Micromixing Performance Research Articles

Numerical and experimental investigation of Tesla micromixers with different three-dimensional herringbone structures

Laminar flow within channels at the micro- or nano-scale of the microfluidic device restricts the rapid mixing of different fluids, leading to reduced reaction velocity. In this study, different three-dimensional herringbone structures were designed to the Tesla micromixers to enhance transverse flow and vortex flow in the channels. Computational fluid dynamics (CFD) simulation results indicated that the sunken herringbone structure provided the most significant enhancement in mixing. The raised herringbone structure exhibited the best energy performance. When Reynolds number (Re) exceeded 60, the mixing indexes (MI) of the Tesla micromixers were over 90%. The improvement in mixing efficiency by both herringbone structures compensated for the weak mixing performance of the Tesla structure at lower Reynolds numbers (Re=0.2-30). Additionally, the mixing experimental results verified the accuracy of the simulation results. This study could provide guidance for improving the mixing performance of micromixers over a wide range of Reynolds numbers (Re=0-100).

Enhanced mixing characteristics of unbaffled U-shaped microreactor coupled oscillatory flow

The Microscale Oscillatory Flow Reactor (MOFR) can achieve good plug flow and micromixing performance simultaneously at laminar net flow conditions. An unbaffled U-shaped microreactor coupled with oscillating flow technology was designed to study the macro and micromixing performance. Firstly, the influence of oscillations on the flow performance was studied to reveal the formation rule of vortex. The simulation results showed that the continuous formation and destruction of periodic vortexes occurred in the microreactor with oscillation. With the increase of oscillation intensity, the vortex size in the radial direction first gradually increased and then becomes stable, and gradually moved axially, resulting in axial diffusion. Secondly, the effect of oscillation on the macromixing and micromixing performance were investigated. The results showed that the coupling oscillation could greatly improve the macromixing and micromixing performance. The macromixing and micromixing performance were promoted simultaneously at lower oscillation intensity and then tended to be flat due to the axial diffusion at high oscillation intensity. When φ>6.05, the minimum micromixing time and the maximum number of tanks can be achieved at the same time. At a velocity ratio of about 23, FoM reached a maximum of about 3.5.

Improvement of mixing efficiency in twisted micromixers: The impact of cross-sectional shape and eccentricity ratio

Microfluidic mixers with twisted geometries show promise for high mixing efficiency, especially at elevated flow rates. However, there is a lack of understanding regarding the optimal geometrical parameters to enhance mixing across various Reynolds numbers. This study aimed to explore the influence of pitch number, cross-section geometry, and eccentricity ratio on the performance of the twisted micromixer. The flow field in these micromixers was solved numerically and the mixing index and pressure drop were calculated for Reynolds numbers of 1 to 400. Twisted micromixers with rectangular cross-sections and aspect ratios of 0.5 and 2 outperformed those with square cross-sections by up to 34% in mixing efficiency, exceeding 90% efficiency for Reynolds numbers from 1 to 400. Moreover, the eccentricity ratio (ER) was studied for the first time in twisted micromixers in this study and demonstrated a critical role in improving the mixing performance. For low to intermediate Reynolds numbers, the highest ER of 0.75 showed the best performance, while for high Reynolds numbers, an ER of 0.5 was optimal. These insights offer valuable direction for designing high-performance micromixers for advanced microfluidic systems.

Mixing Performance of a Passive Micromixer Based on Split-to-Circulate (STC) Flow Characteristics.

We propose a novel passive micromixer leveraging STC (split-to-circulate) flow characteristics and analyze its mixing performance comprehensively. Three distinct designs incorporating submerged circular walls were explored to achieve STC flow characteristics, facilitating flow along a convex surface and flow impingement on a concave surface. Across a broad Reynolds number range (0.1 to 80), the present micromixer substantially enhances mixing, with a degree of mixing (DOM) consistently exceeding 0.84. Particularly, the mixing enhancement is prominent within the low and intermediate range of Reynolds numbers (0.1<Re<20). This enhancement stems from key flow characteristics of STC: the formation of saddle points around convex walls and flow impingement on concave walls. Compared to other passive micromixers, the DOM of the present micromixer stands out as notably high over a broad range of Reynolds numbers (0.1≤Re≤80).

