Phase Particles Research Articles

Modelling the dynamic gas/particle partitioning process of semi-volatile organic compounds emitted from point sources: Quantitative analysis and impact assessment

The deleterious impact of pollution point sources on the surrounding environment and human has long been a focal point of environmental research. When considering the local atmospheric dispersion of semi-volatile organic compounds (SVOCs) around the emission sites, it is essential to account the dynamic process for the gas/particle (G/P) partitioning, which involves the transition from an initial state to a steady state. In this study, we have developed a model that enables the prediction of the dynamic process for G/P partitioning of SVOCs, particularly considering the influence from emission. It is important to note that the dynamic processes of the concentrations of SVOCs in particle phase (CP) and in gas phase (CG) differ significantly. These differences arise due to the influence of two critical factors: particulate proportion of SVOCs in the emissions (ϕ0) and octanol-air partitioning coefficient (KOA). The validity of our model was assessed by comparing its predictions of the extremum value of the G/P partitioning quotient (KP) with the results obtained from the steady-state model. Remarkably, the characteristic time (tC), used to evaluate the timescale required for SVOCs to reach steady state, demonstrated different variations with KOA for CP and CG. Additionally, the values of tC were quite different for CP and CG, which were markedly influenced by ϕ0. For some SVOCs with high KOA values, it took approximately 35 h to reach steady state. Furthermore, it was found that the time to achieve 95 % of steady state (t95 ≈ 3tC) could reach approximately 105 h. This duration is sufficient for chemicals to disperse from their emission site to the surrounding areas. Therefore, it is crucial to consider the dynamic process of G/P partitioning in local atmospheric transport studies. Moreover, the influence of ϕ0 should be incorporated into future investigations examining the dynamic process of G/P partitioning.

Sources of Wintertime Atmospheric Organic Pollutants in a Large Canadian City: Insights from Particle and Gas Phase Measurements

Sources of Wintertime Atmospheric Organic Pollutants in a Large Canadian City: Insights from Particle and Gas Phase Measurements

Unsteady MHD dusty fluid flow over a cone in the vicinity of porous medium: a numerical study

This research presents an unsteady free convection magnetohydrodynamics (MHD) dusty fluid flow over a vertical cone enclosed inside a porous medium. The Crank–Nicolson approach is used to get the numerical solutions for these non-linear partial differential equations (PDEs). The velocity and temperature distributions are graphed numerically for a wide range of physical parameters to highlight important characteristics of the solutions. The results showed that increasing the porosity parameter leads to a rise in the velocity profile for the fluid and dust phases, while doing the reverse with the rise of the magnetic parameter, fluid-particle interaction parameter, and mass concentration of the particle phase parameter. Additionally, it is shown that the temperature profile rises as the magnetic parameter and the mass concentration of particle phase parameter grow, whereas the fluid-particle interaction parameter and porosity parameter show the opposite tendency.

Displacement Mechanism and Flow Characteristics of Polymer Particle Dispersion System Based on Capillary Bundle Model

During the development of oil reservoirs, a rapid increase in water cut following reservoir flooding leads to inefficient or ineffective circulation of injected water, rendering a significant portion of the remaining oil in the reservoir inaccessible. The displacement method using polymer particle dispersion systems effectively solves the issue of rapid water breakthrough in oil reservoirs. Owing to the particle phase separation phenomenon, polymer particles can selectively penetrate into the larger pores where water circulation is inefficient, enhance their flow resistance, and thereby achieve equilibrium displacement along with an increased swept volume. This paper investigates the heterogeneous distribution of polymer particles within a porous medium, incorporates the red blood cell dendrite concentration distribution theory from biological fluid mechanics, and develops a mathematical model to delineate the viscosity characteristics of polymer particle dispersion systems, taking into account the phase separation phenomenon. Building on this foundation, it formulates a capillary bundle model for the polymer particle dispersion system specifically designed for oil displacement and proceeds to determine its relative permeability curve. Simulation outcomes reveal that at a water saturation level of 0.063, the concentration of polymer particles in fractured large pore capillaries is markedly elevated, yet capillaries with a pore size under 26 μm remain devoid of polymer particles. With the increase of water saturation, the concentration of polymer particles in large pore capillaries reduces, whereas it progressively augments in medium pore capillaries. Upon reaching a peak water saturation of 0.751, capillaries smaller than 18 μm are entirely free of polymer particles. These findings suggest that the heterogeneous distribution of polymer particles markedly inhibits the percolation capabilities of the dispersed system following a water phase breakthrough, facilitating the entry of more dispersion into oil-laden capillaries and thus enhancing the flow capacity of the oil phase.

