Particle Volume Distribution Research Articles

Insights into particle dispersion and damage mechanisms in functionally graded metal matrix composites with random microstructure-based finite element model

This study investigates the impact of Al2O3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm {Al_2O_3}$$\\end{document} particle volume fraction and distribution on the deformation and damage of particle-reinforced metal matrix composites, particularly in the context of functionally graded metal matrix composites. In this study, a two-dimensional nonlinear random microstructure-based finite element modeling approach implemented in ABAQUS/Explicit with a Python-generated script to analyze the deformation and damage mechanisms in AA6061-T6/Al2O3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm{AA6061\\mbox{-}T6/Al_2O_{3}}$$\\end{document} composites. The plastic deformation and ductile cracking of the matrix are captured using the Gurson–Tvergaard–Needleman model, whereas particle fracture is modelled using the Johnson–Holmquist II model. Matrix-particle interface decohesion is simulated using the surface-based cohesive zone method. The findings reveal that functionally graded metal matrix composites exhibit higher hardness values (HRB\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{HRB}$$\\end{document}) than traditional metal matrix composites. The results highlight the importance of functionally graded metal matrix composites. Functionally graded metal matrix composites with a Gaussian distribution and a particle volume fraction of 10% achieve HRB\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{HRB}$$\\end{document} values comparable to particle-reinforced metal matrix composites with a particle volume fraction of 20%, with only a 2% difference in HRB\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{HRB}$$\\end{document}. Thus, HRB\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{HRB}$$\\end{document} can be improved significantly by employing a low particle volume fraction and incorporating a Gaussian distribution across the material thickness. Furthermore, functionally graded metal matrix composites with a Gaussian distribution exhibit higher HRB\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{HRB}$$\\end{document} values and better agreement with experimental distribution functions when compared to those with a power-law distribution.

Crack Initiation in Compacted Graphite Iron with Random Microstructure: Effect of Volume Fraction and Distribution of Particles.

Thanks to the distinctive morphology of graphite particles in its microstructure, compacted graphite iron (CGI) exhibits excellent thermal conductivity together with high strength and durability. CGI is extensively used in many applications, e.g., engine cylinder heads and brakes. The structural integrity of such metal-matrix materials is controlled by the generation and growth of microcracks. Although the effects of the volume fraction and morphology of graphite inclusions on the tensile response of CGI were investigated in recent years, their influence on crack initiation is still unknown. Experimental studies of crack initiation require a considerable amount of time and resources due to the highly complicated geometries of graphite inclusions scattered throughout the metallic matrix. Therefore, developing a 2D computational framework for CGI with a random microstructure capable of predicting the crack initiation and path is desirable. In this work, an integrated numerical model is developed for the analysis of the effects of volume fraction and nodularity on the mechanical properties of CGI as well as its damage and failure behaviours. Finite-element models of random microstructure are generated using an in-house Python script. The determination of spacings between a graphite inclusion and its four adjacent particles is performed with a plugin, written in Java and implemented in ImageJ. To analyse the orientation effect of inclusions, a statistical analysis is implemented for representative elements in this research. Further, Johnson-Cook damage criteria are used to predict crack initiation in the developed models. The numerical simulations are validated with conventional tensile-test data. The created models can support the understanding of the fracture behaviour of CGI under mechanical load, and the proposed approach can be utilised to design metal-matrix composites with optimised mechanical properties and performance.

Numerical analysis of coarse particle two-phase flow in deep-sea mining vertical pipe transport with forced vibration

Exploring the dynamics and flow characteristics of coarse particles within vertical lifting pipes is essential to ensure safe and efficient pipeline transportation. This study combines computational fluid dynamics (CFD) and the discrete element method (DEM) to investigate the behavior of coarse particle solid–liquid two-phase flow in a vertical pipe utilized for deep-sea mining under forced vibration and compares it with that in stationary pipes. This study examined the effects of pipe amplitude, vibration frequency, and initial internal flow velocity separately. The amplitude values tested were 0D (static), 1D, 2D, 3D, and 4D, where D represents pipe diameter. The vibration frequencies of 0 Hz (static), 0.25 Hz, 0.5 Hz, 1 Hz, and 2 Hz were tested, respectively. Finally, initial velocities of 1 m/s, 2 m/s, 3 m/s, and 4 m/s were tested. Compared with stationary pipes, particle-induced turbulence gradually disrupts the flow field, leading to a more dispersed particle volume distribution during pipe vibration. An increase in the amplitude and vibration frequency of the pipe results in an augmentation of the pressure drop within the pipe. By comparing the results of the vibrating pipe with those of the stationary pipe, the effect of the pipe vibration gradually weakened as the initial velocity increased.

