Mixed Particles Research Articles

Effects of coating structures prepared under various mixing strength conditions for main and smaller admixed particles on improving compacted packing fraction

Particle flowability can be improved by admixing with particles smaller than the original main particles. However, the effects of the admixed particle coating structure for the main particle surface on the improvement of flowability are not fully understood. In this study, we investigated the effects of coating structures prepared under various mixing strength conditions (compression force and rotational speed) on particle compaction flowability. The main and admixed particles for various mass ratios were mixed in various mixing strength conditions and the compacted packing fractions of the mixed particles were measured. SEM images and SAXS were used to analyze the surface coating ratio, coating diameter, and fractal dimension of the admixed particles on the main particle surfaces. The difference in fractal dimension calculated from the SAXS data and the coating diameter ranges of the admixed particle agglomerates obtained from SEM images showed that the improvement mainly depended on coating structures in agglomerates 30–60 nm in size of the admixed particles. An optimal coating structure for improving the compaction flowability was an average gap between agglomerates on the main particle surfaces of around 2–3 times the coating diameter. This result was explained by a linked rigid three-body model movement.

Using particle-resolved aerosol model simulations to guide the interpretations of cloud condensation nuclei experimental data

Ambient aerosol particles can undergo dynamic mixing processes as they coagulate with particles from other air masses and emission sources. Therefore, aerosols exist in a spectrum, from externally mixed to internally mixed. The mixing state of aerosols can affect their ability to uptake water (hygroscopicity) and their cloud condensation nuclei (CCN) activity, modifying their contribution to the planet’s total radiative budget. However, current water-uptake measurement methods may not be able to capture the complex mixing state. In this research, the dynamic mixing process was simulated by the particle-resolved aerosol model PartMC and also created by experiments in a laminar flow mixing tube. The mixing evolution of ammonium sulfate and sucrose binary mixtures were observed along with the changes in their water uptake properties expressed as the single hygroscopicity parameter, κ. The use of a mixing simulation in conjunction with experiments allow for better identification of the particle mixing state and the particle water uptake and show that no one kappa value can capture the complexity of mixing across the mixed particle size distribution. In other words, the PartMC simulations can be used as a guiding tool to interpret a system’s mixing state based on its experimental droplet activation spectra. This work demonstrates the importance of the integration and use of mixing models to aid in mixing state determination and hygroscopicity measurements of mixed systems.Copyright © 2023 American Association for Aerosol Research

Investigating the magnitude and temporal localization of inertial particle mixing in turbulent channel flows

Mixing of inertial point particles in a turbulent channel flow at Reτ=950 is investigated by means of direct numerical simulations. We consider inertial particles, at varying Stokes number, released from pairs of sources located at different positions inside the channel and analyze the rate at which particles come into close proximity to each other. To do so, we employ a Lagrangian framework, which is suitable for the analysis of trajectories and in general for the study of mixing and dispersion problems. By varying the release position of particles along the wall-normal direction we obtain a thorough description of mixing in an anisotropic turbulent flow. Moreover, we analyze the effects of particle inertia and show that these are not univocal but also depend on the position and alignment of the sources, owing in particular to the dependence of the flow timescales on the distance from the wall.

Enhancing the flowability of limestone water suspension for economical transportation by variation in particle size distribution

Hydrotransport is increasingly a popular technology due to its low specific energy consumption and nonpolluting nature. The current work presents a thorough characterization of a limestone sample to explore the influence of blending medium and coarse particles with fine particulate slurry on the rheology, slurryability, and stability of a limestone water suspension. Various bench-scale studies are performed to identify the physicochemical, morphological, and flow features of limestone samples. Eight separate bi-modal slurry samples are prepared using limestone materials with three unique particle size ranges (53, 53–75, and 75–106 µm). The rheological properties of the slurry are tested at shear rates ranging from 50 to 500 1/s, and regression analysis is used to determine the nature of the slurry. The solid concentration of the suspension sample ranges between 10 and 70% with a flow velocity range of 0.25–1.5 m/s through a 100 mm diameter pipeline. Finally, essential criteria such as apparent viscosity, settling properties, pressure drop, and specific energy consumption are used to determine the optimal particle size distribution. The ideal proportion of medium particles (53–75 µm) mixing in the fine particulate slurry suspension is 40%, while the fraction of coarse particles (75–106 µm) is 30% (by weight).

