Equivalent Radius Research Articles

Numerical scattering simulations for estimating soot aggregate morphology from nephelometer scattering measurements

Nephelometers are regularly used for air quality monitoring through scattering measurements of aerosols in the atmosphere. Less attention has been paid to the potential of estimating soot morphological parameters from nephelometer measurements in combination with scattering theory. In this work, we perform a fundamental laboratory study where an Ecotech Aurora 3000 nephelometer is used for measuring the scattering properties of soot with different characteristics. The nephelometer monitors the forward and backward scattering at three wavelengths (450 nm, 525 nm, and 635 nm) to retrieve information on the ratio of forward and backward scattering intensities, as well as the scattering wavelength dependence. An inverse scattering method, based on the Rayleigh–Debye–Gans theory, for determination of the equivalent fractal dimension (Df) and radius of gyration (Rg) of soot particles from the experimental scattering data was developed. It is shown that the inverse method can estimate Rg and Df when Rg<185nm and from the wavelength dependence, information on the relative amount of organic soot could be obtained. For validation, estimated parameters are compared with the morphological parameters of soot sampled from the mini-CAST soot generator and evaluated using transmission electron microscopy (TEM). Uncertainties and limitations of the procedure are discussed.

Plastic buckling of axially compressed cones using the equivalent cylinder approach

This paper aims to propose an equivalent cylinder radius for the buckling behavior of relatively thick steel conical shells subjected to axial compression. This is both experimental and numerical/theoretical work. Test data on this subject is scarce and the existing design recommendations have not been validated experimentally, especially in the plastic buckling region. In order to authenticate the appropriateness of these existing rules and suggest others, collapse tests were conducted at the University of Liverpool and Universiti Teknikal Malaysia Melaka on cones and their equivalent cylinder counterparts. The first set of experiments consisted of two nominally identical cones and one equivalent cylinder. These mild steel models were CNC-machined, with the cones having the following geometric parameters: r2 = 99 mm, r1 = 49 mm, h = 100 mm, β = 26.56°, wall thickness of 3 mm. The equivalent cylinder was machined using the DNV CV 30.1 equivalent cylinder radius. The results show that the equivalent cylinder overestimates the conical models by 35% and 44% respectively.The second set of four steel models consisted of: two cones having, r2 = 70 mm, r1 = 40 mm, h = 112 mm, β = 15°, wall thickness of 2 mm, and two equivalent cylinders designed according to ‘ECCS 2008 equivalent cylinder radius’. All four shells were manufactured in pairs using the traditional welding process. It has become evident here that the experimental collapse load predicted by the equivalent cylinders underestimated that of the cones by about 9%. Furthermore, numerical calculation indicated that the equivalent cylinder radius, suggested by the ECCS 2008, mimics its conical counterpart with good accuracy for cones with cone angle, 5° ≤ β ≤ 20°. However, for cones with large cone angle, β > 20°, one obtains large discrepancies between the cone and the equivalent cylinder. This highlights the weakness of the ECCS 2008 recommended equivalent cylinder radius. Finally, a new equivalent cylinder radius for axially compressed cones is suggested with better accuracy as compared to the ECCS current recommendation, and this in turn could be useful for design purposes.

Experimental study on ultra high pressure hydraulic cutting seam pressure relief and permeability enhancement of strip drilling along seam in C19 coal seam of Shiping No.1 Coal Mine

In view of the low permeability of C19 coal seam in Shiping No.1 coal mine, the large amount of drilling work and the long time of reaching the standard of extraction, which seriously restricts the replacement of mining, the ultra-high pressure hydraulic cutting technology is adopted to improve the permeability of coal seam. After using ultra-high pressure hydraulic slotting, the average single hole chip removal is 3.31t, the average chip removal per cutter is 0.38t, the width of slotting slot is 4cm, and the equivalent radius of slotting slot is 1.59m. The field test results show that the pressure relief and permeability enhancement effect of 11719 lifting machine roadway (East) in Shiping No.1 mine is significantly improved under this parameter condition. The single hole drainage pure quantity of slotted drilling is 7.8 times that of ordinary drilling, the concentration is increased by 2-2.4 times, the drilling construction quantity is reduced by 30.6%, the drilling drainage time is shortened by 80.7%, and the drilling gas drainage efficiency is greatly improved.

