Micromixing Efficiency Research Articles

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.

Micromixing efficiency and enhancement methods for non-Newtonian fluids in millimeter channel reactors

Micromixing efficiency and enhancement methods for non-Newtonian fluids in millimeter channel reactors

Micro-mixing enhancement in a Taylor-Couette reactor using the inner rotors with various surface configurations

This study investigates the effects of various inner cylinder configurations on micromixing and fluid dynamics within a Taylor-Couette (TC) reactor using the inner cylinders with different surface designs, including the traditional smooth-surfaced rotor cylinder. The four innovative inner cylinders were specifically designed with axial corrugations (N40 and N80) and three-dimensional rough surfaces (NZ40 and NZ80). Micromixing efficiency was assessed experimentally using the iodide-iodate reaction as a probe. To further understand the impact of the rotors' surface structures on micromixing, computational fluid dynamics (CFD) modelling was utilized to analyse the fluid dynamics within the TC reactor. An incorporation model was employed to calculate the micromixing time. The experimental findings reveal that the segregation index decreases with increasing rotation speed for all inner cylinders. Besides, NZ80′s micro-mixing efficiency surpasses that of its counterparts, NZ40, N40, and N80. The CFD modelling results underscore the significant influence of the inner cylinder's surface configuration on the turbulence dissipation rate and volume probability distribution, which are likely to contribute positively to the micromixing efficiency within the TC reactor. Furthermore, the empirical correlations obtained have been established to understand the micro-mixing time within TC reactors using different rotating cylinders.

Enhancing mixing efficiency of a circular electroosmotic micromixer with cross-reciprocal electrodes

Enhancing mixing efficiency in microscale processes for sensitive biomedical, pharmaceutical, and chemical applications is crucial, particularly when operating under low-velocity constraints. This study presents a comprehensive investigation into the impact of various factors on microfluidic mixing within a circular mixing chamber micromixer, utilizing electroosmotic principles. The governing equations are solved numerically using the finite element technique-based solver. This research examines the effects of microchamber diameter (D), inlet velocity (uo), alternating current (AC) voltage amplitude (ϕo), and AC frequency (f) on fluid mixing dynamics. Several key findings are noted from this study. The reduction of the circular microchamber diameter decreases the linear distance between cross-reciprocally placed microelectrodes, resulting in increased electroosmosis force and mixing efficiency. The voltage amplitude within the specified range shows increased mixing efficiency when fluid species are combined at appropriate velocity and AC frequency. The highest mixing efficiency of 98.84% is achieved with the following parameters: flow velocity (uo) of 150 μm/s, AC frequency of 4 Hz, voltage amplitude of 500 mV, and microchamber diameter of 20 μm. At a frequency of 12 Hz and voltage amplitude of 500 mV, the mixing efficiency exceeds 94.66% across a wide range of input velocities (100–200 μm/s), enabling versatile control in microfluidic devices. The nonlinear interaction between electroosmotic flow and microchamber geometry significantly contributes to this enhanced mixing efficiency. These results demonstrate the potential for optimizing microfluidic mixing processes through careful parameter tuning, particularly in applications requiring high efficiency at low flow rates. Thus, this study provides valuable insights for designing more effective microfluidic systems in various scientific and industrial fields.

Continuous Flow Synthesis of Ethyl Diazoacetate and CFD Analysis of Micromixing Efficiency in a Microreactor

Continuous Flow Synthesis of Ethyl Diazoacetate and CFD Analysis of Micromixing Efficiency in a Microreactor

Enhancing mixing performance in a square electroosmotic micromixer through an off-set inlet and outlet design

This study addresses the critical need to enhance mixing quality and cost efficiency in electroosmotic micromixers, crucial for various applications, such as chemical synthesis, medical diagnostics, and biotechnology, utilizing the precision of microfluidic devices. The intricate dynamics of time-dependent electroosmotic vortices induced by microelectrodes are investigated, exploring the nonlinear physics principles driving mixing enhancement. Specifically, an examination is made of how nonlinear phenomena, such as convective flow instabilities, chaotic advection, and nonlinear interactions between fluid flow and channel geometry, contribute to observed improvements in mixing performance. Through comprehensive numerical simulations employing finite element-based solvers, the impact of relevant parameters, such as voltage amplitude (V0), frequency (f), Reynolds number (Re), and Debye parameter (k), on mixing performance is systematically analyzed. Findings reveal that optimizing these parameters, coupled with the strategic design of micromixers featuring offset inlets and outlets, leads to a remarkable mixing quality of 98.44%. Furthermore, a methodology is proposed for selecting the optimal micromixer configuration (MM1), balancing mixing quality, and cost efficiency. This study advances the understanding of electroosmotic micromixers and provides practical guidelines for optimizing microfluidic device performance in diverse applications.

