High Mixing Index Research Articles

CFD–DEM modeling of particle segregation behavior in a simulated flash smelting furnace

Particle behavior plays a crucial role in flash smelting furnaces, but limited understanding is hindering further development of this modern pyrometallurgical process. This study presents a two-way coupled CFD–DEM approach to investigate particle distribution, collision, and segregation behaviors within a furnace. The simulation results are validated against experimental data, demonstrating good agreement. The effects of the particle mass–flow rate and size distribution are then analyzed. The results indicate that small particles are carried by airflows to the center of the particle-dense region, whereas large particles remain at the outer part, worsening segregation. Increasing the mass–flow rate significantly increases the particle number density and number of particle collisions but barely influences size-induced segregation. In contrast, enlarging the size of fed particles reduces particle number density and broadens dense distribution within a safe range. This ensures the necessary space and high mixing index of the particles, which benefits high-rate smelting processes.

The Design and Investigation of Hybrid a Microfluidic Micromixer

Today, microfluidics has become a revolutionary interdisciplinary topic with considerable attention in a wide range of biotechnology applications. In this research work, a numerical investigation of a microfluidic micromixer is carried out using a hybrid actuation approach with different micropillar shapes and gaps. For this purpose, COMSOL Multiphysics v.5.2. is used with three different physics, such as thermoviscous acoustic physics to solve acoustic governing equations, laminar physics to solve fluid flow governing equations, and diluted transport species to solve mixing governing equations. The simulations were carried out at different Reynolds numbers such as 2, 4, 6, 8, 10, and 12 with an oscillation frequency of 15 kHz. The results were in the form of acoustic characteristics such as acoustic pressure, acoustic velocity, acoustic stream, mixing index, and fluid flow behaviour at various Reynolds numbers. The results revealed that the inclusion of micropillars improved the mixing performance and strength of the acoustic field, resulting in an improvement of the mixing performance compared to the case without micropillars. In addition, the mixing performance is also investigated at different Reynolds numbers, and a higher mixing index is investigated at lower Reynolds numbers. Moreover, it was also investigated that blade-shaped micropillars with 0.150 mm gaps deliver the best results compared to the other cases, and the maximum and minimum values of the mixing index are 0.97 and 0.72, respectively, at Reynolds number 2. The main reason behind this larger mixing index at low Reynolds numbers is due to the inclusion of micropillars that enhance the diffusion rate and contact area, leading to the homogenisation of the heterogeneous fluids in the microchamber. The obtained results can be extremely helpful for the design and modifications of a hybrid microfluidics micromixer.

Smart scale-up of micromixers for efficient continuous biodiesel synthesis: A numerical study for process intensification

This study focuses on developing continuous processes for biodiesel synthesis, overcoming limitations of conventional batch reactions, such as biphasic reaction and thermodynamic equilibrium, and reducing production costs. While microreactors are promising for enhancing mixing and transfer rates at smaller scales, scaling up to larger channels results in decreased efficiency and product yield. Microfluidic devices, useful in continuous biodiesel production, lose mixing efficiency when scaled up, affecting product yield. The present study proposes a novel microreactor design with static elements, aiming to improve fluid mixing and reaction performance at higher volumes. The smart scale-up strategy includes an optimized micromixer design, enlarged channel cross-sectional area, and an additional obstacle-free channel. Using a Fractional Design followed by a Central Compound Rotational Design, optimal values for key design variables are identified. Computational tests show a high mixing index (M > 0.77) across a wide range of Reynolds numbers (Re = 0.1–100). Numerical simulations under optimal conditions indicate high conversions (>91 %) for residence times above 60 s. This design promises advancements in industrial-scale biodiesel production, with improved flow and reactant distribution, potentially reducing the number of micro/millidevices needed.