3D printing of customised particles for powder rheology, mixing and segregation study

Due to the heterogeneity of particle shape and surface, it remains a big challenge for quantitative analysis of the detrimental influencing factors for certain powder kinematics. The current study aims to investigate the relative effect of particle shape and surface on the bulk properties by printing of specific particle shapes with distinct surface textures using Binder Jetting. The FT4 powder rheometer is used to analyse the powder bulk behaviour and as a blending rig for binary particle mixing and segregation study. It is found that both particle shape and surface have significant effects on the powder flow and compressibility. Specifically, surface has overcome shape effect on the flowability of irregular-shaped particles and compressibility of all particles. Different shapes exhibit different segregation behaviours when mixed with spheres. With “ideal and colourful” particles created, we anticipate in providing a strong experimental validation for simulation study of particle dynamics.

Experimental investigation of the lateral mixing of large and light particles immersed in a fluidized bed

Fluidized bed reactors for solid fuel conversion are characterized by the presence of a small fraction of fuel particles that are significantly larger (usually 1–2 orders of magnitude larger) and lighter (2–20-fold less dense) compared to the bulk solids. This difference in physical properties strongly influences the mixing of the fuel particles and therefore affects the mass, momentum and heat transfers between the fuel particles and the surrounding bed. This work uses Magnetic Particle Tracking (MPT) to acquire highly resolved trajectories for single tracer particles immersed in a bubbling fluidized bed operated under ambient conditions and with a cross-sectional area of 0.45 m2. This bed size is sufficiently large to abrogate the influence of the reactor walls, allowing data post-processing to study the free movement of the tracer particle, which has not been available to date. This required the enhancement of the MPT system from that in previous works: 12 sensors and a communication protocol in series are here applied, which showed good performance in both spatial accuracy (1 mm) and time resolution (100 Hz). The bed material used in the experiments was glass beads (mean particle size of 106 µm, particle density of 2,486 kg/m3). Two different tracer particles, with diameters of 18 mm but with different densities (572 kg/m3 and 1,015 kg/m3) were used to mimic the sizes and densities of the solid fuel particles. Fluidization velocity was varied within 0.2–0.7 m/s and two fixed bed heights (50 mm and 130 mm) were tested. Based on the trajectories, dispersion coefficients were calculated for quantitative evaluation of the solids mixing. The results reveal that increased bed height yields higher dispersion coefficients with a higher sensitivity for fluidization velocity. The properties of the tracer particles appear, within the tested range, to exert little impact on its lateral dispersion. From the velocity maps generated, a swirling pattern was observed in the vicinity of the walls, while zones of preferential ascendent or descendant movement were observed in the cross-section centre, although clearly defined mixing cells were not exhibited.

Estimation of the Just Suspension Speed of Mixed Particles in a Solid-Liquid Stirred Tank

Based on the model equation for homogeneous particles, we propose a model equation for just suspension speed for mixed particles. If the correlation equation of Zwietering holds, the just suspension speed of mixed particles [njs,mix(XT)] is given as a function of the volume fraction of particle i (φi) and the just suspension speed of uniform particle i [njs,i(XT)]. njs,mix(XT)=[∑injs,i(XT)20/3φi∑injs,i(XT)10/3φi]3/10 The calculated values using the proposed model equation were in close agreement with the experimental data. Furthermore, the results were in good agreement with the literature data for mixed particles containing four-component system. The study also confirmed the usefulness of the proposed model equation, since the existing correlation equation did not correlate well with the experimental data.

Neutrinos, mixed bosons, quantum reference frames and entanglement

We discuss the relevance of quantum reference frames in the description of mixed particle states. We show that the notion of a rest frame for mixed particles, which is classically ill-defined, can be introduced in the context of quantum frames. We discuss the possible implications, displaying a new form of frame-dependent entanglement that characterizes reactions involving mixed particles, and suggest a possible route to extract observables related to such an entanglement.

Carbon sequestration by multiple biological pump pathways in a coastal upwelling biome

Multiple processes transport carbon into the deep ocean as part of the biological carbon pump, leading to long-term carbon sequestration. However, our ability to predict future changes in these processes is hampered by the absence of studies that have simultaneously quantified all carbon pump pathways. Here, we quantify carbon export and sequestration in the California Current Ecosystem resulting from (1) sinking particles, (2) active transport by diel vertical migration, and (3) the physical pump (subduction + vertical mixing of particles). We find that sinking particles are the most important and export 9.0 mmol C m−2 d−1 across 100-m depth while sequestering 3.9 Pg C. The physical pump exports more carbon from the shallow ocean than active transport (3.8 vs. 2.9 mmol C m−2 d−1), although active transport sequesters more carbon (1.0 vs. 0.8 Pg C) because of deeper remineralization depths. We discuss the implications of these results for understanding biological carbon pump responses to climate change.

