Micromixing Characteristics Research Articles

PIV experiments and CFD simulations of liquid–liquid mixing in a planetary centrifugal mixer (PCM)

A new type of blade-free mixer, the planetary centrifugal mixer (PCM), has recently attracted widespread interest. The aim of this study was to simulate the macromixing and micromixing characteristics of two miscible liquids in a PCM. Particle image velocimetry experiments were performed to validate the computational fluid dynamics model. The mixing index and the potential of diffusive mixing based on the intensity and scale of segregation were employed to accurately evaluate the mixing homogeneity. The results showed the remarkable mixing efficiency of the PCM; the mixing process was 95% completed in 10 s in most cases. Chaotic flows and vortices were observed in the PCM, which promoted mixing. After optimizing the design, the mixing time was reduced by 54%, and the extensional efficiency, velocity magnitude, and strain rate were increased by 38%, 35%, and 58%, respectively.

Experimental Study on Micromixing Characteristics of Coaxial Mixer in Solid–Liquid Systems

Experimental Study on Micromixing Characteristics of Coaxial Mixer in Solid–Liquid Systems

Experimental investigation on micromixing characteristics of coaxial mixers in viscous system

AbstractAn experimental investigation into the micromixing performance of coaxial mixers in a viscous system is reported, in which the iodide‐iodate reaction system is chosen to quantitatively characterize the product distributions. The effects of feeding time, feeding position, impeller speed, inner impeller configuration, and operation mode on the segregation index, Xs, are examined. It is revealed that the feeding near the inner impeller benefits micromixing and should be regarded as the preferred position. The presence of the rotating outer impeller causes the micromixing performance of the coaxial mixer to be significantly better than the single‐shaft mixer. While an increase in the outer impeller speed has a limited influence on micromixing, the inner impeller speed is the dominant influencing factor, that is, the Xs decreases obviously when the inner impeller speed is increased. On the other hand, the coaxial mixers with multiple and axial inner impellers have a better micromixing performance at the same specific power consumption, PV, than that with single and radial inner impellers. Among the configurations consisting of a Rushton impeller (RT), six‐straight‐blade turbine impeller (SBT), and six‐pitched (45°)‐blade turbine impeller (PBT), the Xs of the coaxial mixer is always the smallest at the same PV when the PBT + RT configuration is used as the inner impeller. In addition, it is found that the difference in Xs that results from various operation modes is small in terms of power consumption; however, the co‐rotation mode is still recommended for the micromixing of the coaxial mixer due to its excellent performance in general.

Micro-mixing characteristics of non-Newtonian fluid in a stirred tank agitated with different impellers

Micro-mixing characteristics of non-Newtonian fluid in a stirred tank agitated with different impellers

Scalar mixing and strain dynamics methodologies for PIV/LIF measurements of vortex ring flows

Fluid mixing operations are central to possibly all chemical, petrochemical, and pharmaceutical industries either being related to biphasic blending in polymerisation processes, cell suspension for biopharmaceuticals production, and fractionation of complex oil mixtures. This work aims at providing a fundamental understanding of the mixing and stretching dynamics occurring in a reactor in the presence of a vortical structure, and the vortex ring was selected as a flow paradigm of vortices commonly encountered in stirred and shaken reactors in laminar flow conditions. High resolution laser induced fluorescence and particle imaging velocimetry measurements were carried out to fully resolve the flow dissipative scales and provide a complete data set to fully assess macro- and micro-mixing characteristics. The analysis builds upon the Lamb-Oseen vortex work of Meunier and Villermaux [“How vortices mix,” J. Fluid Mech. 476, 213–222 (2003)] and the engulfment model of Baldyga and Bourne [“Simplification of micromixing calculations. I. Derivation and application of new model,” Chem. Eng. J. 42, 83–92 (1989); “Simplification of micromixing calculations. II. New applications,” ibid. 42, 93–101 (1989)] which are valid for diffusion-free conditions, and a comparison is made between three methodologies to assess mixing characteristics. The first method is commonly used in macro-mixing studies and is based on a control area analysis by estimating the variation in time of the concentration standard deviation, while the other two are formulated to provide an insight into local segregation dynamics, by either using an iso-concentration approach or an iso-concentration gradient approach to take into account diffusion.