Computational damage analysis of metal matrix composites to identify optimum particle characteristics in indentation process

This paper presents an integrated numerical model that investigates the effects of Al2O3 particle volume fraction, distribution, size, shape, and clustering on the deformation, damage, and failure behaviors of particle-reinforced metal matrix composites. Additionally, the effects of the cohesive strength of the matrix-particle interface and the initial void volume fraction on these behaviors are investigated. In this study, random microstructure-based finite element modeling approach is used. The Gurson-Tvergaard-Needleman model is used to capture the plastic deformation and ductile cracking of the matrix, whereas the Johnson–Holmquist II model is used to model particle fracture. The matrix-particle interface decohesion is modeled using the surface-based cohesive zone method. A two-dimensional nonlinear finite element model augmented with Python-generated code is developed in ABAQUS/Explicit to analyze the damage mechanisms in AA6061-T6/Al2O3 particle-reinforced metal matrix composites. The results show that Al2O3 particle enhance the ability of particle-reinforced metal matrix composites to resist deformation. However, this enhancement is dependent on the indentation location, particulate characteristics, and the applied load. An increase in the particle volume fraction increases the risk of particle fracture, particularly when particles are close to the material surface. Circular particles are the optimal choice for the reinforcement of particle-reinforced metal matrix composites. The predictions are in good agreement with the experimental data, particularly in terms of Rockwell hardness and deformation characteristics.

Cometary dust collected by MIDAS on board Rosetta

Context. The MIDAS (Micro-Imaging Dust Analysis System) atomic force microscope on board the Rosetta comet orbiter investigated and measured the 3D topography of a few hundred of nm to tens of μm sized dust particles of 67P/Churyumov-Gerasimenko with resolutions down to a few nanometers, giving insights into the physical processes of our early Solar System. Aims. We analyze the shapes of the cometary dust particles collected by MIDAS on the basis of a recently updated particle catalog with the aim to determine which structural properties remained pristine. Methods. We develop a set of shape descriptors and metrics such as aspect ratio, elongation, circularity, convexity, and particle surface and volume distribution, which can be used to describe the distribution of particle shapes. Furthermore, we compare the structure of the MIDAS dust particles and the clusters in which the particles were deposited to those found in previous laboratory experiments and by Rosetta/COSIMA. Finally, we combine our findings to calculate a pristineness score for MIDAS particles and determine the most pristine particles and their properties. Results. We find that the morphological properties of all cometary dust particles at the micrometer scale are surprisingly homogeneous despite originating from diverse cometary environments (e.g., different collection targets that are associated with cometary activities/source regions and collection velocities/periods). There is only a weak trend between shape descriptors and particle characteristics such as size, collection targets, and cluster morphology. We next find that the types of clusters found by MIDAS show good agreement with those defined by previous laboratory experiments, however, there are some differences to those found by Rosetta/COSIMA. Furthermore, our pristineness score shows that almost half of MIDAS particles suffered severe alteration by impact, which indicates structural modification by impact (e.g., flattening and/or fragmentation) is inevitable despite the very low collection speeds (i.e., ~3–7 m s−1). Based on our result, we rate 19 out of 1082 MIDAS particles at least moderately pristine that is they are not substantially flattened by impact, not fragmented, and/or not part of a fragmentation cluster.

An efficient implementation of a conservative finite volume scheme with constant and linear reconstructions for solving the coagulation equation

Population balances provide an economic means of describing dense particulate phases with particle-particle interactions. Here, we focus on particle coagulation and address the evaluation of the corresponding integral source terms within the scope of a conservative finite volume formulation. Based on one kernel evaluation for every pair of parent cells, efficient analytical formulas are derived that obviate the explicit decomposition of the integration domains into elementary geometrical shapes and are valid for arbitrary volume-grids. Considering the volume-weighted cell averages as degrees of freedom, the formulas are presented for both cell-wise constant and linear reconstructions of the particle volume distribution. We find the latter to be effective at mitigating the unphysically heavy tails that are characteristic of solutions obtained with piecewise constant reconstructions. For Brownian coagulation, the computational expense is mainly caused by the kernel evaluations, while the cost of the parent-daughter pairing and integration algorithm is almost negligibly small.

