic performance of the 3D model very different from that of the simplified 2D model. This discrepancy significantly limits the usefulness of performing topology optimization involving fluidic flow in 2D—at least if special care is not taken. Inspired by the electric circuit analogy method, we limit the widths of the microchannels in the 2D optimization process. To reduce the difference of fluidic performance between the 2D model and its 3D counterpart, we propose an applicable 2D optimization model, and ensure the manufacturability of the obtained layout, combinations of several morphology-mimicking filters impose maximum or minimum length scales on the solid phase or the fluidic phase. Two typical Lab-on-chip functional units, Tesla valve and fluidic channel splitter, are used to illustrate the validity of the proposed application of length scale control. Full article
(This article belongs to the Special Issue Optimization of Microfluidic Devices)
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Open AccessArticle
Cell Lysis Based on an Oscillating Microbubble Array
Micromachines 2020, 11(3), 288; https://doi.org/10.3390/mi11030288 - 10 Mar 2020
Cited by 1 | Viewed by 812
Abstract
Cell lysis is a process of breaking cell membranes to release intracellular substances such as DNA, RNA, protein, or organelles from a cell. The detection of DNA, RNA, or protein from the lysed cells is of importance for cancer diagnostics and drug screening. [...] Read more.
Cell lysis is a process of breaking cell membranes to release intracellular substances such as DNA, RNA, protein, or organelles from a cell. The detection of DNA, RNA, or protein from the lysed cells is of importance for cancer diagnostics and drug screening. In this study, we develop a microbubble array that enables the realization of multiple cell lysis induced by the shear stress resulting from the individual oscillating microbubbles. The oscillating microbubbles in the channel have similar vibration amplitudes, and the intracellular substances can be released from the individual cells efficiently. Moreover, the efficiency of cell lysis increases with increments of input voltage and sonication time. By means of DNA agarose-gel electrophoresis, a sufficient extraction amount of DNA released from the lysed cells can be detected, and there is no significant difference in lysis efficiency when compared to cell lysis achieved using commercial kits. With the advantages of the simple manufacturing process, low cost, high efficiency, and high speed, this device can serve as an efficient and versatile tool for the single-cell sequencing of cell biology research, disease diagnosis, and stem cell therapy. Full article
(This article belongs to the Special Issue Optimization of Microfluidic Devices)
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Open AccessArticle
Mixing Optimization in Grooved Serpentine Microchannels
Micromachines 2020, 11(1), 61; https://doi.org/10.3390/mi11010061 - 04 Jan 2020
Cited by 5 | Viewed by 899
Abstract
Computational fluid dynamics modeling at Reynolds numbers ranging from 10 to 100 was used to characterize the performance of a new type of micromixer employing a serpentine channel with a grooved surface. The new topology exploits the overlap between the typical Dean flows [...] Read more.
Computational fluid dynamics modeling at Reynolds numbers ranging from 10 to 100 was used to characterize the performance of a new type of micromixer employing a serpentine channel with a grooved surface. The new topology exploits the overlap between the typical Dean flows present in curved channels due to the centrifugal forces experienced by the fluids, and the helical flows induced by slanted groove-ridge patterns with respect to the direction of the flow. The resulting flows are complex, with multiple vortices and saddle points, leading to enhanced mixing across the section of the channel. The optimization of the mixers with respect to the inner radius of curvature (Rin) of the serpentine channel identifies the designs in which the mixing index quality is both high (M > 0.95) and independent of the Reynolds number across all the values investigated. Full article
(This article belongs to the Special Issue Optimization of Microfluidic Devices)
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Open AccessArticle
Engineered Lateral Roughness Element Implementation and Working Fluid Alteration to Intensify Hydrodynamic Cavitating Flows on a Chip for Energy Harvesting
Micromachines 2020, 11(1), 49; https://doi.org/10.3390/mi11010049 - 30 Dec 2019
Cited by 4 | Viewed by 973
Abstract
Hydrodynamic cavitation is considered an effective tool to be used in different applications, such as surface cleaning, ones in the food industry, energy harvesting, water treatment, biomedical applications, and heat transfer enhancement. Thus, both characterization and intensification of cavitation phenomenon are of great [...] Read more.