Particle composition and morphology over urban environment (New Delhi): Plausible effects on wheat leaves

Particulate matter (PM) deposition on leaves adversely affects physical, chemical and biological nature of agricultural crops resulting in their loss of productivity and yield. Wheat being a staple food in major parts of Northern India and around the World, has been selected for research purpose by designing a study to explore the probable effects of PM deposition on wheat leaves and wheat crops to ensure the food security. PM5 (Particulate matter with aerodynamic diameter <5 μm) and Dry Deposited Particulate Matter (DDPM) on wheat leaves (Leaf_DDPM) were collected from the wheat crop field in Indian Agriculture Research Institute (IARI), New Delhi for growing and harvesting season of wheat crops (i.e. December 2014 to April 2015). The EDS (Energy Dispersive Spectroscopy) analysis was used for this study and the individual particle analysis revealed the presence of both acidic and alkaline components like C, Al, Si, Fe, Ca, K, S and Mg. The offline characterization tool i.e. SEM (Scanning Electron Microscope) was utilized for obtaining the micrographs which clearly showed the presence of some angular, sharp-edged and spherical particles consisting of both smooth and rough texture. Apart from that, prevalence of slightly non-spherical particles with aspect ratio of range (>1.20–1.40) and CIR (>0.70–0.80) for both PM5 and leaf_DDPM were observed. The size distribution of individual particles for both PM5(#194 particles) and Leaf_DDPM(#657 particles) revealed that Surface Equivalent Radius (SER) and Volume Equivalent Radius (VER) of particles observed to be 0.40–0.80 μm while surface area to be 0–1 μm2. These particles may easily block stomatal openings (with typical diameter range: 42–51 μm) of wheat leaves and damage internal leaf tissues while particle VER determines the interaction of incoming solar radiation with leaf surfaces. Average PM5 concentrations ± Standard deviations (μg/m3) were reported to be 231.05 ± 113.03. The XRF (X-Ray Fluorescence) spectrometer analysis of bulk PM5 revealed the concentrations of non-carbonaceous elements (μg/m3) as N (67.34 ± 16.09), Si (27.44 ± 11.01), Al (7.79 ± 3.37), S (3.88 ± 2.24), Na (2.29 ± 0.94), Mg (1.65 ± 0.62), K (0.51 ± 0.26), Ca (0.60 ± 0.26), Fe (0.54 ± 0.26), Cr (1.10 ± 0.70), Zn (0.05 ± 0.03), P (0.10 ± 0.03), Cu (0.07 ± 0.06). The dominant elemental oxides were calculated as SiO2, Al2O3, SO42−, Na2O, MgO, K2O, CaO, Fe2O3, Cr2O3, ZnO, P2O5, Cu2O with variable concentrations. In high humid conditions, with relative humidity (~85%) during the vegetative and flowering growth stages of wheat crops, presence of C and S rich acidic and hygroscopic particles may cause the corrosion of wheat leaves that ultimately affect the wheat crops.

Improving the mechanical-mathematical model of grain mass separation in a fluidized bed

This paper has substantiated the prospect of modeling the processes of separating grain mass into fractions as one of the tasks in the production of high-quality seed material. It has been determined that this could optimize the parameters of separation processes and design new working surfaces for its implementation. It is noted that modeling should take into consideration the influence of the structural and kinematic parameters of grain cleaning machines, the physical and mechanical properties of raw materials, the intralayer processes and forces. The reported theoretical study has improved the mechanical-mathematical model of grain mass separation in a pseudo-fluidized bed according to its density. The model establishes a relationship between the effective coefficient of dynamic viscosity and the density of particles in the discrete and continuous phases and the volumetric concentration of discrete phase particles. At the same time, the porosity of a fluidized bed has been accounted for, as well as the longitudinal and transverse angles of inclination of the base surface to the horizontal plane, the amplitude and frequency of oscillations of the particles of the continuous phase; the direction angle of oscillations relative to the perpendicular to the base surface. The adequacy of the improved mechanical-mathematical model has been confirmed by comparing the experimental and theoretical results of grain mass fractionation modeling. It was found that the differences in the density values of the separated fractions of GM did not exceed 7...8 %, that is, they were within the margin of error. It has been established that the improved model of grain mass separation in a fluidized bed could be used to determine the rational values for the parameters of a pneumatic sorting table that is used for the fractionation of the corresponding seed material. The initial data, in this case, are the density of the continuous and solid phases of grain mass, the friction coefficient of the seeds, and the equivalent radius of the particle. The result of modeling is the rational values of the amplitude and oscillation frequency of the working surface of the pneumatic sorting table, and the angles of inclination of the working surface