Hammer milling switchgrass from weathered bales

Considering that grasses have been targeted as raw material for bioenergy and will have to be handled in mass flow manner to be efficient, there is need to understand how grasses can be ground into easily flowing particles. For a biorefinery, the biomass will inevitably have to be stored, more than likely in an environment exposed to the elements. Consequently, there is a need to understand how the weathered material will interact with processing equipment like a hammermill. Grinding tests with switchgrass stored for a year in the open (weathered) and undercover (unweathered) were undertaken. The switchgrass was ground in an 18.64 kW hammermill with screen openings 9.52, 31.75, and ∞ mm (no screen). Results from this preliminary evaluation show that both weathered switchgrass (WSG) and unweathered switchgrass (USG) had grinding rates similarly increasing as the screen openings size increased with the unweathered material having a slightly higher throughput. When analyzed as a volume distribution of ground particles in machine vision methodology, switchgrass condition did not affect the particle size distribution parameters of the ground material. However, the geometric mean length for WSG increased from 6 mm to 37 mm with increasing screen size for WSG, whereas the geometric mean length for USG increased but only from 6 mm to 31 mm. While future studies are needed, the results however serve as a reference for preprocess grinding of biomass, either fresh or weathered (common in large-scale storage), for bioenergy/industrial use in obtaining the desired particle size at a given production rate.

Quantitative determination of surface spins contribution of magnetization, anisotropy constant, and cation distribution of manganese ferrite-silica nanocomposite

We investigate the impact of silica concentration on the morphology, structure and and magnetic properties of xMnFe2O4-(100-x)SiO2, x=100, 15, and 10, nanocomposites synthesized by a rapid, one-step auto-combustion method. XRD patterns show formation of single-phase cubic spinel structure of MnFe2O4 in all samples without any evidence of secondary phase crystallization. According to TEM analysis, the maximum crystallite size was found for 100MnFe/Si, while 15MnFe/Si has the lowest mean size, being 7.2 nm.Cation distributions were determined using Mossbauer spectroscopy measuremnts and it was confrimed that the iron species are exclusively in Fe3+ valence state for xMnFe/Si nanocomposites. The impact of disordered surface spins on the total magnetization was systematically investigated by defining a modified Langevin function. Extensive morphological, magnetic and Mossbauer studies depicted that the MnFe2O4/Silica ratio, cations arrangement, interparticle interactions, particle volume distribution and, also, volume/surface ratio, largely impact on the magnetic characteristics of MnFe/Si nanocomposites.

Numerical Study on Transportation of Cemented Paste Backfill Slurry in Bend Pipe

With the development of coal mining, the use of elbows has diversified the forms of underground backfill pipelines, which has inevitably complicated the transportation characteristics of filling slurry in the pipeline, thus affecting the entire backfilling system. The objective of this study is to numerically investigate the running state of cemented paste backfilling (CPB) slurry and coarse particles at different velocities by transporting in bend pipes. To better understand the transportation state of CPB slurry in pipeline, a computational fluid dynamics (CFD) model—mixture model was developed to study the transportation of CPB slurry. The volume distribution of coarse particles in slurry under different pipe types and different flow rates, as well as the velocity profiles of slurry at different positions, were simulated and analyzed, and the pressure losses under different pipe types were compared. The results show that the distribution of coarse particles varies with the tube type, and the effect of coarse particles on the position of tube wall changes with the increase in velocity. The high-speed zone of CPB slurry will move toward the outer wall of the elbow with the increase in velocity. The pressure loss of CPB slurry in the vertical–horizontal pipeline is larger than that in the horizontal–vertical pipeline, and the difference is larger in the bend section. This study provides a theoretical and meaningful reference for CPB slurry backfilling operations in different bends.