Hydrodynamic cavitation is considered an effective tool to be used in different applications, such as surface cleaning, ones in the food industry, energy harvesting, water treatment, biomedical applications, and heat transfer enhancement. Thus, both characterization and intensification of cavitation phenomenon are of great importance. This study involves design and optimization of cavitation on chip devices by utilizing wall roughness elements and working fluid alteration. Seven different microfluidic devices were fabricated and tested. In order to harvest more energy from cavitating flows, different roughness elements were used to decrease the inlet pressure (input to the system), at which cavitation inception occurs. The implemented wall roughness elements were engineered structures in the shape of equilateral triangles embedded in the design of the microfluidic devices. The cavitation phenomena were also studied using ethanol as the working fluid, so that the fluid behavior differences in the tested cavitation on chip devices were explained and compared. The employment of the wall roughness elements was an effective approach to optimize the performances of the devices. The experimental results exhibited entirely different flow patterns for ethanol compared to water, which suggests the dominant effect of the surface tension on hydrodynamic cavitation in microfluidic channels. Full article
(This article belongs to the Special Issue Optimization of Microfluidic Devices)
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Open AccessArticle
Flow-Based Three-Dimensional Co-Culture Model for Long-Term Hepatotoxicity Prediction
Micromachines 2020, 11(1), 36; https://doi.org/10.3390/mi11010036 - 27 Dec 2019
Cited by 4 | Viewed by 972
Abstract
We developed concave microwell arrays to establish a size-controllable 3-D co-culture liver model for in vitro drug toxicity testing, to predict hepatotoxicity. The interaction of hepatocytes with hepatic stellate cells (HSCs) was investigated by co-culturing primary 3-D hepatocyte spheroids and HSCs (heterosphere), using [...] Read more.
We developed concave microwell arrays to establish a size-controllable 3-D co-culture liver model for in vitro drug toxicity testing, to predict hepatotoxicity. The interaction of hepatocytes with hepatic stellate cells (HSCs) was investigated by co-culturing primary 3-D hepatocyte spheroids and HSCs (heterosphere), using 3-D liver-on-a-chip. The effect of HSCs was investigated during spheroid formation; they were involved in controlling the organization of spheroidal aggregates and the formation of tight cell–cell contacts. Scanning electron microscopy (SEM) images showed that co-cultured spheroids with smoother surfaces in the flow chip aggregated more tightly and rapidly, compared to mono-cultured spheroids, until 13 days. Metabolic function analysis revealed that heterospheres secreted 40% more albumin and urea than hepatospheres on day 13. Additionally, an acetaminophen (AAP) and isoniazid (INH) concentration-dependent increase in CYP3A4 expression was detected in the 3-D cultures, and an increase in Lactate dehydrogenase (LDH) release after AAP and INH treatment was observed. CYP1A2, Mrp1 and UGT1A5 mRNA expression levels in the heterospheres and hepatospheres were evaluated from days 3 to 13. To examine the potential for toxicity testing in the flow-conditioned culture of the heterospheres, we evaluated cytotoxicity using the endpoint LDH release in the heterospheres and hepatospheres. IC50 values for AAP and INH after 24 h of exposure were calculated from the dose–response curves of the compounds. Flow-conditioned heterosphere culture results suggest that it may be suitable for long-term culture and cytotoxicity testing. Thus, our co-culture system closely resembles the in vivo environment and allows long-term in vitro hepatotoxicity prediction. Full article
(This article belongs to the Special Issue Optimization of Microfluidic Devices)
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Open AccessArticle
Effects of Channel Wall Twisting on the Mixing in a T-Shaped Micro-Channel
Micromachines 2020, 11(1), 26; https://doi.org/10.3390/mi11010026 - 24 Dec 2019
Cited by 2 | Viewed by 503
Abstract
A new design scheme is proposed for twisting the walls of a microchannel, and its performance is demonstrated numerically. The numerical study was carried out for a T-shaped microchannel with twist angles in the range of 0 to 34π. The Reynolds number range [...] Read more.
