Efficient Mixing Research Articles

Development of silver dichromate-geopolymer composite: An innovative catalyst for simultaneous desulfurization and denitrogenation for cleaner petroleum fuel

Rising global energy demands necessitate cleaner fuel technologies due to stringent environmental regulations. Emerging techniques like oxidative desulfurization and denitrogenation offer advantages over traditional hydrotreatment, selectively oxidizing sulfur and nitrogen compounds without damaging hydrocarbon structures. This research employs nano-crystalline silver dichromate-geopolymer composites catalysts prepared by direct precipitation, sonochemical, surfactant-assisted and surfactant assisted sonochemical routes for oxidizing sulfur and nitrogen compounds in fuel oil. Surfactant assisted preparation aided in generating catalysts with controlled size, while sonochemical synthesis facilitated uniform dispersion of the particles. The uniform dispersion, controlled particle size, and low agglomeration along with unclogged pores aided the sonochemically prepared catalyst in demonstrating superior catalytic performance over other counterparts in individual sulfur oxidation tests. In contrast, due to the high rate of oxidation and high affinity to occupy active sites, the catalyst prepared by surfactant assisted sonochemical route performed better than its sonochemical counterpart in individual nitrogen compound oxidation tests. The prepared catalysts were thoroughly characterized by different analytical characterization techniques. Single component oxidation resulted in 80.86 and 98.94% conversion of sulfur and nitrogen, while simultaneous oxidation resulted in 58.41% sulfur oxidation and 95.69% nitrogen conversion. Due to the cavitation effect, efficient mixing and a high local temperature and pressure created due to the introduction of ultrasound, the conversion rose to 88.02 and 98.02% for sulfur and nitrogen, respectively. Post oxidation, the oxidation products were removed by extraction, leading to 100% removal of nitrogen and 85% removal of sulfur. The proposed mechanism suggested the oxidation of both the compounds to occur through the formation of active Cr(VI)-peroxo species.

Optimization of three-dimensional Tesla valve-based passive micromixer for gradient functional materials mixing

With the rapid development of three-dimensional (3D) printing technology, the field of multi-material fabrication, particularly in the production of functionally graded materials, has achieved revolutionary advancements. However, the structures of micromixers, which are central to this technology, have not been sufficiently studied. This study introduces an optimized passive micromixer design based on a 3D Tesla valve, specifically engineered for the efficient mixing of Fe3O4 particles within an epoxy resin E51 matrix. The micromixer leverages the fluid dynamics of the Tesla valve, where sudden changes in flow direction generate secondary flows that enhance mixing performance by disrupting laminar flow and inducing chaotic advection, thereby increasing the interfacial area between different material components. This process significantly improves mixing efficiency in the fabrication of gradient materials. Through theoretical analysis and computational simulations, the study identifies optimal configurations for the Tesla valve system, emphasizing mixing dynamics that enhance material gradient formation. The findings reveal that optimal mixing efficiency is achieved with a configuration comprising three Tesla valves. This optimal setup includes a 0.5-mm opening width at the turning point, an immediate transition from the turning point to the straight pipe (0 mm length), a 0.25-mm structural height for the Tesla valve, and an outlet distance of 0.25 mm from the curved pipe. Hopefully, this study can provide a robust reference for the significant potential of future applications in the realm of multi-material 3D printing, thereby fostering its substantial growth prospects.

The evolution of the coronal loop structure due to the phase mixing of high and low-frequency Alfvén waves

