Micromixing Efficiency Research Articles

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.

Micromixing efficiency of a novel helical tube reactor: CFD prediction and experimental characterization

A novel helical tube reactor (HTR) consisting of a pre-mixer and a helical tube was designed for mixing and reaction process intensification. The pre-mixer was used to adjust and change the premixing behavior between the involved reactants, which eventually determines the environment for micromixing. Two types of pre-mixers, co-current flow pre-mixer (CCM) and cross-flow pre-mixer (CRM), were employed and their mixing performance was studied by computational fluid dynamics (CFD) simulations. Results revealed that the CRM has better mixing performance than the CCM, suggesting that the predicted micromixing efficiency of the HTR consisting of the CRM (CRM-HTR) may be better than that comprising the CCM (CCM-HTR). Furthermore, the iodide–iodate reaction system was used separately to characterize the micromixing efficiency of the HTR comprising the different types of pre-mixers, and the results are in agreement with those of CFD which predicted better micromixing performance in the CRM-HTR than the CCM-HTR. Additionally, the effects of feed position and initial dispersion size of acid solution, volumetric flow ratio, and viscosity on micromixing efficiency of the CRM-HTR were investigated. A comparison between the CRM-HTR and a straight tube reactor (CRM-TR) with a length equivalent to that of the CRM-HTR revealed that CRM-HTR has better micromixing efficiency. Moreover, the effects of curvature ratio and number of turns on micromixing efficiency of the CRM-HTR were also conducted. The results demonstrated that the curvature ratio had an important influence on the micromixing. This work shows that the novel CRM-HTR has great potential for chemical reaction process intensification.

Liquid–liquid two-phase mass transfer in T-type micromixers with different junctions and cylindrical pits

Abstract This paper reports an experimental investigation of flow pattern and liquid–liquid two-phase mass transfer in different T-type micromixers with novel shapes. These micromixers were rectangular with a dimension of 0.5 mm width, 1 mm depth and 100 mm long. New configurations of T-micromixers were fabricated with change in their junction shapes and designing pits on the mixing channel to achieve the efficient mixing and mass transfer. Mixing and mass transfer in micro-mixers with one pit on T-junction and array of pits, in collinear and non-collinear orientation, on mixing channel was examined. Water–propionic acid–1-octanol was chosen for mass transfer analyzing. Results show that various type of two-phase flow pattern established at examined geometries. Results also depict that diameter of pit at the junction and designing of pit on mixing channel and its diameter has significant effect on mass transfer coefficient and extraction efficiency. The highest enhancement in the extraction efficiency of micromixer with pitted junction-non collinear channels was 28.7% compared with micromixer with Plain junction. In addition, extraction efficiencies in the micromixers with pitted mixing channel-collinear channels and pitted mixing channel-non collinear channels increased up to 55.7% and 78.7% compared with that of plain junction, respectively.

Computational Fluid Dynamics Analysis of the Micromixing Efficiency in a Rotating-Packed-Bed Reactor

Micromixing in rotating-packed-bed (RPB) reactors is of great significance for their process-intensifying performance. On the basis of the iodide–iodate reaction system, a two-dimensional computational framework of RPB was developed to investigate the micromixing efficiency in a RPB. The volume-of-fluid multiphase model, laminar finite-rate model, and the Reynolds stress model were adopted to simulate the volumetric fraction of the liquid phase, the concentration distributions, and the effects of rotating speed and liquid flow velocity on the micromixing performance of a RPB. The computational fluid dynamics results showed that the micromixing and reaction processes occurred mainly in the inlet region of RPB packing, which further confirmed the end effect of the packing. An increase of the rotating speed and liquid flow velocity could remarkably enhance the micromixing efficiency in a RPB. On the basis of the incorporation model, the micromixing time in a RPB was estimated as 0.05−0.30 ms, indicating a re...

