Mixing Enhancement Research Articles

Synergistic Solvation as the Enhancement of Local Mixing.

Mixing two solvents can sometimes make a much better solvent than expected from their weighted mean. This phenomenon, called synergistic solvation, has commonly been explained via the Hildebrand and Hansen solubility parameters, yet their inability in other solubilization phenomena, most notably hydrotropy, necessitates an alternative route to elucidating solubilization. While, recently, the universal theory of solubilization was founded on the statistical thermodynamic fluctuation theory (as a generalization of the Kirkwood-Buff theory), its demand for experimental data processing has been a hindrance for its wider application. This can be overcome by the solubility isotherm theory, which is founded on the fluctuation theory yet reduces experimental data processing significantly to the level of isotherm analysis in sorption. The isotherm analysis identifies the driving force of synergistic solvation as the enhancement of solvent mixing around the solute, opposite in behavior to hydrotropy (characterized by the enhancement of demixing or self-association around the solute). Thus, the fluctuation theory, including its solubility isotherms, provides a universal language for solubilization across the historic subcategorization of solubilizers, for which different (and often contradictory) mechanistic models have been proposed.

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.

Experimental and numerical assessment and performance optimization of a novel T-arrow microfluidic device to mix two fluids with different thermophysical properties

Micromixers are critical parts of integrated microfluidic systems and their performance improvement has been a crucial problem for many investigators. Since the mixing enhancement in passive micromixers is hindered by the low-Reynolds number regime, multiple inlets have been recommended to create chaotic advection and improve the mixing quality. In this paper, a novel T-arrow micromixer is introduced to augment the mixing index (MI) of two liquids with different thermophysical properties. Numerical and experimental investigations are carried out by changing the distance between the inlets (a), the angle of the arrow-shaped inlet (α), the velocity ratio (VR), and the width-to-height aspect ratio (AR). Five optimization algorithms are also utilized to optimize the micromixer performance to achieve the most appropriate geometrical characteristics. It is found that MI is enhanced significantly by adding a Y-type inlet compared to a T-shaped mixer. The results demonstrate that while MI declines with a, there are optimal values for α, VR, and AR. Besides, parallel optimization of MI and pressure drop recommends two optimal micromixers with mixing energy cost (MEC) of 2841 Pa and 3370 Pa.

Mechanism analysis and mixing characterization of variable-speed mechanical mixing enhancement

Abstract In response to the observed phenomenon of poor fluid mixing within the reactor, this study proposes a novel mixing method to enhance fluid mixing efficiency. In this study, numerical simulation and purification tests were carried out for the purification of zinc sulfate solution. Numerical simulations were conducted to compare the effects of variable-speed stirring and uniform-speed stirring on mixing efficiency, considering both momentum transfer process and mass transfer process. The purification test further demonstrated a significant improvement in the reaction rate under variable-speed stirring, as evidenced by the analysis of purification efficiency and microscopic morphology. It was elaborated that the enhancement mechanism of variable-speed stirring involved disrupting the periodic order structure in the tank, leading to the generation of a multi-scale vortex that increased stirring kinetic energy to form a shear force. This force contributed to reducing the velocity slip between the impurity ions and zinc particles, consequently decreasing reaction time and enhancing purification rate. The results indicated that sinusoidal stirring yielded the most effective mixing. When implemented in practical production settings, it enhanced dimensionless mixing efficiency by 24.83 % compared to the homogeneous stirring system. Additionally, it reduced reaction time by 15.47 % and decreased mixing energy per unit volume by 32.38 %, while simultaneously lowering energy consumption by 24.77 %.

Numerical investigation of induction of chaotic micromixing via vibration switching

Enhanced mixing in microfluidic systems is necessary in many applications such as chemical processing, biological assays, and diagnosis. We are developing a microfluidic system to efficiently mix minute reagents (down to several microliters) using vibration-induced flow (VIF), in which a net flow is generated around a micropillar by applying periodic vibration. In this study, we numerically investigate the enhancement in chaotic mixing using the VIF technique and periodic switching of vibrations. By extending our previous numerical simulation model, we investigate the flow field and trajectories of fluid particles in three-dimensional space. We demonstrate that chaotic advection characteristics can be observed by periodically switching the vibrational direction of a substrate using simple cylindrical pillars. In addition, using an appropriate interval for switching the vibration axes yields better mixing performance. The extent of chaotic advection is evaluated quantitatively using the Lyapunov exponent considering various vibration parameters, such as the vibration amplitude, separation distance between each pillar and pillar shape. The flow field induced by a large-amplitude and sharp-edged wall pillar provides excellent mixing results. Thus, VIF is successfully applied to obtain an efficient mixing strategy with the aid of the chaotic theory.