A new design scheme is proposed for twisting the walls of a microchannel, and its performance is demonstrated numerically. The numerical study was carried out for a T-shaped microchannel with twist angles in the range of 0 to 34π. The Reynolds number range was 0.15 to 6. The T-shaped microchannel consists of two inlet branches and an outlet branch. The mixing performance was analyzed in terms of the degree of mixing and relative mixing cost. All numerical results show that the twisting scheme is an effective way to enhance the mixing in a T-shaped microchannel. The mixing enhancement is realized by the swirling of two fluids in the cross section and is more prominent as the Reynolds number decreases. The twist angle was optimized to maximize the degree of mixing (DOM), which increases with the length of the outlet branch. The twist angle was also optimized in terms of the relative mixing cost (MC). The two optimum twisting angles are generally not coincident. The optimum twist angle shows a dependence on the length of the outlet branch but it is not affected much by the Reynolds number. Full article
(This article belongs to the Special Issue Optimization of Microfluidic Devices)
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Open AccessArticle
Microfluidic Transportation Control of Larval Zebrafish through Optomotor Regulations under a Pressure-Driven Flow
Micromachines 2019, 10(12), 880; https://doi.org/10.3390/mi10120880 - 14 Dec 2019
Cited by 5 | Viewed by 808
Abstract
To perform zebrafish larvae-related experiments within a microfluidic environment, the larvae need to be anesthetized and subsequently transported into respective test sections through mechanical or manual means. However, anesthetization tends to affect larval sensory perceptions, hindering their natural behaviors. Taking into account that [...] Read more.
To perform zebrafish larvae-related experiments within a microfluidic environment, the larvae need to be anesthetized and subsequently transported into respective test sections through mechanical or manual means. However, anesthetization tends to affect larval sensory perceptions, hindering their natural behaviors. Taking into account that juvenile larvae move naturally within their environment by accessing visual as well as hydromechanical cues, this work proposes an experimental framework to transport nonanesthetized larvae within a microfluidic environment by harmonically tuning both of the aforementioned cues. To provide visual cues, computer-animated moving gratings were provided through an in-house-developed control interface that drove the larval optomotor response. In the meantime, to provide hydromechanical cues, the flow rate was tuned using a syringe pump that affected the zebrafish larvae’s lateral line movement. The results obtained (corresponding to different test conditions) suggest that the magnitude of both modalities plays a crucial role in larval transportation and orientation control. For instance, with a flow rate tuning of 0.1 mL/min along with grating parameters of 1 Hz temporal frequency, the average transportation time for larvae that were 5 days postfertilization was recorded at 1.29 ± 0.49 s, which was approximately three times faster than the transportation time required only in the presence of hydromechanical cues. Full article
(This article belongs to the Special Issue Optimization of Microfluidic Devices)
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Open AccessArticle
Parametric Investigation on a Micro-Array Heat Sink with Staggered Trapezoidal Bumps
Micromachines 2019, 10(12), 845; https://doi.org/10.3390/mi10120845 - 04 Dec 2019
Cited by 1 | Viewed by 620
Abstract
More efficient heat sinks are required due to the rapid increase of power density in microelectronic devices. In this study, a micro-array heat sink with stagger trapezoidal bumps was designed. Numerical simulations for the flow and heat transfer under various conditions were carried [...] Read more.
More efficient heat sinks are required due to the rapid increase of power density in microelectronic devices. In this study, a micro-array heat sink with stagger trapezoidal bumps was designed. Numerical simulations for the flow and heat transfer under various conditions were carried out to help us to fully understand the mechanisms of the heat transfer enhancement in such a heat sink. The effects of the structure of the heat sink, parameters of the bumps, and volume fraction of the nanofluid on the performance of heat sink were studied. The results show us that the bumps in the heat sink can result in chaotic convection, interrupting the thermal boundary layer and increasing the cooling area, subsequently improving the heat transfer performance. Furthermore, parametric investigations for trapezoidal bumps were conducted to obtain preferential values for parameters, such as the bump width, fore rake angle of the bump, bump height, and bump pitch. Full article
(This article belongs to the Special Issue Optimization of Microfluidic Devices)
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Open AccessArticle
Asymmetrical Split-and-Recombine Micromixer with Baffles
Micromachines 2019, 10(12), 844; https://doi.org/10.3390/mi10120844 - 03 Dec 2019
Cited by 5 | Viewed by 752
Abstract
The present work proposes a planar micromixer design comprising hybrid mixing modules of split-and-recombine units and curved channels with radial baffles. The mixing performance was evaluated numerically by solving the continuity and momentum equations along with the advection-diffusion equation in a Reynolds number [...] Read more.