Design and scale-up of a superb micromixer with fan-shaped obstacles for synthesis of Dolutegravir intermediate

Micromixer have received significant attention for fluid mixing enhancement, while traditional micromixers have long mixing times and unstable mixing effects, which has discouraged their commercial development. Herein, we report a methodology for the design, optimization, scale-up fabrication and performance evaluation of a novel micromixer. A combination of Solidworks modeling, Design of Experiments and Computational Fluid Dynamics numerical simulation is used to optimize the configuration of micromixer. Analysis and optimization of experimental results from CFD numerical simulations revealed the channel width had the greatest impact on the performance of the micromixer. Based on the DoE results, two optimized micromixers (FOM-A and FOM-B) were developed and subjected to a series of numerical simulations at Reynolds number 0.5 ≤ Re ≤ 100. Both micromixers had a high mixing index (> 94%) and maintained a low pressure drop. Next, the FOM-B was scaled up and used as a microreactor for the synthesis of Dolutegravir intermediate. A 98% yield was obtained at a residence time of 4 min. Furthermore, the mass transfer performance of the FOM-B microreactor was measured and a mass transfer coefficient of 0.5012 s−1 was obtained at liquid flow rate of 20 mL/min, which is double the value of other commercial microreactors.

Investigating hydrothermal mass transfer in an extremely low-pressure drop passive mixer: A three-dimensional simulation study

Static mixers with low-pressure drops have been used for mixing in many biomedical and chemical applications. This study evaluates fluid flow with hydrothermal mass transfer in two types of vortex generators in a rectangular channel. The pressure drops in this new three-dimensional model were meager for Reynolds numbers of 50, 100, and 150. The extremely low-pressure drop passive mixer (ELPD) is a rectangular duct 400 mm in length and 20 × 20 mm in height and width. To improve the static mixer's thermal and mass transfer performance, five conical barriers and four longitudinal twisted tapes, sized at 3, 6, and 9 mm, were utilized, which were used as vortex generators. The vorticities and chaotic flow resulting from these vortices cause improved mixing by elongating and folding the fluid particles responsible for mixing in laminar flow. The simulation used water as the principal fluid and a red dye as a tracer. The results of this analysis are summarized in terms of a very low-pressure drop with a high mixing index for different heights and different Reynolds numbers. The study found that utilizing an ELPD with a bar height of 9 mm resulted in significantly enhanced mixing performance across the tested range of Reynolds numbers. This improvement was as high as 94%, and the associated pressure drop was the lowest among all tested configurations. Conversely, the research revealed that the 6 mm twisted tape height performed poorly in terms of both mixing improvement and heat transfer compared to the 3 mm and 9 mm heights. Considering these findings, utilizing an ELPD with a 9 mm bar height is recommended for optimal mixing performance.

Mixing performance of T-shape micromixers equipped with 3D printed Gyroid matrices: A numerical evaluation

This paper introduces innovative T-shape micromixers equipped with various 3D printed Gyroid matrices aiming to boost the mixing performance. A regular Gyroid matrix has been adapted into more complicated twisted, functionally graded, and stochastic Gyroid structures to promote a chaotic flow regime. A numerical model has been derived and validated to investigate the impact of various Gyroid matrices on the mixing index, pressure drop, and performance index of T-shape micromixers at various Reynolds and Schmidt numbers. The results indicate that, among all structures, the twisted Gyroid matrix provides the highest enhancement in the mixing performance by boosting the mixing index up to 172%. Moreover, the twisted micromixer provided a 135% higher mixing index with a mixing channel that is 41% shorter as compared to a full-length plain micromixer. The novel design, therefore, could be implemented in developing more compact and more efficient microfluidic systems in chemical and pharmaceutical integrated micro-operations.

Numerical Analysis of Mixing Performance in an Electroosmotic Micromixer with Cosine Channel Walls.

Micromixers have significant potential in the field of chemical synthesis and biological pharmaceuticals, etc. In this study, the design and numerical simulations of a passive micromixer and a novel active electroosmotic micromixer by assembling electrode pairs were both presented with a cosine channel wall. The finite element method (FEM) coupled with Multiphysics modeling was used. To propose an efficient micromixer structure, firstly, different geometrical parameters such as amplitude-to-wavelength ratio (a/c) and mixing units (N) in the steady state without an electric field were investigated. This paper aims to seek a high-quality mixing solution. Therefore, based on the optimization of the above parameters of the passive micromixer, a new type of electroosmotic micromixer with an AC electric field was proposed. The results show that the vortices generated by electroosmosis can effectively induce fluid mixing. The effects of key parameters such as the Reynolds number, the number of electrode pairs, phase shift, voltage, and electrode frequency on the mixing performance were specifically discussed through numerical analysis. The mixing efficiency of the electroosmotic micromixer is quantitatively analyzed, which can be achieved at 96%. The proposed micromixer has a simple structure that can obtain a fast response and high mixing index.