Hovering of an Electrically Actuated Spacecraft in a Small-Body Plasma Field

This paper presents simulation models and an analysis of the hovering capability of an electrostatic spacecraft around a small celestial body. The hovering capabilities of an electrically actuated spacecraft are evaluated by combining orbital dynamics analysis with 3-D fully kinetic particle-in-cell simulations of asteroid/spacecraft interactions with the solar-wind plasma. The zero-velocity curves obtained from the analysis allow the identification of the equilibrium points for different levels of charge. The analysis of the system equilibria indicates the presence of equilibrium points in the combined gravitational, electrostatic, and solar illumination fields, most of which can be obtained by charging the spacecraft negatively. The charge-to-mass ratio needed to hover is obtained for different orbital positions, and an analysis of the sensitivity of the equilibria with respect to the spacecraft equivalent radius and with respect to the sun-to-main-body distance provides additional insight into the system dynamics.

Measurement and assessment of corona current density for HVDC bundle conductors by FDM integrated with full multigrid technique

This paper presents an intensive measurement and analysis of monopolar ionized fields in bundled high voltage direct current (HVDC) conductors using the finite difference method based on the full multigrid technique. The positive feature of this study is that it considers the comprehensive representation of the bundle conductor, unlike the existing studies that approximate the bundle conductor with an equivalent conductor radius. Firstly, the proposed method is compared with previous experimental results. Secondly, a flexible laboratory model for the bundled HVDC conductors is constructed. Thirdly, the laboratory model is exploited to validate the numerically computed current density distribution on the ground plane and corona current for different bundles’ numbers and different distances between bundles. Bundles of one, two, and four conductors are adopted in the experimental setup. For the same applied voltage, the results verified that the corona current decreases by increasing the bundles’ number and/or minimizing the spacing between bundles. Consequently, the obtained results confirmed that corona power losses can be minimized, without needing the traditional procedures that involve increasing either the conductor radius or its height above the ground. The results of the proposed numerical approach concurred well with the present and past laboratory results.

Investigation on laser cavitation micro-forming process: Deformation behavior of 1060 aluminum foil and bubble evolution in a gap

Abstract The water-jet and shock waves generated by laser-induced cavitation were employed to the laser cavitation micro-forming (LCMF). The LCMF is a new method for fabricating micro features on two pieces of metal foils simultaneously. The mechanism of LCMF was investigated at the non-dimensional parameter γ (γ = L/2Req, where L is the width of the gap, and Req is the equivalent radius). The dynamic characteristics of laser-induced cavitation bubble in a gap were studied using a high-speed photography and numerical simulation. The shock waves were detected by the hydrophone and the velocity field distribution was obtained from numerical simulation. The 1060 aluminum foil was used in LCMF, and the surface morphology, forming depth, surface roughness and thickness distribution of the formed aluminum micropores were investigated. The results indicate that the non-dimensional parameter γ has a great impact on bubble evolution in a gap. At γ = 1.29, the pressure intensity of plasma shock wave, bubble collapse shock wave and water-jet are 72.7 MPa, 40 MPa and 65.3 MPa, respectively. The forming depth, surface roughness and thickness thinning ratio decreased with the increase of γ, and maximum thickness thinning occurred at the fillet.