The present work proposes a planar micromixer design comprising hybrid mixing modules of split-and-recombine units and curved channels with radial baffles. The mixing performance was evaluated numerically by solving the continuity and momentum equations along with the advection-diffusion equation in a Reynolds number range of 0.1–80. The variance of the concentration of the mixed species was considered to quantify the mixing index. The micromixer showed far better mixing performance over whole Reynolds number range than an earlier split-and-recombine micromixer. The mixer achieved mixing indices greater than 90% at Re ≥ 20 and a mixing index of 99.8% at Re = 80. The response of the mixing quality to the change of three geometrical parameters was also studied. A mixing index over 80% was achieved within 63% of the full length at Re = 20. Full article
(This article belongs to the Special Issue Optimization of Microfluidic Devices)
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Open AccessArticle
Design Optimization for a Microfluidic Crossflow Filtration System Incorporating a Micromixer
Micromachines 2019, 10(12), 836; https://doi.org/10.3390/mi10120836 - 30 Nov 2019
Cited by 2 | Viewed by 1052
Abstract
In this study, we report on a numerical study on design optimization for a microfluidic crossflow filtration system incorporated with the staggered herringbone micromixer (SHM). Computational fluid dynamics (CFD) and the Taguchi method were employed to find out an optimal set of design [...] Read more.
In this study, we report on a numerical study on design optimization for a microfluidic crossflow filtration system incorporated with the staggered herringbone micromixer (SHM). Computational fluid dynamics (CFD) and the Taguchi method were employed to find out an optimal set of design parameters, mitigating fouling in the filtration system. The flow and the mass transfer characteristics in a reference SHM model and a plain rectangular microchannel were numerically investigated in detail. Downwelling flows in the SHM model lead to backtransport of foulants from the permeable wall, which slows down the development of the concentration boundary layer in the filtration system. Four design parameters — the number of grooves, the groove depth, the interspace between two neighboring grooves, and the interspace between half mixing periods — were chosen to construct a set of numerical experiments using an orthogonal array L 9 ( 3 4 ) from the Taguchi method. The Analysis of Variance (ANOVA) using the evaluated signal-to-noise (SN) ratios enabled us to identify the contribution of each design parameter on the performance. The proposed optimal SHM model indeed showed the lowest growth rate of the wall concentration compared to other SHM models. Full article
(This article belongs to the Special Issue Optimization of Microfluidic Devices)
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Open AccessArticle
Effects of Bridge-Shaped Microchannel Geometry on the Performance of a Micro Laminar Flow Fuel Cell
Micromachines 2019, 10(12), 822; https://doi.org/10.3390/mi10120822 - 27 Nov 2019
Cited by 1 | Viewed by 939
Abstract
A laminar flow micro fuel cell comprising of bridge-shaped microchannel is investigated to find out the effects of the cross-section shape of the microchannel on the performance. A parametric study is performed by varying the heights and widths of the channel and bridge [...] Read more.
A laminar flow micro fuel cell comprising of bridge-shaped microchannel is investigated to find out the effects of the cross-section shape of the microchannel on the performance. A parametric study is performed by varying the heights and widths of the channel and bridge shape. Nine different microchannel cross-section shapes are evaluated to find effective microchannel cross-sections by combining three bridge shapes with three channel shapes. A three-dimensional fully coupled numerical model is used to calculate the fuel cell’s performance. Navier-Stokes, convection and diffusion, and Butler-Volmer equations are implemented using the numerical model. A narrow channel with a wide bridge shape shows the best performance among the tested nine cross-sectional shapes, which is increased by about 78% compared to the square channel with the square bridge shape. Full article
(This article belongs to the Special Issue Optimization of Microfluidic Devices)
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Open AccessArticle
Development and Optimization of an Airborne Formaldehyde Microfluidic Analytical Device Based on Passive Uptake through a Microporous Tube
Micromachines 2019, 10(12), 807; https://doi.org/10.3390/mi10120807 - 23 Nov 2019
Cited by 5 | Viewed by 599
Abstract
This paper describes a compact microfluidic analytical device developed for the detection of low airborne formaldehyde concentrations. This microdevice was based on a three-step analysis, i.e., the passive gaseous formaldehyde uptake using a microporous membrane into an acetylacetone solution, the derivatization with acetylacetone [...] Read more.