Numerical investigation of CH4/H2/air micro-mixing combustion flow in a micro gas turbine combustor with different head-end structures

In order to investigate the premixed combustion characteristics of CH4/H2/air in a micro-mixing combustor, the effects of different micro-mixing head-ends (HE1, HE2, HE3) and hydrogen mixing ratios on the temperature distribution, heat transfer process, emission characteristic, flames shape are analyzed. The results show that compared with swirl head-end combustion, the micro-mixing combustion performance is better. Among the three head-ends, HE3 has the best combustion characteristics and stable flames. The temperature distribution in the high-temperature zone is uniform, and low-temperature zone is concentrated near the jet, which can suppress the flashback. The velocity and temperature gradient near the central axis of jet streams show a strong synergistic effect. The flames are plume shaped and flames stability is mainly influenced by the H2 combustion process. Increasing the jet diameter, decreasing the jet spacing and increasing the hydrogen mixing ratio all contribute to the flames stability, but these three methods can stabilize the flames by affecting fluid Reynolds number, interaction between small flames and combustion rate, respectively. Moreover, small jet diameter and high hydrogen mixing ratio can reduce OTDF, which contributes to improve outlet temperature uniformity.

Investigation of effects of impeller geometry on the spatial distribution of turbulent field and micro-mixing performance in a stirred reactor equipped with multiple impellers

There are few studies on the effects of spatial distribution of hydrodynamics on the micro-mixing in stirred reactors. In this work, a statistical approach is introduced to quantitatively assess the spatial distributions of hydrodynamic parameters, using the turbulent dissipation rate as an example. According to the results, the effects of impeller geometry and angular velocity on the turbulent dissipation rate can be well described in terms of the volume-averaged values and spatial distribution functions. In the present study, a more uniform distribution of the turbulent dissipation rate is achieved by the multiple impellers with an inclinational angle of 15° at the same rotational speed. However, increasing the inclinational angle can decrease the volume-averaged value. The cumulative percentage of area-averaged turbulent dissipation rate is well modeled by an exponential function. The effects of impeller types on the meso- and micro-mixing processes are also investigated. It is found that the micro-mixing process has more significant influences than the meso-mixing process in the bottom region and near the free surface. The effects of impeller types on the micro-mixing performance are further investigated using the Villermaux–Dushman reaction system, both experimentally and numerically. An empirical correlation that considers the spatial distribution of turbulent parameters for the reaction rate of I2 synthesis is proposed. The results show that the predictions of segregation index, which represents micro-mixing performance, are improved by a numerical model coupled with the new reaction rate model.

Chaotic-flow-driven mixing in T- and V-shaped micromixers

T- and V-shaped (or arrow-shaped) micromixers enable the control of rapid chemical reactions by permitting accelerated mixing. Their mixing performance has been extensively investigated at moderate flow rates, which correspond to Reynolds numbers of the order of several hundreds. However, this operating range does not align with the recent applications of microreactors in organic synthesis. Therefore, this study examined mixing times in T- and V-shaped micromixers with 250-µm-wide channels at high flow rates (Reynolds numbers of up to 1500). The progress of mixing between an acidic solution and a basic solution containing a pH-sensitive fluorescent molecule was visualized by fluorescence microscopy imaging. An image analysis of 200 frames for each condition helped evaluate the degree of mixing and its stability over time under chaotic flow. The performance and stability of the V-shaped micromixer were significantly enhanced when the flow-rate ratio was changed from 1:1 to 1:2. The difference in momentum between the two inlet streams suppressed the undesirable alternation of the flow patterns at the junction. The effects of the choice of fluids (in the lower- and higher-flow-rate sides) on the reaction selectivity were explored through a numerical analysis. It was clarified that the substrate-side flow rate has to be set lower than that of the reactant side in the competing consecutive reaction system. Moreover, a short mixing time of 1 ms was achieved using the V-shaped micromixer at a flow-rate ratio of 1:2 and Re of 1500. These findings provide practical guidelines for the design and operation of microreactor systems.