Effect of particle size and particle loading on the mixing behavior of rod-like particles and spherical particles in a fluidized bed

The spherical inert particles are typically added to a fluidized bed system to promote the fluidization of non-spherical particles. In this study, the mixing behavior of binary mixtures of rod-like particles and spherical particles in a bubbling fluidized bed was investigated using a computational fluid dynamics-discrete element method (CFD-DEM) simulation. The 2k factorial experimental design was used to study the effect of particle size and rod-like particle loading on the average mixing index, as measured by the Lacey mixing index. The use of smaller spheres and rod diameters resulted in a high average mixing index despite increasing the rod weight. The effect estimates from the factorial experimental design indicated that the rod diameter was the most crucial factor for the average mixing index. Furthermore, the sphere diameter also had a significant effect. Nevertheless, the rod weight and interaction of parameters had a slight effect on the average mixing index. These findings confirmed the significance of using inert spherical particles for improving the hydrodynamics properties of non-spherical particles, including the mixing behavior of the binary mixtures system.

Mixing characteristics and pressure drop analysis in a spiral micromixer

In this work, numerical computations are performed to analyze the mixing characteristics and pressure drop in a spiral micromixer. The effects of variation in width and depth of the micromixer are investigated for Reynolds number ( Re) in the range of 0.1 ≤ Re≤100. Results are enumerated in terms of mass contours, streamlines, mixing index and pressure drop. It is observed that the designed spiral micromixer provides a better mixing for both low and high Re values, and moreover, the mixing index remains almost the same with the variation of the depth and width of the mixer for Re > 50. The mixing index first decreases with Re, reaches a minimum value, and thereafter again increases with a further increase in Re in the range of 0.1 ≤ Re≤50. For intermediate Reynolds number, a high mixing index is observed in micromixer having higher depth and lower width. Although the driving pressure force increases with the increase in Reynolds number, it decreases with the increase in width and depth of the micromixer.

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

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

Effect of Thermal Energy and Ultrasonication on Mixing Efficiency in Passive Micromixers

Micromixing is a key process in microfluidics technology. However, rapid and efficient fluid mixing is difficult to achieve inside the microchannels due to unfavourable laminar flow. Active micromixers employing ultrasound and thermal energy are effective in enhancing the micromixing process; however, integration of these energy sources within the devices is a non-trivial task. In this study, ultrasound and thermal energy have been extraneously applied at the upstream of the micromixer to significantly reduce fabrication complexity. A novel Dean micromixer was laser-fabricated to passively increase mixing performance and compared with T- and Y-micromixers at Reynolds numbers between 5 to 100. The micromixers had a relatively higher mixing index at lower Reynolds number, attributed to higher residence time. Dean micromixer exhibits higher mixing performance (about 27% better) than T- and Y-micromixers for 40 ≤ Re ≤ 100. Influence of ultrasound and heat on mixing is more significant at 5 ≤ Re ≤ 20 due to the prolonged mechanical effects. It can be observed that mixing index increases by about 6% to 10% once the temperature of the sonicated fluids increases from 30 °C to 60 °C. The proposed method is potentially useful as direct contact of the inductive energy sources may cause unwanted substrate damage and structural deformation especially for applications in biological analysis and chemical synthesis.

Comparative study of mixing behaviors using non-Newtonian fluid flows in passive micromixers

High-performances micromixers are widely used in various industrial applications. Mixing in the laminar regime and at low Reynolds numbers is of major importance in some processes. Implementing the physical phenomenon of chaotic advection to improve the mixing efficiency is a well-established technique, therefore, the secondary flows resulting from this technique are very intense and act at the microscopic level on homogenization. This study aims to compare different configurations of passive micromixers. The four examined micromixers are: Two-Layer Crossing Channels Micromixer (TLCCM), Semicircular Serpentine Micromixer (SCSM-90), Curved micromixer with Grooves (CG), and C-Shape micromixer. All micromixer geometries have the same hydraulic diameter and the equivalent unfolded length. The numerical simulations have been carried out at low Reynolds numbers using the CFD Fluent code to solve the 3D momentum equations, the continuity equation, and the species transport equation. The employed non-Newtonian shear-thinning fluids are the CMC solutions which are modeled by the power-law model with power-law index range from 0.73 to 1 and the generalized Reynolds number varies between 0.1 and 50. The mixing efficiency has been evaluated by calculating the mixing index (MI) based on the standard deviation of the mass fraction in different cross-sections. To examine the obtained results, the mass fraction distributions, the velocity profiles, and the mixing energy cost (MEC) have been presented. The results show that the TLCCM micromixer has a high mixing index which exceeds 0.96 for all the generalized Reynolds number values and the considered power-law index, it also has a lower mixing energy cost compared to other studied micromixers.

