Type Micromixer Research Articles

Mixing Enhancement of Newtonian Liquids in a Curvature Induced Split and Recombine Micromixer

The influence of a curvature induced flow path in the form of a split and recombine microchannel is studied and compared with the output of a straight type micromixer. The mixing efficiency of ethanol into water is analyzed for diffusion dominated flows. Apart from parametric variations, the Dean flow analysis at different locations of the channels showed higher capability of the curvature induced geometries. The aspect of layer mixing is also examined by the strength of the expansion or contraction along the flow path, which signifies the effect of curvature upon the extent of mixing. Mixing efficiency as high as 94% has been achieved for the elliptical type of micromixer. Additionally, the influence of curvature toward the gradual increase and enhancement of mixing has been demonstrated with the gradual increase of the area of contact available in the split and recombine sections.

Mixing and Flow Transition in an Optimized Electrokinetic Turbulent Micromixer.

Micromixer is a key element in a lab on a chip for broad applications in the analysis and measurement of chemistry and engineering. Previous investigations reported that electrokinetic (EK) turbulence could be realized in a "Y" type micromixer with a cross-sectional dimension of 100 μm order. Although the ultrafast turbulent mixing can be generated at a bulk flow Reynolds number on the order of unity, the micromixer has not been optimized. In this investigation, we systematically investigated the influence of electric field intensity, AC frequency, electric conductivity ratio, and channel width at the entrance on the mixing effect and transition electric Rayleigh number in the "Y" type electrokinetic turbulent micromixer. It is found that the optimal mixing is realized in a 350 μm wide micromixer, under 100 kHz and 1.14 × 105 V/m AC electric field, with an electric conductivity ratio of 1:3000. Under these conditions, a degree of mixedness of 0.93 can be achieved at 84 μm from the entrance and 100 ms. A further investigation of the critical electric field and the critical electric Rayleigh number indicates that the most unstable condition of EK flow instability is inconsistent with that of the optimal mixing in EK turbulence. To predict the evolution of EK flow under high Raσ and guide the design of EK turbulent micromixers, it is necessary to apply a computational turbulence model instead of linear instability analysis.

A cross-mixing channel 3D-SAR micromixer with high mixing performance

Abstract As an important part of laboratory-on-a-chip (LOC) and micro-total analysis system (μTAS), micromixers are widely used in the fields of biological analysis and chemical synthesis. Most of them are used for the pretreatment of the detection and analysis system to realize the full mixing between the sample and the target to improve the accuracy of the inspection system. A new type of 3D-SAR micromixer with cross-channel structures was put forward after the systemic simulation by using CFD software. The mixing performance and mechanism of 3D-SAR micromixer with/without cross-mixing channel has been investigated with different Reynolds numbers (Re). The results show that the 3D-SAR micromixer with or without cross-mixing channel structures are of excellent mixing performance when the Re was high (Re > 50), and the mixing index is close to 1. While the concentration stratification of the two fluids in the cross-mixing channel (CMC) 3D-SAR micromixer is obviously better than that of no-cross-mixing channel (NCMC) 3D-SAR micromixer when Re is low (Re < 10). It is because the two fluids in the cross-mixing channel rotate counterclockwise at the mixing unit, which induces a vortex and increases the contact area between the two fluids. The mixing performance is greatly improved, and the mixing index at the outlet is more than 0.9. Meanwhile, in order to optimize the higher pressure drop of the CMC micromixer, a new 3D-SAR micromixer with the unbalanced-cross-mixing channel (UCMC) is proposed based on the CMC structure. This channel structure can meet the requirements of high mixing index and low-pressure drop at the same time, which is helpful to design and manufacture of new type micromixer.

Numerical analysis of non-aligned inputs M-type micromixers with different shaped obstacles for biomedical applications