ABSTRACT Coronal loops are known to host Alfvén waves propagating in the corona from the lower layers of the solar atmosphere and because of their internal structure, phase mixing is likely to occur. The structure of the coronal loop could be significantly affected by the thermodynamic feedback of the heating generated by phase mixing. However, this phenomenon can be sensitive to the period of the propagating Alfvén waves due to how short period waves can be easily dissipated and the way long-period waves may accumulate considerable energy in resonating coronal loops. Using the Lare2d code, a coronal loop model of a field-aligned thermodynamic equilibrium and a cross-field background heating profile is created, with an additional forcing term added to drive Alfvén waves with coronal amplitudes between $5{\!-\!}30 \, \mathrm{km} \, \mathrm{s}^{-1}$. We show that high-frequency waves can generate heating corresponding to a ${\sim} 10~{{\ \rm per\ cent}}$ increase of the initial coronal shell temperature, chromospheric upflows of up to $0.6 \, \mathrm{km} \, \mathrm{s}^{-1}$ and a coronal shell mass increase of ${\sim} 15~{{\ \rm per\ cent}}$. These changes are sufficient to alter and maintain a new coronal loop density structure, broadening the region where efficient phase mixing (and therefore heating) occurs. In contrast, low-frequency waves are unable to be effectively dissipated, resulting in minimal changes to the loop structure. We see little evidence of wave energy accumulation in the corona and are unable to conclude that the dissipation of low-frequency Alfvén waves can be an effective heating mechanism in coronal loops in the setup used in this study.

Analysis of the Dispersive and Distributive Mixing Effect of Screw Elements on the Co-Rotating Twin-Screw Extruder with Particle Tracking.

Compounding is an important step in processing base polymers and is used to incorporate various additives into a polymer. For this purpose, different screw elements are used for dispersive and distributive mixing on a co-rotating twin-screw extruder. Optimising the screw configuration requires precise knowledge of the screw elements' mixing properties, which have not been thoroughly investigated. This study analyses the mixing behaviour of individual screw elements regarding dispersive and distributive mixing using 3D CFD flow simulations with subsequent particle tracking. For distributive mixing, the particle distribution behind the screw elements in the XY plane is analysed and the mixing index MQ, which relates the standard deviation and the mean value of the triangular areas between the particles, is calculated. For dispersive mixing, the maximum shear stress on the particle path and the integral of the shear stress over the residence time of each individual particle are determined. The results show that screw element geometry and rotation speed have a significant influence on dispersive and distributive mixing. In addition, better dispersive mixing is achievable with highly viscous materials. These findings enable the optimisation of the mixing zone of a co-rotating twin-screw extruder for the efficient mixing of mineral fillers.

Enhanced Acoustic Mixing in Silicon-Based Chips with Sharp-Edged Micro-Structures

The small dimensions of microfluidic channels allow for fast diffusive or passive mixing, which is beneficial for time-sensitive applications such as chemical reactions, biological assays, and the transport of to-be-detected species to sensors. In microfluidics, the need for fast mixing within milliseconds arises primarily because these devices are often used in fields where rapid and efficient mixing significantly impacts the performance and outcome of the processes. Active mixing with acoustics in microfluidic devices involves using acoustic waves to enhance the mixing of fluids within microchannels. Using sharp corners and wall patterns in acoustofluidic devices significantly enhances the mixing by acoustic streaming around these features. The streaming patterns around the sharp edges are particularly effective for the mixing because they can produce strong lateral flows that rapidly homogenize liquids. This work presents extensive characterizations of the effect of sharp-edged structures on acoustic mixing in bulk acoustic wave (BAW) mode in a silicon microdevice. The effect of side wall patterns in different angles and shapes, their positions, the type of piezoelectric transducer, and its amplitude and frequency have been studied. Following the patterning of the channel walls, a mixing time of 25 times faster was reached, compared to channels with smooth side walls exhibiting conventional BAW behavior. The average locally determined acoustic streaming velocity inside the channel becomes 14 times faster if sharp corners of 10° are added to the wall.

Formulating PEO-polycarbonate blends as solid polymer electrolytes by solvent-free extrusion

Liquid electrolytes are currently state-of-the-art for commercial Li-ion batteries. However, their use implicates inherent challenges, including safety concerns associated with flammability, limited thermal stability, and susceptibility to dendrite formation on the lithium metal anode, that can compromise the battery lifespan. Solid-state polymer electrolytes offer an alternative to conventional liquid electrolytes, aiming to mitigate safety, stability, and performance drawbacks. This study investigates the preparation and the comprehensive characterization of polyethylene oxide (PEO) and polycarbonate (PC) blends obtained through extrusion process. The process is solvent-free and easily scalable at the industrial level; it grants the efficient dispersion and mixing of PEO and PC. Blends at different ratios of PEO (Mw of 4 × 105 and 4 × 106 g mol˗1) and two types of PCs (namely, polyethylene and polypropylene carbonate) including lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are prepared. Optimization and investigation of the relative effects between the application of different PCs and the variable ratios of PEO/PCs on the mechanical, morphologic and electrochemical properties of the final polymeric membranes is carried out for future applications of these systems, as efficient electrolytes in all-solid-state lithium batteries.