Effect of the distribution of anisotropy constants on the magnetic properties of iron oxide nanoparticles

The distribution of shape anisotropy constants in two colloids of iron oxide nanoparticles has been measured from the distribution of particle elongations within each system. The results are in good agreement with the values calculated from a temperature decay of remanence measurement. For a fluid with a saturation magnetisation of 420 emu/cc and an average particle elongation of ∼ 1.3, the distribution of energy barriers is controlled by both the distribution of particle sizes and particle elongations. For a fluid with a saturation magnetisation of 320 emu/cc and a wide distribution of particle sizes, the energy barrier to reversal can be assumed to be controlled by the distribution of particle volumes. These results highlight the need to take into account the distribution of anisotropy constants when making predictions of the heating properties of assemblies of magnetic nanoparticles for hyperthermia applications.

Adjusting the initial milk pH before freezing affected physico-chemical properties of thawed goat milk

This experiment was conducted to study the effects of initial goat milk pH on changes in some physico-chemical properties of milk during freeze-thaw cycles, and to investigate the possible causes by freeze-thawing for 5 cycles to magnify the changes. Raw goat milk was adjusted to 3 alternative pH levels, which were 1) original milk pH, 2) adjusted to original pH-0.2, and 3) adjusted to original pH+0.2. All the milk samples were packed in plastic bags and kept at -18±2°C for 5 days, then thawed at room temperature at 25°C (1 cycle) and this was repeated for 5 cycles. Milk samples from each treatment and each cycle were analyzed for pH, presence of sediment, viscosity, fat droplet size, particle size distribution, heat stability and changes in mineral content of milk serum. The result showed that the goat milk had an original pH of 6.69 (T6.69) that was adjusted to 6.49 (T6.49) and 6.89 (T6.89). During freeze-thawing all the treatment groups exhibited decreasing pH and increasing sediment, milk viscosity and fat droplet size, with only slight differences between treatments. The important differences were in heat stability, as the T6.49 treatment resulted in a heat stability decrease from 80 mins initially to 46 mins (42.50% decrease) at the 5th cycle, whereas T6.89 treatment only had an 8.89% change in heat stability. Average particle diameter (D3,2), volume distribution (D4,3) and uniform distribution (span) increased with freeze-thaw cycles, which clearly showed in T6.49 and T6.69 cases but not distinctly in T6.89. In conclusion, milk pH affected the quality of milk after freeze-thawing. Adjusting pH to 6.89 before freezing in this study reduced changes of pH, sediment formation, coalescence of protein, and heat stability of thawed goat milk; such adjustment is beneficial for further milk processing in the dairy industry.

Physical and chemical properties of dust in the Pre-Aral region of Uzbekistan

The aim of this work is study of physical and chemical properties of dust of the Pre-Aral region of Uzbekistan such as Karakalpakstan and Khorezm that are located near the three deserts such as the Aralkum, Karakum, and Kyzylkum. The dust particles fell on glass have been collected in Karakalpakstan and Khorezm and studied systematically by employing wide range of methods. Particle volume vs size distribution has been measured with maximum around 600 nm and ~ 10 µm. The major and minor constituent materials present in the dust have been studied systematically by X-ray fluorescence spectroscopy, energy dispersive X-ray diffraction, and inductively coupled plasma optical emission spectroscopy. Main characteristic absorption bands corresponding to Si–O, Si–O-Si bonding in quartz and Fe–O bonds in hematite Fe2O3 have been identified by infrared and Raman spectroscopy. Quartz, hematite, lime, corundum, magnesia, and several other trace minerals have been identified in the dust particles. X-ray diffraction peaks corresponding to quartz, hematite, and corundum are sharp and are found to be more crystalline with some level of disorder. Analysis of the particle size and crystallinity on human being has been performed: disordered or crystalline quartz can create the lung disease; the particles in the size of 0.5–0.7 µm may produce diseases such as chronic silicosis, silicosis, and silica tuberculosis whereas hematite might create lung disease. Dust particles worsen optical transmittance of glass of the panels.Graphical abstract

Characterization of suspended particulate matter in contrasting coastal marine environments with angle-resolved polarized light scattering measurements.

