Micromixing Performance Research Articles

On multi-objective optimization of geometry of staggered herringbone micromixer

A design methodology for micromixers is presented which systematically integrates computational fluid dynamics (CFD) with an optimization methodology based on the use of design of experiments (DOE), function approximation technique (FA) and multi-objective genetic algorithm (MOGA). The methodology allows the simultaneous investigation of the effect of geometric parameters on the mixing performance of micromixers whose design strategy is based fundamentally on the generation of chaotic advection. The methodology has been applied on a Staggered Herringbone Micromixer (SHM) at several Reynolds numbers. The geometric features of the SHM are optimized and their effects on mixing are evaluated. The degree of mixing and the pressure drop are the performance criteria to define the efficiency of the micromixer for different design requirements.

Performance analysis of a folding flow micromixer

The performance of a folding flow micromixer in the Stokes flow regime is investigated computationally and experimentally. Consistency with a previously derived general scaling relation is demonstrated and the geometric parameters in the scaling relation are determined for this mixer. Measured data from a second similar mixer are correctly predicted using the scaling relation, thus showing that the approach allows quantitative prediction of mixing. This paper focuses on the errors associated with such predictions. Basic errors, expressed as variations in the standard deviation of the concentration profile, were estimated to be −10% for the computation and −30% for the experiment at the highest values of Peclet number considered. It is shown that this experimental error was mostly due to depth averaging of the spectroscopic technique used for concentration measurement at the high Peclet numbers. However, extra uncertainty is associated with chip fabrication tolerances and this was investigated further. Measurements at the outlet of nine different mixer chips of notionally identical design revealed variations in mixing of ±26%. This variation was attributed to misalignment of the glass layers determining the geometry of the mixer in the chip. Thus, the combination of measurement error and misalignment means predictions of the concentration standard deviation for the mixer may get non-uniformity wrong by up to 50%. Ensuring a required uniformity, however, simply requires adding a few further elements to the mixer to allow for this uncertainty. Application of the scaling relation to mixer design is highlighted by a discussion of the options available for improving the performance of the experimental mixer.

Mixing performance of a chaotic micro-mixer

Micro-mixing of liquids is a difficult problem since the mixing performance is governed by the slow diffusive mass transfer. In the present work a novel chaotic micro-mixer, which combines several features, viz. curved channels for induction of secondary flows, split-and-recombine structures and flow separation due to forward- and backward-facing steps, is investigated. Image processing technique is used to monitor the extent of mixing. In the study by Jiang et al. [Jiang, F., Drese, K.S., Hardt, S., Kuepper, M. and Schönfeld, F., 2004, Helical flows and chaotic mixing in curved micro channels. AIChE J, 50: 2297–2305], it is shown that simple planar meandering channels induce chaotic convection by means of alternating Dean flows for sufficiently high flow rates. The mixing performance, however, is drastically decreased for lower Dean numbers (i.e., K < 150). The novel mixer design overcomes this drawback by combining different mixing methods. Especially at relatively low Dean numbers the mixing performance is found to be superior in comparison to the planar meandering mixer. Moreover, the dependence of the mixing performance on the viscosity and viscosity differences is investigated. Finally, a simple correlation for the prediction of the mixing time is proposed.

Development of a fully integrated microfluidic system for sensing infectious viral disease

An active micromixer system utilizing the magnetic force was developed and examined for its ability to facilitate the mixing of more than two fluid flows. The mixing performance of the active micromixer was evaluated in aqueous–aqueous systems including dyes for visual observation. A complete analytical microfluidic system was developed by integrating various functional modules into a single chip, thus allowing cell lysis, sample preparation, purification of intracellular molecules, and subsequent analysis. Upon loading the cell samples and lysis solution into the mixing chamber, the integrated microfluidic device allows efficient cell disruption by rotation of a micromagnetic disk and control of mixing time using the Teflon‐coated hydrophobic film as a microvalve. This inflow is followed by separating the cell debris and contaminated proteins from the cell lysate sample using the acrylamide (AAm)‐functionalized SPE. The inflow of partially purified cell lysate sample containing the gold binding polypeptide (GBP)‐fusion protein was bound onto the gold micropatterns by means of its metal binding affinity. The GBP‐fusion method allows immobilization of proteins in bioactive forms onto the gold surface without surface modification suitable for studying antigen–antibody interaction. It was used for the detection of severe acute respiratory syndrome (SARS), an infectious viral disease, as an example case.