Experimental study of bubble-droplet interaction in water; the effect of water salinity on the drainage time

Interaction between an air bubble and an oil droplet in aqueous mediums was studied experimentally to investigate the encapsulation phenomena in ternary fluid systems. A special experimental setup was designed, and the influence of the bubble-droplet size and water salinity on the drainage times of the intervening pseudo-emulsion film were investigated. The drainage, coverage, and rupture times for the studied sizes (200–700 µm) were found to be in the range of 0.07–5.6 s, 20–70 ms, and less than 1 ms, respectively. The drainage times for de-ionized water first increase with equivalent radius, from slightly more than 1 s to around 3 s, then decrease into 1 s again for radiuses larger than 550 µm. On the other hand, a decrease in the measured drainage times was observed in the high salt concentrations (1 M NaCl), and their values remain less than 1 s for the studied bubble-droplet radius. The results also show that the drainage times in pure water are scattered, while the obtained data for the salt solution suggests a concentrative nature. Based on the interplay between capillary and disjoining pressures, it was argued that in the latter case, the outcome of the interaction is independent of the random fluctuations and instabilities and seems to be deterministic, while for the former, these microscopic events control the drainage and coalescence process.

A New Integrated Technique for Saturation Height Function Modeling based on Modified EQR Method

Equivalent Radius (EQR) is a relatively new normalized capillary pressure method for modeling of the saturation height function. In this method petrophysical data such as well logs, special and routine core analysis have been used in an integrated manner.&#x0D; The main purpose of this study is to investigate dynamic behavior of the fluid flow through porous media with a new integrated technique for saturation height function modeling. Amongst different methods, EQR method that originally developed by Engstrom in 1996 has been selected for further study. Although this method can model the initial water saturation with high accuracy but it only can be applicable for low permeability formations. However, there is still an incomplete understanding its application for other rock units with higher degree of porosity and permeability. For this purpose, we present a Modified EQR (MEQR) based on iterative curve fitting procedure. To demonstrate the capabilities of MEQR method, one of the Iranian oil field data located in southwest of Iran with quite high degree of permeability in its porous sandstone layers has been used.&#x0D; It is shown that this technique can accurately predict the initial water saturation in all rock types and in each cell of the reservoir with very good correlation coefficient achieved in comparison with interpreted saturation well logs.

Nicodrilus nocturnus and Allolobophora icterica drill compacted soils but do not decrease their bulk density – A laboratory experiment using two contrasted soils at two different compaction levels

Earthworms are known to play an important role in soil processes, especially in the regeneration of soil structure. However, quantitative studies about their role on soil physical properties are still scarce. In this study the effects of two earthworm species (Nicodrilus nocturnus as anecic, Allolobophora icterica as endogeic) following three treatments (N. nocturnus only, A. icterica only and both species with 80% weight of N. nocturnus and 20% of A. icterica) on soil specific volumes and pore properties are evaluated in mesocosms (30 cm height and 15 cm diameter) for a loamy Anthrosol and a silt loam Luvisol. The soils were repacked to bulk density observed in the field (1,15 and 1,25 g cm−3 respectively) and to compacted bulk density (1,4 and 1,5 g cm−3 respectively). Except earthworm-free controls, introduced earthworm biomass was close to 500 g.m−2. The experiment lasted 23 weeks, under constant temperature and soil matrix potential, and earthworms were fed with hay. The impact of earthworms on soil porosities and specific volumes was assessed using (i) computed tomography on mesocosm and (ii) shrinkage analysis on undisturbed cubic samples (150 cm3). Anecic surface cast bulk density was determined after wax coating.At mesocosm scale, the specific volume of compacted soils increased significantly with the anecic and mixed earthworm treatments (+1.9% for the Anthrosol and +2.6% for the Luvisol), while no change was observed with endogeics regardless of the initial level of compaction or the soil type. After subtracting the burrow volumes, the remaining soil matrix specific volume showed significant decrease with earthworms in case of loose soils, particularly with endogeics with 5.6% decrease of the specific soil matrix volume, while the compacted soil matrix was not decompacted. At undisturbed cubic sample scale, shrinkage analysis confirmed these observations with earthworms decreasing the larger structural pores and promoting a more rigid plasma. Anecic surface casts showed intermediate bulk density (0.82 cm3 g−1 for the Anthrosol and 0.73 cm3 g−1 for the Luvisol) between compacted (0.73 cm3 g−1 for the Anthrosol and 0.67 cm3 g−1 for the Luvisol) and loose (0.88 cm3 g−1 for the Anthrosol and 0.81 cm3 g−1 for the Luvisol) soil matrices. We concluded that the decompaction effect of earthworms was due to the opening of burrows at mesocosm soil scale, while the matrix volume was i) either compacted in case of loose soil especially with endogeics at the expense of the >150 µm equivalent radius structural pores or ii) unchanged in case of compacted soil. Our results support the conclusion that earthworms alone cannot regenerate the matrix of compacted soils and even compact the soil matrix in case of loose soils.

