Formation Of Dust Particles Research Articles

Investigating the Role of the Low-Level Jet in Two Winters Severe Dust Rising in Southwest Iran

The dust storms with local and non-local dust sources mostly affect Khuzestan province in southwest (SW) Iran. In this study, the role of the low-level jet in the activation of the internal dust events in SW Iran during two severe dust cases was investigated. For this purpose, the fifth-generation ECMWF reanalysis for the global climate and weather (ERA5) data was used to identify the synoptic patterns and the low-level jet (LLJ) characteristics in the study area. Furthermore, the images of the moderate resolution imaging spectroradiometer (MODIS) sensor, the outputs of the hybrid single-particle Lagrangian integrated trajectory (HYSPLIT) model, and a weather research and forecasting model coupled with chemistry (WRF-Chem) were used to investigate the propagation and transport of the dust particles. The results of the synoptic analysis in both dust cases show the simultaneous occurrence of the divergence zone associated with cyclonic curvature in the subtropical jet stream (STJ) at 300 hPa, causing convergence at 925 hPa, upward motion, and the development of low surface pressure in SW Iran. Examining the vertical wind profile shows the existence of the maximum horizontal wind speeds of 975 to 875 hPa, along with the positive and negative shear below and above it, respectively, which emphasizes the existence of the LLJ and its role in local dust emission. The results of the comparison between the satellite images, WRF-Chem, and HYSPLIT model outputs show the formation and transportation of dust particles from the inner regions of Khuzestan in SW Iran. The horizontal dust surface distribution, vertical raised dust mass, and kinetic energy transfers are well simulated by the WRF-Chem model when LLJ broke at 09:00 to 12:00 UTC. The most important finding of this research is that, for the first time, the role of low-level jet is investigated in the activation of internal dust events in SW Iran.

Mechanisms and Thermochemistry of Reactions of SiO and Si2O2 with OH and H2O.

This paper reports on computational studies of gas-phase reactions of SiO and Si2O2. The oxidation of SiO can initiate efficient formation of silica or silicate dust particles in a wide range of environments. Both OH radicals and H2O molecules are often present in these environments, and their reactions with SiO and the smallest SiO cluster, Si2O2, affect the efficiency of eventual dust formation. Density functional theory calculations on these reactions, benchmarked against accurate coupled cluster calculations, indicate that the Si2O2 + OH reaction should be faster than SiO + OH. The reaction SiO + H2O → SiO2 + H2 is both endothermic and has high activation energies to reaction. Instead, the formation of molecular complexes is efficient. The reaction of Si2O2 with H2O, which has been suggested as efficient for producing Si2O3, might not be as efficient as previously thought. If the H2O molecules dissociate to form OH radicals, oxidation of SiO and Si2O2 could be accelerated instead.

Mechanisms of SiO oxidation: Implications for dust formation

Reactions of SiO molecules have been postulated to initiate efficient formation of silicate dust particles in outflows around dying (AGB) stars. Both OH radicals and H2O molecules can be present in these environments and their reactions with SiO and the smallest SiO cluster, Si2O2, affect the efficiency of eventual dust formation. Rate coefficients of gas-phase oxidation and clustering reactions of SiO, Si2O2 and Si2O3 have been calculated using master equation calculations based on density functional theory calculations. The calculations show that the reactions involving OH are fast. Reactions involving H2O are not efficient routes to oxidation but may under the right conditions lead to hydroxylated species. The reaction of Si2O2 with H2O, which has been suggested as efficient producing Si2O3, is therefore not as efficient as previously thought. If H2O molecules dissociate to form OH radicals, oxidation of SiO and dust formation could be accelerated. Kinetics simulations of oxygen-rich circumstellar environments using our proposed reaction scheme suggest that under typical conditions only small amounts of SiO2 and Si2O2 are formed and that most of the silicon remains as molecular SiO.