High-Grade Astrocytoma with Piloid Features: A Dual Institutional Review of Imaging Findings of a Novel Entity.

High-grade astrocytoma with piloid features (HGAP) is a recently identified brain tumor characterized by a distinct DNA methylation profile. Predominantly located in the posterior fossa of adults, HGAP is notably prevalent in individuals with neurofibromatosis type 1. We present an image-centric review of HGAP and explore the association between HGAP and neurofibromatosis type 1. Data were collected from 8 HGAP patients treated at two tertiary care institutions between January 2020 and October 2023. Demographic details, clinical records, management, and tumor molecular profiles were analyzed. Tumor characteristics, including location and imaging features on MR imaging, were reviewed. Clinical or imaging features suggestive of neurofibromatosis 1 or the presence of NF1 gene alteration were documented. The mean age at presentation was 45.5 years (male/female = 5:3). Tumors were midline, localized in the posterior fossa (n = 4), diencephalic/thalamic (n = 2), and spinal cord (n = 2). HGAP lesions were T1 hypointense, T2-hyperintense, mostly without diffusion restriction, predominantly peripheral irregular enhancement with central necrosis (n = 3) followed by mixed heterogeneous enhancement (n = 2). Two NF1 mutation carriers showed signs of neurofibromatosis type 1 before HGAP diagnosis, with one diagnosed during HGAP evaluation, strengthening the HGAP-NF1 link, particularly in patients with posterior fossa masses. All tumors were IDH1 wild-type, often with ATRX, CDKN2A/B, and NF1 gene alteration. Six patients underwent surgical resection followed by adjuvant chemoradiation. Six patients were alive, and two died during the last follow-up. Histone H3 mutations were not detected in our cohort, such as the common H3K27M typically seen in diffuse midline gliomas, linked to aggressive clinical behavior and poor prognosis. HGAP lesions may involve the brain or spine and tend to be midline or paramedian in location. Underlying neurofibromatosis type 1 diagnosis or imaging findings are important diagnostic cues.

Novel spacer geometries for membrane distillation mixing enhancement

Membrane distillation is an emerging promising desalination method that requires further improvement in order to become industrially viable. Due to the fact that evaporation is the primary process in membrane distillation, one strategy to boost membrane permeate flux is to optimize the energy supply to the water interface by increasing mixing in the hot channel via the use of optimized spacers. Contemporary spacer designs predominantly induce turbulence, resulting in elevated pumping energy requirements. This study introduces novel spacer geometries, inspired by industrial mixer designs, to surmount the limitations of conventional spacer configurations. The mixing efficiency, thermal performance, and pressure drop induced by the two novel geometries are studied and compared to those of commonly utilized spacer designs. It is confirmed, that the first of these novel geometries significantly enhances mixing, whereas the other causes a lower pressure drop and appears to be a viable solution when a spacer is a necessary structural component. In the course of the analysis, it is also shown that the coefficient of variation coupled with the Nusselt number at the membrane can be used to assess spacers' performance.

Influence of passive strut on the mixing and combustion performance enhancement

The scramjet engine is one of the possible means of reaching supersonic speed using airbreathing engines. As the inflow of air is at supersonic speed, proper mixing and combustion is a challenge. Researchers have used multi-strut arrangements to address the problem. However, the additional supply of fuel from multiple struts with inefficient mixing and combustion leads to losses in terms of fuel and efficiency. Alternatively, the multi-strut configuration could be used to improve the combustion and mixing efficiency passively. In the present investigation, two strut configurations, a fuel injection strut, and a passive strut, have been used. The computational study was done by solving steady Reynolds averaged Navier-Stokes (RANS) equations along with the Shear Stress Transport (SST) k-ω turbulence model, species, and ideal gas equation. Eddy dissipation model was used to solve reacting flow. The introduction of a passive strut in the wake of the fuel injection strut leads to vortices upstream and downstream of the passive strut. These vortices were observed to be responsible for enhancing the mixing and combustion. It was found that judicious placement of the passive strut in the wake of the combustion zone can enhance both the mixing as well as combustion efficiency with minimal loss in total pressure.

