Microchannel Mixer Research Articles

Decarbonization of simulated biogas with microchannel mixer by pressurized water scrubbing

Pressurized water scrubbing is an environmentally friendly technology for the decarbonization of biogas. However, the key bottlenecks such as low efficiency, high cost of water consumption and secondary CO2 emission by water absorption and desorption in the process of decarbonization are still necessary to be solved. This study focused on improve the mass transfer effect by introduce finger-crossed microchannel in the process of simulated biogas decarbonization using pressurized water scrubbing. The simulated biogas was mixed with pressurized water in the finger-crossed microchannel, and the gas-water mixture was continuously separated in the gas-water separation tank. The effects of pressure (26–30 bar), temperature (5–30 °C), gas-water ratio (5:1–12:1), liquid volumetric flowrate (5–10 mL/min), and other factors on the decarbonization were investigated. The overall mass transfer coefficient based on the liquid phase and the CO2 flux were also calculated and analyzed. The decarbonization parameters were optimized using the response surface methodology as follows: temperature 20 °C, pressure 29/27 bar, gas-water ratio 10:1, liquid volumetric flowrate 5 mL/min. The process remained stable, achieving 98 % removal of CO2 under optimal conditions. Furthermore, the CO2 concentration in the purified gas was maintained below 3 %. Additionally, a significant number of micro-nano bubbles were observed in the absorption water obtained through this mixer, and the releasing of CO2 from the water lasted 5 days. These results indicated the excellent decarbonization performance of the finger-crossed microchannel in pressurized water scrubbing and potential application value of new ways of CO2 absorption water without desorption.

An Eight-Step Continuous-Flow Total Synthesis of Vitamin B1

Vitamin B1 is widely applied in the healthcare and food industry as an antineuritic and antioxidant to maintain the normal functioning of nerve conduction, the heart, and the gastrointestinal tract. This study reports on an integrated eight-step continuous-flow synthesis of vitamin B1 from commercially available 2-cyanoacetamide. The proposed continuous-flow process is based on advances in chemistry, engineering, and equipment design, and affords improved performance and safety compared with batch-mode manufacturing. Several challenges were precisely investigated and controlled, including mixing, unexpected clogging, solvent switches, an exothermic reaction, and the prevention of side reactions, using various micro-channel flow reactors, mixers, separators, and continuous filters. Vitamin B1 was produced with a separated yield of 47.7% and high purity, with a total residence time of about 3.5 h. This eight-step continuous-flow protocol enables technology involving up to six of the key principles of green chemistry. Hence, the application of flow technology is of paramount importance for improving security, reducing waste, and, in particular, improving the efficiency of batch operations that require several days for manufacturing.

Analysis of a Square Split-and-Recombined Electroosmotic Micromixer with Non-aligned Inlet-Outlet Channels

ABSTRACT In micro-scale sensitive medicinal and biochemical systems, improving mixing efficiency with small velocity limitations is critical. This work examines the influencing key parameters and their implications on mixing efficiency in a new two-dimensional electroosmotic micromixer (EM) with nonaligned input and outlet microchannels. The micromixer uses electroosmosis force generated by microelectrodes mounted on the walls of a square split and recombine (SSAR) mixing chamber to blend fluids of various concentrations, which enter into an intake microchannel from different inlets. The governing equations along with the specified boundary conditions are solved by the finite element-based solver. Thorough investigations are executed to explore how the mixing performance of the new microchannel mixer is affected by both flow (inlet velocity) and electric field (electrode potential arrangement, voltage magnitude, AC frequency, and phase difference) parameters. The results revealed that only adding electrode pairs always doesn’t increase the mixing efficiency of SSAR-EM, rather electrode polarity configuration along with an increase in electrode pair optimizes fluid mixing. Also, according to the present observations, the mixing performance of SSAR-EM is strongly sensitive to the input fluid velocity, the phase difference applied to the micro-electrodes, the AC frequency, and the amplitude of the alternating voltage. Corresponding to optimal parameters (i.e. velocity of 50 µm/s, AC-frequency of 8 Hz, voltage of 100 mV, and phase difference of 7π/36-radian), the mixing efficiency of SSAR-EM becomes 98.26%.