Micromixing in a rotating packed bed with blade packings

The micromixing efficiency of a rotating packed bed (RPB) with blade packings, which is determined by a parallel competing reaction system, is related to the rotational speed, the total liquid flow rate, the outer radius of the blade, the inner radius of the blade, the number of blades, and the liquid viscosity. Experimental results show that increasing the rotational speed, the total liquid flow rate, and the number of blades effectively increased the micromixing efficiency. Increasing the outer radius of the blade and the liquid viscosity did not almost affect micromixing efficiency. The inner radius of the blade had a particular effect on micromixing efficiency: the micromixing efficiency firstly decreased and then increased as the inner radius of the blade was increased. Although the micromixing efficiency in the RPB with blade packings was lower than that in the RPB with structured packings, the mean size of the magnesium hydroxide nanoparticles that were prepared using the RPB with blade packings was close to that of those prepared using the RPB with structured packings. Accordingly, the RPB with blade packings is a promising reactor for preparing nanoparticles with high micromixing efficiency.

Process intensification by the use of micro devices for liquid fractionation with supercritical carbon dioxide

The present study is focused on the process intensification of extraction with supercritical fluids by using micro-devices. The main purpose is to investigate the efficiency and applicability of micro-mixers in supercritical fluid extraction processes. Two micro-devices with different mixing principles, multilamination and T-type lamination, were used and results were compared. The extraction experiments were carried out in a micro-device apparatus designed for high-pressure processes, in which the micro-device is the unit where the solvent and the liquid feed come into contact. Experiments on the continuous extraction of ethanol from aqueous solutions using supercritical CO2 as solvent were performed to study the feasibility of the extraction process in a micro-device apparatus. The separation of both liquid and vapour phases was achieved by changes of temperature and pressure. The experiments were carried out at 101bar and 60°C. Different ethanol concentrations in the feed and solvent-to-feed ratio values were considered. Results obtained with the two different micro-devices were compared. A phase equilibrium model using Peng Robinson equation of state was developed in ASPEN-Plus® and calculations were performed to confirm that equilibrium was achieved through the extraction process and that one theoretical stage can be reached in a micro-device stage.

Numerical and experimental analyses of planar micromixer with gaps and baffles based on field synergy principle

The characteristics of fluid flow and mass transfer in a novel micromixer with gaps and baffles are studied numerically and experimentally. Based on the principles of multiple vortices, abrupt contraction/expansion and twice split/recombine, the effects of gaps and baffles are investigated considering both mixing performance and pressure drop at Reynolds numbers ranging from 0.1 to 60. The mixing efficiency of the novel micromixer is found to be as high as over 94% at extremely low (Re=0.1) or high Reynolds number (Re≥40). The mechanism of mass transfer enhancement in the novel micromixer is analyzed by the field synergy principle. It is found that the novel micromixer is helpful to mass transfer enhancement which can be attributed to a good synergy between the velocity field and the concentration field. It is shown that the field synergy principle provides an alternative way to evaluate the performance of micromixers. In addition, the influence of the different locations of gaps and baffles on the mixing performance is analyzed. The comprehensive performance of micromixers is investigated by the field synergy principle and the ratio of the mixing index to the pressure drop (MI/PD). The merits of rapid mixing, low energy consumption and short mixing length make the novel micromixer more promising in microfluidic application.

Micromixing Efficiency Enhancement in a Rotating Packed Bed Reactor with Surface-Modified Nickel Foam Packing

Micromixing, the mixing at the molecular scale, is believed to play a substantial role in many industrial processes. In this work, a novel surface-modified nickel foam packing (SNP) loaded in a rotating packed bed (RPB) reactor was first proposed to improve the micromixing efficiency studied by adopting the iodide–iodate reaction as a working system. Experimental results showed that the RPB reactor with the SNP presented better micromixing efficiency, compared to the RPB reactor with the nonmodified nickel foam packing (NNP) or traditional stainless steel wire mesh packing (SWP). It could be found that the segregation index (XS) decreased as the rotational speed and liquid flow rate each increased, while it increased with increasing acid concentration and volumetric ratio. Moreover, the micromixing time (tm) was calculated using an incorporation model based on the experimental data. Compared with NNP or SWP, the minimum tm value of SNP (tm = 3.28 ms) is less than that of NNP (tm = 5.68 ms) or SWP (tm = 8....