Mixing behavior of the rhombic micromixers over a wide Reynolds number range using Taguchi method and 3D numerical simulations

A planar micromixer with rhombic microchannels and a converging-diverging element has been systematically investigated by the Taguchi method, CFD-ACE simulations and experiments. To reduce the footprint and extend the operation range of Reynolds number, Taguchi method was used to numerically study the performance of the micromixer in a L(9) orthogonal array. Mixing efficiency is prominently influenced by geometrical parameters and Reynolds number (Re). The four factors in a L(9) orthogonal array are number of rhombi, turning angle, width of the rhombic channel and width of the throat. The degree of sensitivity by Taguchi method can be ranked as: Number of rhombi > Width of the rhombic channel > Width of the throat > Turning angle of the rhombic channel. Increasing the number of rhombi, reducing the width of the rhombic channel and throat and lowering the turning angle resulted in better fluid mixing efficiency. The optimal design of the micromixer in simulations indicates over 90% mixing efficiency at both Re > or = 80 and Re < or = 0.1. Experimental results in the optimal simulations are consistent with the simulated one. This planar rhombic micromixer has simplified the complex fabrication process of the multi-layer or three-dimensional micromixers and improved the performance of a previous rhombic micromixer at a reduced footprint and lower Re.

Enzyme-linked immunosorvent assay using vertical microreactor stack with microbeads

The advantages of vertical microreactor stack with three-dimensional (3D) structure for immunoassay are discussed. The vertical microreactor stack uses vertical fluid flow operation with multifunctional fluid filters. The multi function of fluid filter is very effective for micromixing and passive valve operation. The mechanism of micromixing is discussed by using computational fluid dynamics (CFD), and we know that the mixing mechanism based on Coanda effect. To evaluate the micromixing performance of fluid filter, we demonstrated enzyme reaction with unique repeat mixing operation. As the results, we proved that the fluid filter has very effective mixing performance. The detection limit, which demonstrated by competition enzyme-linked immunosorvent assay (ELISA), is comparable with recommended detection limit, which suggested by Japanese ministry for the environment.

Analysis of a chaotic micromixer by novel methods of particle tracking and FRET

Two novel numerical and experimental methods are proposed for quantitatively analyzing the chaotic mixing in a circulation-disturbance micromixer (CDM). A particle-tracking approach incorporated with the geometric distribution of particles is derived to evaluate the mixing performance. This method provides additional evaluation about the degree of particles scattering, when compared to the Shannon entropy method. In addition, the fluorescence resonance energy transfer (FRET) method using R-Phycoerythrin (RPE) and cross-linked allophycocyanin (clAPC) is developed to demonstrate both the mixing performance and the applicability of CDM for biochemical reaction. The two proposed indices, including the particle-tracking distribution and FRET factor, are verified to sufficiently reveal the periodic constructive interference of the vortices in a CDM and a slanted groove micromixer. They also explicitly indicate the mixing performance of the chaotic micromixers. The methodologies are expected to be applied successfully for performance analysis of various micromixers or microreactors, and thus have a great potential for μTAS applications.

Application of vertical microreactor stack with polystylene microbeads to immunoassay

The advantages of vertical microreactor stack with three-dimensional (3D) structure for immunoassay are discussed. The vertical microreactor stack uses vertical fluid flow operation with multifunctional fluid filters. The multifunction of fluid filter is very effective for micromixing and passive valve operation. The mechanism of micromixing is discussed by using computational fluid dynamics (CFD), and the results suggest that the mixing mechanism based on two main effects. One is Coanda effect and the other is Taylor dispersion induced in enormously high aspect ratio capillary and liquid plug. We demonstrated enzyme reaction with unique repeat mixing operation, to evaluate the micromixing performance of fluid filter. As the results, we proved that the fluid filter has very effective mixing performance. The detection limit, which demonstrated by competition enzyme-linked immunosorvent assay (ELISA), is comparable with recommended detection limit, which suggested by Japanese ministry for the environment.