Micromixing simulation of novel large-double-blade impeller

The novel large-double-blade impeller spans a wide range of industrial application areas owing to its obvious advantages in the rapid reactions. So it is indeed necessary to have a profound understanding of micromixing characteristics about the novel large-double-blade impeller. This paper establishes a model to analyze the three main factors’ effect on the segregation index through the numerical simulation which is used to research the performance of novel large-double-blade impeller. The three main factors are separately feed discretization number, feeding location and agitation speed. Through the analysis above, the turbulent energy dissipation rate and concentration distribution of H+, I3− would be deduced. Meanwhile, it compared with the Fullzone (FZ) impeller and double ribbon (DHR) impeller. The results show that (1) when the feed discretization number is over 35, the segregation index would tend to be the fixed specific value. And only in that situation, the effect of macro mixture could be ignored. (2) The optimized feeding location is in the blade area with a vast, turbulent energy dissipation rate to achieve a better micromixing performance, which is demonstrate by the consumption curve of H+ and the generation contour of I3−. (3) The main spot of the consumption of H+ and the generation of I3− is on the one side of the feeding location. Besides, compared with FZ impeller and DHR impeller in the same scale and operating condition, novel large-double-blade impeller has a better micromixing performance.

Separation of indium from iron in a rotating packed bed contactor using Di-2-ethylhexylphosphoric acid

Abstract In order to separate In(III) and Fe(III) from the sulfate leaching solution, solvent extraction with Di-2-ethylhexylphosphoric acid (D2EHPA) was investigated using a Impinging Stream–Rotating Packed Bed (IS–RPB) contactor in laboratory scale. The effects of operating parameters, such as feed solution pH, flow rate ratio, the high gravity factor, the concentration of D2EHPA, initial iron concentration, stripping solution concentration were examined. The experimental results showed that the IS–RPB was effective in the separation of In(III) and Fe(III)under favorable operating conditions. The extraction and stripping efficiency as high as 99% could be achieved, at a separation factor in excess of 3000. Compared with other mixing devices, IS–RPB contactor has better micromixing characteristics, which has a good application prospect.

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 characteristics in a gas–liquid–solid stirred tank with settling particles

The parallel-competing iodide–iodate reaction scheme was used to study the micromixing performance in a multi-phase stirred tank of 0.3m diameter. The impeller combination consisted of a half elliptical blade disk turbine below two down-pimping wide-blade hydrofoils, identified as HEDT+2WHD. Nitrogen and glass beads of 100μm diameter and density 2500kg·m−3 were used as the dispersed phases. The micromixing could be improved by sparging gas because of its additional potential energy. Also, micromixing could be improved by the solid particles with high kinetic energy near the impeller tip. In a gas–solid–liquid system, the gas–liquid film vibration with damping, due to the frequent collisions between the bubbles and particles, led to the decrease of the turbulence level in the liquid and caused eventually the deterioration of the micromixing. A Damping Film Dissipation model is formulated to shed light on the above micromixing performances. At last, the micromixing time tm according to the incorporation model varied from 1.9ms to 6.7ms in our experiments.

Mixing Characteristics and Bubble Behavior in an Airlift Internal Loop Reactor with Low Aspect Ratio

The present study summarizes the results of macro- and micro-mixing characteristics in an airlift internal loop reactor with low aspect ratio (H/D≤5) using the electrolytic tracer response technique and the method of parallel competing reactions respectively. The micro-mixing has never been investigated in airlift loop reactors. The dual-tip electrical conductivity probe technique is used for measurement of local bubble behavior in the reactor. The effects of several operating parameters and geometric variables are investigated. It is found that the increase in superficial gas velocity corresponds to the increase in energy input, liquid circulation velocity and shear rate, decreasing the macro-mixing time and segregation index. Moreover, it is shown that top clearance and draft diameter affect flow resistance. However, the bubble redistribution with a screen mesh on the perforated plate distributor for macro-mixing is insignificant. The top region with a high energy dissipation rate is a suitable location for feeding reactants. The analysis of present experimental data provides a valuable insight into the interaction between gas and liquid phases for mixing and improves the understanding of intrinsic roles of hydrodynamics upon the reactor design and operating parameter selection.

Micromixing Efficiency of a Spinning Disk Reactor

This work presents the experimental investigation of the micromixing characteristics of a spinning disk reactor (SDR) by using a system of competitive parallel reactions, particularly the iodide–iodate reaction (Villermaux–Dushman reaction). The objective of this study is to analyze the influence of various operating parameters such as the rotational speed of the disk, the feed location, and the surface structure of the disk on the mixing quality. It is shown that the micromixing efficiency can be particularly controlled by variation of the disk speed. These results are further validated by the investigation of the precipitation reaction of barium sulfate. This synthesis offers fast reaction kinetics with induction times in the range of milliseconds, resulting in a mixing time which lies in the range of this for efficient mixers like microreactors. The use of the spinning disk technology enables one to produce particles continuously with controllable mean sizes down to 27 nm, without the risk of fouling o...

