Mixing Homogeneity Research Articles

Impact of Horizontal Model Resolution on Mixing and Dispersion in the Northeastern Gulf of Mexico

AbstractIn this paper, the importance of model horizontal resolution in mixing and dispersion is investigated by comparing two data‐assimilative high‐resolution simulations (4 and 1 km), one of which is submesoscale‐permitting. By employing both Eulerian and Lagrangian metrics, upper‐ocean differences between the mesoscale‐resolving and submesoscale‐permitting simulations are examined in the northeastern Gulf of Mexico, a region of high mesoscale and submesoscale activity. Mixing in both simulations is explored by conducting Lagrangian experiments to track the generation of Lagrangian coherent structures (LCSs) and their associated transport barriers. Finite‐time Lyapunov exponent (FTLE) fields show higher separation rates of fluid particles in the submesoscale‐permitting case, which indicate more vigorous mixing with differences being more pronounced in the shelf regions (depths ≤ 500 m). The extent of the mixing homogeneity is examined using probability density functions (PDFs) of FTLEs with results suggesting that mixing is heterogeneous in both simulations, but some homogeneity is exhibited in the submesoscale‐permitting case. The FTLE fields also indicate that chaotic advection dominates turbulent mixing in both simulations regardless of the horizontal resolution. In the submesoscale‐permitting experiment, however, smaller scale LCSs emerge as noise‐like filaments that suggest a larger turbulent mixing component than in the mesoscale‐resolving experiment. The impact of resolution is then explored by investigating the spread of oil particles at the location of the Deepwater Horizon oil spill.

Ferromagnetic nanotracers based on Fe and Co oxides: synthesis and their role in assessing the quality of mixing liquid feeds

Ensuring homogeneity of the feed mixing is crucial for animal health and productivity. The growing complexity of feed formulations increases the need for uniform mixtures, particularly for young animals, where balanced feed significantly affects growth and consumption. Ferromagnetic microtracers, developed by MicroTracers Inc., are used to monitor mixing uniformity in dry feed production. These microtracers, including iron-based types, are effective due to their magnetic properties, facilitating detection, and separation. However, they are less suitable for liquid feeds, leading to the development of magnetic nanotracers based on the iron oxide for liquid feed applications. Nanoparticle Tracking Analysis (NTA) is used to measure the size and distribution of nanoparticles in liquid feeds, ensuring thus effective mixing. The stability and uniform distribution of magnetic nanoparticles are crucial, with various surfactants, such as dimethylamine salt of oleic acid (DMAOA) and ammonium oleate, influencing particle size and aggregation. DMAOA provides better dispersion and stability, essential for quality control in feed production. The concentration of cobalt in nanoparticles FexCoyOz was determined by a modified spectrophotometric method.

Evaluation of powder mixing homogeneity for laser-directed energy deposition (L-DED) of functionally graded materials

Evaluation of powder mixing homogeneity for laser-directed energy deposition (L-DED) of functionally graded materials

A novel static mixer for blending hydrogen into natural gas pipelines

A novel static mixer is designed specifically to blend hydrogen into natural gas pipelines, and its effectiveness is validated by numerical simulation method. Firstly, the structural model of the proposed static mixer model for hydrogen-methane blending is introduced, and the evaluation indicators are defined. Secondly, the computational fluid dynamic model for the mixing process is established based on the Large Eddy Simulation(LES) method, and the accuracy of the numerical results is validated against the experimental data of a benchmark gas mixing model. Subsequently, using LES, effects structural parameters (angle and height of trapezoidal baffle, number of mixing elements, and spacing and installation distance of mixing elements) and flow parameters (main flow velocity and hydrogen blending ratio) on the mixing homogeneity and pressure drop of the static mixer are investigated systematically to explore the optimal design and operational conditions. The numerical results showed that the static mixer can significantly improve the mixing efficiency of hydrogen and natural gas with acceptable pressure loss. In the range of flow conditions concerned, a best performance of mixing could be obtained by installing the mixer at a distance of 3D (D is the diameter of the natural gas pipeline) downstream the blending point, setting the spacing between mixing elements as 1D and employing four mixing elements. Finally, the underlying physics of mass transportation are analyzed based on the vortex structures generated by the mixer.