Fire Parameters of Spruce (Picea abies Karst. (L.)) Dust Layer from Different Wood Technologies Slovak Case Study

The issue of the formation of wood dust particles in the work environment is still an actual topic in terms of its impact on employee health and the risk of fire or explosion in a woodworking operation. This article deals with the characteristics of spruce dust (Picea abies Karst. (L.)), which was taken from several types of wood technology. Experimental samples of spruce dust were taken from four types of sawing technologies, including grinding, briquetting and from the suction device container. The physical parameters of the samples taken were monitored and the particle size analysis was determined. The granulometric composition of the samples is significantly different. The sample of spruce wood dust from sawing has the most numerous fraction (250 µm), while the sample from grinding has the most numerous fraction 63–250 µm (87%).The aim of the paper was to monitor the minimum ignition temperature of the settled spruce dust layer and to look for a significant dependence of the minimum ignition temperature and ignition time on the type of spruce dust sample. A significant dependence was not confirmed. Significant moisture dependence of the samples was confirmed; the highest humidity was observed in the container, the lowest in sawing.

Contribution of leading edge shape to a damaging of castellated tungsten targets exposed to repetitive QSPA plasma loads

The castellated tungsten monoblock is considered one of the preferred reference designs of components faced to plasma in the divertor of a fusion reactor. The behavior of such components during the development of transient events (disruptions or/and of Edge Localized Modes (ELMs)) is still among the most critical issues for future thermonuclear devices. Experimental studies of castellated tungsten surface erosion have been performed within the powerful quasi-stationary plasma accelerator QSPA Kh-50 in conditions relevant to unmitigated ITER Type I ELMs. The surface energy load from the impacting hydrogen plasma streams was 0.9 MJ m−2 during 0.25 ms to achieve pronounced melting of the target surface. The studies of solid and liquid particle generation were performed at sequentially oblique plasma exposure of the different chosen edges of the castellated structure. It was determined that most of the W droplets are ejected from the sharp leading edge of the target due to the development of instabilities in the plasma-liquid metal interface. At the same time, the formation of solid dust particles is mainly attributed to the cracking during the surface cooling after the plasma pulse. Particle velocities typically achieve tens m s−1. Both the re-solidified droplets as well as dust particles have been collected on the special plate near the exposed surface. The maximal size of collected particles reached tens of micrometers. Such particles could either fly away with the next plasma pulses or mix with the material of the collecting plate in the course of repetitive plasma pulses. Thin (submicron) layers of re-deposited tungsten also formed on the surface of the collecting plate.

Formation of Dust Particles in Process Multiphase Reactors

Formation of Dust Particles in Process Multiphase Reactors

Development of micro- and nanoindentation methods for assessing the mechanical properties of coals and their propensity to destruction

The destruction of coals in the processes of mining, storage, transportation and processing is associated, among other, with their mechanical properties. As a rule, the mechanical properties of coals are evaluated by the resul ts of measurements of such characteristics as tensile and compressive strength, stiffness (elastic modulus) and Poisson’s ratio, etc. For this, experiments are carried out on specially prepared samples in tensile testing machines and mechanical presses. Such integral indicators characterize the mechanical behavior of coals at the macro scale and do not allow assessing the influence of structural features on the initiation of defects leading to destruction. In this regard, the characteristics of the mechanical properties of coals, obtained in areas comparable to the levels of microcracks initiation, are of interest. Micro- and nanoindentation techniques are quite simple to implement for obtaining the reliable information on various mechanical properties of materials at the appropriate scale levels. This paper is dedicated to an overview of the current state of research on the use of these methods to assess the mechanical properties of coals and their individual macerals, as well as their ability to crush with the formation of dust particles. The use of micro- and nanoindentation techniques made it possible to establish the differences in the mechanical properties of individual macerals of coals, as well as to characterize the heterogeneity of the distribution of various indicators characterizing mechanical properties within the individual macerals. Based on experimental data on nanoindentation and Raman spectroscopy, it was shown that the change in the mechanical properties (values of the modulus of elasticity and hardness) of vitrinite in the series of coal metamorphism is associated with an increase in the proportion of graphitized components in organic matter. Nanoindentation methods, combined with an analytical mathematical apparatus, made it possible to obtain data on the ability of coals to crush under mechanical effects with the formation of particles with sizes comparable to those of hazardous aerosol dust (class PM 2.5). The method of cyclic nanoindentation with an increasing maximum load was proposed as a method for determining the degree of coal tendency to fracture with the formation of dust. Its application made it possible to reveal the characteristics of irreversible changes occurring in the structure of coals during destruction. They are expressed in a change in their mechanical properties (stiffness and fracturing ability) with an increase in the applied load. The use of the cyclic nanoindentation method is a promising method for the qualitative and quantitative analysis of the degree of coal propensity to crushing with the formation of dust. This work was carried out with the financial support of the Russian Science Foundation (Grant No. 18-77-10052).