Microbial Protein and Metabolite Profiles of Klebsiella oxytoca M5A1 in a Bubble Column Bioreactor.

The production of microbial proteins (MPs) has emerged as a critical focus in biotechnology, driven by the need for sustainable and scalable alternatives to traditional protein sources. This study investigates the efficacy of two experimental setups in producing MPs using the nitrogen-fixing bacterium Klebsiella oxytoca M5A1. K. oxytoca M5A1, known for its facultative anaerobic growth and capability to fix atmospheric nitrogen, offers a promising avenue for environmentally friendly protein production. This research compares the performance of a simple bubble column (BC) bioreactor, which promotes efficient mixing and cross-membrane gas transfer, with static fermentation, a traditional method lacking agitation and aeration. The study involved the parallel cultivation of K. oxytoca M5A1 in both systems, with key parameters such as microbial growth, glucose utilization, protein concentration, and metabolite profiles monitored over a 48 h period. The results indicate that the BC bioreactor consistently outperformed static fermentation regarding the growth rate, protein yield, and glucose utilization efficiency. The BC exhibited a significant increase in protein production, reaching 299.90 µg/mL at 48 h, compared to 219.44 µg/mL in static fermentation. The organic acid profile reveals both synthesis and utilization regimes of varying patterns. These findings highlight the advantages of the BC bioreactor for MP production, particularly its ability to maintain aerobic conditions that support higher growth and yield.

Теоретические исследования процесса смешивания кормов центробежным смесителем

The article presents theoretical studies aimed at understanding the physical processes occurring in the production of compound feeds using a centrifugal cascade mixer, which open up new horizons in optimizing feed production technology. Special attention in these studies is paid to the analysis of the mixing process, which, as it turned out, is closely interrelated with the principles of operation of the dispenser. As a result of the analysis, it was found that the dispenser and mixer should be considered as a single system, regardless of the mixing mechanism used in the production process. This made it possible to develop a cascade mixer of feed materials of centrifugal type and continuous action, which is an innovative solution in the field of feed production. This mixer provides a homogeneous mixture of loose feed components and can be integrated into production lines for the preparation of both feed and combined mineral briquettes. The key advantage of the proposed mixer is the use of a centrifugal force field, which, unlike the gravity field, provides more efficient mixing. In this case, the process of preparing compound feeds can be represented as a sequence of three key stages: the metered supply of components, the introduction of one component into the composition of another, transportation (removal) of the finished product from the working area of the mixer. The research allowed us to obtain analytical dependences of the components of the centrifugal force on the angular velocity of the rotor and its radius. This allows you to optimize the operating parameters of the mixer to achieve maximum mixing efficiency. During the research, a mathematical model of the spatial motion of a particle in a mixer was developed. The model is presented in the form of Lagrange equations of the second kind, the generalized coordinates of which are the displacement of the particle along the cone and the polar angle of the particle position. This makes it possible to solve the optimization problems of centrifugal mixers according to a given objective function. Thanks to the conducted research, it was possible to develop an innovative mixer that provides a homogeneous mixture of components of loose compound feeds. The use of centrifugal forces in the mixer made it possible to increase the mixing efficiency and ensure that the final product meets the requirements of the formulation. The research results are of great practical importance and can be used to improve feed production technologies. Keywords: COMPOUND FEED, FEED MIXTURE, MIXER, DISPENSER, CENTRIFUGAL MIXER, PARTICLE MOTION IN THE MIXER

Spatial and temporal mush heterogeneity during eruptions recorded in clinopyroxene from the 2021 paroxysms at Mt. Etna, Italy