Continuous synthesis of ZIF-67 by a microchannel mixer: A recyclable approach

Microfluidic synthesis of a Zeolitic-Imidazole Framework ZIF-67 at ambient temperature and pressure is reported. With a metal/ligand/triethylamine (TEA) ratio of 1/4/4, ZIF-67 can be produced with a high space-time yield (STY) of 57000 kg m−3 d−1 and a production rate of 285 g h−1 in ethanol. It can be produced with a similar STY in water solution as well. Given the importance of sustainable synthesis, the recycling process of the mother liquor was investigated. The mother liquor can be recycled 5 times with high yield and crystallinity in ethanol, but not applicable in water solution. The morphology and particle sizes of ZIF-67 can be regulated in a controlling manner in a water-ethanol mixed solvent. Moreover, the influence of TEA on the characteristic of the ZIF-67 structure was investigated in detail.

The optimal aspect ratio of the T-shaped rectangular microchannel mixer to achieve excellent mixing and hydraulic comprehensive performance

The optimal aspect ratio of the T-shaped rectangular microchannel mixer to achieve excellent mixing and hydraulic comprehensive performance

OPTIMAL ANALYSIS OF THE HYDRAULIC AND MIXING PERFORMANCES OF SYMMETRIC T-SHAPED RECTANGULAR MICROCHANNEL MIXER

This paper theoretically and numerically investigates the hydraulic resistance, mixing efficiency, and comprehensive mixing and hydraulic performance characterized by the outlet mixing efficiency to hydraulic resistance ratio of the symmetric T-shaped rectangular microchannel mixer with uniform channel height. The influences of multi-parameters including width ratio of inlet channel and outlet channel, channel height, and two different inlet conditions of inlet velocity and inlet flowrate on the hydraulic and mixing performance of the micromixer are investigated. This work found that the comprehensive performance first increases and then decreases with the increasing channel width ratio of inlet channel and outlet channel, indicating the existence of an optimal channel width ratio to reach the best comprehensive mixing and hydraulic performance. This result is similar to the conclusion of classical Murray’s law and can be considered as an extension of classical Murray’s law in the field of microscale mixing. The effects of the channel height, channel length ratio and different inlet conditions on the optimal width ratio are analyzed.

Development of a microfluidic perfusion 3D cell culture system

Recently, 3-dimensional in vitro cell cultures have gained much attention in biomedical sciences because of the closer relevance between in vitro cell cultures and in vivo environments. This paper presents a microfluidic perfusion 3D cell culture system with consistent control of long-term culture conditions to mimic an in vivo microenvironment. It consists of two sudden expansion reservoirs to trap incoming air bubbles, gradient generators to provide a linear concentration, and microchannel mixers. Specifically, the air bubbles disturb a flow in the microfluidic channel resulting in the instability of the perfusion cell culture conditions. For long-term stable operation, the sudden expansion reservoir is designed to trap air bubbles by using buoyancy before they enter the culture system. The performance of the developed microfluidic perfusion 3D cell culture system was examined experimentally and compared with analytical results. Finally, it was applied to test the cytotoxicity of cells infected with Ewing’s sarcoma. Cell death was observed for different concentrations of H2O2. For future work, the developed microfluidic perfusion 3D cell culture system can be used to examine the behavior of cells treated with various drugs and concentrations for high-throughput drug screening.

Numerical Investigation of Fluid Mixing in a Micro-Channel Mixer with Two Rotating Stirrers by Using the Incompressible SPH Method

Fluid mixing is a crucial and challenging process for microfluidic systems, which are widely used in biochemical processes. Because of their fast performance, active micromixers that use stirrer blades are considered for biological applications. In the present study, by using a robust and convenient Incompressible Smoothed Particle Hydrodynamics (ISPH) method, miscible mixing within a two-blade micromixer is investigated. The problem discussed herein is represented by an active micromixer comprising two stir-bars that rotate to mix the fluids. Because of its Lagrangian nature, Smoothed Particle Hydrodynamics is an appropriate and convenient method for simulating moving boundary problems and tracking the particles in the mixing process. Previous investigations have been carried out for mixing flow for a low Schmidt number. However, a low Schmidt number is barely applicable for liquid mixing. Hence, in the present study, the Schmidt number is considered to be Sc=1000. The present results show that the two-blade micro-channel mixer considerably improves the mixing rate in comparison with the one-blade micro-channel mixer.