Fluid mixing in lab-on-a-chip devices at laminar flow conditions result in a low mixing index. The reason is dominant diffusion over the convection process. The mixing index can be improved by certain changes in the micromixer structural design like introducing obstacles in the path of fluid flow. These obstacles will make dominant the advection process over the diffusion process. The main contribution of this work is based on proposing the novel hybrid type micromixer design for enhancing the mixing quality. Three non-aligned M-type and non-aligned M-type with obstacles passive type micromixers are analyzed by COMSOL5.5. These designs are hybrid types because different structural changes are combined in a single design for mixing improvement. First of all the straight non-aligned inlets, M-type passive micromixer (SMTM) is analyzed. It is observed that mixing performance is improved because of M-shaped mixing units and non-aligned inlets. This improvement is deemed to be not enough so different shaped obstacles are introduced in the micromixer design. These designs based on obstacles are named horizontal rectangular M-type micromixer, square M-type micromixer, and vertical rectangular M-type micromixer. The mixing index for SMTM, square M-type micromixer, horizontal rectangular M-type micromixer, and vertical rectangular M-type micromixer at Reynolds number Re = 60 is respectively given by 71.1%, 83.21%, 84.45%, and 89.99%. The mixing index of vertical rectangular M-type micromixer was 59.34% − 87.65% for Re = 0.5–100. Vertical rectangular M-type micromixer is concluded with the better-mixing capability design among the proposed ones. Based on these simulation results, the vertical rectangular M-type micromixer design can be utilized for mixing purposes in biomedical applications like nanoparticle synthesis and biomedical sample preparation for drug delivery.

Performance characterization of passive micromixer with dual opposing strips on microchannel walls

Micromixers are an extremely important component in integrated microfluidic systems; however, achieving uniform mixing in laminar flow with a low Reynolds number can be exceedingly difficult. This study developed a chaotic advection type micromixer using dual opposing strips on microchannel walls, which generated two-layer vortices, enlarged the contact interface, and increased diffusion flux between the mixing liquids, ultimately leading to superior mixing performance. Numerical simulation was employed in the design of the micromixer and a micromilling machine was used in conjunction with PDMS casting for the fabrication of the microfluidic devices. Experiments conducted at flow velocities of 1mm/s, 5mm/s, and 10mm/s produced the following results: (1) 90% mixing performance in a channel length of 15mm at the three flow velocities, (2) an increase in flow velocity deteriorated the mixing performance because the geometric groove features reverse the mixing performance achieved by previous features, (3) misalignment between the top and bottom micro strips detracted from mixing performance.

Continuous Flow Controlled Synthesis of Gold Nanoparticles Using Pulsed Mixing Microfluidic System

To prepare the gold nanoparticles (AuNPs) with uniform sizes, fine morphology, and good monodispersity, a pulsed mixing microfluidic system based on PZT actuation was presented. The system includes PZT micropump and Y type micromixer. By adjusting voltage (entrance flow rate), pulsed frequency, phase, and other parameters, a variety of mixing modes can be achieved, so as to realize the controllable synthesis of nanoparticles in a certain range. By numerical simulation and analysis, the channel section size, entrance angle, and pulse frequency were optimized. Based on the optimized structure and working parameters, the test prototype has been manufactured in lab, and the related synthesis tests of AuNPs were carried out. The test results indicate that AuNPs with uniform morphology and good monodispersity can be synthesized using the system with the section size (0.4 mm × 0.4 mm), the entrance channel angle (60°) under condition of the pulsed frequency (300 Hz), and the entrance flow rate (4 mL/min). The average diameter and its standard deviation of AuNPs synthesized were 21.6 nm, 4.83 nm, respectively. The research work above can be applied to the fields such as the controlled synthesis of noble metal nanoparticles, biomedicine, and microchemical system.

Optimization of structure and working parameters of Y type micro-mixer in two-phase pulsating mixing

In order to improve the mixing efficiency of different reactants in microscale,a study on optimization of the structure and working parameters of the Y type pulsing micro mixer is conducted,in which the effects of the structure and parameters on mixing performance are taken into consideration.By simulation analysis,the channel section size,entrance angle,entrance flow rate and pulsation frequency are optimized.Based on the optimized structure and working parameters,a test prototype was made in lab.Using chemical reaction probe method,the prototype is tested.After detecting the size and distribution of gold nanoparticles by controllable synthesis,the mixing performance is evaluated synthetically.The test results indicate that when the entrance flow rate and working frequency are ascertained,there exist corresponding optimum values of the section size and flow rate of the Y type pulsing micro mixer.The entrance flow rate and working frequency are important parameters which influence each other.A certain flow rate corresponds to an optimum mixing frequency.

Optimized Simulation and Validation of Particle Advection in Asymmetric Staggered Herringbone Type Micromixers

This paper presents and compares two different strategies in the numerical simulation of passive microfluidic mixers based on chaotic advection. In addition to flow velocity field calculations, concentration distributions of molecules and trajectories of microscale particles were determined and compared to evaluate the performance of the applied modeling approaches in the proposed geometries. A staggered herringbone type micromixer (SHM) was selected and studied in order to demonstrate finite element modeling issues. The selected microstructures were fabricated by a soft lithography technique, utilizing multilayer SU-8 epoxy-based photoresist as a molding replica for polydimethylsiloxane (PDMS) casting. The mixing processes in the microfluidic systems were characterized by applying molecular and particle (cell) solutions and adequate microscopic visualization techniques. We proved that modeling of the molecular concentration field is more costly, in regards to computational time, than the particle trajectory based method. However, both approaches showed adequate qualitative agreement with the experimental results.