On the study of teardrop shaped split and collision (TS-SAC) micromixers with balanced and unbalanced split of subchannels

ABSTRACT A teardrop-shaped split and collision (TS-SAC) micromixer based on the concept of balanced/unbalanced splits and collisions of fluid streams is presented. Numerical study is carried out for Reynolds numbers in the range of 0.1–75. In-depth flow and mixing dynamics for the micromixers are studied to assess mixing performance qualitatively. In order to produce unbalanced collision of the two fluid streams, difference in mass flow rate in the two sub-channels is utilized. The performance characteristics, viz., mixing index, pressure drop, mixing cost and mixing sensitivity are used to study mixing performance. A significant effect of unbalanced collisions of the fluid streams on the mixing enhancement is observed. Micromixer shows interesting mixing dynamics for different ratios sub-channels widths. A high mixing index and a low-pressure drop are observed for the micromixer with highest ratio of the widths of sub-channels. However, a low mixing index and a high-pressure drop are observed for the micromixer with lowest ratio of the widths of sub-channels.

Design and Analysis of New Micromixers Based on Distillation Column Trays

AbstractFour passive micromixer designs (G1, G2, G3, and G4) based on distillation columns trays are proposed. The performance of the devices is assessed by numerical simulations. The mixing performance is investigated for different Reynolds numbers and channel heights for oil/ethanol flow. G1 and G4 designs provided a high mixing index. The G1 device achieved superior mixing performance with a moderate pressure drop due to the induced flow recirculation pattern for a relatively high flow rate, highlighting the potential use of such microdevice for scale‐up and numbering‐up of microdevices in modular chemical plant processing.

Fluidization and mixing behaviors of Geldart groups A, B and C particles assisted by vertical vibration in fluidized bed

Geldart groups A (NiO – 1300 μm, green), B (MoO3 - 480 μm, white), and C (NiO – 30 μm, gray color and MoS2 – 25 μm, black) particles were used in a transparent, acrylic fluidized bed reactor. The experiment was carried out for four cases by setting the position of the particles injected in the reactor as a variable. For these cases, Geldart group C particles (which are typically difficult to fluidize) were included. When easily fluidizable particles were placed at the bottom of the fluidized bed reactor, particle circulation and bubbling occurred. Channeling occurred when there were particles that were difficult to fluidize. Homogeneous fluidization was possible with vibration when channeling occurred. With the increasing vibration frequency, the pressure drop increased, and the minimum fluidization velocity decreased. The occurrence of channeling via vibration resulted in a high mixing index and variations in the pressure drop.

Effect of Rotating Cylinder on Mixing Performance in a Cylindrical Double-Ribbon Mixer

Uniform mixing is highly essential in the food manufacturing, pharmaceutical, chemical, and cement industries. However, based on the various process requirements, these industries use different mixers to achieve their commercial outputs. Most of these industries rely on sample-based verification of the mixing index, which may not produce accurate results. Adopting a non-sampling mixing index method is more accurate. In this study, we used the discrete element method (DEM) to simulate the mixing of multiple components contained in a typical commercial whey protein mixture. An effective non-sampling mixing index, the subdomain-based mixing index (SMI), was incorporated to assess the mixing levels. The main motivation for this study was to acquire a high mixing index in the least possible mixing time to boost the manufacturing rate. For this purpose, a half-filled cylindrical double ribbon mixer was simulated, and the SMI outputs are presented for the following four cases: (1) rotating ribbon, (2) rotating cylinder, (3) rotating cylinder with a static ribbon, and (4) rotating cylinder and ribbon. For the given simulation conditions, the SMI values ranged from 0 (segregation condition) to 0.91–0.94 (fully randomly mixed condition) within a time range of 0–60 s.

