High Mixing Efficiency Research Articles

AC electrothermal actuation mechanism for on-chip mixing of high ionic strength fluids

The ability to maintain a relative low temperature rise, portability and also achieve fast mixing process is major advantage for high ionic strength processing, where high conductive fluids handled by AC electrothermal (ACET) effects. In this study we examine the frequency dependency of AC electroosmotic (ACEO) and ACET effects, to generate high efficient temperature gradients and corresponding conductivity/permittivity gradients with relatively low temperature rise. We drive the electrodes by amplitude-modulated (AM) sine-wave and it generates non-uniform electric field with small temperature rise, in comparison with the simple sine-wave. The excitation parameters such as voltage amplitude A, sine-wave frequency fc, and also modulation frequency fm, were optimized to achieving both high mixing efficiency and low temperature rise. Technological details of proposed silicon/PDMS fabrication method has been discussed in details for the AC Electrothermally-driven micromixer and a set of numerical simulations were done for the microactuator. An effective ACET flow along with the low temperature rise is observed in optimal frequency range of 0.1 MHz < fc < 9 MHz. A full mixing efficiency achieved by using only three pairs of the electrodes and with the maximum temperature rise of 5.5 K. The reduction in temperature rise is very important for extending ACET mixing applications and device portability. As a proof of chaotic regime, two particles released inside the channel and particle tracing accomplished, the results showed that the particles were stretched and folded. The technological details of fabrication process and thermal effects handling has been discussed in details.

Pumping Induced By Bio-Mimetic Magnetic Micro-Cilia in Creeping Flows

The inertial effects in creeping flow regimes are negligible. Most motile micro-organisms manipulate fluid by oscillatory Cilia or Flagella. The pumping action by a cilium is attributed to the asymmetry in the power and recovery strokes. Further, the ratio of viscous forces to Elastic forces (given by sperm-number) on a cilium determines the efficiency of the pumping. In this presentation we demonstrate magnetic micro-cilia based pumping techniques. We experimentally determine the optimum sperm-number for maximum pumping efficiency. For this, we surface micro-machine high aspect ratio cilia, which are actuated magnetically. These micro-features are fabricated by evaporating NiFe alloy at room temperature, on to patterned photoresist. The evaporated alloy curls upwards when the seed layer is removed to release the cilia, thus making a free standing ‘C’ shaped magnetic microstructure. This is actuated using an external rotating permanent magnet. The time period for the power stroke and recovery stroke are different, which determines the asymmetry in the cilium trajectory. This manipulates the fluid around it. We also demonstrate the active mixing these cilia can produce in the microchannel. We suggest the use of these micro-cilia in capturing bacteria. Selective immobilization of the cilia can lead to highly specific capture of bacteria. We predict high capture rates which will enable easy detection. These simple to fabricate micro cilia can easily be incorporated into many microfluidic systems which require high pumping, mixing and capture efficiencies. The figure bellow shows an image of Cilia actuated by an external magnetic field. Figure 1

Design and Simulation of a Chaotic Micromixer with Diamond-Like Micropillar Based on Artificial Neural Network

Abstract Microfluidic mixing is an essential part of the process of microfluidic chip technology in the analysis, and micromixer has also become the key components of microfluidic chip analysis system. For DNA hybridization, protein folding and enzyme reaction, some biochemical processes need to react quickly to achieve on analysis and research has the vital significance. A simple, rapid and low-cost passive micromixer is presented in this paper. In order to improve the mixing efficiency of the species, the concept of a splitting and recombination (SAR) was used to shorten the mixing time of the species. This study simulated the species mixing in a micromixer with traditional T-type micromixer and diamond-like micropillar in laminar flow state through COMSOL multiphysics 3.5a to computational fluid dynamics (CFD). Linking artificial neural network (ANN) and CFD was used to optimize the diamond-like micropillar. Finally, simulation results proved that the micromixer with SAR diamond-like concept achieves a high-efficiency mixing than T-type micromixer. Numerical results also show that the mixing efficiency of the SAR micromixer with diamond-like micropillar can be up to 99 %, and that efficiency can reach rapidly 90 % in a short channel distance.