Singular integrals with product kernels associated with mixed homogeneities and Hardy spaces

Singular integrals with product kernels associated with mixed homogeneities and Hardy spaces

How particle size reduction improves pectin extraction efficiency in carrot pomace

Particle size reduction of raw materials is suggested to improve the extraction efficiency of pectin. However, conflicting reports have been published in literature, questioning to what extent particle size reduction is beneficial. This study investigated the role of reduced particle size and altered microstructure on the extraction efficiency and structure of pectin obtained from carrot pomace. High shear mixing and high pressure homogenization at different pressure levels (5–100 MPa) resulted in samples with a median particle diameter between 563 μm and 68 μm. Particle size reduction was shown to increase the pectin extraction yield. High shear mixing followed by high pressure homogenization, more specifically, resulted in a 50% increase of the pectin yield, resulting in the extraction of 62% of the pectin content. Interestingly, the extent to which the extraction yield was improved was more related to changes in the microstructure than to the particle size as such, with tissue disruption leading to more outspoken changes in pectin extractability than further disintegration of cell fragments. The additional fraction of extracted pectin is thought to originate from the middle lamella rather than the primary cell wall. Overall, particle size reduction did not alter the molecular structure of the extracted pectin.

A draft tube to improve mixing in swirling flow-based solid–liquid mixing reactors

The Swirl Flow Reactor (SFR) is a recently proposed specially designed reactor to address challenges of solid–liquid mixing for high-temperature and high-pressure processes. Previous research has shown that the mixing homogeneity of the SFR is not yet optimal and has still potential for improvement. To enhance the homogeneity of the SFR and to optimize the utilization of the previously identified Precessing Vortex Core at the nozzle, an improvement is proposed by the inclusion of a draft tube in the reactor center. Computational Fluid Dynamics is used to study the flow structure, particle distribution, and large-scale coherent structures in the SFR. The improved SFR has been validated for its more homogeneous mixing, where the homogeneity is improved from 0.945 for the original reactor to 0.991 in the new proposed design. Also, the influence of the draft tube on the fluctuating velocities and turbulence within the improved SFR has been indicated. In addition, Spectral Proper Orthogonal Decomposition (SPOD) is used to identify and reconstruct the coherent structures in the reactor. A flattened double-layer helical precessing vortex core (PVC) and its second-order harmonic at frequencies of 35.8 Hz and 71 Hz have been identified, which introduce extra large scale mixing near the nozzle of the reactor.

Active-mixing printhead for on-the-fly composition adjustment of multi component materials in Direct Ink Writing

Multi-Material Additive Manufacturing (MMAM) enables the grading of material properties and the integration of functions within printed parts. While most MMAM methods are limited to process single-component or pre-mixed multi-component materials, the in-process mixing and extrusion of multi-component materials enables innovative material properties and use cases. When processing liquid multi-component materials, the individual component streams need to be homogenized in-process, but the required volume in conventional passive mixing hinders rapid transitions in material composition. In this paper, a two component printhead is presented which combines an active mixing approach with a continuous composition adjustment for a third additive. The approach to control the mixing composition is to influence the hydrodynamic equilibrium of individual material streams before merging them near the point of extrusion. The printhead’s functionality is verified in terms of mixing homogeneity and transition speed between material compositions.