High Production Rate Synthesis of CdS Nanoparticles Using a Reverse Oscillatory Flow Method

A reverse oscillatory flow (ROF) mixing system is discussed having a reaction channel 460 μm high by 152 mm wide for high flow rate processing of nanoparticle (NP) chemistries. The ROF system is demonstrated to produce CdS nanoparticles at a production rate of 115.7 g/h with a coefficient of variation (CV) for particle size down to 19%. These production rates are substantially higher than those achieved using other microchannel mixers while maintaining comparable size distributions. Advantages of the ROF approach include the use of larger microchannels which make the reactor easier to fabricate and less vulnerable to clogging.

Investigation on pressure drop characteristic and mass transfer performance of gas–liquid flow in micro-channels

Pressure drop characteristics and mass transfer performance of gas-liquid two-phase flow in micro-channels with different surface wettabilities were experimentally investigated. Side-entry T micro-channel mixers made of glass and polydimethylsiloxane were tested. Frictional pressure drop was found to decrease as the hydrophobicity of the channel surface increased. The flow patterns observed in the experiment were classified as slug flow and continuous gas phase flows. The modified Hagen-Poiseuille equation and Lockhart-Martinelli model were developed to predict the pressure drop for these two types of flow, respectively. The effect of surface wettability was heuristically incorporated in the present models which can correlate well the experimental results. Mass transfer performance was studied by the physical absorption of oxygen into de-ionized water. The results show that the volumetric mass transfer coefficients in hydrophobic micro-channels are generally higher than those in hydrophilic ones. The empirical correlations of overall volumetric mass transfer coefficients were proposed.

SOLUBLE POLYMER DIRECTED CONTROLLED SYNTHESIS OF GOLD NANOPARTICLES: EFFECT OF CLOUD POINT, REDUCING AGENT, AND MIXING METHOD ON NANOPARTICLES PREPARATION

Au(0) metallic nanoparticles (Au NPs) were first prepared in triblock copolymer poly (methyl vinyl ether) PMVE-water dispersions. The wax formed from cloud point appearance in PMVE (0.6 wt.%)-water on heating the solution at 40°C worked as a template to trap the reduced Au NPs of 3 nm (σ = 0.8) size. Cooling the solution to 25°C, the cloud point disappeared as a result the particles aggregated to larger oval shape crystals with major and minor diameters 99.5 nm (σ = 4.5) and 84 nm (σ = 2), respectively when solution was stirred for one week for the completion of reaction. Smaller (4.4. nm (σ = 1.2)) particles were obtained when Au salt HAuCl4⋅3H2O (hydrogen tetrachloroaurate (III) trihydrate) was reduced by 5 equivalents of NaBH4 , whereas the addition of 10 equivalents NaOH gave larger particles of 13 nm (σ = 2.4) diameter. PMVE polymer alone acted as a reducing and stabilizing agent but the time of completion of reduction was much longer (one week) compared to the reduction conducted by NaBH4 or NaOH where the reaction completed in 15 min. In neat PMVE polymer-water dispersions a number of mixing methods employed to reduce Au salt followed the order: combination of sonication and stirring > sonication > stirring. Au NPs formation was 27%, 21%, and 5%, respectively in 4 h of reaction time. The mixing experiments justified the development of microchannel mixers for NPs production on a large scale.

Human Mesenchymal Stem Cells Migration on Matrices with Distinct Elasticity Gradient Magnitudes