Influence of Viscosity on Micromixing Efficiency in a Rotating Packed Bed with Premixed Liquid Distributor

Influence of Viscosity on Micromixing Efficiency in a Rotating Packed Bed with Premixed Liquid Distributor

Uncertainty Analysis of Mixing Efficiency Variation in Passive Micromixers due to Geometric Tolerances

The geometric layout is the key factor for enhancing the efficiency of the fluid mixing in passive micromixers. Therefore, by adjusting the geometric design and by controlling the geometric parameters, one can enhance the mixing process. However, through any fabrication process, the geometric parameters present slight, inherent variation from the designed values than might affect the performance of the micromixer. This paper proposes a numerical study on the influence of the unavoidable geometric tolerances on the mixing efficiency in passive micromixers. A probabilistic simulation model, based on the Monte Carlo method, is developed and implemented for this purpose. An uncertainty simulation model shows that significant deviations from the deterministic design can appear due to small variations in the geometric parameters values and demonstrates how a more realistic mixing performance can be estimated.

Experimental study on micromixing characteristics of novel large-double-blade impeller

Large-double-blade (LDB) impeller is a new type of agitator based on Fullzone (FZ) impeller and Maxblend (MB) impeller. To investigate its micromixing characteristics in rapid-reaction situations, we conducted experiments in a 380mm diameter stirred tank. The effect of feeding time, feeding location, agitating speed and viscosity on micromixing characteristics of the novel large-double-blade impeller was investigated, adopting the iodide–iodate parallel competing reaction system. The micromixing characteristics of the novel large-double-blade impeller were also compared with that of double helicon ribbon (DHR) impeller and FZ impeller, which were widely used in process industries. The results indicate that segregation index decreases with increasing feeding time, and won׳t stabilize until the feeding time is greater than its critical value, when macromixing effects can be neglected. In addition, it is favorable for micromixing effects to feed in the impeller regions with high local energy dissipating rate. Segregation index is negatively correlated with stirring speed, whereas the rate of decline tends to be smaller at higher stirring speed, which means that the strengthening effect of improving rotation speed on micromixing efficiency decreases. Moreover, whether the systematic viscosity is high or not, the novel LDB impeller has the advantage of better micromixing effects over FZ and DHR impellers with the same power consumption per unit volume (Pv ).

Micromixing efficiency in a T-shaped confined impinging jet reactor

Confined impinging jet reactor (CIJR) offers advantages for chemical rapid processes and has become an important new reactor used in the chemical industry. The micromixing efficiency in a T-shaped CIJR for two tubes of inner diameter of 3mm was studied by using a parallel competing iodide–iodate reaction as the working system. In this work, the effects of different operating conditions, such as impinging velocity and acid concentration, on segregation index were investigated. In addition, the effects of the inner nozzles diameter and the distance L between the jet axis and the top wall of the mixing chamber on the micromixing efficiency were also considered. It is concluded that the best range of L in this CIJR is 6.5–12.5mm. Based on the incorporation model, the estimated minimum micromixing time tm of CIJR approximately equals to 2×10−4s. These experimental results indicate clearly that CIJR possesses a much better micromixing performance compared with the conventional stirred tank (micromixing time of 2×10−3 to 2×10−2s). Hence, it can be envisioned that CIJR has more promising applications in various industrial processes.

Effect of microchannel confluence angles on size reduction of curcumin nano-suspension via liquid anti-solvent precipitation process

In this paper, an experimental evidence is provided to investigate the potential of microchannel reactors (MCRs) for uniform particle size distribution (PSD) of curcumin nano-particles via liquid anti-solvent precipitation (LASP) technique. For this purpose, three arrangements of microchannel reactors (MCRs) were designed with 800μm in diameter by 30mm in length in various confluence angles of 45°, 90°, and 135°. The influence of confluence angle was investigated in terms of particle size reduction, short-term, and physical stability. PSD, SEM imaging, XRD, DSC, FTIR, and zeta potential measurements were also employed to characterize the produced nano-suspentions.Upon application of the MCR with confluence angle of 135°, the precipitated particle size was found 181nm, indicating that this geometry of micrormixer can establish higher micromixing efficiency. The superior performance of MCRs with large contact angle and understanding of mixing phenomena was further linked to pressure drop, dissipation rate and size of generated nano-particles under various total liquid flow rates.