Experimental and numerical investigations on micromixing performance of multi-orifice cross-flow jet mixers

Experimental and numerical investigations on micromixing performance of multi-orifice cross-flow jet mixers

Mixing performance of T-shaped wavy-walled micromixers with embedded obstacles

This research systematically investigates the impact of microchannel geometry on key parameters governing mixing efficiency and cost. The study focuses on passive T-shaped micromixers with modified sinusoidal wavy walls, analyzing a spectrum of configurations ranging from the raccoon to serpentine by varying the wall phase angles. The traditional T-shaped micromixer serves as a foundational reference, and we systematically vary phase angles, amplitudes, and wavelengths of the wavy walls to comprehensively address all possible configurations. Additionally, different shaped obstacles such as circular, square, diamond, and triangular obstacles are strategically introduced to further enhance mixing performance. The findings reveal intricate relationships and dependencies among geometric factors, shedding light on configurations that significantly enhance mixing efficiencies. Notably, a specific wavy micromixer configuration, characterized by a carefully tuned phase difference, amplitude, and wavelength, exhibits the highest mixing index in the absence of obstacles. The introduction of obstacles, particularly circular ones, further enhances mixing efficiency. As Reynolds (Re) and Schmidt (Sc) numbers increase, the mixing index decreases, and the mixing cost rises. This work adds a quantitative dimension to understanding the interplay between geometric parameters, flow conditions, and mixing performance in passive micromixers with systematic wavy walls and embedded obstacles.

Continuous and size-control synthesis of lipopolyplex nanoparticles enabled by controlled micromixing performance for mRNA delivery

Continuous and size-control synthesis of lipopolyplex nanoparticles enabled by controlled micromixing performance for mRNA delivery

Performance of microball micromixers using a programmable magnetic system by applying novel movement patterns

The rapid achievement of a desirable mixing level at microscales is one of the most challenging aspects of microfluidic systems, whereby micromixers could open the door to efficient mixing on lab-on-a-chip platforms. Although a wide range of strategies have been explored in active and passive micromixers to improve the mixing, the ability to optionally control the mixing is a key factor that is often overlooked. Hereupon, in this study, the adjustable mixing in a novel 3D-printed micromixer by analyzing the effect of various movement patterns of an actuator is examined. In this micromixer, a stainless steel microball is driven as an actuator using a programmable magnetic system. Initially, with the continuous and non-continuous revolving of the microball, the mixing index in these movement patterns are evaluated. The results show that the mixing index in the proposed micromixer reaches as high as 90% for Reynolds number of 5 by the pendular motion of the microball. Eventually, the main mixing zone of this micromixer is developed by adding inlet and outlet mixing zones, each containing a microball. This on-demand micromixer can pave the way for chemical and biological applications under various operating conditions in a wide range of Reynolds numbers.

Enhancement of liquid–liquid micromixing performance in curved capillary microreactor by generation of Dean vortices

Micromixing efficiency is an important parameter for evaluating the multiphase mass transfer performance and reaction efficiency of microreactor. In this work, the novel curved capillary reactor with different shapes were designed to generate Dean flow, which was used to enhance the liquid–liquid micromixing performance. The Villermaux–Dushman probe reaction was employed to characterize the micromixing performance in different curved cpillary microreactor. The effects of experiment parameters such as liquid flow rate, inner diameter, tube length, and curve diameter on micromixing performance were systematically investigated. Under the optimal condition, the minimum value of the segmentation factor XS was 0.008. It was worth noting that at the low Reynolds number (Re < 30), the change of curved shape on capillary microreactor can significantly improve the micromixing performance with XS reduced by 37.5%. Further, the correlations of segment index XS with dimensionless factor as Reynolds number or Dean number were developed, which can be used to predict the liquid–liquid micromixing performance in capillary microreactor.