This paper describes a compact microfluidic analytical device developed for the detection of low airborne formaldehyde concentrations. This microdevice was based on a three-step analysis, i.e., the passive gaseous formaldehyde uptake using a microporous membrane into an acetylacetone solution, the derivatization with acetylacetone to form 3,5-diacetyl-1,4-dihydrolutidine, and the quantification of the latter using fluorescence detection. For a rapid and easier implementation, a cylindrical geometry of the microporous element was considered to perform laboratory-controlled experiments with known formaldehyde concentrations and to establish the proof of concept. This work reports the evaluation of the uptake performance according to the microporous tube length, the liquid flow rate inside the tube, the gas flow rate outside the tube, and the gaseous formaldehyde concentration. A 10.0 cm microporous tube combined with a gas flow rate of 250 NmL/min (normal milliliters per minute) and a liquid flow rate of 17 µL/min were found to be the optimized conditions. In these experimental conditions, the fluorescence signal increased linearly with the gaseous formaldehyde concentration in the range 0–118 µg/m3, with the detection limit being estimated as 0.13 µg/m3 when considering a signal-to-noise ratio of 3. Full article
(This article belongs to the Special Issue Optimization of Microfluidic Devices)
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Open AccessArticle
Elaboration of the Demulsification Process of W/O Emulsion with Three-Dimensional Electric Spiral Plate-Type Microchannel
Micromachines 2019, 10(11), 751; https://doi.org/10.3390/mi10110751 - 01 Nov 2019
Cited by 1 | Viewed by 558
Abstract
Rapid and efficient demulsification (destabilizing of an emulsion) processes of a water in oil (W/O) emulsion were carried out in a three-dimensional electric spiral plate-type microchannel (3D-ESPM). In this experiment, the demulsifying efficiency of emulsions by 3D-ESPM was compared with that by gravity [...] Read more.
Rapid and efficient demulsification (destabilizing of an emulsion) processes of a water in oil (W/O) emulsion were carried out in a three-dimensional electric spiral plate-type microchannel (3D-ESPM). In this experiment, the demulsifying efficiency of emulsions by 3D-ESPM was compared with that by gravity settling, the factors influencing demulsifying efficiency were investigated, and the induction period, cut size and residence time in the demulsification process were studied. The results showed that in contrast to the gravity settling method, 3D-ESPM can directly separate the disperse phase (water) instead of the continuous phase (oil). The maximum demulsifying efficiency of W/O emulsion in a single pass through the 3D-ESPM reached 90.3%, with a microchannel height of 200 μm, electric field intensity of 250 V /cm, microchannel angle of 180°, microchannel with 18 plates and a flow rate of 2 mL /min. An induction period of 0.6 s during the demulsification process was simulated with experimental data fitting. When the residence time of emulsion in 3D-ESPM was longer than the induction period, its demulsifying efficiency increased as the increase of the flow velocity due to the droplet coalescence effects of Dean vortices in the spiral microchannel. For this device a cut size of droplets of 4.5 μm was deduced. Our results showed that the demulsification process of W/O emulsion was intensified by 3D-ESPM based on the coupling effect between electric field-induced droplets migration and microfluidic hydrodynamic trapping. Full article
(This article belongs to the Special Issue Optimization of Microfluidic Devices)
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Open AccessArticle
Single and Multi-Objective Optimization of a Three-Dimensional Unbalanced Split-and-Recombine Micromixer
Micromachines 2019, 10(10), 711; https://doi.org/10.3390/mi10100711 - 21 Oct 2019
Cited by 3 | Viewed by 1040
Abstract
The three-dimensional geometry of a micromixer with an asymmetrical split-and-recombine mechanism was optimized to enhance the fluid-mixing capability at a Reynolds number of 20. Single and multi-objective optimizations were carried out by using particle swarm optimization and a genetic algorithm on a modeled [...] Read more.