A Study on Micromixing Process Utilizing Gas-Liquid Free Interface

We propose a new micromixing process utilizing gas-liquid free interface. This new process enhances mixing by narrowing and winding flow due to the existence of bubbles. Moreover, because shear stress does not work on gas-liquid free interface, this process will reduce pressure drop. Through flow experiment and CFD analysis, we compared the mixing performance of the new micromixer with that of conventional Y flow micromixer. The experimental result proved that the new micromixer can promote more mixing than Y flow micromixer. Furthermore, the CFD analysis revealed that the new micromixer can reduce pressure drop.

Macro- and micromixing studies in an unbaffled vessel agitated by a Rushton turbine

Macromixing characteristics, power number and visual observation of the vortex behaviour and micromixing in an unbaffled tank agitated with a Rushton turbine are reported. The latter has also been compared in detail with earlier results from an identical tank containing baffles. The maximum mean specific energy dissipation rate, ε ¯ T , in the unbaffled tank that can be utilised without severe air incorporation is ∼ 0.18 W / kg compared to ∼ 1.2 W / kg with baffles. However, at this lower ε ¯ T , the micromixing efficiency is always significantly greater without baffles except when addition is made onto the top of the liquid or into the trailing vortex very close to the impeller. In these latter cases, they are approximately the same but even a small submergence of the feed tube below the liquid surface greatly enhances micromixing in the unbaffled case whilst it is still very poor with baffles. This good micromixing performance of the unbaffled vessel was very unexpected. Furthermore, an established method of estimating the local ε T gave values of ε T / ε ¯ T = φ ⪢ 1 at every feed position where measurement was undertaken. Since the spatially averaged value of φ = 1 , this result suggests the possibility that the accepted concept of micromixing being totally controlled by the local ε T at the feed point may not be valid for such swirling flows.

A novel 3D porous micromixer fabricated using selective ultrasonic foaming

This paper presents a novel 3D porous micromixer fabricated using a selective ultrasonic foaming technique. The 3D porous structure can split, stretch, fold and break the mixing flows effectively and thus dramatically improves the mixing efficiency of microfluidic flows. In the paper, we report on the fabrication and performance of the 3D porous micromixer. The effects of flow rate, mixing length and pore size were studied using flow visualization experiments. It is shown that the proposed micromixer performs very well for flows with a wide range of Reynolds numbers. Sufficient mixing results can be achieved with a short mixing length for flows with Reynolds numbers as low as 0.1.

Mesomixing scale controlling and its effect on micromixing performance

To direct highly efficient microdevice design, the mixing performance of different mixing methods was investigated. Three different microstructured mixers representing three kinds of mixing methods were utilized in this work. The mesomixing scale was adjusted through different ways in these mixers and the micromixing performance was characterized by a parallel competing reaction. A dimensionless parameter of mesomixing scale with different forms in these mixers was defined by considering contacting surface and mixing volume, and its relation with the segregation index which characterized the micromixing performance was investigated. All results indicate the enhancement of the micromixing performance with the decrease of the mesomixing scale. The mixing potential of different mixing method was discussed and it shows that the droplet cross-flow mixing method has the highest mixing potential. A linear relationship between the dimensionless parameter of mesomixing scale and the segregation index has been obtained. The results could provide much better understanding of how mesomixing scales affect the micromixing performance, which are very helpful for designing new micromixing devices and optimizing the geometric structures and operation conditions.

Optimizing Micromixer Design for Enhancing Dielectrophoretic Microconcentrator Performance

We present an investigation into optimizing micromixer design for enhancing dielectrophoretic (DEP) microconcentrator performance. DEP-based microconcentrators use the dielectrophoretic force to collect particles on electrodes. Because the DEP force generated by electrodes decays rapidly away from the electrodes, DEP-based microconcentrators are only effective at capturing particles from a limited cross section of the input liquid stream. Adding a mixer can circulate the input liquid, increasing the probability that particles will drift near the electrodes for capture. Because mixers for DEP-based microconcentrators aim to circulate particles, rather than mix two species, design specifications for such mixers may be significantly different from that for conventional mixers. Here we investigated the performance of patterned-groove micromixers on particle trapping efficiency in DEP-based microconcentrators numerically and experimentally. We used modeling software to simulate the particle motion due to various forces on the particle (DEP, hydrodynamic, etc.), allowing us to predict trapping efficiency. We also conducted trapping experiments and measured the capture efficiency of different micromixer configurations, including the slanted groove, staggered herringbone, and herringbone mixers. Finally, we used these analyses to illustrate the design principles of mixers for DEP-based concentrators.