Characterization and modelling of water mixing energies and particle behavior during wave generation in CanmetENERGY Devon spill test tank

A mesoscale oil spill test tank located in Natural Resources Canada research facility at CanmetENERGY Devon (AB, Canada) was used to study the mixing energy and particle behavior near the shorelines. Four types of waves have been generated in the tank where the instantaneous velocities were measured using an acoustic doppler velocimeter (ADV), and the energy dissipation rate was obtained. Below the water surface of 0.2 m, the energy dissipation rate reached the magnitude of 10−4 W/kg slightly away from the tank beach and increased to 10−3 W/kg in the beach region. For the most typical wave conditions, Large-Eddy Simulation (LES) were conducted and the result was consistent with experimental observation. The simulation further revealed that the energy dissipation rate reached 1.0 W/kg at the water surface near the beach region. The velocities and sub-grid diffusion from LES were used to track the movement of fictitious neutrally buoyant, buoyant, and heavy particles by a Lagrangian particle-tracking model. It was found that the droplet inertia has significant impact for 500 μm particles. Under the specific gravity of 0.88, the particles accumulated close to the beach, while the particles with specific gravity of 1.20 settled to the bottom wall regardless of the existence of waves.

Void fraction for random loose packing of multi-size mixed cylindrical particles

Most particles in industrial applications are mixed cylindrical particles with the same diameter and different aspect ratios (ARs). In this study, the void fraction of packed bed with binary, ternary, quaternary, and quintuple mixtures of cylindrical particles is explored by discrete element method (DEM). The concept of equivalent AR is proposed for predicting void fraction of packing of mixed cylindrical particles based on previous research. Results show that (1) the correlation between equivalent AR and void fraction is higher when ARVave is used, and the prediction error is only −0.57%–6.21%. (2) Better prediction results can be obtained using ARNave in some cases, such as for packing of mixed cylindrical particles with small AR intervals and wide distribution. However, the prediction results are unsatisfactory in the case of larger AR intervals and cylindrical particles with AR = 1. (3) The R2 can be increased to 0.983 when corrected by multiplying by 96.87%.

Evaluating fundamental biochar properties in relation to water holding capacity

Biochar products that hold and release water within a stable carbonised porous structure provide many opportunities for climate mitigation and a range of applications such as for soil amendments. Biochar that are produced from various organic feedstocks by pyrolysis can provide multiple co-benefits to soil including improving soil health and productivity, pH buffering, contaminant control, nutrient storage, and release, however, there are also risks for biochar application in soils. This study evaluated fundamental biochar properties that influence Water Holding Capacity (WHC) of biochar products and provides recommendations for testing and optimising biochar products prior to soil applications. A total of 21 biochar samples (locally sourced, commercially available, and standard biochars) were characterised for particle properties, salinity, pH and ash content, porosity, and surface area (with N2 as adsorbate), surface SEM imaging, and several water testing methods. Biochar products with mixed particle size, irregular shapes, and hydrophilic properties were able to rapidly store relatively large volumes of water (up to 400% wt.). In contrast, relatively less water (as low as 78% wt.) was taken up by small-sized biochar products with smooth surfaces, along with hydrophobic biochars that were identified by the water drop penetration test (rather than contact angle test). Water was stored mostly in interpore spaces (between biochar particles) although intra-pore spaces (meso-pore and micropore scale) were also significant for some biochars. The type of organic feedstock did not appear to directly affect water holding, although further work is needed to evaluate mesopore scale processes and pyrolytic conditions that could influence the biochemical and hydrological behaviour of biochar. Biochars with high salinity, and carbon structures that are not alkaline pose potential risks when used as soil amendments.

Insights into the single-particle composition, size, mixing state, and aspect ratio of freshly emitted mineral dust from field measurements in the Moroccan Sahara using electron microscopy