Numerical Simulation of the Hydrodynamic Cavitation of the Impinging Streams Mixer

The impinging streams mixer is a new type micromixer. The cavitation phenomenon occurring in the mixers with T-shaped impinging streams (TS), conical impinging streams (CIS), vortex streams(VS) were investigated, respectively. The distribution of flow field in the mixer was simulated and calculated by commercial software Fluent 6.2.1. The results showed that under the same working conditions, a more obvious hydrodynamic cavitation may occur in the CIS type impinging stream than that in the CIS type or the VS type, and the vortex flow lead to an extension of the material residence time in the mixer. The distribution of turbulent kinetic energy and gas holdup were obtained by numerical simulating hydrodynamic cavitation under different entrance pressure conditions. It is showed that when the outlet pressure keeps a constant value, hydrodynamic cavitation can be enhanced by increasing the entrance pressure. The above research can be contributed to the producing of biodiesel and the solving of the key technical problem of oil and alcohol heterogeneous mixing.

Numerical study on shape optimization of groove micromixers

The performance of a homogeneous T-mixer can be enhanced significantly by the stimulation of secondary/transverse flows in the microchannel. The groove-based micromixers generate helical flows within the microchannel to augment the mixing performance. These micromixers are extensively studied with respect to planar geometric parameters such as groove width, groove spacing, channel height, etc. The effect of groove shape on mixing performance has not been systematically studied. Previous studies have focused on two or three different predefined groove shapes, typically involving slanted grooves, asymmetric herringbone grooves, and their variations. In this computational study, we analyze the effect of groove shape on micromixing performance and search for the optimal groove shape for a pressure-driven flow across the microchannel. The groove shape is parametrically represented by Bezier curves which could take any shape within a constrained plane. The control points of the Bezier curve are chosen as optimization parameters to identify the optimal groove shape which maximizes the mixing for given operating conditions. The optimization is carried out for pressure-driven flow with and without staggered arrangement of grooves. The resulting single groove optimal design improves the mixing efficiency from 0.18 for T-mixer to 0.85 for the same operating conditions (Re ~0.42, Pe ~4,200). Unlike previous studies, axial mixing index profiles are presented for different micromixers which clearly distinguish the effect of flow field on the mixing performance. Various parametric studies are carried out to compare the optimal groove structure with other common groove type (staggered, herringbone, etc.) micromixers for a range of Pe between 400 and 6,200. The improved mixing performance in optimal designs is due to a continuously growing finger-like structure of the interface which enhances the overall mass transfer.

Experimental Investigation of Split and Recombination Micromixer in Confront with Basic T- and O- type Micromixers

The paper presents an experimental comparison of three types of static micromixer. Efficiencies of a split and recombination micromixer (SAR) based on plate symmetrical modules (PSM) and basic T-type and O-type mixers are examined. Experimental tests were carried out in the laminar flow regime with a low Reynolds number range, 0.083 ≤ Re ≤ 4.166 and image-based techniques were used to evaluate mixing efficiency. Experimental results illustrate that the micromixers with splitting and recombination have outstanding mixing efficiency than those of without SAR process. Indeed split and recombine (SAR) structures of the flow channels result in the reduction of the diffusion distance of two fluids and optimize the diffusion process and after a short distance from inlet high mixing efficiency can be achieved. Also, experimental data show that the SAR PSM mixer is up to 99% efficient, and that efficiency reaches 90% in a short distance, demonstrating this type of mixer’s high mixing performance and the effect of splitting and recombination on the degree of mixing and the efficiency of the micromixer.Both of the T- and O-type micromixers are designed and fabricated from plexiglas using a computer milling process.