Micromixing Efficiency of Viscous Media in Novel Impinging Stream-Rotating Packed Bed Reactor

Micromixing efficiency of viscous media in novel IS-RPB reactor was studied by using iodide-iodate test reaction as working system. Experiments were carried out in glycerol-water solution with different viscosities. The effects of high gravity factor, liquid flow rate, acid concentration, liquid flow ratio, and viscosity on segregation index and micromixing time were investigated. The experimental results showed that the IS-RPB was effective in enhancing micromixing when the liquid viscosity increased. Furthermore, the micromixing time tm of the IS-RPB reactor was determined based on the incorporation model, and its value was in the range of 10–5–10–4 s. Compared with other mixing devices, IS-RPB reactor has better micromixing characteristics than other reactors, which has a good application prospect.

Biodiesel production in a rotating packed bed using K/γ-Al 2O 3 solid catalyst

The methanolysis of soybean oil with a K/γ-Al 2O 3 catalyst using a rotating packed bed (RPB) for the production of fatty acid methyl esters (biodiesel) is presented. The RPB, which provides high centrifugal force and has an adjustable rotational speed, was employed as a novel heterogeneously catalyzed transesterification reactor. The methanol-to-oil molar ratio, the catalyst dosage, the rotational speed of the packed-bed rotator, and the reaction temperature were investigated for their effects on the yield of fatty acid methyl esters ( Y FAME) in the RPB. Furthermore, the modified first-order reaction kinetics was employed to study the transesterification reaction rate of the K/γ-Al 2O 3 catalyzed RPB system. In addition, the transesterification performance and durability of the K/γ-Al 2O 3 catalyst with respect to Y FAME using the RPB system were evaluated, allowing for further comparison with other heterogeneously catalyzed transesterification reactors. Based on the results, the RPB system is considered as a practical, heterogeneously catalyzed transesterification reactor due to its excellent micromixing characteristics.

Ideal micromixing performance in packed microchannels

In this work, the hydrodynamics and the micromixing characteristics in the packed and non-packed microchannels were studied experimentally at low Reynolds numbers (8–300). The mixing performances in microchannels were observed with high-speed CCD camera, and were evaluated in terms of a segregation index by the Villermaux/Dushman method. The fluid elements were drastically stretched, folded, and sheared with the effects of micro-particles in packed microchannels, resulting in extremely shorter diffusion distance and larger effective interfacial area, and much higher micromixing efficiency compared with those of non-packed microchannels. Under enough packing length and appropriate packing position of micro-particles, the ideal micromixing performance could be obtained in packed microchannels. Furthermore, the micromixing time in packed microchannels was determined based on the incorporation model, and its value was in the range of 0–0.1 ms.

Continuous-flow Esterification of Free Fatty Acids in a Rotating Packed Bed

The continuous-flow esterification of free fatty acids (FFAs) with methanol for the production of fatty acid methyl esters (FAMEs) using a rotating packed bed (RPB) is presented herein. The RPB, which provides a high centrifugal force and has an adjustable rotational speed, was employed as a novel esterification reactor. The following variables were investigated for their effects on the esterification efficiency: the methanol-FFA molar ratio, the estimated hydraulic retention time, the rotational speed of the packed bed, the reaction temperature, and the catalyst dosage. The conversion of the FFAs in the RPB system significantly depended on the experimental conditions, which influenced the residence time distribution, the esterification reaction rate, and the micromixing intensity. Due to its excellent micromixing characteristics, the RPB system exhibited good efficiency for the esterification reaction in continuous-flow operation. The RPB system achieved the conversion of the FFAs of 10.0−96.6% and the p...

A new impinging stream–rotating packed bed reactor for improvement of micromixing iodide and iodate

A novel concept of a liquid–liquid contact reactor, the so-called impinging stream–rotating packed bed (IS–RPB), was presented for improvement of micromixing iodide and iodate. The micromixing efficiency of IS–RPB was studied by adopting iodide–iodate reaction system. The effects of operational conditions (e.g. high gravity factor, liquid flow rate, liquid flow ratio and acid concentration) on micromixing efficiency (characterized by segregation index X s ) were investigated. In addition, the effects of different impinging distance and impinging angle on micromixing efficiency were also considered. Besides, IS, RPB and IS–RPB reactors were contrasted with micromixing characteristics in the same experimental conditions. Comparison with other mixing devices, IS–RPB reactor has better micromixing characteristics than other reactors, which has a good application prospect.