Abstract. The chemical and morphological properties of mineral dust aerosols emitted by wind erosion from arid and semi-arid regions influence climate, ocean, and land ecosystems; air quality; and multiple socio-economic sectors. However, there is an incomplete understanding of the emitted dust particle size distribution (PSD) in terms of its constituent minerals that typically result from the fragmentation of soil aggregates during wind erosion. The emitted dust PSD affects the duration of particle transport and thus each mineral's global distribution, along with its specific effect upon climate. This lack of understanding is largely due to the scarcity of relevant in situ measurements in dust sources. To advance our understanding of the physicochemical properties of the emitted dust PSD, we present insights into the elemental composition and morphology of individual dust particles collected during the FRontiers in dust minerAloGical coMposition and its Effects upoN climaTe (FRAGMENT) field campaign in the Moroccan Sahara in September 2019. We analyzed more than 300 000 freshly emitted individual particles by performing offline analysis in the laboratory using scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectrometry (EDX). Eight major particle-type classes were identified with clay minerals making up the majority of the analyzed particles both by number and mass, followed by quartz, whereas carbonates and feldspar contributed to a lesser extent. We provide an exhaustive analysis of the PSD and potential mixing state of different particle types, focusing largely on iron-rich (Fe oxide-hydroxides) and feldspar particles, which are key to the effects of dust upon radiation and clouds, respectively. Nearly pure or externally mixed Fe oxide-hydroxides are present mostly in diameters smaller than 2 µm, with the highest fraction below 1 µm at about 3.75 % abundance by mass. Fe oxide-hydroxides tend to be increasingly internally mixed with other minerals, especially clays, as particle size increases; i.e., the volume fraction of Fe oxide-hydroxides in aggregates decreases with particle size. Pure (externally mixed) feldspar represented 3.2 % of all the particles by mass, of which we estimated about a 10th to be K-feldspar. The externally mixed total feldspar and K-feldspar abundances are relatively invariant with particle size, in contrast to the increasing abundance of feldspar-like (internally mixed) aggregates with particle size with mass fractions ranging from 5 % to 18 %. We also found that overall the median aspect ratio is rather constant across particle size and mineral groups, although we obtain slightly higher aspect ratios for internally mixed particles. The detailed information on the composition of freshly emitted individual dust particles and quantitative analysis of their mixing state presented here can be used to constrain climate models including mineral species in their representation of the dust cycle.

The Effect of Ball-Powder Ratio on The Mechanical and Structural Properties of CuZrB Composite Materials Fabricated by Powder Metallurgy

Copper matrix composites exhibit excellent mechanical and thermal properties. The composite consists of copper (Cu), zirconium (Zr), and boron (B) and is produced using the powder metallurgy technique. The high-energy ball milling was applied for mechanical alloying of the Cu-Zr-B powder mixture to achieve the desired ratio for obtaining a copper matrix reinforced with ZrB2 ceramic particles. The milling times of 10 and 40 hours for two different ball-to-powder ratios are investigated for a powder mixture with a composition of Cu-2.71Zr-2.27B (wt.%). XRD and SEM analyses were employed to determine structural and morphological changes in the mechanically alloyed powder mixture. Investigation of the morphological parameters shows that with prolonged milling, the shape of mixed particles becomes more uniform, while their structural parameters have been drastically changed. It is determined that during high-energy ball milling of the Cu-2.71Zr-2.27B (wt.%), the size of the copper powder decreases as the mechanical alloying increases for both ball-powder ratios. Dislocation densities reach their maximum value at around 30 hours of mechanical alloying for both ball-powder ratios, with dislocation density being higher for the 1:15 ratio, after which they decrease owing to the recrystallization of the copper matrix. XRD analysis shows no presence of ZrB2 reinforcement particles or oxides during milling.

Pressure‐controlled secondary flows and mixing in sheared Platonic solid‐shaped particles

AbstractGranular materials exhibit unique secondary flow behaviors upon shearing. We demonstrate, using particle dynamics simulations, that the secondary flow patterns are controlled by a pressure exerted on particle bed. A threshold pressure, at which vortex flow transitions to disturbed or chaotic flow, depends on particle shape, that influences interparticle contacts and rheological performance. Our results show that the flow patterns are essentially determined by a dimensionless term combining pressure and granular temperature for all the spherical and Platonic solid‐shaped particles explored. Particle mixing is promoted by the vortex flow or disturbed flow with strong diffusion. The highest mixing rate under a specified pressure is obtained for cubic particles, due to the significant microstructural ordering near the boundaries causing a high gradient of packing density. These findings shed light on how applied pressure and particle shape affect secondary flows which is critical to the understanding and control of granular mixing.

Forecasting by Combining Chaotic PSO and Automated LSSVR

An automatic least square support vector regression (LSSVR) optimization method that uses mixed kernel chaotic particle swarm optimization (CPSO) to handle regression issues has been provided. The LSSVR model is composed of three components. The position of the particles (solution) in a chaotic sequence with good randomness and ergodicity of the initial characteristics is taken into consideration in the first section. The binary particle swarm optimization (PSO) used to choose potential input characteristic combinations makes up the second section. The final step involves using a chaotic search to narrow down the set of potential input characteristics before combining the PSO-optimized parameters to create CP-LSSVR. The CP-LSSVR is used to forecast the impressive datasets testing targets obtained from the UCI dataset for purposes of illustration and evaluation. The results suggest CP-LSSVR has a good predictive capability discussed in this paper and can build a projected model utilizing a limited number of characteristics.