Filtration performance of the granular bed filter used for industrial flue gas purification: A review of simulation and experiment

The dust particles contained in the industrial flue gas are discharged from many industrial factories, which have seriously polluted the air and endangered the health of not only human beings but also the animals living on the earth, so they are gaining much attention all over the world. In order to provide possible solutions to the above problems, many filtration technologies have been proposed and developed. As a promising filtration method, the granular bed filter (GBF) based filtration technology has been widely used in the filtration of high temperature flue gas with complex components in recent years owing to its advantages of high efficiency, low cost, simplicity, and resistance to high temperature and high pressure. Inspired by the development of numerical simulation method and experimental technology, the performance of GBF has been optimized and improved, much deeper insight of the formation and growth of dust particles has been obtained. This review focus on the basic principle of the GBF and its performance investigated by numerical and experimental methods. The reviews and outlooks of investigations on the influence factors of GBF filtration performance and the development of performance optimization method of the GBF were also presented. In addition, the microscale mechanism of the agglomeration and growth of dust particles contained in the industrial flue gas during the filtration in the GBF by means of molecular dynamics simulation were introduced, the numerical and experimental method of dust particles filtration in GBF were also discussed. Finally, available recommendations for future research of GBF are proposed, which is expected to be helpful for actual industrial engineering applications.

Simulation of Dust Particle Trajectories in an Electrostatic Probe with the Purpose of Increasing Its Efficiency

Formation of dust particles and clusters is observed in almost all modern fusion devices. Accumulation of dust in next-generation thermonuclear installations can significantly affect plasma parameters and lead to accumulation of unacceptably large amounts of tritium. The use of a specially developed electrostatic probe is planned in the international thermonuclear experimental reactor ITER to collect dust for further analysis. The article describes a numerical model of movement of dust particles in an electrostatic probe. Dust particle trajectories inside the probe are analyzed. Several electrostatic probe design modifications are proposed on the basis of the analysis in order to increase the efficiency of dust collection.

Increasing of an electrostatic probe capacity and efficiency for metal dust collection in ITER

Formation of dust particles and clusters is observed in almost all modern fusion devices. Accumulation of dust in next-generation thermonuclear installations can significantly affect plasma parameters and lead to accumulation of unacceptably large amounts of tritium. The use of a specially developed electrostatic probe is planned in the international thermonuclear experimental reactor ITER to collect dust for further analysis. The article describes a numerical model of dust particles movement in an electrostatic probe. Dust particles trajectories inside the probe were analyzed. Several electrostatic probe design modifications were proposed on the basis of the analysis in order to increase the efficiency of dust collection.

IGNITION AND PROPERTIES OF RF CAPACITIVE DISCHARGE IN ACETYLENE

In the present work, we measured breakdown and extinction curves of radio-frequency discharge in acetylene as well as dependences of active current, power and gas pressure on the discharge burning time, and also optical emission spectra. It was found that in the region of low acetylene pressures (to the left of the minimum of the breakdown curve), the discharge can cover only a part of the electrode surface. Immediately after the ignition of the discharge, due to the intense deposition of the polymer film and the formation of dust particles in the plasma volume, the gas pressure decreases sharply (by the factor of 2-5), while the active current and power increase and then reach saturation. In the discharge with intense polymerization, the lines of atomic and molecular hydrogen dominate in the emission spectrum of the discharge. The film deposited on the surface of the electrodes and the tube walls, as well as the dust particles formed, are amorphous, the maximum peak of XRD spectrum is observed at 2θ = 18°, and the light absorption by the deposited films is highest at 440 nm wavelength.