Numerical Analysis Of Mixing Under Low And High Frequency Pulsations At Serpentine Micromixers

Abstract The numerical investigation of the mixing process in complex geometry micromixers, as a function of various inlet conditions and various micromixer vibrations, was performed. The examined devices were two-dimensional (2D) and three-dimensional (3D) types of serpentine micromixers with two inlets. Entering fluids were perturbed with a wide range of the frequency (0 - 50 Hz) of pulsations. Additionally, mixing fluids also entered in the same or opposite phase of pulsations. The performed numerical calculations were 3D to capture the proximity of all the walls, which has a substantial influence on microchannel flow. The geometry of the 3D type serpentine micromixer corresponded to the physically existing device, characterised by excellent mixing properties but also a challenging production process (Malecha et al., 2009). It was shown that low-frequency perturbations could improve the average mixing efficiency of the 2D micromixer by only about 2% and additionally led to a disadvantageously non-uniform mixture quality in time. It was also shown that high-frequency mixing could level these fluctuations and more significantly improve the mixing quality. In the second part of the paper a faster and simplified method of evaluation of mixing quality was introduced. This method was based on calculating the length of the contact interface between mixing fluids. It was used to evaluate the 2D type serpentine micromixer performance under various types of vibrations and under a wide range of vibration frequencies.

Experimental and CFD studies on the intensified micromixing performance of micro-impinging stream reactors built from commercial T-junctions

A micro-impinging stream reactor (MISR) at the size of ~1mm has been built from commercial T-junctions and steel micro-capillaries, which has advantages of intensified micromixing and easy construction. By using a big-sized and very short outlet tube, the two injecting streams could impinge intensely within the limited chamber of the T-junction to achieve a quick mixing at the micro-scale. The effects of both operating parameters and geometric parameters of MISR, e.g., inlet jet Reynolds number (Rej), volumetric flow ratio (R), outlet configuration, outlet length (L), and inlet diameter (di), on the micromixing efficiency have been studied by experiments with the Villermaux–Dushman reaction as well as by computational fluid dynamics (CFD) method. Both experimental and numerical results agreed well and demonstrated that the inlet jet Reynolds number (Rej) and inlet size played a key role for the micromixing performance. The outlet configuration also had a great influence on micromixing, but the effects of the length of outlet channel were insignificant. This work showed that MISR will have a great potential for both reaction and separation process intensifications.

New protocol of the Villermaux–Dushman reaction system to characterize micromixing effect in viscous media

This paper presents the results of the characterization of a new method for quantification of the micromixing efficiency in a viscous medium in stirred tank reactors. The used method is inspired by a chemical system based on two competitive reactions, the iodide–iodate reaction system (Villermaux–Dushman method), whose products selectivity is a measure of the mixing efficiency. The approach proposes a new protocol based on a phosphate buffer and the use of HydroxyEthylCellulose (HEC, 720, 000g/mol) as an inert viscosifying agent, exhibiting various interesting properties (no disturbance of the spectrophotometric measure, low cost, low required amount, eco-friendly product). This agent is almost Newtonian up to 0.25wt% in water and becomes non-Newtonian above 0.5wt%. By means of its use, the viscosity of the reactive medium can be raised by around two orders of magnitude while adding less than 1wt% HEC to the water solution. Preliminary micromixing results of moderate viscous solutions (50mP as with HEC 0.5wt%) in a stirred tank reactor are presented.

Real-time remote control of artificial cilia actuation using fingertip drawing for efficient micromixing.