Mixing and inter-scale energy transfer in Richtmyer–Meshkov turbulence

This work investigates the compressible turbulence induced by Richtmyer–Meshkov (RM) instability using high-resolution Navier–Stokes simulations. Special attention is paid to the characteristics of RM turbulence including the mixing width growth, the turbulent kinetic energy (TKE) decay, the mixing degree, inhomogeneity and anisotropy. Three distinct initial perturbation spectra are designed at the interface to reveal the initial condition imprint on the RM turbulence. Results show that cases with initial large-scale perturbations present a stronger imprint on statistical characteristics and also a quicker growth of mixing width, whereas cases with small-scale perturbations present a faster TKE decay, greater mixing level, higher isotropy and homogeneity. A thorough analysis on the inter-scale energy transfer in RM turbulence is also presented with the coarse-graining approach that exposes the two subfilter-scale (SFS) energy fluxes (i.e. deformation work and baropycnal work). A strong correlation between the nonlinear model of baropycnal work (Fluids, 4(2), 2019) and the simulation results is confirmed for the first time, demonstrating its potential in modelling the RM turbulence. Two primary mechanisms of baropycnal work (the straining and baroclinic generation processes) are explored with this nonlinear model. The evolutions of two SFS energy fluxes exhibit distinct behaviours at various filter scales, in different flow regions and under various flow motions (strain and rotation). It is found that all three cases share the common inter-scale energy transfer dynamics, which is important for modelling the RM turbulence.

Investigation of thermodynamic state evolution, phase transition and mixing of the hydrocarbon droplet in convective supercritical environments

Liquid alkane droplets transit to supercritical fluids under supercritical conditions. However, the subsequent thermodynamic state evolution, phase transition, and mixing in this case, which directly influences combustion in actual diesel engines, need further investigation. We studied the thermodynamic state evolution, phase transition, and mixing of n-heptane droplets in supercritical laminar nitrogen streams through a set of conservation equations. Non-ideal thermodynamic and transport properties were calculated to incorporate the dramatic variation of physical properties in the supercritical regime. We focus on the effects of Reynolds number, ambient pressure, and droplet size on the thermodynamic state evolution, phase transition and mixing of droplets. Results showed that increasing the Reynolds number can accelerate the evolution of thermodynamic states, which leads to the faster transition of droplets from the liquid phase and supercritical fluids to gas-phase mixtures. With the increased Reynolds number, the phase transition rate is increased and the mixing homogeneity is improved due to the enhanced mass transfer. Caused by the negative correlation between mass transfer and ambient pressure, in higher pressure, droplets after the supercritical transition require more time to transition from supercritical fluids to vapor-phase mixtures. Increasing ambient pressure inhibited the droplet phase transition process and deteriorated the mixing homogeneity, but no significant influence was shown on the droplet dynamic evolution process. Smaller droplets transition faster from liquid phase and supercritical fluids to vapor-phase mixtures. The faster thermodynamic state evolution and faster dynamic evolution process of the smaller droplet leads to its more rapid homogeneous mixing with ambient gasses, but the mode of dynamics is independent of the droplet size.

Optimization of simulation model adaptability and CFD of particles of Geldart‐B in a gas–solid fluidized bed for silicone monomer synthesis

AbstractThe flow characteristics of gas–solid in fluidized bed reactors constrain or promote the reaction process by affecting gas–solid mixing homogeneity, heat transfer timeliness, and fluidization stability. To improve the production efficiency of silicone monomers, this work shows a comparative analysis of the effects of geometric modelling in different dimensions, flow state, and the interphase exchange coefficient on the characteristics of particles of Geldart‐B in a gas–solid fluidized bed for silicone monomer synthesis based on two‐fluid models (TFM). The results of different dimensional simulations show that the third dimension plays an important role in the bubble behaviour and the particle volume fraction spatial distribution within the fluidization zone, and the three‐dimensional simulation results are closer to the experimental data, and the maximum average error of the simulation results is 4.52% lower than that of the two‐dimensional simulation results. Meanwhile, the flow model has a greater influence on the bubble behaviour during the flow process, whereas the interphase force model has little effect on the flow state of small‐diameter particles. However, for large‐diameter particles, the interphase force model is closely related to the bubble behaviour and the direction and size of the vortex, and the lift model prediction of bubble breakage and coalescence behaviours are higher than the experimental results from the power spectrum results. The inlet velocity has a greater effect on the formation of vortices near the wall; with the same inlet velocity, the more dispersed the particle distribution in the bed, and the more uniform the gas–solid mixing.