Semianalytic Functions to Calculate the Deposition Coefficients for Ice Crystal Vapor Growth in Bin and Bulk Microphysical Models

AbstractNumerical cloud models require estimates of the vapor growth rate for ice crystals. Current bulk and bin microphysical parameterizations generally assume that vapor growth is diffusion limited, though some parameterizations include the influence of surface attachment kinetics through a constant deposition coefficient. A parameterization for variable deposition coefficients is provided herein. The parameterization is an explicit function of the ambient ice supersaturation and temperature, and an implicit function of crystal dimensions and pressure. The parameterization is valid for variable surface types including growth by dislocations and growth by step nucleation. Deposition coefficients are predicted for the two primary growth directions of crystals, allowing for the evolution of the primary habits. Comparisons with benchmark calculations of instantaneous mass growth indicate that the parameterization is accurate to within a relative error of 1%. Parcel model simulations using Lagrangian microphysics as a benchmark indicate that the bulk parameterization captures the evolution of mass mixing ratio and fall speed with typical relative errors of less than 10%, whereas the average axis lengths can have errors of up to 20%. The bin model produces greater accuracy with relative errors often less than 10%. The deposition coefficient parameterization can be used in any bulk and bin scheme, with low error, if an equivalent volume spherical radius is provided.

Characteristics of Passive Solute Transport across Primary Rat Alveolar Epithelial Cell Monolayers.

Primary rat alveolar epithelial cell monolayers (RAECM) were grown without (type I cell-like phenotype, RAECM-I) or with (type II cell-like phenotype, RAECM-II) keratinocyte growth factor to assess passive transport of 11 hydrophilic solutes. We estimated apparent permeability (Papp) in the absence/presence of calcium chelator EGTA to determine the effects of perturbing tight junctions on “equivalent” pores. Papp across RAECM-I and -II in the absence of EGTA are similar and decrease as solute size increases. We modeled Papp of the hydrophilic solutes across RAECM-I/-II as taking place via heterogeneous populations of equivalent pores comprised of small (0.41/0.32 nm radius) and large (9.88/11.56 nm radius) pores, respectively. Total equivalent pore area is dominated by small equivalent pores (99.92–99.97%). The number of small and large equivalent pores in RAECM-I was 8.55 and 1.29 times greater, respectively, than those in RAECM-II. With EGTA, the large pore radius in RAECM-I/-II increased by 1.58/4.34 times and the small equivalent pore radius increased by 1.84/1.90 times, respectively. These results indicate that passive diffusion of hydrophilic solutes across an alveolar epithelium occurs via small and large equivalent pores, reflecting interactions of transmembrane proteins expressed in intercellular tight junctions of alveolar epithelial cells.

A practical building energy consumption anomaly detection method based on parameter adaptive setting DBSCAN

In order to realize the Building Energy Consumption Anomaly Detection (BECAD) for the green building assessment, the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) is adopted for data clustering. To deal with the parameter setting difficulty of the DBSCAN, a practical parameter adaptive setting method is proposed. The presented method determines values of the DBSCAN parameters, MinPts and ε, according to four distribution characteristics (average data distance, data local densities, cosine similarity, and equivalent space radius) of data, and does not need prior knowledge of the datasets. Furthermore, parameter values determined by the proposed method can improve the clustering effect of the DBSCAN on datasets with various data densities. After testing the proposed method with open datasets, DBSCAN with the parameter adaptive setting method is applied to the BECAD. Experiment results show that identified building energy utilization patterns and abnormal buildings are reasonable and the results can offer the management departments a clear understanding of building energy consumption patterns, as well as decision supports to make subsequent improvement measures.