Low-efficiency diffusion mechanism poses a significant barrier to the enhancement of micromixing efficiency in microfluidics. Actuating artificial cilia to increase the contact area of two flow streams during micromixing provides a promising alternative to enhance the mixing performance. Real-time adjustment of beating behavior in artificial cilia is necessary to accommodate various biological/chemical reagents with different hydrodynamic properties that are processed in a single microfluidic platform during micromixing. Equipping the microfluidic device with a self-troubleshooting feature for the end user, such as a bubble removal function during the process of multiple chemical solution injections, is also essential for robust micromixing. To meet these requirements, we initiated a new beating control concept by controlling the beating behavior of the artificial cilia through remote and simultaneous actuation of human fingertip drawing. A series of micromixing test cases under extreme flow conditions (Re < 10(-3)) was conducted in the designed micromixer with high mixing performance. Satisfactory micromixing efficiency was achieved even with a rapid beating trajectory of the artificial cilia actuated through the fingertip motion of end users. The analytical paradigm and results allow end users to troubleshoot technical difficulties encountered during micromixing operations.

Effects of Magnetic Particles Entrance Arrangements on Mixing Efficiency of a Magnetic Bead Micromixer

In this study, a computer code is developed to numerically investigate a magnetic bead micromixer under different conditions. The micromixer consists of a microchannel and numerous micro magnetic particles which enter the micromixer by fluid flows and are actuated by an alternating magnetic field normal to the main flow. An important feature of micromixer which is not considered before by researchers is the particle entrance arrangement into the micromixer. This parameter could effectively affect the micromixer efficiency. There are two general micro magnetic particle entrance arrangements in magnetic bead micromixers: determined position entrance and random position entrance. In the case of determined position entrances, micro magnetic particles enter the micromixer at specific positions of entrance cross section. However, in a random position entrance, particles enter the microchannel with no order. In this study mixing efficiencies of identical magnetic bead micromixers which only differ in particle entrance arrangement are numerically investigated and compared. The results reported in this paper illustrate that the prepared computer code can be one of the most powerful and beneficial tools for the magnetic bead micromixer performance analysis. In addition, the results show that some features of the magnetic bead micromixer are strongly affected by the entrance arrangement of the particles.

Micromixing Characteristics in an Aerated Stirred Tank with Half Elliptical Blade Disk Turbine

Abstract The parallel-competing iodide-iodate reaction scheme was used to investigate the micromixing efficiency in an aerated stirred tank of 0.30 m diameter agitated by a half elliptical blade disk turbine. The mean specific energy dissipation rate Pm ranged from 0.5 to 2.2 W/kg, while the superficial gas velocity VS ranged from 0.015 to 0.047 m/s. Four sub-surface feed positions were considered. When the tank is fed just under the liquid surface or in the near-wall region, the micromixing efficiency can be enhanced by introducing gases with superficial gas velocities higher than 0.031 m/s. The effects of gas on the micromixing performance become complicated, while the tank is fed in the impeller discharging region. The increase of gas flow rate does not always have good effects on the micromixing performance. Moreover, the way to feed sulfuric acid can strongly affect the efficiency of the reaction scheme. For a single liquid phase, the micromixing time tm according to the incorporation model varies from 5 × 10−3 to 3 × 10−2 s. The dimensionless local specific energy dissipation rate Φ near the liquid surface is almost independent of Pm, while Φ in the impeller discharging area decreases with increasing Pm.

Effects of Magnetic Particles Entrance Arrangements on Mixing Efficiency of a Magnetic Bead Micromixer

Abstract In this study, a computer code is developed to numerically investigate a magnetic bead micromixer under different conditions. The micromixer consists of a microchannel and numerous micro magnetic particles which enter the micromixer by fluid flows and are actuated by an alternating magnetic field normal to the main flow. An important feature of micromixer which is not considered before by researchers is the particle entrance arrangement into the micromixer. This parameter could effectively affect the micromixer efficiency. There are two general micro magnetic particle entrance arrangements in magnetic bead micromixers: determined position entrance and random position entrance. In the case of determined position entrances, micro magnetic particles enter the micromixer at specific positions of entrance cross section. However, in a random position entrance, particles enter the microchannel with no order. In this study mixing efficiencies of identical magnetic bead micromixers which only differ in particle entrance arrangement are numerically investigated and compared. The results reported in this paper illustrate that the prepared computer code can be one of the most powerful and beneficial tools for the magnetic bead micromixer performance analysis. In addition, the results show that some features of the magnetic bead micromixer are strongly affected by the entrance arrangement of the particles.