Enabling a novel solvent method on Albendazole solid dispersion to improve the in vivo bioavailability

Albendazole, a vital medication endorsed by the World Health Organization for combating parasitic infections, encounters a challenge stemming from its low solubility, significantly impeding absorption and bioavailability. Albendazole has near-insolubility in most organic solvents, so the solid dispersions of albendazole were predominantly using the fusion method. However, the solvent method could offer the advantage of achieving molecular-level mixing homogeneity. In this investigation, we incorporated the pH adjustment to prepare albendazole solid dispersion using a solvent method, which utilizes trace amounts of HCl in methanol, yielding notably enhanced albendazole solubility. Subsequently, carriers such as PEG6000/Poloxamer 188 (PEG: polyethylene glycol) and PVP K30/Poloxamer 188 (PVP: polyvinylpyrrolidone) were employed to create albendazole solid dispersions. Comprehensive characterization through dissolution rate analysis, PXRD (Powder X-ray diffraction), SEM (Scanning electron microscopy), DSC (differential scanning calorimetry), and pharmacokinetic (PK) studies in mice and rats was conducted. The findings indicate that the solid dispersion effectively transforms the crystalline state of albendazole into an amorphous state, resulting in significantly enhanced in vivo absorption and a 5.9-fold increase in exposure. Besides, the exposure increased 1.64 times of commercial albendazole tablets. Notably, PEG6000/Poloxamer 188 and PVP K30/Poloxamer 188 solid dispersions exhibited superior dissolution rates and pharmacokinetic profiles compared to commercially available albendazole tablets.

Numerical Study on Effect of Aggregate Moisture on Mixing Process.

During the concrete mixing process, the transition of aggregates from a dry to a moist state introduces a crucial dynamic that significantly influences particle interaction, consequently impacting mixing homogeneity. In this paper, based on the discrete element method, the effect of aggregate moisture on the mixing process of sand and stone was investigated. The interaction between dry particles was described by the Hertz-Mindlin model, while the interaction between wet particles was calculated by the linear cohesion model considering the liquid bridge force. Additionally, a functional relationship between the moisture content and the parameters of the linear cohesive contact model was established. The results show that the numerical method can be employed to simulate the mixing process. Notably, when the moisture content of pebbles ranges from 0% to 0.75% and that of sand ranges from 0% to 10.9%, the linear cohesion model is deemed suitable. The standard deviation of the mixing homogeneity of wet particles is lower than that of dry particles for short mixing time, indicating that a small amount of liquid enhances mixing homogeneity. However, moisture has no obvious effect on mixing homogeneity for a long mixing time. This nuanced understanding of the interplay between moisture, particle interactions, and mixing duration contributes valuable insights to optimize concrete mixing processes.

Characterization and Environmental Risk Assessment of Coal-based Solid Waste Towards Underground Backfilling

This study evaluated the feasibility of coal-based solid waste as a subsurface fill material based on its physicochemical properties and potential environmental risks. The results show that the special physical structure and the chemical composition of coal-based solid wastes are advantageous as filling materials. In terms of physical structure, the spheres improve the flowability and mixing homogeneity of the mixture, while lumps give stabilizing support; the special chemical compositions also improve the strength, durability and corrosion resistance of the filler. The contents of Cd, As, Cr, Cu, Ni and Co in coal-based solid waste are less directly harmful to the environment, but arsenic showed a relatively strong enrichment. Cd in coal gangue and desulfurized gypsum were medium or very high risk due to strong migration and bioavailability, respectively, while Co in desulfurized gypsum present a medium risk. Both coal gangue and desulfurized gypsum may contaminate the underground environment, the other materials pose less threat to the environmental. In engineering applications, attention should be paid to the main contaminant As, as well as Cd and Co because of their mobility and high bioactive fraction, to reduce potential environmental risk.