Occurrence, seasonal variations, and spatial distributions of current-use organoamine pesticides in the atmosphere of Shanghai, China

An increasing trend in pesticide usage requires a better understanding of the occurrence, fate, and exposure risk of current-use organoamine pesticides (CUOAPs) in the atmosphere as the population grows and climate changes. 33 target CUOAPs were measured in 89 atmospheric samples collected in different seasons from Shanghai, including gaseous and particulate phases. The total concentrations of gaseous phase CUOAPs ranged from 407 to 2980 pg/m3, with an average value of 887 ± 426 pg/m3. Conversely, the total concentrations of particulate CUOAPs were found to be one to two orders of magnitude lower than those in the gas phase, with low detection frequencies. Diphenylamine and Molinate were ubiquitous and predominant in the gaseous CUOAPs. The average total concentrations of gaseous CUOAPs were significantly higher in spring than those in winter and autumn seasons. Gaseous CUOAPs concentrations increased from rural to downtown areas during spring, showing different spatial distribution from winter and autumn. A significant correlation was observed between temperature and the presence of Dicloran, Pirimicarb, Diphenylamine, and Acetochlor. Agricultural activities and city pest control may be the main sources of CUOAPs, while meteorological factors including temperature and wind speed also impact the dispersal of these chemicals in the atmosphere. The increased risk of exposure was observed to be higher during the spring season compared to the autumn and winter seasons, aligning with the pattern of heightened utilization of CUOAPs during the planting and growing phases. The daily inhalation exposure of CUOAPs did not exceed the current oral reference dose.

Microstructure evolution and mechanical properties of large-size AZ31 magnesium alloy block fabricated by wire arc additive manufacturing

With the urgent demand for lightweight and integrated structural parts in the aerospace field, the use of cold metal transfer wire arc additive manufacturing (CMT-WAAM) to form large-size magnesium alloy structural parts has become a research hotspot. In this paper, a large AZ31 magnesium alloy multilayer block with a lower porosity was successfully prepared by CMT-WAAM. The AZ31 block exhibits a fully equiaxed grain morphology, the average grain diameters of the top, middle, and bottom are 16.1 µm, 12.4 µm, and 10.4 µm, respectively. The submicron spherical particles measuring 0.09 to 0.4 µm are Mg17Al12 phases, irregular particles are Al8Mn5 + Mg17Al12 composite phases and large particles measuring 5 to 10 µm are Al8Mn5 in AZ31 block. The UTS of CMT-WAAM AZ31 block from the bottom of 239.9 ± 5.0 MPa to the top of 237.3 ± 3.1 MPa, and the EL from the bottom of 22.7 ± 0.6 % to the top of 30.0 ± 1.1 %, exceeding the casting standards. In the CMT-WAAM processed AZ31 alloy, the pre-existing coarse second phase particles in the AZ31 filaments acted as nucleating agents, and the electromagnetic stirring effect in the WAAM process broke up the dendrites and increased the number density of nucleation sites to improve the rate of nucleation, and the complex thermal conditions in the WAAM process restricted the growth of the grains and the precipitated phases. The mechanical properties of AZ31 alloy were improved by effectively refining its grain size and precipitated phase size.