Micromixing efficiency of non-Newtonian fluid in rotating packed beds with novel tube-tube premixers

Rotating packed beds (RPBs), as the typical chemical intensification devices, have been widely applied in liquid-phase fast reactions and precipitation processes. In this study, three novel tube-tube premixers were designed, and three-dimensional CFD models of the flow and mixing processes for non-Newtonian fluids in tube-tube premixers were established. Meanwhile, the micromixing efficiency in RPBs with different tube-tube premixers was experimentally investigated. The results show that TG-2 premixer exhibits the best premixing performance. The segregation index decreases as the rotational speed or flow rate increases, indicating the increase in micromixing efficiency. With the increase of CMC mass fraction, the segregation index initially decreases and then increases. Moreover, the micromixing efficiency of TG-0-RPB is the highest in aqueous solution, the micromixing efficiency of TG-4-RPB is the highest in 0.2 wt.% CMC system, and the micromixing efficiency of TG-2-RPB is the highest when the CMC concentrations is equal to or greater than 0.4 wt.%. The micromixing times of non-Newtonian fluid in RPBs range from 2 to 10 ms.

Synthesis of zeolite X from fly ash in an impinging stream reactor and its mechanisms

The conventional hydrothermal method with magnetic stirring for the synthesis of zeolite X from fly ash has some problems, such as low micromixing efficiency, low mass transfer rate, and long synthesis time. In this study, impinging stream reactor is used to improve the mass transfer and micromixing and the mechanism how the nucleation and crystallization of zeolite is accelerated is explored. The results show that premixing in the impinging stream reactor can reduce the stirring and aging time from 4 h to 20 min because the hydroxyl free radicals resulting from the cavitation effect can accelerate the crystallization of zeolite. After collision, the viscosity of the system is increased from 0.22 Pa·s to 3 Pa·s, which can increase the residence time of cavitation bubbles in the gel solution and effectively inhibit the aggregation of crystal nuclei. As a result, the crystal nuclei in the system are well dispersed. The impinging stream reactor can also accelerate the mass transfer between liquid and solid phases and improve the micromixing of raw materials, so that the polymerization between Si and Al is increased and the nucleation of zeolite X is accelerated. The degree of order of zeolite X samples obtained by premixing in the impinging stream reactor is much higher than that obtained by magnetic stirring. The relative crystallinity after crystallization for 12 h (100 %) is higher than that obtained by magnetic stirring (94.93 %); and the n(Si/Al) is lower than that obtained by magnetic stirring. It is concluded that premixing in the impinging stream reactor can improve the polymerization of aluminosilicate and accelerate the nucleation and crystallization of zeolite X. Under the same conditions, zeolite X synthesized by premixing in the impinging stream reactor has better CO2 adsorption capacity than those synthesized by magnetic stirring and industrial synthesis.

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

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.

Enhancement of the mixing efficiency of double T-shaped micromixers using a combined passive scheme

Corrugating channel walls and using cylindrical elements can be employed as a combined technique to improve mixing in micromixers. In this study, the mixing process in three-dimensional double T-shaped micromixers with mixing wavy-walled channel in the presence of cylindrical elements is simulated. The objective is to investigate the effects of the geometry of wavy walls and cylindrical elements on the mixing and hydraulic performance of micromixers at a wide range of Reynolds numbers from 10 to 110 and a Schmidt number of 500. Accordingly, the corresponding Peclet numbers vary between 5000 and 55,000. Six different micromixers including double smooth-walled, in-phase wavy-walled, and opposite-in-phase wavy-walled micromixers without elements and with the presence of elements are considered. The results show that the wavy walls significantly increase the mixing index. However, the extent of this effect depends on whether the waves on the channel walls are in-phase or opposite-in-phase. Moreover, the use of cylindrical elements can considerably enhance the mixing efficiency of wavy channels compared to smooth ones. This positive effect increases with the increase in the Reynolds number. Also, the figure-of-merit (FoM) values over 1 illustrate the excellence of the proposed configurations. FoM touches the amazing value of 1.96 in the in-phase micromixer with element at Re = 20.