Optical proxies based on light scattering measurements have potential to improve the study and monitoring of aquatic environments. In this study, we evaluated several optical proxies for characterization of particle mass concentration, composition, and size distribution of suspended particulate matter from two contrasting coastal marine environments. We expanded upon our previous study of Southern California coastal waters, which generally contained high proportions of organic particles, by conducting angle-resolved polarized light scattering measurements in predominantly turbid and inorganic-particle dominated Arctic coastal waters near Prudhoe Bay, Alaska. We observed that the particulate backscattering coefficient bbp was the most effective proxy for the mass concentration of suspended particulate matter (SPM) when compared with particulate scattering and attenuation coefficients bp and cp. Improvements were seen with bbp as a proxy for the concentration of particulate organic carbon (POC), although only if particulate assemblages were previously classified in terms of particle composition. We found that the ratio of polarized-light scattering measurements at 110º and 18º was superior in performance as a proxy for the composition parameter POC/SPM in comparison to the particulate backscattering ratio bbp/bp. The maximum value of the degree of linear polarization DoLPp,max observed within the range of scattering angles 89°-106° was found to provide a reasonably good proxy for a particle size parameter (i.e., 90th percentile of particle volume distribution) which characterizes the proportions of small- and large-sized particles. These findings can inform the development of polarized light scattering sensors to enhance the capabilities of autonomous platforms.

Characterization of WC-doped NiCrBSi coatings deposited by Laser Cladding; effects of particle size and content of WC powder

Tungsten carbide doped NiCrBSi coatings have been deposited by Laser Cladding (LC) on steel agricultural knives in order to improve their life time. The influence of the mass fraction as well as the particle size of the tungsten carbide powder on structure, microstructure and mechanical properties was analyzed. The mechanical characteristics were studied from micro-hardness tests, pin-on-disc wear tests and cutting tests of plant material. The coating hardness is stable when carbide powder content in the mixture is between 35 and 60 wt%. Then this hardness increases significantly when the carbide content reaches 70 wt%. The wear coefficient in dry conditions decreases when the carbide powder content is increased from 35 to 40 wt%. Further increase of the carbide powder content in the mixture does not affect the wear coefficient. The coating hardness increases with the particle size of the carbide powder. The cutting test shows that the finest particle size (20–53 μm) of the carbide powder leads to the lowest values of the cutting-edge wear and the mass loss. This is attributed mainly to the better volume distribution of tungsten carbide particles as well as to the resistance of the matrix due to precipitation of the Ni4W phase.

Evolution of the Magnetic and Structural Properties with the Chemical Composition in Oleate-Capped MnxCo1–xFe2O4 Nanoparticles

Understanding the complex link among composition, microstructure, and magnetic properties paves the way to the rational design of well-defined magnetic materials. In this context, the evolution of the magnetic and structural properties in a series of oleate-capped manganese-substituted cobalt ferrites (MnxCo1–xFe2O4) with variable Co/Mn molar ratios is deeply discussed. Single-phase ferrites with similar crystallite and particle sizes (about 10 nm), size dispersity (14%), and weight percentage of capping oleate molecules (17%) were obtained by an oleate-based solvothermal approach. The similarities among the samples permitted the interpretation of the results exclusively on the basis of the actual composition, beyond the other parameters. The temperature and magnetic field dependences of the magnetization were studied together with the interparticle interactions by DC magnetometry. Characteristic temperatures (Tmax, Tdiff, and Tb), coercivity, anisotropy field, and reduced remanence were found to be affected by the Co/Mn ratio, mainly due to the magnetic anisotropy, interparticle interactions, and particle volume distribution. In addition, the cobalt and manganese distributions were hypothesized on the basis of the chemical composition, the inversion degree obtained by 57Fe Mössbauer spectroscopy, the anisotropy constant, and the saturation magnetization.

Investigation into flow and heat transfer characteristics of sparse particles in beam fluidized bed receiver

In this paper, numerical simulation is carried out for the beam-type fluidized bed receiver. The mixture of air and inert particles is used as heat transfer medium in the simulation. Eulerian–Lagrange method and DO radiation model are used to describe the flow and heat transfer characteristics of gas and inert particles in fluidized bed receiver. At the same time, DPM method is used to consider the effect of particles on radiation field and the interaction between particles and flow field. Tracking particle wrapping and the temperature distribution, flow and heat transfer process of particles are analyzed. The particle temperature distribution is mainly concentrated in 550–800K, and 70% of the particles participate in effective heat transfer in terms of radial particle temperature and volume distribution. When the number of high temperature particles reaches 50%, the heat absorption capacity of mixed medium is optimal. At the same time, the fitting function with particle volume fraction as independent variable is obtained.