Configuration of a Premixer and Grooved Surface to Intensify the Micromixing Performance of a Spinning Disc Reactor

Configuration of a Premixer and Grooved Surface to Intensify the Micromixing Performance of a Spinning Disc Reactor

Particle Tracking and Micromixing Performance Characterization with a Mobile Device.

Strategies to stir and mix reagents in microfluid devices have evolved concomitantly with advancements in manufacturing techniques and sensing. While there is a large array of reported designs to combine and homogenize liquids, most of the characterization has been focused on setups with two inlets and one outlet. While this configuration is helpful to directly evaluate the effects of features and parameters on the mixing degree, it does not portray the conditions for experiments that involve more than two substances required to be subsequently combined. In this work, we present a mixing characterization methodology based on particle tracking as an alternative to the most common approach to measure homogeneity using the standard deviation of pixel intensities from a grayscale image. The proposed algorithm is implemented on a free and open-source mobile application (MIQUOD) for Android devices, numerically tested on COMSOL Multiphysics, and experimentally tested on a bidimensional split and recombine micromixer and a three-dimensional micromixer with sinusoidal grooves for different Reynolds numbers and geometrical features for samples with fluids seeded with red, blue, and green microparticles. The application uses concentration field data and particle track data to evaluate up to eleven performance metrics. Furthermore, with the insights from the experimental and numerical data, a mixing index for particles (mp) is proposed to characterize mixing performance for scenarios with multiple input reagents.

Numerical and experimental study on the synergistic effect of vortex and contact surface of fluid in the inlet section of micromixer

The promoting effect of vortex on the mixing performance of micromixer is difficult to be quantitatively evaluated. In this study, the concept of flux across line (FAL) is proposed for the first time to quantitatively analyze the influence of synergistic effect between the vortex and the contact surface of fluid on the mixing. The FAL value of T-shaped and cross-shaped micromixers is obtained by integrating the velocity component after decomposing the velocity vector on the cross section of the straight channel. The intensity distribution and development of vortex in the inlet section are quantitatively revealed by numerical simulation at Re = 50. According to the FAL analysis, a two-layer feed T-shaped micromixer (TLFT-shaped) is designed to verify the effective synergy between vortex and contact surface of fluid. The FAL value of TLFT-shaped is 40–50 % higher than that of cross-shaped, the promoting effect of vortex on mixing is reflected in the mixing index, which experiences a notable 56 % increase. The concentration distributions of visualization experiments and simulations are consistent, which proves the accuracy of simulation results. The FAL analysis can quantitatively evaluate the promotion effect of vortex on mixing, which provides valuable guidance for the design of microfluidic devices.

Effect of Multiple Structural Parameters on the Performance of a Micromixer with Baffles, Obstacles, and Gaps.

As an essential component of chip laboratories and microfluidic systems, micromixers are widely used in fields such as chemical and biological analysis. In this work, a square cavity micromixer with multiple structural parameters (baffles, obstacles, and gaps) has been proposed to further improve the mixing performance of micromixers. This study examines the comprehensive effects of various structural parameters on mixing performance. The impact of baffle length, obstacle length-to-width ratio, gap width, and obstacle shape on the mixing index and pressure drop were numerically studied at different Reynolds numbers (Re). The results show that the mixing index increases with baffle length and obstacle length-to-width ratio and decreases with gap width at Re = 0.1, 1, 10, 20, 40, and 60. The mixing index can reach more than 0.98 in the range of Re ≥ 20 when the baffle length is 150 μm, the obstacle length-to-width ratio is 600/100, and the gap width is 200 μm. The pressure drop of the microchannel is proportional to baffle length and obstacle length-to-width ratio. Combining baffles and obstacles can further improve the mixing performance of square cavity micromixers. A longer baffle length, larger obstacle length-to-width ratio, narrower gap width, and a more symmetrical structure are conducive to improving the mixing index. However, the impact of pressure drop must also be considered comprehensively. The research results provide references and new ideas for passive micromixer structural design.