Evolutions of the unfrozen water content of saturated sandstones during freezing process and the freeze-induced damage characteristics

The precise determination of unfrozen water content is of great significance to understand the freezing process of pore water and reveal the freeze-induced damage mechanism for frozen rock mass. In this study, low field nuclear magnetic resonance (LF-NMR) tests were conducted on five types of frozen sandstone samples. The changes in the T2 distribution and unfrozen water content (including unfrozen bound water content and unfrozen movable water content) were obtained and then analyzed. The experimental results indicate that there is little unfrozen movable water exists in the sandstone sample at the temperature of -5 °C and lower, whereas the amount of the unfrozen bound water is slowly decreased during the freezing process. The pore size distribution largely dominates the speed of water-ice phase transition and the total ice volume in the sandstone samples. A larger equivalent average pore radius (rm) leads to a higher speed of water-ice phase transition. The freeze-induced strains of the frozen sandstones were theoretically calculated based on a frost heave model. It is indicated that the freezing strain increases rapidly in the temperature range of 0 °C to -10 °C, while tends to be stable with further decreasing the temperature. Owing to the different pore size distributions, the movable water induces more substantial freezing strain than the bound water in terms of the Wuding sandstone and Linyi sandstone having an rm larger than 1.6 μs. However, it is exactly inverted for the other three sandstones including the Tengchong sandstone, Luzhou sandstone and Zigong sandstone with much smaller rm. The study provides a reasonable method for quantifying the unfrozen water content and freeze-induced strain in frozen rock, as well as important guidance for the design and construction of rock engineering in cold regions.

Simulation Analysis of Gas Bubble Formation and Escape in Non-Newtonian Drilling Fluids

In this study, the formation and escape movements of a bubble injected in non-Newtonian drilling fluid through a pore were numerically simulated using a volume of fluid method. The pattern of a single bubble and the pressure and velocity fields of the surrounding liquid phase during the bubble formation were analyzed and compared with experimental results; based on the comparison, the formation and escape properties of the bubble were further studied. In particular, the effects of static shear force, consistency coefficient, and flow behavior index on the growth and escape time of the bubble were analyzed. The results show that, owing to the effect of velocity on the viscosity of a non-Newtonian drilling fluid, the escape time and volume of the bubble increase with an increase in static shear force, consistency coefficient, and flow behavior index. Among the three parameters, the flow behavior index has the greatest effect. This is because the shear disturbance of a bubble to its surrounding fluid during its growth and escape, caused by the shear thinning of a yield-power-law fluid, reduces the fluid viscosity. The shear thinning decreases, and the resistance to the bubble increases as the flow behavior index approaches 1, leading to larger bubble formation times and separation volumes. An empirical formula for predicting the equivalent radius of bubbles considering the liquid yield stress, inertial force, viscous force, and surface tension is established. The average error of predicting the equivalent radius of detached bubble is 0.80%, which can provide a reference for the better study of bubble migration and flow pattern in non-Newtonian fluid.

Acoustic backscattering observations from non-spherical gas bubbles with ka between 0.03 and 4.4.

The study of gas bubbles in liquid media is of importance in many areas of research. Gas bubbles are often studied using in situ measurement techniques; however, acoustic inversion techniques have also been used to extract physical properties of gas bubbles. These inversion techniques rely on existing analytical scattering models; however, these models often assume that the gas bubbles are spherical in shape and have an equivalent bubble radius, a, that is small compared to the incident acoustic wavelength (ka ≪ 1), which is not always valid. This study aims to understand how the departure from these assumptions affects the acoustic backscattering cross section, σbs, of non-spherical gas bubbles. Experimental estimates of σbs of non-spherical gas bubbles of different sizes, with ka values ranging between 0.03 and 4.4, were compared to four commonly known analytical σbs models. All models performed equally at predicting σbs for ka smaller than 0.5; however, there was no model that better predicted the experimental estimates of σbs for ka larger than 0.5, regardless of bubble shape. Large variabilities in the experimental estimates of σbs are observed for ka larger than 0.5, which are caused by the variability in bubble shape and size, as well as the bubble's orientation.