Adult mesenchymal stem cells (MSCs) respond to extracellular niche elasticity, which varies dramatically between tissues that MSCs inhabit. Similarly, as MSCs egress from bone marrow and hone to tissues, they may encounter stiffness gradients brought on either by pathological conditions, e.g. myocardial infarction ∼8.7±1.5kPa/mm, or through normal tissue variation, e.g. muscle ∼0.6±0.9kPa/mm. We have recently shown that MSCs can undergo directed migration in response to shallow, physiological (∼1kPa/mm) stiffness gradients before differentiating, suggesting the importance of spatial changes in stiffness. Such gradients, however, contain aphysical ranges, e.g. 1-15kPa, and more refined gradients of both range and gradient strength that mimic tissue interfaces are needed to better understand how mechanical cues dictate MSC migration versus differentiation. Using a polydimethylsiloxane microchannel mixer, we generated a polymer solution with a one-dimensional crosslinker concentration of constant monomer and photoinitiator but varying crosslinker. Photopolymerizing the solution inside the device yields a 3mm wide hydrogel with varying mechanical properties. Stiffness gradients of varying strength (1-30kPa/mm) and range (0.1-100 kPa) are achieved by varying the relative concentration of crosslinker from the input solutions. MSCs responded to stiffness gradients with a physiological range, e.g. mimicking the myotendenous junction, but of varying strength, i.e. 1-30kPa/mm. However, migration velocities of MSCs on gels of varying gradient strength were similar. Cell morphology was stiffness dependent with cells exhibiting increased spread areas on the stiffer regions, suggesting that the previously observed correlation between substrate mechanics, cell motility, and morphology exists over a physiological stiffness range but is independent of gradient strength. Efforts to define optimal myogenic stiffness and studies with C2C12 muscle cells are ongoing. These findings imply that MSCs in vivo may contribute better to repairs in stiffer regions of tissues where they may preferentially accumulate.

Computational study of convective–diffusive mixing in a microchannel mixer

Scalar mixing due to convection and diffusion in a microchannel mixer is studied using CFD. A method is developed to quantitatively measure the effect of false diffusion on scalar decay rate. This method computes an average false diffusivity from a given numerical solution and it is not limited to any particular numerical scheme. It is found that a range of molecular diffusivity exist in which average false diffusion is smaller than molecular diffusion and scalar decay rates can be computed accurately with CFD in the mixer. This range of molecular diffusivity covers most of the liquid solutions encountered in chemical and biochemical engineering. When effective diffusivity is used, this range can be further expanded. The predicted mixing structures agree well with experimental results in literature. The classical lamellar structures of the baker's transformation are strongly affected by diffusion. The striation doubling process is destroyed by diffusion broadening at very early stage in the mixer. The optimal mixing is achieved at low Re when the mixing mechanism in the mixer is the baker's transformation. At higher Re, secondary flow is generated and the mixing mechanism is the competition of the kinematics of the baker's transformation and the dynamics of the cross sectional flow. Results show that the secondary flow hinders mixing and the scalar decays at lower exponential rates than when the mixing is due to the baker's transformation alone.

Effects of forced solution flow on lysozyme crystal growth

AbstractIn order to study quantitatively the effects of forced solution on crystal growth, we designed a new set of experimental equipment, in particular, a microchannel mixer was used as crystallization container so that the consumption of protein samples was much reduced and thus an exact syringe pump could be used for precise control of the flow rates. Since the mixer's section was designed to be rectangular, the solution velocity in its center was steady and constant, and thus repeatable experiments were facilitated. Experimental results showed that the effects of forced solution on protein crystal growth were different under different levels of supersaturation, and new results were obtained for cases of high supersaturation. When the supersaturation is σ = 2.3, with increasing flow rates the growth rates of the lysozyme crystal's (110) face hardly change when the flow rates are lower than 1300 μm/s, and decrease quickly afterwards. When the flow rate reaches 2000 μm/s, the crystal nearly ceases to grow. When the supersaturation is σ = 2.7, with increasing flow rates the (110) face growth rates increase at the beginning then reach the maximum values at 1700 μm/s – 1900 μm/s and decrease afterwards, approaching zero or so when the flow rate reaches 12000 μm/s. The higher the supersaturation, the larger the flow rate at which the crystal ceases to grow. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Seed Assisted Phase Control of TiOPc: Application of Microfluidic Mixing

AbstractMicrofluidic mixing was applied to conventional acid pasting process to re-crystallize organic nanocrystals of Titanyl phthalocyanine (TiOPc). TiOPc nanocrystals were re-crystallized in a two step process. Seed particles were prepared by mixing TiOPc, dissolved in concentrated sulfuric acid with deionized water using high speed microchannel mixers. Seed particles were then subjected to post-precipitation treatment to achieve final crystalline product. Effects of seed preparation conditions, such as mixing efficiency (mixer type) and mixing temperature on the structure of final product were studied. Time evolution of optical absorption spectra was examined with a view to elucidate structure evolution during early stages of seed formation process.