Estimation of Ultrahigh Resolution PM2.5 Mass Concentrations Based on Mie Scattering Theory by Using Landsat8 OLI Images over Pearl River Delta

The aerosol optical depth (AOD), retrieved by satellites, has been widely used to estimate ground-level PM2.5 mass concentrations, due to its advantage of large-scale spatial continuity. However, it is difficult to obtain urban-scale pollution patterns from the coarse resolution retrieval results (e.g., 1 km, 3 km, or 10 km) at present, and little research has been conducted on PM2.5 mass concentration retrieval from high resolution remote sensing data. In this study, a physical model is proposed based on Mie scattering theory to evaluate the PM2.5 mass concentrations by using Landsat8 Operational Land Imager (OLI) images. First, the Second Simulation of the Satellite Signal in the Solar Spectrum (6S) model (which can simulate the transmission process of solar radiation in the Earth-atmosphere system and calculate the radiance at the top of the atmosphere) is used to build a lookup table to retrieve the AOD of the coast and blue bands based on the improved deep blue (DB) method. Then, the Angstrom formula is used to obtain the AOD of the green and red bands. Second, the dry near-surface AOD of four bands (coast, blue, green, red) is obtained through vertical correction and humidity correction. Third, aerosol particles are divided into four types based on the standard radiation atmosphere (SRA) model, and the optical properties of different aerosol types are analyzed to derive the volume distribution of aerosol particles. Finally, the relationship between the dry near-surface AOD of each band and the volume distribution of four aerosol particles is correlated, based on Mie scattering theory, and a physical model is established between the AOD and PM2.5 mass concentrations. Then, the distribution of PM2.5 mass concentrations is obtained. The retrieval results show that the distribution of AOD and PM2.5 at the urban scale in detail. The AOD results show that a reasonable relationship with a correlation coefficient (R2) of 0.66 and root mean square error (RMSE) of 0.1037 between Landsat8 OLI AOD and MODO4 DB AOD at 550 nm. The PM2.5 retrieval results are compared with the PM2.5 values measured by ground monitoring stations. The RMSEs for a certain day in different years, including 2017, 2018, 2019, and 2020, are 11.9470 μg/m³, 11.9787 μg/m³, 7.4217 μg/m³, and 5.4723 μg/m³, respectively. The total RMSE is 10.0224 μg/m³. The ultrahigh resolution PM2.5 results can provide pollution details at the urban scale and support better decisions on urban atmospheric environmental governance.