Textural and compositional zoning of volcanic minerals archives pre-eruptive magma processes. Crystals erupted simultaneously may be sampled from different regions of the plumbing system and hence record variable histories due to complex magma dynamics. In addition, crystals erupted throughout the course of an eruption may record temporal variations in the plumbing system. To resolve mush variability on both spatial and temporal scales, we investigate clinopyroxene erupted during a series of paroxysmal episodes between February–April 2021 at Mt. Etna, Italy. Using a combination of high-resolution geochemical techniques, we observe that Cr enrichments in clinopyroxene mantle zones, grown upon eruption-triggering mafic rejuvenation, exhibit both temporal and spatial (sample-scale) variability. Temporal variability correlates with changes in glass compositions, attesting to the ability of clinopyroxene to track magma maficity throughout an eruption. Spatial variability, indicated by the scatter of Cr concentrations, is greatest for the first event and lowest for the final paroxysm. In conjunction with core textures, degree of sector enrichment and thermobarometry, our data suggest that the onset of the paroxysms was preceded by the remobilisation of a mid-crustal clinopyroxene mush (534 ± 46 MPa) by hot, mafic magma causing variable resorption of mush-derived crystal cores. Towards the end of the eruption, waning magma supply led to less efficient mush remobolisation and mixing, resulting in homogenous crystal populations. Our results highlight that clinopyroxene Cr contents and sector enrichment can be used to track mafic rejuvenation and magma evolution throughout eruptions, while also reflecting spatial heterogeneities within the plumbing system.

Impact of Ball Milling on the Microstructure of Polyethylene Terephthalate.

Polyethylene terephthalate (PET) is a semi-crystalline polymer that finds broad use. Consequently, it contributes to the accumulation of plastics in the environment, warranting PET recycling technologies. Ball milling is a commonly used technique for the micronization of plastics before transformation. It has also recently been reported as an efficient mixing strategy for the enzymatic hydrolysis of plastics in moist-solid mixtures. However, the effect of milling on the microstructure of PET has not been systematically investigated. Thus, the primary objective of this study is to characterize the changes to the PET microstructure caused by various ball milling conditions. PET of different forms was examined, including pre- and post-consumer PET, as well as textiles. The material was treated to a range of milling frequencies and duration, before analysis of particle size, crystallinity by differential scanning calorimetry and powder X-ray diffraction, and morphology by scanning electron microscopy. Interestingly, our results suggest the convergence of crystallinity to ~30% within 15 minutes of milling at 30 Hz. These results are consistent with an equilibrium between amorphous and crystalline regions of the polymer being established during ball milling. The combined data constitutes a reference guide for PET milling and recycling research.

Mixing enhancement assisted by dual plate cavity in supersonic flow

Fast and efficient mixing of high-speed shear flow formed by fuel and oxidizer is of great importance for the improvement of rocket-based combined cycle engine performance. Nevertheless, the existence of compressibility effects of high-speed flow significantly inhibits the growth process of a mixing layer. Moreover, a finite-length combustor of the engine calls for more effective enhanced-mixing strategies to complete mixing in a shorter streamwise distance. To this end, in present paper, the strategy called dual plate cavity (DPC) is proposed to promote mixing. Three cases including the benchmark, front-DPC and back-DPC cases are selected to perform the comparative study. By means of high-order direct numerical simulations, the structure evolution characteristics and turbulence intensity distributions are researched. The index of velocity thickness is utilized to assess the mixing layer growth. The results indicate that with the introduction of DPC, the mixing process is dramatically promoted. The penetration behavior of newly found T-shaped structures into the upper main stream can engulf more fluid into the mixing region. Specifically, in the back-DPC case, the coexistence of both large-scale and small-scale structures in the far flow field can improve the turbulence intensity. The spatial correlation analysis results show that with the influence of DPC, the structure sizes are much larger than that of the benchmark case in the same streamwise position. Meanwhile, the contour line equal to 0.5 possesses property of distortion for the back-DPC case. The drastic pulsation of a mixing layer edge can obviously promote the mixing process. Through exploration of the enhanced-mixing mechanisms, this work indicates that the proposed DPC strategy is a good candidate for efficient mixing, and in the future, more detailed work including three-dimensional simulations concerning the strategy optimization is suggested to be performed.