Optimization of micromixer with triangular baffles for chemical process in millidevices

A new micromixer design (MTB – micromixer with triangular baffles and circular obstructions) was proposed aiming the combination of three mass transfer enhancements mechanisms: reduction of molecular diffusion path, split and recombination of streams and vortex generation. The geometric variables were also optimized considering the mixing performance and the required pressure drop. The optimal design was used for the mixing of different binary mixtures (vegetable oil/ethanol and water/ethanol) under the Reynolds number range from 0.01 to 200 and the chemical reaction process of vegetable oil transesterification with ethanolic solution of sodium hydroxide (biodiesel synthesis). High mixing index (M = 0.99) was observed for the oil/ethanol mixing for several channel heights (200 μm – 2000 μm) and widths (1500 μm – 3000 μm). The geometry W3000H400 (i.e., MTB with channel width of 3000 μm and height of 400 μm) was employed as the millireactor, providing a maximum oil conversion of 92.67% for a residence time of 30 s. For the water/ethanol mixing, the geometry W1500H200 was used. High mixing index (M = 0.99) was observed at very low Reynolds number (Re = 0.1) and also in higher Reynolds numbers of 50 and 100. Moreover, at Re = 0.1, high mixing index (M ≌ 0.90) was obtained already at 3.5 mm of channel length. However, for higher Reynolds number the fluids required longer distances to achieve superior mixing, about 10.5 mm at Re = 100. The MTB, unlike the ones found in the literature, can be used in microdevices (e.g., sensors) with low flow rates and in microdevices with large dimensions (eg, millidevices and milireactors) with high flow rates, allowing an easier application in chemical process aiming the commercial production.

Evaluation of the mixing performance in a planar passive micromixer with circular and square mixing chambers

In this paper, passive planar micromixers based on circular and square mixing chambers spaced at equidistant along the length of micromixer are proposed to operate in the laminar flow regime for high mixing index. Numerical simulations are conducted to evaluate the performance of proposed micromixers by solving the Navier–Stokes equation and convection–diffusion equation. A COMSOL Multiphysics 5.0 is used for computational fluid dynamics. Numerical simulation of mixing of fluids in a micromixer with circular and square chambers in a laminar flow regime has been carried out. Four performance parameters namely, mixing index, pressure drop, pumping power, and performance index are used to evaluate different design configurations of micromixers. Analysis of mixing index based on the standard deviation of the mass fraction is carried with different constriction channel width such as 200, 250, and 300 µm for a range of Reynolds number from 0.1 to 75. The both micromixers show over 95% mixing at the exit for the range 15–75 of Reynolds number at constriction width of 200 µm. Especially, about 99% mixing is achieved at Reynolds number less than one i.e. at 0.1. The effect of Reynolds number on the pressure drop is also investigated. Thus, the proposed micromixers can be used in microfluidic systems which require fast mixing at Re less than 1 and greater than 15.

Effects of rotational speed and fill level on particle mixing in a stirred tank with different impellers

Abstract The particle mixing was studied in a cylindrical stirred tank with elliptical dished bottom by experiments and simulations. The impeller types used were double helical ribbon (HR) + bottom HR, pitched blade ribbon + bottom HR, inner and outer HR + bottom HR, and pitched blade ribbon + Pfaudler + bottom HR labeled as impellers I to IV, respectively. The quantitative correlations among the rotational speed, fill level and power consumption for impeller I and impeller II were obtained by experiments to validate the discrete element method (DEM) simulations. The particle mixing at different operating conditions was simulated via DEM simulations to calculate the mixing index using the Lacey method, which is a statistical method to provide a mathematical understanding of the mixing state in a binary mixture. The simulation results reveal that as the rotational speed increases, the final mixing index increases, and as the fill level increases, the final mixing index decreases. At the same operating conditions, impeller III is the optimal combination, which provides the highest mixing index at the same revolutions.

Effective mixing in a short serpentine split-and-recombination micromixer

Abstract A micromixer with a three-dimensional serpentine split-and-recombination structure is proposed to provide a high mixing index in a short length, even at low Reynolds numbers. The fluid flow and mixing performance were analyzed numerically using three-dimensional Navier-Stokes equations and the convection-diffusion equation for mass transport in a Reynolds number range of 0.1–200. The mixing performance is represented by the mixing index, which is defined using the mass fraction variance of mixing fluids in a plane. The overall mixing performance of the proposed micromixer is compared with that of previous micromixers. The effects of the number of mixing units on the mixing performance were estimated. A parametric study was performed using five geometric parameters of the micromixer. The proposed micromixer shows mixing indices larger than 0.87 throughout the Reynolds number range in a short length of 1500 μm, which is hardly achieved in previous micromixers.