Heart-Like Micro-Flow Mixer

AbstractMicromixers are the microfluidic devices able to rapidly mix more than two liquids, with low pressure drop and high mixing efficiency (εmixing). In this study, the effect of Reynolds number ratio (Rer) and aspect ratio (AR) of heart-like biometric micromixer applied would be investigated by a numerical simulation and experimental confirmation. Results show that the heart-like biometric micromixer resulting from the coupling effect of the split and recombination (SAR) and biometric design can produce a high mixing efficiency, low pressure drop and short mixing path under a case of low Reynolds number. Two dimensional results also find that a flow mixing efficiency of εmixing=0.89 and an optimal mixing index of Midx=115 could be achieved at a flow condition of Rer=0.75 and Re2=0.1 of the middle-inlet channel I2. In additional, the three dimensional results indicate that a high flow mixing efficiency of εmixing=0.84 and the lowest pressure drop of 164.2 Pa was obtained at the flow conditions of Rer=0.9 and AR=10 when the middle-inlet channel I2was Re2=0.1. These findings will be useful to improvement the efficiency for micromixcers of biometric design in the future.

Configurable ACET micro-manipulator for high conductive mediums by using a novel electrode engineering

The ability to control and manipulate the high ionic strength fluids is major advantage for fluidic on-chip biological analysis. In this study we proposed an AC electrothermally-driven configurable flow for forward/reverse pumping and also clockwise/anti-clockwise rotational effects. Electrode discretization allow us to generate such a configurable AC electrothermal effects by simple switching the electric potential over the various asymmetric electrodes. Taguchi optimization method have been applied for discretized electrode dimensions and pumping/rotational effects was numerically studied by solving the coupled multi-physic fluidic, convection---diffusion, thermal and electric field equations. High efficient mixing process (above 90 %) achieved by exciting the electrodes in time-varying clockwise and anti-clockwise rotational mode. Thereafter, three particles released inside the channel and the particles were stretched, folded and finally separated by exciting the electrodes in rotational mode (a proof of chaotic regime). We investigate the proposed ACET characteristic, the results confirmed that the proposed system is efficient for high conductive mediums and the efficiency increase by increasing the non-uniform electric field intensity. Based on the frequency analysis from 100 to 500 MHz, the working frequency range of the configurable system is increases by increasing the electric conductivity of solution.

폴리우레탄 발포 노즐 형상이 혼합 성능에 미치는 영향

For reaction injection molding (RIM) polyurethane was mixed in the mixing head by impingement mixing, injected into the mold, and cured quickly, as soon as the mold is filled. The shape of the nozzle in the mixing head is critical to improve the quality of polyurethane. To achieve homogeneous mixing, an intensive turbulence energy in the mixing nozzle is essential. In this study, a mixing nozzle for RIM was designed, and mixing efficiency was investigated based on experiment. Experiments were conducted with different combinations of nozzle tips and exit diameter to measure the mixing efficiency by measuring jet force and investigating mixing image with high speed camera. Jet force increased gradually and reaches steady state conditions. The jet force depended on shape of nozzle tip and outlet sizes. These results suggest that optimized nozzle configurations are necessary for high efficiency mixing with RIM.

Harvesting of microalgae species using Mg-sericite flocculant.

In this study, Mg-sericite was used as a flocculant to harvest freshwater microalgae Chlorella vulgaris. Mg-sericite separated successfully >99% of the C. vulgaris at the following optimal parameters: sericite and MgCl2 ratio (S/M ratio) of 45 to 15, mixing time of 5 min, mixing rate 100 to 150 rpm and settling time of 5 min. The harvesting efficiency was pH dependent. The highest harvesting efficiency (99 ± 0.3%) was obtained at S/M ratio 40 and pH 9-11. These results indicated that a biopolymer, Mg-sericite, can be a promising flocculant due to its high efficiency, low-dose requirements, and short mixing and settling times. In addition, Mg-sericite does not contaminate the growth medium, which can be recycled to reduce not only the cost and the demand for water, but also the extra operational costs for reusing the growth medium. This harvesting method is helpful to lower the production cost of algae for biodiesel.

Geometric effects on mixing performance in a novel passive micromixer with trapezoidal-zigzag channels

A novel passive micromixer, called a trapezoidal-zigzag micromixer (TZM), is reported. A TZM is composed of trapezoidal channels in a zigzag and split–recombine arrangement that enables multiple mixing mechanisms, including splitting–recombining, twisting, transversal flows, vortices, and chaotic advection. The effects of geometric parameters of the TZM on mixing performance are systematically investigated by the Taguchi method and numerical simulations in COMSOL Multiphysics. The number of mixing units, the slope angle of the trapezoidal channel, the height of the constriction element, and the width ratio between the middle-trapezoidal channel and the side-trapezoidal channel are the four parameters under study. The mixing performance of the TZM is investigated at three different Reynolds number (Re) values of 0.5, 5, and 50. The results showed that a TZM with six mixing units, a trapezoidal slope angle of 75°, a constricting height of 100 µm, and a width ratio of 0.5 has the highest mixing efficiency. This optimal TZM has a mixing efficiency greater than 85% for Re values from 0.1 to 80. In particular, for Re ⩽ 0.9 and Re ⩾ 20, the mixing efficiency of the optimal TZM is greater than 90%. The proposed TZM has a higher mixing efficiency and a smaller footprint than previously reported micromixers.