A continuous-flow biodiesel production process using a rotating packed bed

The continuous-flow transesterification of soybean oil with methanol using a rotating packed bed (RPB) for the production of fatty acid methyl esters (biodiesel) is presented herein. The RPB, which provides high centrifugal force and has an adjustable rotational speed, is employed as a novel transesterification reactor. In this study, biodiesel is synthesized via the methanolysis of soybean oil using potassium hydroxide as the catalyst. The following variables were investigated for their effects on transesterification efficiency: the methanol–oil molar ratio, the estimated hydraulic retention time, the rotational speed of the packed-bed rotator, the reaction temperature, and the catalyst dosage. The yield of the fatty acid methyl esters ( Y FAME) in the RPB system depends significantly on the experimental conditions, which influence the residence time distribution, the transesterification reaction rate, and the micromixing intensity. Due to its excellent micromixing characteristics, the RPB system shows satisfactory transesterification efficiency. The values of Y FAME, productivity of FAMEs ( P FAME), and P FAME per unit reactor volume ( P FAME/ V R) in the RPB are used to evaluate the performance for biodiesel production and allow for further comparison with other continuous transesterification reactors. Consequently, a RPB is considered a practical transesterification reactor with high transesterification efficiency.

Compartmental Modeling of a Structured Heat Exchanger Reactor: Conversion and Temperature Profiles Predictions

Since the last ten years numerous studies have been carried out to develop micro-reactors or micro-structured reactors in order to improve scale of production, economics, safety and environmental impact of chemical production. Consequently Alfa Laval Vicarb has developed a new structured heat exchanger reactor. The design of the reactor is based on high performances heat plate exchanger in which small inserts allow a good mixing of the reactants and to improve the heat transfer phenomena or to increase the heat transfer coefficient. This new technology of heat plate exchange reactors has a modular structure where the exchange zones have two possible configurations: co- and counter counter-current. The structure of the reactor is also flexible, that makes possible to have multiple reactants injections and different local temperature control points. In order to have a rapid prediction of conversion and temperature profiles, a mathematical model conserving the same notion of the structure of the reactor has been developed. This mathematical model is a simple compartmental model which presents advantages in terms of flexibility, possible online simulations and rapid prediction simulations. The structure of the model has been determined with the help of tracer experiment and computational fluid dynamics simulations. Heat and mass transfer equations are written considering each cell and using experimental heat transfer data then chemical kinetics from literature are introduced to the model. A sub-compartmental model has been developed in order to predict the micro-mixing phenomena. Four reactions for which the kinetic laws of reactions are well known have been selected to test the model: alkaline hydrolysis of ethyl acetate, alkaline hydrolysis of ethylene glycol diacetate, oxidation of sodium thiosulphate by hydrogen peroxide and Bourne reactions. The results of comparison between simulations and experimental data in terms of yield, selectivity, temperature profiles and micro-mixing characteristics are in reasonable agreement.

Synthesis and application of nanoparticles by a high gravity method

Synthesis and application of nanoparticles by a high gravity method

A particle's eye view of crystallizer fluid mechanics

It has been recognized for some time that flow and mixing in industrial crystallizers has an effect on the kinetics of growth, nucleation and agglomeration and consequently on the crystal size distribution. Yet, a common assumption in population balance modelling is that the fluid mechanical environment experienced by growing crystals is uniform. In practice, however, industrial crystallizers provide extremely varied flow conditions, with local velocities, shear rates and energy dissipation rates varying by orders of magnitude throughout the vessel. A computational fluid dynamics simulation of the flow in a stirred tank was used to illustrate that, in a Lagrangian sense, the particles experienced regions with very different local micromixing characteristics, mean velocities, slip velocities, shear rates and turbulence levels; the sampling of these regions depended only slightly on the particle size and, for the flow considered here, the Eulerian and particle Lagrangian statistics were similar. However, the distribution of slip velocities experienced by the crystals was strongly dependent on the particle microscale and macroscale Stokes numbers. The consequent effects for the estimation of the average growth, nucleation and agglomeration kinetics used in population balances were also considered.