O perando lab-Based X-Ray Computed Tomography of Zn-Air Batteries

In recent years, zinc-air (Zn-air) batteries have attracted increasing attention thanks to their high theoretical energy density, high relative abundance of materials, safety and relative low cost, compared with lithium counterparts1. Whilst they have been widely used in hearing aid technologies2, Zn-based technologies are considered promising for grid-based storage applications and back-up power2. However, challenges still remain for the wide-range adoption of the technology, including challenges facing finding good bi-functional catalysts, avoiding dendrite growth on the Zn anode and increasing cyclability and lifetime. Whilst there is a significant research focus on improved cathode materials, less work has focused on the complex charge/discharge reactions of the zinc anode 3. Thus, this work has a particular focus on characterisation and electrode engineering of the anode.X-ray computed tomography (CT), which is a non-destructive 3D imaging technique capable of imaging inside samples, has been widely used in recent years for imaging energy materials4. A significant advantage of the technique is the ability to carry out 4D studies (i.e. three spatial dimensions plus time), which allows for morphological evolution to be elucidated during device operation. Thus, structural features (like dendrites, or the conversion of zinc to zinc oxide) can be visualised and correlated to electrochemical performance. For Zn-air batteries, X-ray CT has been used in a number of studies, although a greater number have used synchrotron X-ray sources than lab-based X-ray instruments5–7.This work will discuss the development of bespoke Zn-air cells suitable for correlative, operando characterisation using lab-based techniques, where 3- and 4D imaging methods, like X-ray CT, are combined with electrochemical studies to deepen the understanding of the reactions of zinc and zinc-oxide during cell discharge and charge, respectively. Electrochemical cell design for operando imaging is a particular challenge, since there is a trade-off between obtaining good electrochemical performance and having a cell whose size is suitable for resolving the desired features of interest in the sample. As shown in Figure 1a), the cell design is relatively simple and transport of air to the cathode occurs via holes milled into the casing. Furthermore, the cell design is highly versatile and can be easily adapted to suit the desired imaging resolution. The ability to carry out multiscale imaging is a particular advantage, given that features of Zn-air cells range from the mm thick electrodes to μm/nm-size particles.Whilst 2D techniques like SEM can only determine surface information about a sample, X-ray CT can examine the interfaces between materials, which is particularly important for understanding how zinc particles evolve during cell operation. The cell sits between a source and detector (Figure 1b), on a rotating stage and the resulting 3D volume can be analysed by segmentation of individual features. Shown in Figure 1c is an example volume of a zinc anode. The particles of zinc can clearly be observed on the top of the carbon paper substrate (Figure 1c). By separating the individual particles and assigning each individual zinc particle a unique number (represented in Figure 1d by the various colours), a range of metrics can be determined, such as number of particles or particle volume distribution (Figure 1e). Insights gained through operando imaging experiments, including a deepened knowledge of the migration and transformation of individual zinc particles, can then be translated into improved electrode design.1 P. Gu, M. Zheng, Q. Zhao, X. Xiao, H. Xue and H. Pang, J. Mater. Chem. A, 2017, 5, 7651–7666.2 V. Caramia and B. Bozzini, Mater. Renew. Sustain. Energy, 2014, 3, 28.3 J. Zhang, Q. Zhou, Y. Tang, L. Zhang and Y. Li, Chem. Sci., 2019, 10, 8924–8929.4 T. M. M. Heenan, C. Tan, J. Hack, D. J. L. Brett and P. R. Shearing, Mater. Today, 2019, 31, 69–85.5 D. Stock, C. Pompe and D. Schröder, Chemie-Ingenieur-Technik, 2019, 91, 555–559.6 M. K. Christensen, J. K. Mathiesen, S. B. Simonsen and P. Norby, J. Mater. Chem. A, 2019, 7, 6459–6466.7 V. Yufit, F. Tariq, D. S. Eastwood, M. Biton, B. Wu, P. D. Lee and N. P. Brandon, Joule, 2019, 3, 485–502. Figure 1

Effect of geometric parameters at open turbine combined structure on flow field distribution of dry granulation for Si3N4 powder

To improve the uniformity of the flow field and the poor axial velocity in the chamber of Si3N4 dry granulation, the influence of geometric parameters at open turbine combined structure on the flow field distribution is studied. The Euler–Euler gas-solid two-phase flow model is established and the physical model of dry granulation chamber under the combined structure is simplified. Under the same radial structure, the volume distribution and velocity field of Si3N4 particles in the granulation chamber with a different number and angle of the axial structure at the open turbine are analyzed by the CFD method. The influence of the axial structure at the open turbine on the flow field distribution of Si3N4 particles under different geometric parameters is compared. The results show that the axial structure of the open turbine in the granulation chamber is the most uniform when the number of blades is 6 and the inclination angle is [Formula: see text], and the circulating flow of the upper and lower parts of Si3N4 powder is strong.

CFD-DEM modelling of the migration of fines in suspension flow through a solid packed bed

In this work, based on the unresolved CFD-DEM framework, a smoothed volume distribution model (SVDM) is developed to simulate the migration of fines in suspension flow through a solid packed bed. In this model, the porosity of coarse solids is calculated by a smoothed particle volume distribution. The model is validated using two solid-liquid systems. Compared with divided particle volume method (DPVM) with a low-resolution mesh, the SVDM method allows a high-resolution mesh and can achieve a high efficiency and applicability. Moreover, the effects of inlet fine concentration and solid/fine size ratio on fines migration behaviour are studied. The results indicate that more holdup of fine powders especially in the upper zone can be captured, when a higher concentration fine phase or a larger size ratio is used. Based on the local holdup information, four powder migration mechanisms are proposed, i.e., size exclusion, powder bridging, powder deposition and powder locking.