Investigation on the effect of vertical baffle plate on droplet size distribution and mixing efficiency in Taylor Reactor

The Taylor reactor is a dynamic mixer based on the principles of Taylor vortex flow. However, traditional Taylor reactors feature smooth inner and outer cylinder surfaces, presenting challenges in achieving uniform mixing and efficient mass transfer. These limitations do not meet the requirements of modern chemical processes for highly efficient mixing equipment. This article introduces a novel Taylor reactor equipped with vertical baffle plates, designed to overcome these challenges. A comprehensive methodology combining CFD-PBM and experimental techniques was employed to investigate both droplet size distribution and mixing performance in the annular gap. Compared to traditional designs, the new device demonstrates significantly lower COV at 0.018 and Sauter mean diameter at 38.3 μm. Optimal mixing efficiency is achieved at rotating Reynolds number (Re) of 1.17 × 105 and inlet Reynolds number (Rei) of 2.65 × 103. Numerical simulation results suggest that vertical baffles effectively enhance liquid-liquid interactions including collision, interface contact, and droplet residence time within the annular gap. Moreover, increased turbulent stress in the flow field contributes to greater vorticity, turbulence intensity, and turbulent kinetic energy resulting in smaller droplet sizes and improved mixing efficiency. These findings provide a theoretical foundation for hydraulic structural optimization design as well as widespread application of Taylor reactors.

Micromixing Strategies for Efficient Mixing Processes: A Comprehensive Review

Abstract The demand for rapid, high-quality, and controlled mixing at the microscale has led to the development of various types of micromixers. Micromixers are commonly categorised as active, or passive based on whether they utilise external energy to enhance mixing. Passive micromixers utilise a complex geometry to enhance the diffusion coefficient at lower Reynolds numbers and induce chaotic advection at higher Reynolds numbers for effectively mixing fluids without external energy. Active micromixers, on the other hand, achieve precise, fast, and controllable mixing by employing external energy sources such as pressure, electric, magnetic, or acoustic fields. Some active methods such as magnetic field-driven micromixers need fluids with specific properties. Others, such as acoustic field-driven micromixers apply to various types of fluids. Bubbles can be used as membranes or stirrers in microfluidic devices for both passive and active micromixers. They are easy to use, compatible with microfluidic systems, low cost, and effective. Improvements in manufacturing methods, notably, 3D printing have emerged as promising methods for the development of new micromixer designs. In this paper, a wide range of micromixer types is reviewed and the main mechanism for enhanced mixing is investigated. This study aims to provide a valuable guide for researchers looking to propose innovative designs. Furthermore, it is shown that combining different methods can lead to more effective micromixers, promising further advancements in microscale mixing technology.

Micromixer driven by bubble-induced acoustic microstreaming for multi-ink 3D bioprinting.

Recently, the 3D printing of cell-laden hydrogel structures, known as bioprinting, has received increasing attention owing to advances in tissue engineering and drug screening. However, a micromixing technology that efficiently mixes viscous bioinks under mild conditions is needed. Therefore, this study presents a novel method for achieving homogeneous mixing of multiple inks in 3D bioprinting through acoustic stimulation. This technique involves generating an acoustic microstream through bubble oscillations inside a 3D bioprinting nozzle. We determined the optimal hole design for trapping a bubble, hole arrangement, and voltage for efficient mixing, resulting in a four-fold increase in mixing efficiency compared to a single bubble arrangement. Subsequently, we propose a nozzle design for efficient mixing during bioprinting. The proposed nozzle design enabled the successful printing of line structures with a uniform mixture of different viscous bioinks, achieving a mixing efficiency of over 80% for mixing 0.5-1.0 wt% sodium alginate aqueous solutions. Additionally, acoustic stimulation had no adverse effects on cell viability, maintaining a high cell viability of 88% after extrusion. This study presents the first use of a bubble micromixer in 3D bioprinting, demonstrating gentle yet effective multi-ink mixing. We believe this approach will broaden 3D printing applications, particularly for constructing functional structures in 3D bioprinting.