Advancing processing of the ternary (Sm,Eu,Gd)Ba2Cu3O7-y superconductor via top-seeded infiltration growth

In this study, we present the fabrication of large single-domain ternary (Sm,Eu,Gd)Ba2Cu3O7-y bulk superconductor with enhanced superconducting properties using various REBa2Cu3Oy (RE-123) as a liquid source via the top-seeded infiltration growth process (TSIG) in air. We employed a 1:1 ratio of REBa2Cu3Oy (RE = Sm, Gd, Y and Er) and Ba3Cu5O8 as a liquid source for fabrication. Impressively, all the obtained bulk samples exhibited a superconducting transition temperature T(c, onset) above 94 K. However, the bulk sample fabricated using Y-123 + Ba3Cu5O8 as a liquid source demonstrated a T(c, onset) of 94.53 K, with a 40.14 % improvement in transition width (ΔTc) and at 77 K the bulk recorded a self-field critical current density (Jc) value of 44.73 kA/cm2 & 10.62 kA/cm2 at 1T resulting in a remarkable 93.08 % improvement in self-field Jc compared to the bulk sample fabricated using Er-123 + Ba3Cu5O8. Microstructural analysis using a scanning electron microscope revealed a significant reduction in the mean size of secondary (211) phase particles, a significant reduction of 38.41 % is observed for the Y-123 + Ba3Cu5O8 employed sample.

Investigation of the fabric effect on the arching effect in granular materials

A series of trapdoor experiments and DEM simulations were carried out in this study to examine the arching effect in granular materials, with the focus being on the influence of the direction for particle deposition. In the tests, particles (e.g. rice grains, PVC particles and nylon particles) were dropped as if they were raining at different directions to construct granular material layers with various fabric orientations. It is shown that the mobilization of arching effect depends on the direction of particle deposition, with the arching ratio ρ increasing at first and then decreasing. The arching effect is the weakest at a deposition angle of θ = 30° in obliquely deposited granular masses. It is also found that the vertical displacement of particles in the ultimate phase increases initially; it then decreases with the variation in the orientation of particle deposition, and the largest displacement occurs at θ = 30°.

Ni decorated three-dimension hierarchical pyramidal ZrO2–Al2O3 nanoporous sheets for methane production

ZrO2–Al2O3 nanocomposites were synthesized by a modified co-precipitation method and loaded with 5%Ni as catalysts for methane production via n-heptane cracking. The as-synthesized nanocomposites were characterized by several techniques such as XRD, N2 adsorption-desorption, XPS, TEM, SEM, AFM, TGA, DTG, NH3 -TPD and Raman analysis. The XRD results confirmed the synthesis of amorphous γ alumina and hexagonal phase of zirconium alumina oxide (Zr5Al3O0.5) solid solution. XRD and SEM analyses showed additional small size Related to monoclinic phase of ZrO2 particles loaded on the Al2O3 surface. BET analyses confirmed the ZrO2–Al2O3 formation in mesoporous sheets structure. TEM images of the neat alumina, 10 ZA and their corresponding Ni loaded samples (Ni@10 ZA) revealed well-defined 3D hierarchical pyramidal structures with a height about 200 nm. All catalysts under this study exhibited high tendency to favor methane production via n-heptane cracking. At higher reaction temperatures, Ni@10 ZA catalyst exhibited higher cracking activity compared to the other prepared catalysts under this investigation which confirmed by NH3 -TPD analysis. A promising yield of methane was achieved at about 88 % coupled with 94.71 % selectivity at reaction temperature of 400 °C. Herein, the data collected through this research work revealed that Ni@10 ZA is a promising candidate for methane production via n-heptane cracking.

Effects of cooling process on the microstructure and mechanical properties of a novel high-V high-Mn TWIP steel for cryogenic storage tank applications

In the present work, a novel high-V high-Mn twinning induced plasticity (TWIP) steel for cryogenic storage tank applications was developed. Furthermore, innovative two-stage cooling processes encompassing ultra-fast cooling and the subsequent furnace cooling were proposed. Effects of cooling process on the microstructure and mechanical properties of the experimental steel were investigated. It was observed that with the change in cooling process (the initial temperature of furnace cooling rised gradually), the dwell time of hot-rolled plates above 600 °C was extended. The extension in dwell time facilitated the precipitation of secondary phase particles, leading to the change in average diameter and volume fraction of secondary phase particles. The yield strength increased with the increasing initial temperature of furnace cooling due to the combined effect of small-sized secondary phase particles inside the grains and large-sized ones located at the grain boundaries. The occurrence of intergranular cracking, primarily caused by the presence of large-sized secondary phase particles at the grain boundaries, was the main factor responsible for the significant reduction in total elongation. The small-sized secondary phase particles inside the grains inhibited deformation twinning, while the large-sized ones at the grain boundaries weaken the binding force between grain boundaries, which ultimately resulted in a decrease in cryogenic impact toughness. The implementation of two-stage cooling processes effectively mitigated the trade-off between yield strength and cryogenic impact toughness, offering a novel approach and valuable insights for optimizing the strength and toughness characteristics of cryogenic high-Mn steels.