Hydrodynamics and mixing performance of Hartridge Roughton mixers: Influence of the mixing chamber design

Mixing efficiency of three Hartridge–Roughton mixers with different geometries is characterized by a segregation index measured via the Villermaux/Dushman test reaction and by Computational Fluid Dynamics. The small values of the segregation index (always lower than 0.025 for the concentrations and the flow rate studied) confirm these vortex mixers achieve very good mixing performance. The use of the Turbulent Mixing Model indicates that mixing times are less than 5ms for inlet flowrates faster than 5L/h. Mixing performance is even better when these devices have a separate mixing chamber upstream of a narrower outlet pipe, whose diameter is half that of the chamber. Computational Fluid Dynamics shows the internal flow depends on the geometry of the mixer and has a direct influence on its efficiency. When no separate chamber is present, the flow has a double spiral structure. The two inlet fluids roll up together as they pass through the mixer, which slows down the mixing process. For precipitation reactions, we recommend the use of a mixer with conical narrowing which has a high mixing efficiency and a lower risk to be obstructed by the particle agglomeration.

An effective passive micromixer with shifted trapezoidal blades using wide Reynolds number range

In this paper, a novel micromixer design, called the shifted trapezoidal blades (STB) micromixer, has been designed and fabricated to provide high mixing efficiency even at low Reynolds number (Re) based on the combination of several mixing principles, including vortices, transversal flows and chaotic advection. Although the STB micromixer has 3D geometrical structure, it can be easily fabricated by one-step photolithography technique, using only one mask and two inclined exposures and an aluminum base with 15° inclines. We conducted intensive numerical study to evaluate the performance of the proposed STB micromixer using COMSOL Multiphysics package with a wide range of Reynolds number from 0.5 to 100. We have fabricated STB micromixers for testing and verification. Both experiment and simulation results demonstrated that the STB micromixer had stable mixing efficiency of 80% or above for Reynolds number values in the range from 0.5 to 100. The most effective mixing performance was achieved at Re=40 in which the STB micromixer had the highest mixing efficiency value (95%) and a moderate pressure drop ΔP=30.27kPa. The proposed STB micromixer provided better mixing performance and smaller footprint compared to the previous micromixers presented in literatures. With a high mixing efficiency and the advantage of being easy to fabricate, the STB micromixer can be utilized in various microfluidic, point-of-care, point-of-need, central automatic diagnosis, and pre-treatment systems including sensor control systems.

The design and performance of a vane mixer based on extensional flow for polymer blends

ABSTRACTA new laboratory‐scale mixing device called the “Vane Mixer” was designed, built, and tested. The vane mixer consists of three vane plasticizing and conveying unit. In comparison with the existing laboratory mixers, material flow in this vane mixer is characterized by a high contribution from extensional flow. As the mixer has mixing chamber of very simple geometry, the cleaning is very easy and the material lost is very small. The influences of mixing time and rotor speed on dispersed phase size were characterized and discussed. Morphology data on model immiscible polystyrene/high density polyethylene (PS/HDPE) blend have proved the high distributive and dispersive mixing efficiency. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41551.

Unsteady asymmetric engulfment regime in a T-mixer

Unsteady flow regimes in a micro T-mixer are investigated. Direct numerical simulations (DNS) show that, in agreement with experimental and numerical results in the literature, when the Reynolds number is increased above a critical value larger than those typical of the steady engulfment regime, the flow remains asymmetric in the mean but becomes periodic in time. The dynamics of this regime is characterized by analyzing the evolution of the three-dimensional vortical structures forming at the confluence of the two inlet flow streams. As the Reynolds number is further increased, the flow remains time-periodic but it continuously switches between a symmetric configuration, similar to that of the vortical regime, and an asymmetric one, close to the engulfment configuration. Three-dimensional linear stability analysis is successively used to characterize the instability leading to the unsteady asymmetric regime, which is also interesting for applications due to its high mixing efficiency. The critical Reynolds number and the instability frequency are in very good agreement with those found in DNS. The sensitivity of this instability to a generic perturbation of the base flow is also investigated. It is shown that the largest sensitivity is to base-flow modifications introduced close to the three-dimensional vortical structures forming at the confluence between the inlet channels. Finally, the sensitivity analysis is specialized to investigate the effect of a generic perturbation of the inlet velocity profile.