Computational fluid dynamics (CFD) simulation modeling for the cultivation of microalgal monoculture in axenic enclosed bubble column photobioreactor (BCPBR)

Researchers are more concerned with axenic-enclosed PBRs, where there is less or no chance of contamination during the production of biochemical and highly valuable metabolites, and monocultures of microalgae are being grown more frequently. It is a closed, manufactured vessel that aids in the photosynthesis of microalgal cells using artificial light or sunlight as the energy source. In this study, the bubble column PBR (BCPBR) was selected because it possessed some advantages over other PBRs for the growth of Chlorella vulgaris. The BCPBR system prevents contact between the enclosed microalgal cells and the environment, allowing the culturing of microalgae species that are difficult to grow in open pond systems. To compare BCPBR performance quantitatively, the efficient mixing expected in BCPBR, as discussed in the literature, was applied to the CFD model. The experimental results observed during the cultivation of C. vulgaris with restaurant wastewater (RWW) in BCPBR clearly showed better mixing, high growth, and improved treatment efficiency. CFD analysis was conducted on the evolution of bubbles in the BCPBR. The Pressure-Implicit with Splitting of Operators (PISO) pressure correction method is used for velocity and pressure coupling. A geo-reconstruct approach is used to construct the interface, and a second-order upwind calculation technique is used to determine the flow parameters. Therefore, CFD simulation in this study will contribute to the following aspects: (i) the volume fraction contours and velocity contours are going to validate the experimental study as the homogenous mixing favors the growth and productivity, (ii) To study how the size of the nozzle and inlet velocity affect the turbulence generated by bubbles in a BCPBR to identify the optimal nozzle size and velocity for the required turbulence.

NUMERICAL AND EXPERIMENTAL RESEARCH ON THE DI-CI ENGINE PERFORMANCE CHARACTERISTICS UNDER LPG - DIESEL DUAL FUEL COMBUSTION MODE

Properties of Liquefied Petroleum Gas (LPG) are suitable as an alternative fuel for internal combustion engines. This work aims to combine both numerical optimization analysis of LPG injector placement angle and subsequent experiment with selected mounting injector angle to investigate the effects of using LPG as a parallel-partial substitute fuel with diesel fuel under dual-fuel combustion mode. An electronic injection fuel control system was applied to the modified intake manifold to generate the appropriate LPG injection. Three mounting angle injector positions including 450, 900 and 1350 in the upstream direction of intake air have been defined by Ansys Fluent to take into account efficient LPG-air mixing. Then, the experiment was conducted with LPG-diesel dual-fuel combustion mode (DFC mode) and compared to entirely diesel combustion mode as baseline data. Different load conditions ranging from idle to 4.0 kW were imposed at a constant engine speed of 1700rpm. The obtained results revealed that the injector’s mounting angle position by 45 opposite to the intake air flow showed the correlation with the calculated LPG-air ratio in dual fuel combustion reaction. In DFC mode, the brake thermal efficiency (BTE) decreased on average by 4.6% and the LPG substitution rate gradually decreased while brake-specific fuel consumption (BSFC) increased for all engine loads. The exhaust temperature in the dual-fuel combustion mode was found to be higher than that of full diesel fuel mode at low loads (less than 2.5 kW) and began to decrease at higher loads.

Gas-rigid-flexible compound blade coupling enhanced experimental study on chaotic mixing of multiphase flow

Efficient fluid mixing is essential for process intensification. This study proposes a new method in which gas-rigid-flexible composite blades are coupled to enhance chaotic mixing in multiphase flow systems. The rigidity and flexibility of the blades were adjusted by intermittent gas injection, which increased the effectiveness of mixing of the liquid-liquid two-phase fluid. This study investigates the influence of different process parameters on the mixing efficiency and quantifies the chaotic characteristics of fluid mixing through pressure-time series analysis of multiscale entropy and the 0–1 test. A high-speed camera recorded the bubble movement in the flow field, while particle image velocimetry (PIV) revealed the enhancement of the properties of the flow field in the system due to the suspended motion of the particles. Using suitable process parameters, gas-rigid-flexible composite blade coupling significantly enhanced the mixing effect, where the mixing time of the G-RFCP system was reduced by 1.42 times compared to that of the CP system. Bubble motion, deformation, and rupture enhanced the mechanical agitation, increasing the intensity of the turbulence and chaotic behaviour. Flow-field analysis indicated a three-fold increase in the vorticity and a 1.04-fold increase in the velocity difference for the G-RFCP system compared with those of the CP system. This study provides theoretical and experimental foundations for understanding chaotic mixing in liquid-liquid two-phase fluids.