Coarsening behavior of M23C6 and Laves phase precipitates during long-term aging in a 10% Cr steel with low nitrogen and high boron contents

The coarsening evolution of M23C6 and Laves phase particles in the 10 % Cr steel with 0.008 % B and 0.003 % N during long-term thermal aging at 650 °C for 40,000 h was examined. Particles located on the prior austenite grain boundaries (PAGBs) were compared with those located on the lath/block boundaries. A 5 times slower coarsening of M23C6 on the lath/block boundaries than on PAGBs was attributed to a smaller interfacial energy. After 10,000 h aging, Laves phase particles tended to disappear on PAGBs, whereas larger particles grew on lath boundaries, resulting in a 2 times higher coarsening rate than on PAGBs.

Creep strength breakdown and the change in back stress strengthening in 10 % Cr martensitic steels during creep at 923 K

The creep strength breakdown in 10 % Cr martensitic steels appeared under creep conditions at a temperature of 923 K and the applied stresses below 120 MPa as a declination from linear regression obtained using short-term creep data. To reveal the origin of creep strength breakdown, the back stress strengthening conception was used. In the initial state, both 10 % Cr martensitic steels had a tempered martensite lath structure with a high dislocation density in the lath interiors and in the lath boundaries, which was stabilized by M23C6 carbides, NbX carbonitrides, and M6C carbides. The shear internal back stresses of 57.5–68.5 MPa and 35–37 MPa were obtained from the creep rate – stress relationship for the regions of high applied stress (above 120 MPa) and low applied stress (below 120 MPa), respectively. The transition from the high stress region to the low stress one in both steels was accompanied by a significant decrease in the dislocation density by an order of magnitude as well as a decrease in particle number density and an increase in the inter-particle spacing in the M23C6 carbide and Laves phase particles located at the low-angle boundaries of the martensitic laths/subgrains. The root mean square superposition of the dislocation and particle contributions to the shear internal back stresses gave the best coincidence with the values obtained from the creep data. The stability of the M23C6 carbide and Laves phase particles located at the low-angle boundaries was concluded to be the key factor suppressing the creep strength breakdown in the 10 % Cr martensitic steels.

Debris-induced consequences on turbulence and vorticity in solar photovoltaic module-generated array wakes

Particle-laden flows in solar photovoltaic (PV) systems are inevitable, where wind-swept debris in open environments are carried by high winds and turbulence, coating panel surfaces or damaging structures. Particle deposition, or soiling, is a well-known issue for large-scale plants which rely on uninhibited solar rays for optimal production. But understanding the mechanisms leading to soiling requires a physical and fluid dynamics-centered focus, since turbulence dominates PV panel wakes and is also known to alter particle concentration and trajectories. This study presents an experimental campaign toward consequences of particle-laden flow between two model PV panels using time-resolved particle image velocimetry. The model array was subjected to varied particle volume fractions, including a tracer particle case and a water droplet case. Characterization of mean velocity, turbulence statistics, and mean kinetic energy within the single phase and, separately, particle phase flows showed modified features due to particle inertia. Images captured at a frequency of 1 kHz in the near wake of the upstream panel allow for a first experimental look at vorticity and convective velocity of vortex structures for single-phase and particle-phase flows which are crucial to debris transport and soiling in PV environments.