An efficient passive planar micromixer with ellipse-like micropillars for continuous mixing of human blood

In this paper, a passive planar micromixer with ellipse-like micropillars is proposed to operate in the laminar flow regime for high mixing efficiency. With a splitting and recombination (SAR) concept, the diffusion distance of the fluids in a micromixer with ellipse-like micropillars was decreased. Thus, space usage for micromixer of an automatic sample collection system is also minimized. Numerical simulation was conducted to evaluate the performance of proposed micromixer by solving the governing Navier–Stokes equation and convection–diffusion equation. With software (COMSOL 4.3) for computational fluid dynamics (CFD) we simulated the mixing of fluids in a micromixer with ellipse-like micropillars and basic T-type mixer in a laminar flow regime. The efficiency of the proposed micromixer is shown in numerical results and is verified by measurement results.

Integrated Ozone Microreactor Technology for Water Treatment

Safe and clean potable water is a basic primary need for daily living and the ability to process water using minimal expenditure of resources provides tremendous advantages. In this work, we present ozone process technology being developed at KWJ Engineering to decontaminate recovered potable water and greywater with a small energy footprint. The technology involves the in-situ generation of ozone, a powerful broad spectrum disinfectant, generated from air. Unique microreactor technology integrated with a low power ozone source enables high efficiency mixing of water and ozone at high mass transfer rates for decontaminating a multitude of pathogens and chemical contaminants. The compactness and low power feature of microreactors and micro-ozone generators creates a portable and scalable system that can provide on the spot potable water in many situations such as disaster relief, rural communities and space habitats.

A microfluidics-based technique for automated and rapid labeling of cells for flow cytometry

Flow cytometry is a powerful technique capable of simultaneous multi-parametric analysis of heterogeneous cell populations for research and clinical applications. In recent years, the flow cytometer has been miniaturized and made portable for application in clinical- and resource-limited settings. The sample preparation procedure, i.e. labeling of cells with antibodies conjugated to fluorescent labels, is a time consuming (∼45 min) and labor-intensive procedure. Microfluidics provides enabling technologies to accomplish rapid and automated sample preparation. Using an integrated microfluidic device consisting of a labeling and washing module, we demonstrate a new protocol that can eliminate sample handling and accomplish sample and reagent metering, high-efficiency mixing, labeling and washing in rapid automated fashion. The labeling module consists of a long microfluidic channel with an integrated chaotic mixer. Samples and reagents are precisely metered into this device to accomplish rapid and high-efficiency mixing. The mixed sample and reagents are collected in a holding syringe and held for up to 8 min following which the mixture is introduced into an inertial washing module to obtain ‘analysis-ready’ samples. The washing module consists of a high aspect ratio channel capable of focusing cells to equilibrium positions close to the channel walls. By introducing the cells and labeling reagents in a narrow stream at the center of the channel flanked on both sides by a wash buffer, the elution of cells into the wash buffer away from the free unbound antibodies is accomplished. After initial calibration experiments to determine appropriate ‘holding time’ to allow antibody binding, both modules were used in conjunction to label MOLT-3 cells (T lymphoblast cell line) with three different antibodies simultaneously. Results confirm no significant difference in mean fluorescence intensity values for all three antibodies labels (p < 0.01) between the conventional procedure (45 min) and our microfluidic approach (12 min).

Numerical Simulation of Mixing Characteristics in a Vane Extruder

The polymer vane extruder, whose plasticating and conveying theory is based on elongational rheology, is a significant development in plastic processing equipment. As a result of its unique structure, it is desirable to use numerical simulation to study it. The results can be useful to set process parameters and optimize its structure. In this paper, numerical simulation of the mixing characteristics of the vane extruder was performed with the finite element computational fluid dynamics program POLYFLOW. To visualize the mixing process of the melts in a vane extruder based on the calculation of the transient flow, a particle tracking method was applied. By using the statistical post-processor program POLYSTAT, dispersive mixing and distributive mixing characteristics were evaluated in terms of shear rate, stretching rate, mixing index, and time average mixing efficiency. The simulation results showed that strong stretching existed in the vane extruder demonstrating that the vane extruder generated a more appropriate flow than a common twin-screw extruder to break material particles into smaller ones. The probability functions of mixing efficiency showed that the position near the outflow had the highest mixing efficiency. Furthermore, the time average mixing efficiency of most particles in the vane extruder were larger than that in a twin-screw extruder, indicating that in the vane extruder more mechanical energy was used to generate stretching.