1447 気液自由界面を利用したマイクロ混合に関する研究(S38-4 混合・界面,S38 マイクロ・ナノフルイズ)

We propose a new micromixing process utilizing gas-liquid free interface. This new process enhances mixing by the narrowing and winding flow due to the existence of bubbles. Moreover, because shear stress does not work on gas-liquid free interface, this process will reduce pressure drop. Through flow experiment and CFD analysis, we compared the mixing performance of the new micromixer with that of conventional Y flow micromixer. The experimental result proved that the new micromixer can promote more mixing than Y flow micromixer. Furthermore, the CFD analysis revealed that the new micromixer can reduce pressure drop.

재순환 영역이 존재하는 마이크로 혼합기

This paper describes enhancement of the mixing efficiency of a multilamination micro mixer by adding a number of recirculation zones downstream of the mixing zone. Numerical simulation was employed to estimate the mixing efficiency and the pressure drop under various conditions. Numerical results indicated that recirculation micro mixer brought about not only the increase of the mixing efficiency but also the decrease of the pressure drop. Micro mixers were fabricated using photosensitive glass by anisotropic wet etching technique. The width and height of the micro channel were and , respectively. The performance of micro mixer was measured using color intensity variation of the fluid. Except for extremely low Re below 40, the recirculation micro mixer of the present study showed improved mixing. And the enhancement of the mixing increased as Re rose. When Re increased beyond 400, more than 90% of the mixing was observed in the experiment.

Improving the mixing performance of side channel type micromixers using an optimal voltage control model

Electroosmotic flow in microchannels is restricted to low Reynolds number regimes. Since the inertia forces are extremely weak in such regimes, turbulent conditions do not readily develop, and hence species mixing occurs primarily as a result of diffusion. Consequently, achieving a thorough species mixing generally relies upon the use of extended mixing channels. This paper aims to improve the mixing performance of conventional side channel type micromixers by specifying the optimal driving voltages to be applied to each channel. In the proposed approach, the driving voltages are identified by constructing a simple theoretical scheme based on a 'flow-rate-ratio' model and Kirchhoff's law. The numerical and experimental results confirm that the optimal voltage control approach provides a better mixing performance than the use of a single driving voltage gradient.

Effects of channel geometry on mixing performance of micromixers using collision of fluid segments

This paper shows effects of design factors for micromixers using the collision of fluid segments on mixing performance. Design factors are collision zone diameter, outlet channel diameter, collision angle of reactant fluids, and number of fluid segments for collision. We evaluate mixing performances of T- and Y-shape micromixers and the K–M mixer using the Villermaux/Dushman reaction. When the Reynolds number in the outlet channel, Re, is less than 200, the fluid segment size determined by only channel geometries, Wc, and Re are significant on mixing performance. From the results in this Re range, we correlate the by-product UV absorbance with the effective fluid segment size after collision, We = Wc/Ren. The absorbance is linearly fitted with We. Thus, We expresses effects of total flow rate, outlet channel diameter, and number of fluid segments for collision on mixing performance. We can improve mixing performance by increasing flow rates as well as reducing channel sizes, leading to avoid extremely small channels to improve mixing performance and a high pressure drop in mixer channels. When Re > 200, high share rates applied to fluid segments also enhance the mixing performance. This indicates that high mixing performance and high throughput can be achieved simultaneously.