Residence-time distribution as a measure of mixing in T-junction and multilaminated/elongational flow micromixers

The ineffective mixing in microchannel mixers or reactors, primarily due to the laminar flow behavior in such microfluidic devices, has become an issue of significant interest to many researchers working in the field of microreaction engineering and related disciplines. The present study describes the numerical and experimental investigation of mixing performance in a proposed multilaminated/elongational flow micromixer (herein referred to as MEFM-4) and a standard T-junction micromixer (TjM). These two micromixers that employ different mixing enhancement strategies were fabricated from silicon using micro-electromechanical systems (MEMS) technology. Computational fluid dynamics (CFD) approach was first used to establish the experimental platform for the mixing study. Tracer experiment utilizing UV–vis absorption spectroscopy detection technique was used to obtain the required concentration data for residence-time distribution (RTD) analysis. The RTD and its coefficient of variation (CoV) were used for indirect characterization of flow and mixing behavior in the micromixers. Using this measure, the proposed MEFM-4, as expected, exhibits a better mixing performance (with its narrower RTD and lower CoV values) than the standard TjM. The comparison of results from the CFD simulation and the experiment shows very good agreement, especially in the low Reynolds number flow regime (Re<29). In combination with matching experiment and advanced microfabrication techniques, CFD simulation is a powerful tool for effective design and evaluation of simple to complex microfluidic devices for useful applications in chemical analysis and synthesis.

Flow Synthesis of Cyanine Dyes for Absorbing Orange Light from the Neon Gas Discharge

Color compensation technology made it possible to enhance the image quality of plasma panel display (PDP) devices. We examined the chemicals used in color compensation filters for PDP units in this study. Neon excitation during the plasma discharge causes orange light with an emission wavelength of 585 nm to be emitted from PDP devices. 1 This emitted orange light is mainly responsible for the degradation of color purity in PDP devices. 2 We synthesized three types of closed chain trimethine cyanines to attenuate unwanted spectral emissions having a wavelength 585 nm. Their common uses in PDP are near infrared absorbance filter. In this study, cyanines have been applied to neon orange light absorbing filter. By varying the number of carbons in the methine bridge of cyanine compound or by modifying the cyanine ring structure, 3,4 it is possible to synthesize cyanine structure absorbing particular wavelength and solvent solubility. A simple closed chain trimethine cyanine chromophore was synthesized by the condensation of 3-ethyl-2,4-dimethyl- pyrrole (kryptopyrrole) and TMOP with perchloric acid as shown in Scheme 1. Cyanine 1 was continuously synthesized using microchannel mixer and an extension tube. Kryptopyrrole was fed into one side of the microchannel mixer and the other reactants were fed into the other side. The reactants were mixed at the microchannel mixer and the reaction was carried out in the extension tube by heating at 60 o C. The microchannel mixer was operated at room temperature to avoid clogging it with precipitated solid particles. The volume of the extension tube was 10 mL, causing the retention time to vary from 0.37 s to 1.6 s depending on the total flow rate used in the experi- ment. We observed that a retention time of 0.37 s was sufficient to convert all reactants into product. A higher mass flow rate resulted in a shorter reactant retention time, thereby reducing the formation of byproducts. Cyanine 1 was produced with a yield of 95% and was 99.5% pure and dissolved in 2-butanone had a sharp absorption band at 580 nm with a half bandwidth of 36 nm. In comparison, azo or anthraquinone compounds typically had bandwidths of over 100 nm. 5 The width of the absorption band is dependent upon how closely the molecular structure in the first excited state resembles that in the ground state. The long conjugated chain structure of 1 was accompanied by a corresponding decrease in bandwidth. 6 The molar absorptivity of 1 was measured as 136,130 M -1 cm -1 . We synthesized a closed chain trimethine cyanine structure using 1-butyl-3-acetyl-2,4-dimethylpyrrole and 1,1,3,3-tetra- methoxypropane in the presence of perchloric acid as shown in Scheme 2. For the first step, several basic reagents were tested to generate a pyrrolyl anion for the alkylation of the nucleus in 3-acetyl-2,4-dimethylpyrrole with 1-bromobutane. Alkylation in the presence of potassium hydroxide in dimethyl sulfoxide gave 1-butyl-3-actyl-2,4-dimethylpyrrole with a 75 % yield. Other strong basic reagents such as potassium hydroxide in a solution of sodium amide or aqueous potassium hydroxide (50%) with tetrabutylammonium bromide in dichloromethane were also tested and delivered yields of 50% and 48%, respec- tively. Alkylation with sodium hydride in dimethyl sulfoxide increased the yield to 95%. The strong base, sodium hydride, reacts with dimethyl sulfoxide to produce dimsyl ions, which can effectively remove protons from the nucleus in 3-acetyl-2,4- dimethylpyrrole, thereby resulting in a more efficient alkylation with 1-bromobutane. The experimental result showed that 2 was obtained with a 70% yield and 98% purity. Some product loss took place during the washing and solid recovery steps. Cyanine 2 dissolved in 2-butanone had a maximum absorption at 580 nm with a half bandwidth of 39 nm. The molar absorp- tivity of 2 in 2-butanone was 32,303 M -1 cm -1 .