A Review on Fluid Flow and Mixing in Microchannel and their Design and Manufacture for Microfluidic Applications

Abstract: The present time has witnessed a never-before-heard interest in and applications of microfluidic devices and systems. In microfluidic systems, fluid flows and is manipulated in microchannels. Mixing is one of the most important criteria for a majority of microfluidic systems, whose laminar nature hinders the efficiency of micromixing. The interface between the flowing fluid and the inner wall surface of the microchannel greatly influences the behaviour of fluidic flow in microfluidics. Many researchers have tried to pattern the surface, introduce obstacles to flow, and include micro- or nanoprotruded structures to enhance the mixing efficiency by manipulating the microchannel flow. New and rapid advances in MEMS and micro/nanofabrication technologies have enabled researchers to experiment with increasingly complex designs, enabling rapid transformation and dissemination of new knowledge in the field of microfluidics. Here, we report the fluid flow characteristics, mixing, and associated phenomena about microfluidic systems. Microfluidic systems and components such as microreactors, micromixers, and microchannels are reviewed in this work. We review active and passive micromixers, with a primary focus on widely used passive micromixers. Various microchannel geometries and their features, mixing efficiencies, numerical analysis, and fabrication methods are reviewed. Applications as well as possible future trends and advancements in this field, are included too. It is expected to make the reader curious and more familiar with the interesting field of microfluidics.

NUMERICAL SIMULATION OF PASSIVE MICROMIXER WITH NOVEL OBSTACLE STRUCTURE

The micromixer is an important prerequisite for realizing the function of the microfluidic chip system. Micromixers are mainly used in protein crystallization, biological reactions, drug delivery and other fields. Efficient micromixers enable fast bioreaction processes. In this paper, according to the principle of plane geometry, micromixers with three different structural obstacles, circular, equilateral triangle and square, are designed to study how to improve the mixing efficiency of the micromixer. In this paper, the influence of the obstacle structure on the mixing efficiency and pressure drop of the micromixer is analyzed. Through numerical simulation, the results show that when Re = 100, the mixing efficiency of the circular obstacle micromixer is up to 97.4%, and the pressure drop is 15,789.597 Pa. In addition, this paper analyzes that the use of cylindrical obstacles can make the fluid generate horizontal and vertical vortex flow, break the usual laminar flow, and significantly improve the mixing efficiency.

Image‐based measurement of engulfment vortex to quantitatively assess micromixing efficiency in a gas–liquid stirred tank

AbstractMicromixing in reactors is typically characterized by chemical test reactions. A novel image‐based measurement system of engulfment vortex (IMEV system) is developed to assess the micromixing efficiency. Over 2000 vortices were recognized from images captured under various experimental cases, and key frames for their formation, engulfment and dissipation were identified. Inspired by the engulfment model (i.e., E model), this work quantified the micromixing time and local turbulent energy dissipation rate with the vortex lifetimes. The micromixing time obtained through the IMEV method is comparable to its value estimated by the micromixing model and segregation index of the test reaction, with a deviation of less than 20%. In turbulent gas–liquid systems, bubbles play a dual role on the local micromixing due to frequent disturbance and phase interface limitation. To summarize, this work offers an alternative approach for micromixing studies and provides valuable insights into dispersed phase effects on the micromixing efficiency.

Micromixing optimization of non-newtonian fluids with heterogeneous zeta potential

This paper aims to improve micromixing in T-shaped microchannels using heterogeneous zeta potential, which is essential for analyzing biochemical fluids in various industrial applications. We investigate the impact of different parameters, including zeta potential, applied electric field, and a number of heterogeneous surface patterns, on microchannel mixing performance. Our results demonstrate that increasing the zeta potential on the heterogeneous pair patches amplifies the recirculation zone, improving mixing performance within the microchannel. Therefore, we recommend increasing the value of heterogeneous zeta potential on the patches to enhance the mixing performance further. Additionally, we examine the non-Newtonian behavior of the fluid using the power law model and find that pseudoplastic fluids (n < 1) have lower mixing performance compared to dilatant fluids (n > 1) due to higher velocity. We evaluate the effects of various parameters on mixing performance to design an efficient micromixer that achieves rapid and homogeneous mixing of sample fluids. Finally, we optimize the micromixing efficiency using Taguchi to achieve the optimum value of mixing. The optimized value of micromixing efficiency for the corresponding non-Newtonian fluid is also determined.