Progress in the study of electrorheological polishing: A review

Electrorheological polishing (ERP) is an important field-assisted polishing method, which can reduce abrasive loss and improve machining efficiency by using the electric field-induced electrorheological (ER) effect to help the abrasive to overcome the centrifugal force caused by high rotating speed during polishing. ERP has many advantages, including high efficiency, high precision, facile polishing for a small object, and a good application prospect in polishing optical devices and hard molds. This review describes the research progress in ERP in the past two decades. The mechanism of electrorheological polishing is analyzed from two aspects of electrorheological effect and dielectrophoresis. According to the time sequence of electrorheological polishing development, two kinds of ERP materials including the simple mixing system and composite particle system are introduced. ERP electrodes including off-axis bipolar electrode, needle-ring electrode, needle-like single electrode, one-sided patterned electrode, and one-sided simple composite electrode are described. From the two characterization quantities of removal rate and surface quality, the industrial factors affecting the ERP effect are discussed. The advantages and disadvantages of ERP and other polishing processes are compared. Finally, the remaining challenges and possible development trends in ERP technology for the future outlook are proposed.

Numerical simulation and mathematical models of ash deposition behavior considering particle properties and operating conditions

A unified model is proposed considering thermophoresis, erosion, dynamic mesh techniques and mixed particle adhesion model based OpenFOAM open-source software. The effects of particle concentration, particle size distribution, flow velocity, probe and air temperature were discussed. Results show that the unified model predicts the deposition thickness at the probe with an average error of 7.66%. Deposition and impact efficiency always show opposite trends to factor changes, which are dominated by particle temperature and size distribution, respectively. Impact efficiency is distributed in 50–65% and the deposition efficiency is 5–25%, which get the efficiency of forming deposition of any ash particles in the boiler may be 2.5–16.25%. Different factors affect the deposition efficiency by influencing the particle temperature, the average particle temperature rises by 30 K with a double increase in flow rate. Also, a change of 10 to 30 K in particle temperature corresponds to a change of 100 K in air temperature. Mathematical models of PCA and BP neural networks based on broad data were proposed, which predict the maximum deposition thickness and probe deposition morphology with an error of 15% and 8.9%. The results of this study can provide a monitoring method and reference for boiler operators and researchers.

Route of biofuel production from macadamia nut shells: effect of parameters on the particles mixing index in fluidized beds

Pyrolysis of macadamia nut shells (MNS) in a fluidized bed reactor has excellent potential to produce bio-oil. High heat transfer rates and uniform temperature in the fluidized bed can be achieved due to effective gas-solid contact in the reactor. However, binary mixtures can lead to the segregation of particles, which negatively affects heat and mass transfer in such a reactor. Therefore, a 2³ statistical experimental design was used to assess the effects of parameters (i.e., air velocity, particle diameter ratio, and mass fraction of MNS) on the mixing index of the bed of MNS and sand. Among the analyzed factors, only DMNS/DS and V/VMF influenced the mixing index (Im) within a confidence interval of 95%. Based on statistical data analysis, an air velocity 20% above the minimum fluidization and particle diameter ratio (DMNS/DS) smaller than 3 results in uniform particle mixing in the bed (i.e., reaching ideal mixing index values). Moreover, the experimental results indicate that fluidized be used for biofuel production from Macadamia nut Shells.

A Composite of Nb2O5 and MoO2 as a High‐Capacity High‐Rate Anode Material for Lithium‐Ion Batteries

AbstractA composite of Nb2O5 and MoO2 was synthesised using a hydrothermal reaction (225 °C) followed by a short heat‐treatment step (600 °C) to achieve a high‐capacity, high‐rate anode for lithium‐ion battery applications. The composite was shown via powder X‐ray diffraction and electron microscopy to be an intimate mix of individual oxide particles rather than an atomically mixed oxide material, and shown by X‐ray fluorescence spectroscopy (XRF) to contain a 45 : 55 ratio of Nb : Mo. This material is demonstrated to show notable rate capability in lithium (Li) half‐cell cycling and rate tests. When cycled at 100 °C the material achieved over 100 mAh g−1 even after 400 cycles and shows a stable reversible capacity of 514 mAh g−1 (at 1 C), realising its theoretical capacity. The composite shows electrochemical results comparable to Nb2O5:C composites yet achieves far higher capacities at low‐rate due to the MoO2 content.