Microstructural Evolution and Tensile Properties of Al-Si Piston Alloys during Long-Term Thermal Exposure

The present study investigated microstructural evolution and changes in tensile properties of an Al-Si piston alloy subjected to thermal exposures at 250 and 350 °C for 150, 300, and 500 h. Microstructural and nanoscale precipitates were characterized using a combination of high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) images and scanning electron microscopy (SEM). The tensile testing was performed. The results demonstrated that the thermal exposure induced granulation of the δ-Al3CuNi particles, alongside precipitation of the θ-Al2Cu phase particles and AlCu clusters within the matrix. Specifically, an increase in the size and number density of the θ-Al2Cu phase particles was observed with exposure time at 250 °C. Conversely, at 350 °C, the θ-Al2Cu particles exhibited a gradual increase in size with prolonged thermal exposure, coupled with a decrease in their number density. AlCu clusters precipitated solely at a thermal exposure temperature of 350 °C, with precipitation intensifying over time. Moreover, a decrease in the alloy’s tensile strength and an increase in elongation were noted after thermal exposure. Finally, the present study discussed the precipitation mechanisms of θ-Al2Cu particles and AlCu clusters within the grains, suggesting that the AlCu clusters exerted a more effective strengthening effect compared to the θ-Al2Cu particles.

Study on the mechanism of second phase formation in high-purity fused silica materials for semiconductor application

Gas bubble is a common defect in high-purity fused silica materials, but the formation of the second phase particles related to gas bubble and its mechanism remain unclear till now. In this work, we have presented a method for characterization of colored gas bubbles in high-purity fused silica crucibles for Czochralski silicon by the means of TEM and EDX. Based on it, the origin of the coloring of the gas bubbles is demonstrated to be induced by the gathering of Fe impurity and then, the formation of high-density second phase—ferric oxide (Fe2O3) crystals around the gas bubbles. Moreover, our results provide insight into the formation mechanism of second phase crystals which can be induced by stress field variations around gas bubbles during the cooling process that probably promoted by volume shrinkage effect and increasing solubility of gas from gas bubbles into fused silica substrate. The understanding of the second phase particle formation mechanism in high-purity fused silica materials is valuable for its further controlling.

Viscoelastic-plastic transition of polyamide/hydrogenated nitrile blends based on Ostwald’s ripening mechanism and its effect on mechanical and tribology properties

The controllable preparation of the phase separation structure of platic/elastomer blends is very important to improve the mechanical properties of materials. In this paper, polyamide 1212/hydrogenated nitrile (PA1212/HNBR) blends were prepared by melt-compounding method. During the mechanical testing, a novel viscoelastic–plastic transition behavior was observed. The addition of polyamide 1212 could effectively reinforce mechanical and frictional properties of HNBR matrix. It was worth noting that 30 wt% PA1212 content was the critical value of viscoelastic–plastic transition of the blends. Meanwhile, the tribological performance of the blends was also decayed at the critical point (i.e. 30 wt% PA1212). Therefore, the uniformly dispersed particle phase structure formed via Ostwald’s ripening mechanism was crucial to the improvement of tribological performance. In addition, the large-scale production of platic/elastomer blends with high-performance can be realized through this controllable preparation technique.

Insight into the Hot Corrosion Behavior of FeMnCrSi/TiC Coatings at 900 °C

This study explores the deposition of an Fe-MnCrSi/TiC coating on 45 steel surfaces using high-velocity arc spraying technology, examining the microstructure and hot corrosion behavior of the resultant layer. The microstructure of the FeMnCrSi/TiC coating primarily consists of an α-Fe (BCC) solid solution, composed of Fe, Mn, Cr, Si, C, and other elements, with a minor presence of β-Fe (FCC) solid-solution phase and unmelted TiC particles. Following 100 h of cyclic 900 °C hot corrosion, Mn on the coating surface preferentially oxidizes, forming a manganese-rich oxide layer. This process reduces the oxygen partial pressure (O2) within the coating, prompting the formation of a dense Cr2O3 layer on the inner side of the oxide layer. Concurrently, the rapid diffusion of Mn and Cr elements triggers the generation of Mn- and Cr-deficient regions at the metal/oxide layer interface, inducing the transformation of the coated metal primary matrix from an FCC + BCC dual phase to an α-Fe (BCC) single phase. After the reaction, the hot corrosion weight gain of the coating reached 12.43 mg/cm2, approximately one-fourteenth of the weight gain of the 45 steel substrates. This weight gain adheres to the parabolic law, suggesting that the FeMnCrSi/TiC coating exhibits excellent corrosion resistance under the given conditions.