A correction method for the incomplete dissociation of sulfuric acid in the Villermaux-Dushman reaction system

The Villermaux-Dushman reaction system is the most popular method for characterizing the micromixing performance of various reactors, which traditionally uses sulfuric acid as the proton source. However, the accurate initial proton concentration (IPC) in this system is hardly accessible owing to the two-step dissociation of the sulfuric acid, resulting in the inaccuracy of the segregation index (XS). In this work, a novel strategy was proposed to correct XS obtained by sulfuric acid as the proton resource via comparing with that obtained by perchloric acid. Under the same theoretical IPC, the micromixing experiments using sulfuric acid and perchloric acid were conducted in different types of reactors, respectively. The conclusions were consistent that an increase of approximately 1.3 times in XS was observed using perchloric acid relative to sulfuric acid. Hence, 1.3 could be considered as the correction coefficient to acquire the exact XS when sulfuric acid, with the concentration ranges from 0.05 to 0.195 mol/L, was used as the proton source. The deviation between the corrected and experimental XS was within ±15%. Overall, this work provides a secure and feasible strategy to accurately evaluate the micromixing performance.

Numerical and Experimental Investigation on a "Tai Chi"-Shaped Planar Passive Micromixer.

(1) Background: Microfluidic chips have found extensive applications in multiple fields due to their excellent analytical performance. As an important platform for micro-mixing, the performance of micromixers has a significant impact on analysis accuracy and rate. However, existing micromixers with high mixing efficiency are accompanied by high pressure drop, which is not conducive to the integration of micro-reaction systems; (2) Methods: This paper proposed a novel "Tai Chi"-shaped planar passive micromixer with high efficiency and low pressure drop. The effect of different structural parameters was investigated, and an optimal structure was obtained. Simulations on the proposed micromixer and two other micromixers were carried out while mixing experiments on the proposed micromixer were performed. The experimental and simulation results were compared; (3) Results: The optimized values of the parameters were that the straight channel width w, ratio K of the outer and inner walls of the circular cavity, width ratio w1/w2 of the arc channel, and number N of mixing units were 200 μm, 2.9, 1/2, and 6, respectively. Moreover, the excellent performance of the proposed micromixer was verified when compared with the other two micromixers; (4) Conclusions: The mixing efficiency M at all Re studied was more than 50%, and at most Re, the M was nearly 100%. Moreover, the pressure drop was less than 18,000 Pa.

Micromixing Performance in a Taylor–Couette Reactor with Ribbed Rotors

The Taylor–Couette reactor (TCR) is becoming an increasingly significant topic in chemical industry. This study investigates the micromixing performance of a ribbed TCR with axial flow in the Villermaux–Dushman reaction system. The local micromixing mechanism of the ribbed TCR was analyzed, and the volume-averaged energy dissipation rate was calculated using CFD. The effects of operating parameters and rib structural parameters on micromixing performance were investigated. The results show that the introduction of ribs eliminates the high shear region between the vortex pairs, resulting in the strong micromixing region being situated on the inner and outer cylinder wall surfaces and the ribbed surface region. Smaller rib spacing, larger rib width, and rib height can strengthen micromixing and result in a smaller segregation index. Micromixing times of ribbed TCRs were calculated using the incorporation model, tm, in the range of 2.0 × 10−5 to 8.0 × 10−3. The results show that ribbed TCRs require a lower energy consumption to achieve a lower tm than other rotating reactors. A correlation equation between tm and five parameters was developed, with a correlation coefficient of 0.951. The accuracy of the volume-averaged energy dissipation rate obtained via CFD was verified through experimental analysis. The correlation between the micromixing time and the volume-averaged energy dissipation rate was established in a form that satisfies Kolmogorov’s turbulence theory for tm. To convert the volume-averaged energy dissipation rate into a local energy dissipation rate, a factor ϕ was introduced and solved using the engulfing diffusion model. This study provides insights into the design and optimization of ribbed TCRs.

Improving the micromixing and thermal performance using a novel microreactor design

Improving the micromixing and thermal performance using a novel microreactor design