Micromixing Performance of Microchannel Reactors after Sizing-Up and Their Application in the Preparation of Ni–Co–S Composites

To investigate the sizing-up effects of microchannel reactors, a 0.6 mm i.d. microchannel reactor along with a 2 mm i.d. tube reactor, a 3 mm i.d. tube reactor, and a 4 mm i.d. tube reactor was assembled, and their micromixing performance was evaluated experimentally with the I–/IO3– parallel competitive reaction system at different Re. The results showed that at low Re, the segregation index XS (used to characterize the micromixing efficiency) of all tube reactors decreased (indicating strengthened micromixing efficiency) noticeably with increasing Re, and the XS of tube reactors with a bigger inner diameter was much larger than that of the reactors with a smaller inner diameter at the same Re. When Re was bigger than 5584, the XS of all tube reactors with different inner diameters would become almost the same as ∼3.4 × 10–4 and remained unchanged with further increasing Re, suggesting a negligible sizing-up effect of the microchannel reactor on the micromixing performance at sufficiently high Re. In addition, Ni–Co–S composites were prepared in the four different tube reactors at the optimal Re of 6700, and the physical and electrochemical properties of the prepared Ni–Co–S composites were almost the same, further demonstrating the negligible sizing-up effects of the microchannel reactor at high Re.

Dynamics of liquid dispersion in a rotating packed bed with single‐layer wire mesh

AbstractThe improvement of liquid dispersion by rotating wire mesh is one of the major causes for the mass transfer and micromixing intensification in rotating packed beds (RPBs). In particular, the initial dispersion region has been proved to have the greatest mass transfer and micromixing efficiency. However, the dispersion mechanism has not been revealed. This study investigated the dynamics of liquid dispersion in an RPB with single‐layer wire mesh. The liquid dispersion behaviors were obtained by high‐speed photography and numerical simulation. The liquid was found to stretch into ligaments and break into the main droplet and several satellite droplets. A new theoretical model was established to reveal the dispersion mechanism of these two stages. The stretching stage depends on the liquid initial momentum and acquired impulse, while the breakup stage was determined by the competition of ligaments recoil and pinch‐off behaviors. The model was validated in good agreement with the experimental and simulation results of the dispersion characteristics.

Controllable preparation of ultrafine KMnF3 perovskite by combining micro-channel reactor and microwave-ultrasonic assistance

In this study, a microwave-ultrasonic assisted countercurrent-flow micro-channel reactor (CFMCR M-U) method was designed to prepare KMnF3 perovskite fluoride as supercapacitor electrode material through a co-precipitation process, in which multiple parameters were precisely controlled and their effects on the material synthesis were investigated. Benefited from the excellent micromixing efficiency of both the microwave-ultrasonic assistance and the microreactor, the KMnF3 particles prepared by the CFMCR M-U method were much smaller (∼120 nm) with a more uniform particle size distribution and less aggregated than those produced without the assistance of microwave-ultrasonic, leading to a more superior electrochemical performance. The KMnF3 synthesized under the optimal CFMCR M-U conditions had an initial specific capacity of 406.00 C·g−1 at a current density of 1 A·g−1. After 2500 charge-discharge cycles at a current density of 5 A·g−1, the KMnF3 particles had a retention rate of 92.21% of the initial specific capacity. For KMnF3//AC (active carbon) asymmetric supercapacitor, 123.9% of the initial specific capacitance remained after 5000 charge-discharge cycles. Therefore, it showed that CFMCR M-U method is a very promising technology for the controlled production of ultrafine KMnF3 particles and other products.

Application of microimpinging stream reactor coupled with ultrasound in Cu/CeZrOx solid solution catalyst preparation for CO2 hydrogenation to methanol

CO2 hydrogenation to methanol process could effectively eliminate CO2 emissions and convert CO2 into different chemicals with H2 produced via green energy. However, the catalysts for the CO2 hydrogenation process suffer from lower CO2 conversion, methanol selectivity, and deactivation. In this study, Cu/CeZrOx solid solution catalyst is prepared (Cu/CeZrOx-M) via a new microimpinging stream reactor coupled with ultrasound. Due to its better micromixing efficiency, the Cu/CeZrOx-M catalyst has smaller particle size and larger BET surface area than that prepared via the conventional batch method (Cu/CeZrOx-B). The Cu/CeZrOx-M catalyst exhibits a higher methanol STY of 222.4 gMeOH/kgcat/h with CO2 conversion of 4.67% and methanol selectivity of 55.6% at 240 °C, and possesses better stability. Combined with the characterizations of structural and electronic state, catalytic higher performance is attributed to the synergistic effect between the oxygen vacancies and higher ratio of Cu+. In-situ DRIFTS reveals that the Cu/CeZrOx-M catalyst follows the formate-intermediated pathway, effectively transferring the formate intermediate into methanol. Furthermore, the microimpinging stream reactor could achieve the precursor solution transmission rate with 10 mL/s. This work provides a novel method for the high-performance catalyst preparation and its mechanism study gives a deep insight into high-performance catalysts development via the bottom-up study.

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.