Passive mixing of co-flowing slugs in grooved microchannels

The anisotropic grooves in a microchannel induce spiral circulation around the flow axis. The stretch and fold of the streams result in a passive mixing. This article describes the effectiveness of induced crossflow, arising from the grooves, placed at the floor of the microchannel. The results from numerical simulation show the extent of local mixing achieved at various positions around the groove. The emphasis here is to understand the mixing when the two streams enter the channel, and displace air while flowing alongside each other. Microchannels with slanted grooves and staggered herringbone type grooves are considered here. The FLUENT 6.2 software and the Open FOAM software were used for the simulation. The latter was primarily utilized for tracking of the interface when a liquid slug displaced air from the micromixer. At a Reynold’s number of about 1.0, low velocity pockets could be identified near the two ends of the ridges. These pockets did not support crossflow and mixing. The herringbone type micromixer was found to have the best mixing effectiveness, when the advection dominates mixing. This advantage is mostly lost at the higher values of diffusivity, as a crossflow became less important for mixing. These observations were made when one of the streams is 1.5 times more viscous than the other, and the mixture-rule governed the viscosity of the mixed stream. When the liquid front enters the microchannel for the first time, the front had to displace air from the channel. At first, the upper part of the channel was swept. This was immediately followed by the sweeping of the groove-part in the floor. Higher hydraulic resistance in the grooves resulted in this non-uniform movement of the front. The co-flow of streams could either be continuous over the entire length of the channel, or in the form of slugs that maintained an interface with air. At a particular position in the channel, the extents of mixing were compared for the two modes of co-flow. The extent of mixing was found smaller in the slug, next to the interface with air. Lack of axial dispersion with preceding liquid stream seems to be the reason for this trend.

Recrystallization of polyethylene submicron particles using a continuous flow micromixer system

Submicron size polyethylene particles were prepared by a thermally induced phase separation process in a split-and-recombine type micromixer. Process parameters such as polyethylene concentration, ratio of nonsolvent to solvent, initial temperature of the nonsolvent and total flow rate play important roles in controlling particle size. The results show that spherical polyethylene particles were obtained with an average diameter ranging from 0.22μm to 0.52μm. The continuous flow micromixer system prevented coagulation, therefore the size of the prepared polyethylene particles can be predicted using the continuous flow micromixer system.

Serpentine microfluidic mixer made in LTCC

Results of investigation of fluid flow, micro-scale mixing and reactive micromixing processes are presented for the serpentine and meander type micromixers. Two approaches are applied. In the first approach the CFD modelling is carried out for a steady-state, laminar flow and mixing of incompressible fluids through a sequence of conduits with rectangular cross-section, and in the second approach the mixing sensitive system of chemical reactions based on simultaneous diazo-coupling between 1- and 2-naphthols is used to characterize experimentally mixing efficiency in the microreactors. Using both approaches the influence of flow conditions upon mixing efficiency in a microdevice is studied. On the grounds of the CFD simulations a prototype I-shaped serpentine micromixer is designed and fabricated in LTCC (Low Temperature Co-fired Ceramics) technology and its performance is compared with performance of the meander micromixer. Results of numerical simulations are experimentally verified by comparison with the selectivity of complex test reactions carried out in micromixers. The method for ranking and comparing mixers based on mixing efficiency that is determined by using complex test reactions is proposed.

준 능동형 로터를 이용한 마이크로 혼합기의 제작 및 혼합특성

Abstract A micro-mixer with a quasi-active rotor was fabricated, and mixing characteristics were evaluated. The proposed micro-mixer combines an active type micro-mixer with a passive type micro-mixer. The micro-rotor, which is a moving part of an active type micro-mixer, is added in a micro-chamber of a passive type vortex micro-mixer. The rotor rotated by inflows tangent to a chamber, causing strong perturbations. The micro-mixers were fabricated using photosensitive glass. Mixing efficiency of the micro-mixers was measured using an image analysis method. Mixing efficiency and characteristics of the micro-rotor mixer were compared with the vortex micro-mixer without a rotor. Mixing efficiency was reduced as Reynolds number increased at a low Reynolds number due to decrease of residence time. Mixing efficiency at higher Reynolds number, on the other hand, was improved even though residence time decreased since the contact surface between fluids increased by twisted flow. The perturbation induced by rotating rotor at greater than Re 200 improved the efficiency of the rotor mixer.

An effective passive microfluidic mixer utilizing chaotic advection

Abstract A Y-junction type micromixer with a square obstacle on the square-wave flow channel for enhancing the mixing ability by using the chaotic advection principle was designed and the mixing efficiency was measured. The micromixer was fabricated on quartz material by SF 6 /Ar inductively coupled plasma (ICP) etching. The mixing capability of the mixer was tested by mixing NaOH and phenolphthalein solutions and analyzing the color density from the image taken by a charge-coupled device (CCD) camera at a given position. The mixing characteristics were measured by varying the flow rate from the micropumps and the channel width of the mixer. The mixing percentage increased slowly with increasing flow rate, but rapidly with decreasing microchannel width.

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.