The three-dimensional geometry of a micromixer with an asymmetrical split-and-recombine mechanism was optimized to enhance the fluid-mixing capability at a Reynolds number of 20. Single and multi-objective optimizations were carried out by using particle swarm optimization and a genetic algorithm on a modeled surrogate surface. Surrogate modeling was performed using the computational results for the mixing. Mixing and flow analyses were carried out by solving the convection–diffusion equation in combination with the three-dimensional continuity and momentum equations. The optimization was carried out with two design variables related to dimensionless geometric parameters. The mixing effectiveness was chosen as the objective function for the single-objective optimization, and the pressure drop and mixing index at the outlet were chosen for the multi-objective optimization. The sampling points in the design space were determined using a design of experiment technique called Latin hypercube sampling. The surrogates for the objective functions were developed using a Kriging model. The single-objective optimization resulted in 58.9% enhancement of the mixing effectiveness compared to the reference design. The multi-objective optimization provided Pareto-optimal solutions that showed a maximum increase of 48.5% in the mixing index and a maximum decrease of 55.0% in the pressure drop in comparison to the reference design. Full article
(This article belongs to the Special Issue Optimization of Microfluidic Devices)
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Open AccessArticle
Chaotic Micromixer Based on 3D Horseshoe Transformation
Micromachines 2019, 10(6), 398; https://doi.org/10.3390/mi10060398 - 14 Jun 2019
Cited by 2 | Viewed by 1033
Abstract
To improve the efficiency of mixing under laminar flow with a low Reynolds number (Re), a novel three-dimensional Horseshoe Transformation (3D HT) was proposed as the basis for the design of a micromixer. Compared with the classical HT, the Lyapunov exponent of the [...] Read more.
To improve the efficiency of mixing under laminar flow with a low Reynolds number (Re), a novel three-dimensional Horseshoe Transformation (3D HT) was proposed as the basis for the design of a micromixer. Compared with the classical HT, the Lyapunov exponent of the 3D HT, which was calculated based on a symbolic dynamic system, proved the chaotic enhancement. Based on the 3D HT, a micromixer with a mixing length of 12 mm containing six mixing units was obtained by sequentially applying “squeeze”, “stretch”, “twice fold”, “inverse transformation”, and “intersection” operations. Numerical simulation and Peclet Number (Pe) calculations indicated that when the squeeze amplitude 0 < α < 1/2, 0 < β < 1/2, the stretch amplitude γ > 4, and Re ≥ 1, the mass transfer in the mixer was dominated by convective diffusion induced by chaotic flow. When Re = 10, at the outlet of the mixing chamber, the simulated mixing index was 96.4%, which was far less than the value at Re = 0.1 (σ = 0.041). Microscope images of the mixing chamber and the curve trend of pH buffer solutions obtained from a mixing experiment were both consistent with the results of the simulation. When Re = 10, the average mixing index of the pH buffer solutions was 91.75%, which proved the excellent mixing efficiency of the mixer based on the 3D HT. Full article
(This article belongs to the Special Issue Optimization of Microfluidic Devices)
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Review

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Open AccessReview
Actuation Mechanism of Microvalves: A Review
Micromachines 2020, 11(2), 172; https://doi.org/10.3390/mi11020172 - 07 Feb 2020
Cited by 12 | Viewed by 1323
Abstract
The microvalve is one of the most important components in microfluidics. With decades of development, the microvalve has been widely used in many industries such as life science, chemical engineering, chip, and so forth. This paper presents a comprehensive review of the progress [...] Read more.
The microvalve is one of the most important components in microfluidics. With decades of development, the microvalve has been widely used in many industries such as life science, chemical engineering, chip, and so forth. This paper presents a comprehensive review of the progress made over the past years about microvalves based on different actuation mechanisms. According to driving sources, plenty of actuation mechanisms are developed and adopted in microvalves, including electricity, magnetism, gas, material and creature, surface acoustic wave, and so on. Although there are currently a variety of microvalves, problems such as leakage, low precision, poor reliability, high energy consumption, and high cost still exist. Problems deserving to be further addressed are suggested, aimed at materials, fabrication methods, controlling performances, flow characteristics, and applications. Full article
(This article belongs to the Special Issue Optimization of Microfluidic Devices)
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