Active micro-mixers utilizing a gradient zeta potential induced by inclined buried shielding electrodes

This study presents a new active micro-mixer which enhances the mixing efficiency by means of a gradient distribution of the surface zeta potential generated by applying a control voltage to an arrangement of inclined buried shielding electrodes. A theoretical model is developed to predict the distribution of the zeta potential and the thickness of the transition layer. The validity of this model is confirmed experimentally. Numerical simulations are performed to characterize the fluid flow patterns and to optimize the design of the micro-mixer. It is shown that optimizing the arrangement of the inclined shielding electrodes leads to a significant enhancement in the mixing performance of the active micro-mixer. The numerical results indicate that a localized flow circulation is generated when the control voltage is applied to the inclined shielding electrodes. The shape of this circulation is dependent on the distribution of the gradient zeta potential, which is determined in turn by the arrangement of the electrodes. The effect of the number of electrode pairs and the layout of the shielding electrodes on the mixing performance of the micro-mixer is explored both numerically and experimentally. It is revealed that the inclined electrode layouts with five electrode pairs provide the highest mixing efficiency of almost 93%. The active micro-mixer developed in this study represents a crucial advancement in microfluidic systems.

Active micro-mixers using surface acoustic waves on Y-cut 128° LiNbO3

This study presents an active method for micro-mixers using surface acoustic waves (SAW) to rapidly mix co-fluent fluids. Mixing is challenging work in microfluidic systems due to their low-Reynolds-number flow conditions. SAW devices were fabricated on 128° Y-cut lithium niobate (LiNbO3). The micro-mixers are these piezoelectric actuators integrated with polydimethylsiloxane microchannels. The effects of the applied voltages on interdigitated transducers (IDTs) and two layouts, parallel- and transversal-type, of micro-mixers on the mixing performance were experimentally explored. The experimental results revealed that the parallel-type mixer achieved a higher mixing effect. Meanwhile, a higher applied voltage on the IDTs led to a significant improvement in the mixing performance of the active micro-mixer. Typical temperature effects associated with the applied voltages on the IDTs were also investigated. Finally, a digestion reaction between a protein (hemoglobin) and an enzyme (trypsin) was performed to verify the capability of the micro-mixers. The protein–enzyme mixture was qualitatively analyzed using mass spectrometry. Using these SAW-based mixers, the amount of digested peptides increased. Additionally, the protein–enzyme mixture was also quantitatively analyzed using high-performance liquid chromatography. Experimental data showed that the amount of digested peptides increased 21.1% using the active mixer. Therefore, the developed micro-mixers can be applied in microfluidic systems for improving mixing efficiency and thus enhancing the bio-reaction.

Active mixing inside microchannels utilizing dynamic variation of gradient zeta potentials

This study presents a new active micromixer with high mixing efficiency achieved by means of a gradient distribution of the surface zeta potential controlled by changing the frequency of voltage applied on shielding electrodes. Gradient surface zeta potential is generated by applying a high voltage to inclined buried shielding electrodes. While alternating the frequency of driving voltage, the zeta potential could be changed accordingly, thus providing a significant mixing effect inside microchannels. A theoretical model is proposed to predict the distribution of zeta potential. The results from this model are critically compared with the well-developed three-capacitor model. Additionally, two time-factor scales, the charge time of capacitor and mixing length flow time, are used to predict the optimum frequency. The prediction of optimum frequency, 0.5 Hz, is consistent with experimental results. Moreover, a five-pair inclined shielding electrode with a frequency of 0.5 Hz leads to a significant improvement in the mixing performance of the active micromixer. Numerical results indicate that a localized flow circulation is generated when the control voltage is applied to the inclined shielding electrodes. Furthermore, the streamlines are experimentally observed by using fluorescent beads. The shape of this circulation is dependent on the distribution of gradient zeta potential, which is determined by the arrangement of electrodes. The effects of the number of electrode pairs and the layout of shielding electrodes on the mixing performance of micromixer are also explored both numerically and experimentally. It is revealed that five-pair inclined electrodes at 0.5 Hz provide the highest mixing efficiency. Finally, a reaction between N-benzoyl-L-arginine-p-nitroanilide and trypsin enzyme is performed to verify the capability of micromixers. The experimental results reveal that the reaction can achieve a higher performance indicating a higher mixing efficiency. The active micromixers could be used in microfluidic systems for improving the mixing efficiency and thus enhancing the bioreaction.