Tuning Sedimentation Through Surface Charge and Particle Shape

AbstractMud forms the foundation of many coastal and tidal environments. Clay suspensions carried downstream from rivers encounter saline waters, which encourages aggregation and sedimentation by reducing electrostatic repulsion among particles. We perform experiments to examine the effects of surface charge on both the rate and style of sedimentation, using kaolinite particles as a model mud suspension and silica spheres with equivalent hydrodynamic radius as a control. Classic hindered settling theory reasonably describes sedimentation rate for repulsive clay particles and silica spheres, which form a highly concentrated jamming front. The hindered settling description breaks down for attractive clay particles, which aggregate to form clay gels that consolidate like a soft solid. Water flow form fracture‐like channels in the bulk of the gel, which disappear as gel enters a creep regime. Results may help toward understanding the effect of surface charge and particle shape on the sedimentation and erodibility of natural mud.

Li-ion distribution and diffusion-induced stress calculations of particles using an image-based finite element method

The realistic particles in lithium batteries have unique microstructures, which should be determined in the analysis of chemo-mechanical behaviors during charge/discharge cycles. In this paper, an image-based finite element method (IBFEM) is developed to investigate the volume expansion, Li-ion distribution, and diffusion-induced stress (DIS) of a realistic particle. A threshold-based segmentation method is proposed to improve the segmentation accuracy based on the improved threshold of each phase. Based on the IBFEM, the active material phase, conductive additive and binder phase, and pore space are segmented and reconstructed using microstructural images. The volume expansion, Li-ion distribution, and DIS of an image-based SnO2 nanoparticle are simulated under galvanostatic/potentiostatic charging process. The predicted lithiation that induced the volume expansion of the SnO2 nanoparticle is approximately coincided with the experiment result observed by TEM. The realistic particle shape and size have a significant impact on the Li-ion distribution and DIS. The concentration profile is analogous to the boundary of the realistic particle at the early stage of lithiation and gradually disappears with further lithiation. The von Mises stress near a concave region is higher than that near a convex region. The maximum von Mises stress in the realistic particle with a larger equivalent radius is higher than that in the smaller particle with the same state of charge. By considering the comprehensive effect of particle shape and size, the size can be increased appropriately while guaranteeing the particle mechanical integrity. These results will contribute to understanding DIS evolution in a realistic particle and can be used to guide the selection of active particles for electrode preparation.

Measurement of time-varying electron density of the plasma generated from a small-size cylindrical RDX explosion by Rayleigh microwave scattering

It is challenging to measure the electron density of the unsteady plasma formed by charged particles generated from explosions in the air, because it is transient and on a microsecond time scale. In this study, the time-varying electron density of the plasma generated from a small cylindrical cyclotrimethylenetrinitramine (RDX) explosion in air was measured, based on the principle of microwave Rayleigh scattering. It was found that the evolution of the electron density is related to the diffusion of the detonation products. The application of the Rayleigh microwave scattering principle is an attempt to estimate the electron density in explosively generated plasma. Using the equivalent radius and length of the detonation products in the bright areas of images taken by a high-speed framing camera, the electron density was determined to be of the order of 1020 m−3. The delay time between the initiation time and the start of variation in the electron-density curve was 2.77–6.93 μs. In the time-varying Rayleigh microwave scattering signal curve of the explosively generated plasma, the electron density had two fluctuation processes. The durations of the first stage and the second stage were 11.32 μs and 19.20 μs, respectively. Both fluctuation processes increased rapidly to a peak value and then rapidly attenuated with time. This revealed the movement characteristics of the charged particles during the explosion.