Solvothermal synthesis of porous FeOx–CeO2−y composite spheres with high mixing homogeneity

FeOx–CeO2−y composites with different homogeneities were synthesized by the solvothermal method, co-precipitation, and physical mixing. FeOx and CeO2−y in the composites synthesized by the solvothermal method and co-precipitation were homogeneously mixed at the nanometer scale, but physical mixing afforded heterogeneously agglomerated composites. The effects of the homogeneity of the composites were evaluated by probe reverse water-gas shift (RWGS) reaction. The improved homogeneity of FeOx and CeO2−y in the composites resulted in higher catalytic activity, product selectivity, and long-term stability in the RWGS reaction at 700 °C. The redox behavior of FeOx was enhanced by finely combined CeO2−y in the case of solvothermally prepared FeOx–CeO2−y, which exhibited excellent crystal structure stability. This study demonstrates the advantages of using the solvothermal method in obtaining homogeneous composites containing multiple metal oxides.

Analyzing Local Shear Rate Distribution in a Dual Coaxial Mixing Bioreactor Handling Herschel–Bulkley Biopolymer Solutions through Computational Fluid Dynamics

For the aeration of highly viscous non-Newtonian fluids, prior studies have demonstrated the improved efficacy of dual coaxial mixing bioreactors fitted with two central impellers and a close clearance anchor. Evaluating the effectiveness of these bioreactors involves considering various mixing characteristics, with a specific emphasis on shear rate distribution. The study of shear rate distribution is critical due to its significant impact on the mixing performance, gas dispersion, and homogeneity in aerated mixing systems comprising shear-thinning fluids. Although yield-pseudoplastic fluids are commonly employed in various industries, there is a research gap when it comes to evaluating shear rate distribution in aerated mixing bioreactors that utilize this fluid type. This study aims to investigate shear rate distribution in an aerated double coaxial bioreactor that handles a 1 wt% xanthan gum solution, known as a Herschel–Bulkley fluid. To achieve this goal, we employed an experimentally validated computational fluid dynamics (CFD) model to assess the effect of different mixing configurations, including down-pumping and co-rotating (Down-Co), up-pumping and co-rotating (Up-Co), down-pumping and counter-rotating (Down-Counter), and up-pumping and counter-rotating (Up-Counter) modes, on the shear rate distribution within the coaxial mixing bioreactor. Our findings revealed that the Up-Co system led to a more uniform local shear distribution and improved mixing performance.

Magma-carbonate interactions drive CO2 production and metal enrichment in shallow dikes and sills at volcanic arcs

Abstract The contribution of CO2 from crustal carbonates into arc magmas is debated, as is its role in the long-term C cycle. To better understand the contributions and mechanisms that drive CO2 production in arc magmas, we examined in detail basaltic dike and sill contacts with carbonate in the Jurassic Bonanza arc on Vancouver Island, Canada. We discovered discrete boundary melts that formed along dike and sill margins in contact with limestone, which display unique Ca, U, and Sr enrichments, Si depletion, and 87Sr/86Sr that approaches host limestone values (~0.708). Binary mixing modeling indicates ~20%–25% limestone assimilation into basalt formed the boundary melts. Contrasting viscosities between boundary and interior melts hinder mixing and chemical homogenization but appear to promote uphill diffusion and metal enrichment within systems that cool in minutes to days. While shallow dikes and sills may be volumetrically minor in an arc magma system, the open flow of magma and large surface area in channels greatly enhances magma-carbonate interactions, and ultimately CO2 production, likely over that of more common and voluminous plutons.