Numerical and experimental mixing studies in a MEMS-based multilaminated/elongational flow micromixer

Improvement of mixing quality in microchannel mixers or reactors has been recognized as a relevant technical issue critical to the development and application of integrated microchemical processing systems. Silicon micro- electro mechanical systems (MEMS) technology was successfully used to fabricate a novel multichannel micromixer. This improved micromixer design basically used the mechanisms of fluid multilamination, elongational flow, and geometric focusing for mixing enhancement. The fabricated triple-stack (Pyrex™/silicon/Pyrex™) multilaminated/elongational flow micromixer (herein referred to as MEFM-4) was evaluated for its mixing performance using residence time distribution (RTD) measure in conjunction with UV–vis absorption spectroscopy detection technique. Using a semi-empirical model and the so-called convolution–deconvolution theorem, a model description of the experimental RTD data was obtained for the flow/mixing unit. This result was compared with numerical RTD predictions based on computational fluid dynamics (CFD) simulations. The simulation results are in good agreement with the experimental data, especially in the low flow-rate range (Reynolds number <13 in this study). However, as expected, the accuracy of the CFD simulations is generally limited at higher flow rates (high Peclet number) because of unavoidable numerical diffusion. This paper describes the efficient design, fabrication and characterization of an effective microchannel mixer for microchemical systems’ applications.

Development of a PDMS-Glass Hybrid Microchannel Mixer Composed of Micropillars and Micronozzles

In this research, a microchannel type mixer composed of micropillars and micronozzles was developed for effective mixing of biochemical samples. To estimate the performance of the newly designed micromixer, flow patterns were simulated using computational fluid dynamics (CFD) software. The simulation showed that the mixing efficiency increased from 87.9% to 97.5% as the flow rate varied from 50 to 500 μl/min. When liquid was injected into the fabricated micromixer, it was difficult to prime the microchannel because of the hydrophobicity of the polydimethylsiloxane (PDMS) surface. To overcome this problem, the inside of the micromixer was coated with polyvinylpyrrolidone (PVP). It was found that 0.25 wt.% PVP concentration in the DI water solution is optimal. After appropriate PVP coating, the DI water and the mixture of blue dye and DI water were mixed in the fabricated micromixer and the mixing efficiency was measured. The mixing efficiency increased from 69.7% to 91.7% as the flow rate increased from 50 to 500 μl/min. The new micromixer showed very good mixing performance when the flow rate was over 300 μl/min. Due to the simple structure and uncomplicated fabrication process, the proposed micromixer can be easily integrated into a micro total analysis system (μ-TAS) or lab-on-a-chip (LOC).

Numerical and experimental study on a channel mixer with a periodic array of cross baffles

In this study we show an enhanced mixing effect with a simple channel having a periodic array of cross baffles. We performed numerical computation to obtain the steady flow field within the channel at low Reynolds numbers by using a commercial code, ANSYS CFX 10.0. A visualization experiment was also conducted to validate our numerical results qualitatively. In evaluating the mixing performance, we employed the Lyapunov exponent. It was shown that the visualized mixing pattern was in a good agreement with that numerically given. Our Liapunov exponent distribution in the space also demonstrates that the proposed channel design indeed exhibits a chaotic stirring at low Reynolds numbers. Our design is thus assumed to be applicable to designing a microchannel mixer with enhanced mixing effect.