Torque generation using synthetic jet actuators

This article presents a novel method of utilizing the thrust generated by synthetic jet actuators to generate torque. Piezoelectric-based synthetic jet actuators were used to create a device with two isolated cavities and orifices. Weight balance and hotwire anemometry were used to quantify the thrust generated by the synthetic jet actuator. Each orifice provides a maximum thrust of 0.15gf, thereby generating a net maximum torque of 17.17gf mm. The torque generated can be used to produce a rotary motion. Such a novel device may be useful where a high-momentum rotary jet may be employed for heat transfer and mixing enhancement.

MTIE-Net: Multi-technology fusion of low-light image enhancement network.

Images obtained in low-light scenes are often accompanied by problems such as low visibility, blurred details, and color distortion, enhancing them can effectively improve the visual effect and provide favorable conditions for advanced visual tasks. In this study, we propose a Multi-Technology Fusion of Low-light Image Enhancement Network (MTIE-Net) that modularizes the enhancement task. MTIE-Net consists of a residual dense decomposition network (RDD-Net) based on Retinex theory, an encoder-decoder denoising network (EDD-Net), and a parallel mixed attention-based self-calibrated illumination enhancement network (PCE-Net). The low-light image is first decomposed by RDD-Net into a lighting map and reflectance map; EDD-Net is used to process noise in the reflectance map; Finally, the lighting map is fused with the denoised reflectance map as an input to PCE-Net, using the Fourier transform for illumination enhancement and detail recovery in the frequency domain. Numerous experimental results show that MTIE-Net outperforms the comparison methods in terms of image visual quality enhancement improvement, denoising, and detail recovery. The application in nighttime face detection also fully demonstrates its promise as a pre-processing means in practical applications.

Mixing enhancement of transverse jets in supersonic crossflow using an actively controlled novel fluidic oscillator

This study investigates the fluid dynamics and mixing characteristics of an oscillating sonic jet injected into a supersonic cross flow of Mach 2.1 using experimental and computational techniques. The oscillating jet is produced by a novel fluidic oscillator, which consists of a primary rectangular duct that expands into an outer duct with sudden expansion. Control jets are injected in the lateral direction from the side walls of the sudden expansion in an out-of-phase manner to oscillate the injected jet in the spanwise direction of the crossflow. Experimental and numerical investigations based on wall static pressure and mass fraction fluctuations, respectively, revealed that the injected jet oscillation frequency matches the control jet frequency. The iso-surface of lambda-2 criterion showed the presence of various dominant vortex structures, such as counter-rotating vortex pairs, horseshoe vortex, sidewall vortices, and trailing vortices. Helicity contour plots showed that the streamwise vortices oscillate in the spanwise direction with the control strategy and promote the spread of the injected jet in the spanwise direction. The spatiotemporal reconstruction (z–t plot) of the density gradients at a particular streamwise location revealed that the bow shock produced by the interaction of the injected jet and the crossflow oscillates with the actuation of the control strategy. The power spectral density of the z–t plot revealed that the shock wave oscillation frequency matches the control jet frequency. The oscillating jet produced by the control strategy showed significant mixing enhancement in supersonic crossflow compared to a simple rectangular injection.

Experimental and numerical study on flow field characteristics of a combustion chamber with double-stage counter-rotating swirlers

To discover a good predictive turbulent model and reveal the mechanism of turbulent mixing enhancement, a new combustion chamber equipped with a double-stage counter-rotating swirler with vane angles of both stages as 45° is proposed and the flow field characteristics are explored by combining 2D-PIV experiment and Reynolds averaged numerical simulation (RANS). Firstly, the performance of various turbulence models in predicting the flow field characteristics is evaluated by comparing them with experimental results. The study concludes that the RNG k-ε turbulence model exhibits superior performance in predicting velocity distribution, recirculation zone length, and vorticity distribution. Hence, it is selected to analyze the influence of the Reynolds number (Re) of swirlers on the flow field characteristics. In this study, seven Re numbers ranged from 5425 to 54,245 were selected for analysis. Through comparison, it appears that changes in Re number have a strengthening effect on the flow field at various locations, including the recirculation zone, wall surface, and shear layer. This suggests that Re number has an influence on turbulence or boundary layer behavior. Interestingly, there seems to be a critical value for Re number of 21,698, which may be related to a competition between Re number and wall effects.