JUSTIFICATION OF RATIONAL OPTIONS FOR APPLICATION OF TECHNICAL MEANS FOR THE PREPARATION OF COMPOST MIXTURE

The goal of the research was to increase the efficiency of compost production from organic raw materials of agroecosystems through the development and implementation of scientifically based complex technical and technological solutions under conditions of accelerated aerobic fermentation. Four operating schemes of rotary drum-blade devices were chosen for research: single- and double-drum aerator, single- and double-drum PRT. The interrelationship between the parameters of the mechanized composting process and the design of the working bodies for the purpose of ensuring the set tasks has been established. In general, the process of functioning of the working body is divided into three processes, which are performed in a complex: loosening (shredding) or separation of shavings (particles) from the total mass, mixing and molding of the edge. The results of the experiments show better indicators of mixing quality and homogeneity for the M-shaped arrangement of the blades on the drum compared to the L-shaped one. The consumed power is less for the L-shaped arrangement of the blades. The conclusions are objective, regardless of the type of raw material and the height of the placement of the working body in relation to the side. As a result of the conducted theoretical and experimental studies, rational options for the use of technical means of compost mixture preparation are substantiated. Under the condition of ensuring the maximum homogeneity of the compass mixture, the largest value of the edge structure index and the minimization of energy consumption: – when processing chicken litter based on sunflower husk (ρ = 360–450 kg/t3, W = 32–44%, Mgran < 2123 t) it is advisable to use a device based on PRT-10 with one L-shaped working body; – when processing chicken litter based on sunflower husks (ρ = 360–450 kg/t3, W = 32–44%, Mgran > 2123 t) it is advisable to use a device based on an aerator with two L-shaped working bodies; – when processing chicken bedding straw cattle manure (ρ = 680–750 kg/ t3, W = 42–66%, Mgran < 2123 t) it is advisable to use a device based on PRT-10 with two L-shaped working bodies; – when processing chicken bedding straw cattle manure (ρ = 680–750 kg/ t3, W = 42–66%, Mgran > 2123 t) it is advisable to use a device based on an aerator with one M-shaped working body.

Mixing hydrogen into natural gas distribution pipeline system through Tee junctions

Hydrogen injection into natural gas distribution pipeline system through Tee junctions is numerically studied, by considering both ideal and Soave–Redlich–Kwong real gas models. The mixing homogeneity length is quantified for various side pipe sizes and perpendicular configurations for distribution-pressure and intermediate-pressure pipelines. The buoyant nature of hydrogen once blended into natural gas pipelines introduces a challenge as it tends to stratify and become trapped near the top wall.Accordingly, a greater side flow momentum leads to a shorter mixing homogeneity length. This reduces up to three to five times particularly when it penetrates deeply into the main flow without getting trapped from the beginning. Consequently, vertical bottom-side injection yields a mixing homogeneity length that is roughly four times shorter than horizontal and five times shorter than vertical top-side injection. Furthermore, employing a real gas model is critical once the pressure rises to intermediate pressures, resulting in a greater homogeneity length.

An Investigation of Particle Motion and Energy Dissipation Mechanisms in Soil–Rock Mixtures with Varying Mixing Degrees under Vibratory Compaction

Soil–rock mixture (S–RM) is a heterogeneous granular material commonly used in engineering applications, but achieving uniform particle mixing is challenging. This study investigated the effect of mixing homogeneity on the compaction of S–RM using the discrete element method (DEM). Specimens with varying degrees of mixing were modeled under realistic vibration loading. The results showed that a higher degree of mixing resulted in a smaller void ratio after compaction. The analysis of particle motion and energy dissipation revealed that not all particle motion during vibration compaction was aligned with the direction of the particle system. However, rotation was more prevalent and contributed to densification. Dashpot energy dissipation did not solely promote changes in the void ratio, while slip energy dissipation did lead to changes in the void ratio, but not entirely towards compaction. Rolling slip energy dissipation primarily occurred during the stage of void ratio changes and significantly promoted compaction. The change in strain energy aligned with the trend of the void ratio but did not directly contribute to its promotion.