Simulation and fabrication of a branch-channel rhombic micromixer for low pressure drop and short mixing length

The planar micromixers merit easy integration with the microsystem but encounter the problems of high pressure drop and long mixing length for high mixing efficiency over 90 %. In this article, an advanced branched rhombic micromixer (BRM) have been designed and investigated by 3D numerical simulations and experiments. Polydimethylsiloxane (PDMS) molding process was used for chip fabrication of the experiment. The CFD-ACE+ software was applied for modeling simulations. Simulation results showed that this optimum geometry design of four-mixing-unit BRM with the branch position at 700 μm high and 100 μm wide can effectively improve the mixing efficiency over 95 % at Reynolds number (Re) 120 with a rather low pressure drop about 9,000 Pa and a short mixing length of 5.5 mm as well. The high mixing efficiency at low pressure drop is attributed to the greatly increased contact interface area and chaotic-convection vortices as well as the low flow resistance with branched channels. The mixing verification is performed by the flow visualization system via the popular rhodamine B dye (10 mM) added DI method for PDMS BRM chips.

Molecular weight and injector configuration effects on the transverse injection flow field properties in supersonic flows

The transverse injection flow field in the high speed conditions is more complex than that in the low speed, and more information should be explored to improve the overall performance of the airbreathing hypersonic propulsion system. The three-dimensional Reynolds-averaged Navier–Stokes (RANS) equations and the two equation SST k–ω has been employed to explore the influences of the molecular weight (hydrogen and nitrogen) and injector configuration (circular, square, diamond and equilateral triangular) on the mean flow field properties in the transverse injection strategy, and the wide range of the jet-to-crossflow pressure ratio (4.86, 10.29, 17.72 and 25.15) has been considered as well. The obtained results show that the low jet-to-crossflow pressure ratio can promote the mixing process between the injectant and the supersonic crossflow irrespective of the injectant species and the injector configuration, and the large molecular weight of the injectant can promote the mixing process as well when the jet-to-crossflow pressure ratio is fixed. The case with the equilateral triangular injector owns the highest mixing efficiency in the range considered in the current study, and it may be induced by the remarkable influence of the counter-rotating vortex pair. The injectant mole fraction decreases more rapidly with the increase of the streamwise distance for the case with the low jet-to-crossflow pressure ratio, and the jet plume spreads in the spanwise direction more rapidly for the case with the diamond injector irrespective of the injectant species.

High-Efficiency Mixing Chip with Liquid Flow Actuators Operated by Surface Acoustic Waves

SUMMARY Surface acoustic wave (SAW) devices can be used as component parts for micro total analysis systems (μTAS) because their structures are very simple. We thus fabricated a mixing chip with liquid flow actuators operated only by SAWs. The chip consists mainly of one Y-type flow channel, two pumps, and one mixer. The pumps are located in the upstream areas of the merging point of the flow channel, and the mixer is located in its downstream area. Additionally, the flow actuators have interdigital transducers (IDTs) to generate the SAWs. The IDTs were fabricated by patterning Al/Cr on a LiNbO3 substrate, and the flow channel wall was made of the epoxy-based negative resist SU-8. Using the mixing chip, we carried out a mixing experiment with two water solutions of different concentrations using glycerin, and a chemical reaction experiment involving luminol luminescence. Through the experiments, it was found that local and rapid mixing of a continuous liquid flow was possible by using the SAW actuators, and the capability of our fabricated mixing chip as a reactor was demonstrated. © 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 97(1): 54–61, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11440

Effects of the number of tangential passages on spray characteristics of a bipropellant atomizer

The liquid–liquid bipropellant pressure swirl atomizers have been widely used in rocket engines to take advantage of their high mixing efficiency within the short length of the combustion chamber. In this kind of engine, the uniform mass distribution and propellant mixture ratio have great influence on combustion efficiency and instability. The present work investigates the effect of the number of tangential passages on the spray cone angle, mass distribution, and propellant mixture ratio of a bipropellant atomizer. Thus, three atomizers were designed, manufactured, and evaluated experimentally. The results showed that the number of tangential passages has some influence on the circumferential mass distribution; however, spray angle and propellant mixture ratio have not presented significant variations.