Enhancing thermal mixing of supercritical water through a confined co-flowing planar jet

Previous studies have reported that the thermal mixing of supercritical water (SCW) would be inhibited by the density gradient in jet flow. The confined co-flowing planar jet which has one central inlet and two outer inlets is expected to enhance thermal mixing through stronger turbulent entrainment induced by double mixing layers. Direct numerical simulations (DNS) of planar jet of supercritical water (653–843 K, 25 MPa) are performed. The effects of the density ratio ρr (1.1, 3, 6) between jet and ambient fluids, the Reynolds number based on the density, velocity, diameter, and viscosity of central inlet Rein=ρinUinDin/μin (1000–4000), and the buoyancy on thermal mixing properties are investigated. We find that increasing ρr results in the decay of turbulence near the double mixing layers and the attenuation of thermal mixing. The self-similar behavior for co-flowing planar jet of supercritical water can be more likely to achieve for the mean field than for the turbulence field. While increasing Rein results in the amplification of turbulence production in the far-field region due to the vortex stretching mechanism induced by larger velocity gradient, the enhancement of thermal mixing is insignificant. The gravity wave along the normal direction leads to density stratification and inhibition of turbulent mixing near the mixing layers when Rein less than 2000. The gravity effect can be neglected when Rein greater than 2000 due to the increasing turbulence production. Finally, we find that the enhancement of thermal mixing can be achieved by increasing the turbulent intensity of outer inlets.

Hydrodynamic cavitation of nematic liquid crystal in Stokes flow behind bluff body with different shapes in microchannel

Hydrodynamic cavitation, which occurs when the local pressure is below the saturated vapor pressure in hydrodynamic flow, is ubiquitous in fluid dynamics and implicated in a myriad of industrial and biomedical applications. Although extensively studied in isotropic liquids, corresponding investigations in anisotropic liquids are largely lacking. In this paper, the hydrodynamic cavitation in the bluff body bypass flow of nematic liquid crystal 5CB in the microchannel is experimentally investigated. By 5CB, we mean the thermotropic liquid crystal 4′-pentyl-4-biphenylcarbonitrile. When the Reynolds number is in the range of 3 × 10−4 < Re < 1.2 × 10−3, a special flow phenomenon behind the bluff body is observed, namely, the disclination loop. The critical Reynolds number of cavitation inception varies with the shape of the bluff body, while the lowest value corresponds to the triangular bluff body. The hydrodynamic cavitation occurs in the Stokes flow regime with the Reynolds number significantly lower than 0.1 for all bluff bodies. There is a close relation between the oscillation behavior of cavitation domains and the structure of the bluff body. In addition, the pressure difference between the inlet and outlet of the microchannel shows linear relation with the Reynolds number rather than the quadratic relation for isotropic fluids, which proves the presence of shear thinning in the flow of nematic liquid crystals. The study in this paper on the hydrodynamic cavitation of nematic liquid crystal can broaden the research on providing new approaches for the enhancement of fluid mixing and heat transfer in microfluidic chips.

Numerical Analysis for Effects of Grid Spacer Vane on Flow-Thermal Characteristics of Two Phase Flow in a 5×5 Rod Bundle

Numerical Analysis for Effects of Grid Spacer Vane on Flow-Thermal Characteristics of Two Phase Flow in a 5×5 Rod Bundle

Symmetry-Breaking-Induced Internal Mixing Enhancement of Droplet Collision

Binary droplet collision is a basic fluid phenomenon for many spray processes in nature and industry involving lots of discrete droplets. It exists an inherent mirror symmetry between two colliding droplets. For specific cases of the collision between two identical droplets, the head-on collision and the off-center collision, respectively, show the axisymmetric and rotational symmetry characteristics, which is useful for the simplification of droplet collision modeling. However, for more general cases of the collision between two droplets involving the disparities of size ratio, surface tension, viscosity, and self-spin motions, the axisymmetric and rotational symmetry droplet deformation and inner flow tend to be broken, leading to many distinct phenomena that cannot occur for the collision between two identical droplets owing to the mirror symmetry. This review focused on interpreting the asymmetric droplet deformation and the collision-induced internal mixing that was affected by those symmetry breaking factors, such as size ratio effects, Marangoni Effects, non-Newtonian effects, and droplet self-spin motion. It helps to understand the droplet internal mixing for hypergolic propellants in the rocket engineering and microscale droplet reactors in the biological engineering, and the modeling of droplet collision in real combustion spray processes.

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.