Viscosity and structure studies of iron-based quaternary melts: The effect of P

This study systematically investigates the underlying principles and mechanisms governing viscosity across the entire range for the Fe-4.5C-0.1Ti-xP (in wt.%) melts. The viscosity profile exhibits distinct variations in different phases. In the solid–liquid transition region, the primary determinant of viscosity is the presence of solid phase particles, while in the region characterized by liquid phase, the primary influencing factor is the number of clusters. Notably, the impact of P content demonstrates a contrasting effect on low-temperature solid phase precipitation and high-temperature liquid phase structure. During the low-temperature solid phase precipitation stage, an increase in P content serves as a catalyst for graphite precipitation, resulting in an increase in system viscosity and, by extension, impacting an increase in system viscosity. In contrast, within the high-temperature liquid phase, the interaction of P with iron (Fe) results in the breakdown of mid-range clusters in the original system, leading to the formation of smaller clusters with a reduced overall cluster volume. Consequently, an increase in P content is associated with a decrease in viscosity. These findings provide a nuanced understanding of the interplay between P content and viscosity throughout different phases of the melt.

Trajectory Tracking Control Design for 4WS Vehicle Based on Particle Swarm Optimization and Phase Plane Analysis

With the rapid development of today’s society, the traffic environment has become more and more complex. As an essential part of intelligent vehicles, trajectory tracking has attracted significant attention for its stability and safety. It is prone to poor accuracy and instability in extreme working conditions like high speed. In this paper, a trajectory tracking control strategy to ensure lateral stability at a high speed and low attachment limit conditions is proposed for distributed drive vehicles. The model predictive controller (MPC) was used to control the front wheel angle, and the particle swarm optimization (PSO) algorithm was designed to optimize the MPC control parameters adaptively. The sliding mode controller controls the rear wheel angle, and the vehicle instability degree is judged by analyzing the β − β˙ phase plane. The controllers of different instability degrees are designed herein. Finally, a torque divider is designed to consider the actuation anti-slip. The designed controller is verified by Carsim and MATLAB-Simulink co-simulation. The results show that the trajectory tracking controller designed in this paper effectively improves the tracking accuracy under the premise of ensuring stability.

A Eulerian Monte Carlo method for the numerical solution of the multivariate population balance equation

Statistical descriptions of particulate phases and granular media based on the notion of a property distribution are particularly advantageous for dense, many-particle dispersions since they support the direct evaluation of Eulerian property statistics, permit a kinematically simple treatment of particle collisions and feature a model complexity that is independent of the number of physical particles. On the minus side, the property distribution is governed by a high-dimensional population balance equation (PBE) whose moment reduction is accompanied by a challenging closure problem and engenders intricate dynamical nonlinearities. Circumventing both the curse of dimensionality and the moment closure problem, we present a Eulerian Monte Carlo (EMC) solution method that harnesses a representation of the property distribution in terms of an ensemble of property samples and is based on a statistical enforcement of the spatially and temporally discretized PBE. After application of a kinetic finite volume scheme, the PBE is subjected to a fractional steps decomposition that separates spatial transport from transport in property space. Conceptually, spatial transport is emulated by assembling the ensemble in one spatial grid cell from samples drawn from the ensembles in neighbouring cells at the previous time point. In this regard, we propose a two-level sampling scheme that is sensitive to large-scale features of the marginal velocity distribution and effectively reduces the instantaneous sampling error. The property transport step, by contrast, is based on the method of characteristics and involves the propagation of individual samples as property characteristics in time. While the sampling error afflicting the property statistics needs to be controlled using a top-level time or ensemble averaging, the EMC method remains well-conditioned for an arbitrary number of samples, is easy to implement and involves a computational expense that scales only linearly with the number of particle properties. Based on two benchmark examples, we analyze the spatial and statistical convergence properties of the EMC method and demonstrate its capacity to capture multiple crossings of particle trajectories. A third example involves the two-way coupled transport of size-polydispersed inertial particles in an inhomogeneous flow field.