Mass transfer and mixing performance in jet-to-counterflow micromixer

As an important component of the fine organic microreaction system, micromixers can realize efficient mixing of different fluids within a short distance. In spite of great progress in micromixer design for high mixing performance over the last decade, micromixers are limited by the narrowness of channels, making it impossible to operate at high throughputs. Here, we propose a novel jet-to-counterflow (JTC) micromixer, which is based on the offset fluctuation jet mechanism to build a jet-to-counterflow zone and an annular liquid film zone to promote the rapid and efficient mixing of fluids. Micro-PIV and dye visualization experiments are used to investigate the internal flow behaviors and mixing performance of the JTC micromixer. The results show that in the “jet-to-counterflow mixing zone”, the jet undergoes the transition of three flow regimes i.e. “no offset jet − stable offset jet − fluctuating offset jet” with the increase of Re under the effects of wall effect and fluid inertia. When Re = 100, the fluctuating offset jet enhances the internal perturbation, which promotes the mixing index of the micromixer within 3 mm up to 78 %. In addition, the fluctuating offset jet intensifies the disturbance of the fluid flow in the annular liquid film zone, which further enhances the fluid mixing. A mixing efficiency of 97 % is achieved in mixing experiments over flow rates ranging from 0.075 – 37.66 mL/min−1. Our results demonstrate that fluctuating offset jet can be used to enhance microfluidic internal perturbation and mixing, which provide new insights into the design of novel micromixers.

Periodic Flows in Microfluidics.

Microfluidics, the science and technology of manipulating fluids in microscale channels, offers numerous advantages, such as low energy consumption, compact device size, precise control, fast reaction, and enhanced portability. These benefits have led to applications in biomedical assays, disease diagnostics, drug discovery, neuroscience, and so on. Fluid flow within microfluidic channels is typically in the laminar flow region, which is characterized by low Reynolds numbers but brings the challenge of efficient mixing of fluids. Periodic flows are time-dependent fluid flows, featuring repetitive patterns that can significantly improve fluid mixing and extend the effective length of microchannels for submicron and nanoparticle manipulation. Besides, periodic flow is crucial in organ-on-a-chip (OoC) for accurately modeling physiological processes, advancing disease understanding, drug development, and personalized medicine. Various techniques for generating periodic flows have been reported, including syringe pumps, peristalsis, and actuation based on electric, magnetic, acoustic, mechanical, pneumatic, and fluidic forces, yet comprehensive reviews on this topic remain limited. This paper aims to provide a comprehensive review of periodic flows in microfluidics, from fundamental mechanisms to generation techniques and applications. The challenges and future perspectives are also discussed to exploit the potential of periodic flows in microfluidics.

Direct numerical simulation of dispersion and mixing in gas–liquid Dean-Taylor flow with influence of a 90° bend

Gas-liquid capillary flow finds widespread applications in reaction engineering, owing to its ability to facilitate precise control and efficient mixing. Incorporating compact and regular design with Coiled Flow Inverter (CFI) enhances process efficiency due to improved mixing as well as heat and mass transfer leading to a narrow residence time distribution. The impact of Dean and Taylor flow phenomena on mixing and dispersion within these systems underscores their significance, but is still not yet fully understood. Direct numerical simulation based on finite element method enables full 3D resolution of the flow field and detailed examination of laminar flow profiles, providing valuable insights into flow dynamics. Notably, the deflection of flow velocity from the center axis contributes is followed by tracking of particle with defined starting positions, aiding in flow visualization and dispersion characterization. In this CFD study, the helical flow with the influence of the centrifugal force and pitch (Dean flow) as well as the capillary two-phase flow (Taylor bubble) is described and characterized by particle dispersion and related histograms. Future prospects in this field include advancements in imaging techniques to capture intricate flow patterns, as well as refined particle tracking methods to better understand complex flow behavior.