Passive Mixing and Convective Heat Transfer Enhancement for Nanofluid Flow across Corrugated Base Microchannels

Vortex generators and pin fins are conventionally used to deliver fluid mixing and improved convective heat transfer. The increased pressure loss following a fractional increase in heat transfer, as well as the complex manufacturing design, leave room for improvement. The present work proposes a novel diverging–converging base corrugation model coupled with vortex generation using simple geometrical modifications across rectangular microchannels to ensure a superior performance. The Nusselt number, friction factor, and flow phenomenon were numerically studied across a Reynolds number range of 50–1000. The optimum cross-section of the microchannel-generating vortices was determined after thorough study, and base corrugation was further added to improve heat transfer. For the vortex–corrugation modeling, the heat transfer enhancement was verified in two optimized cases: (1) curved corrugated model, (2) interacting corrugated model. In the first case, an optimized curve generating Dean vortices was coupled with base corrugation. An overall increase in the Nusselt number of up to 32.69% and the thermal performance of “1.285 TPF” were observed at a high Reynolds number. The interacting channels with connecting bridges of varying width were found to generate vortices in the counter-flow configuration. The thermal performance of “1.25 TPF” was almost identical to the curved corrugated model; however, a major decrease in pressure, with a loss of 26.88%, was observed for this configuration.

Mixing performance improvement of T-shaped micromixer using novel structural design of channel and obstacles

Micromixers play a crucial role in mixing different fluids within microfluidic systems. Therefore, it is essential to analyze parameters, such as dimensional characteristics, mixing length, micromixer efficiency, and the mixing process, to enhance their performance. In this study, we examine various T-shaped micromixer designs, including triangular, rectangular, and trapezius configurations, to evaluate their mixing performance and compare them with a corresponding circular micromixer. Additionally, we investigate the effects of obstacles, varying their angles and distances, in the circular micromixer to determine trends in mixing improvement across cases. The micromixers have minimal dimensions, resulting in laminar flow. By comparing the outcomes of the proposed cases with those without obstacles, we find that the triangular micromixer exhibits the highest mixing performance with 8.3% improvement with respect to the circular case. Furthermore, while the rectangular case initially displayed the weakest performance at lower Reynolds numbers, a discernible enhancement was observed as Reynolds numbers increased. This improvement was attributed to the emergence of vortices at Re = 20. The performance showed a substantial increase, reaching a coefficient of 0.98 at Re = 40, a value closely approaching that of the triangular case. Among the three obstacles, one obstacle is varied at four different angles (0°, 60°, 90°, and 120°), while the other two obstacles remain fixed at distances of 150 and 200 μm. In cases involving obstacles, a noteworthy enhancement was evident when compared to cases without obstacles. In these cases, the introduction of obstacles resulted in a remarkable 34% improvement in the mixing index compared to obstacle-free scenarios. This improvement can be attributed to the observed flow behavior, where the formation of vortices, even at low Reynolds numbers, emerges as a key factor contributing to this enhancement. In addition, we assess the mixing enhancement to identify the most efficient arrangement of obstacles. The results indicate angles of 90° and 120° are more effective than others in improving mixing proficiency.

Shock induced variable density flows in the vacuum microchannel: I. medium laser fluence

Laser-matter interactions with metal target cause plasma explosion and shock accelerated variable density flow instabilities in the Semiconfined Configuration (SCC). Their study gives deeper insight into the flow instabilities present in all microchannel devices. Blast wave motion along the SCC microchanel causes the Kelvin–Helmholtz (KH) instability and formation of vortex filaments for the critical Reynolds number. Appearing in all shear layers—it affects the fluid transport efficiency. Shear layer acceleration causes a Raleigh-Taylor instability (RTI). Oriented bubble growth by discrete merging indicates anisotropic RTI mixing. Similar RTI flame instability appears in the conversion of chemical energy into electricity affecting microcombustion efficiency. Another case of anisotropic RTI is the flow boiling for cooling of chips and microelectronic devices. The RTI boiling which appears for the critical heat flux is based on rising surface vapor columns (oriented bubble growth) with liquid counterflow (spike prominences) for the critical wavelength at density interface. The RT bubble merging graph trees determine turbulent mixing which affects the heat transfer rates. Bottom-wall turbulent flow in the SCC microchannel causes streaks of the low momentum fluid and formation of hairpin vortex packets with lattice organization. This makes possible to quantify parameters responsible for the evolution of hairpin vortex packets in the microchannel devices. Appearing from the low to the high Reynolds numbers they affect the transport properties, control of the fluid motion, enhancement of mixing, or the separation of fluids. Fluid particle ejecta—thin supersonic jets - evolve into long needle-like jets which start spiraling, helical pairing and swirling in the field of thermal gradients. Such instabilities appear in the microcombustion flame instability and in the space micropropulsion systems. Oscillating and spiral flames appear in the presence of thermal gradient in the microchannel, due to the combined effects of thermal gradient fields and the mixture flow rates.