Plasma chemistry and dust-particle generation in pure methane plasma: Influence of the RF electrode cleanliness

Hydrocarbon dust-particles are formed and grown to a large size (around 1 μm) in a low pressure capacitively coupled radio frequency discharge in methane. The methane decomposition leads to the formation of both spherical dust-particles in the plasma bulk and coating on the electrodes. Under ion bombardment, the coating on the biased top electrode peels off, leading to the fall of flakes. To better understand the role played by the electrode surface state on the plasma chemistry and on the dust-particle growth, experiments are carried out in two different initial conditions for the electrodes: (i) without any coating and (ii) with a homogeneous hydrocarbon coating. Spherical dust-particle growth is followed using the temporal evolution of the DC self-bias voltage. At the end of the experiment, dust-particles and flakes are collected and observed by scanning electron microscopy. Using mass spectrometry, temporal evolutions of neutrals, ionic species, and positive ion energies are investigated. Between the two experimental conditions, no strong differences were observed on the plasma chemistry. However, the self-bias voltage is strongly modified as well as the dust-particle growth and dynamics.

The influence of the thermal modification of pine (Pinus sylvestris L.) wood on the creation of fine dust particles in plane milling: Fine dust creation in the plane milling of thermally modified pine wood.

ObjectivesThe aim of the study was to determine the effect of parameters of the thermal modification process and machining on the size distribution of dust particles of Scots pine (Pinus sylvestris L.) generated during lengthwise milling.MethodUnmodified wood and thermally modified wood at temperatures of 130, 160, 190, and 220°C were milled lengthwise at cutting depths of 0.5 and 2 mm. Particle size analysis was done using the sieving method. The content of the finest particles was measured using the laser diffraction method.ResultsThe results indicate that at smaller cutting depths, more smaller particles were formed regardless of the wood modification temperature. Thermal treatment of wood does not cause significant differences in the general particle size distribution of dust. However, the content of the finest dust particles depends on the temperature of wood modification. When machined, wood thermally modified at higher temperatures results in the formation of more dust particles that may pose health risks to employees. This is particularly noticeable at a smaller cutting depth.ConclusionWith the increase of the temperature of the modification, the share of the finest dust particles, which are a potential threat to the health of employees, increases. To reduce dust emissions during milling of thermally modified wood, the highest possible cutting depth should be used.

Study of the behavior of fine tungsten crystallic and amorphous particles in varying conditions

Formation of dust particles and their agglomerates with sizes ranging from tenths to hundreds of microns is observed in many modern plasma facilities. Dust accumulation can significantly affect discharge parameters in future thermonuclear facilities and lead to the accumulation of dangerously high amounts of tritium. Experiments on the generation of tungsten and tungsten-aluminium dust made of flakes formed during exfoliation of coating deposited on chamber walls from tungsten and aluminium targets sputtered by ions are described in this paper. A comparative analysis of the behavior of such dust and dust (figure 1), formed by crystal particles with simple geometric shapes (“crystal particles”) in electric field, their degassing and change occurring in temperatures of up to 2000 K is conducted.

Efficiency of Tungsten Dust Collection of Different Types of Dust Particles by Electrostatic Probe

Formation of dust particles and clusters is observed in almost every modern thermonuclear facility. Accumulation of dust in the next generation thermonuclear installations can dramatically affect the plasma parameters and lead to the accumulation of unacceptably large amounts of tritium. Experiments on collection of dust particles by a model of electrostatic probe developed for collection of metallic dust at ITER are described in the article. Experiments on the generation of tungsten dust consisting of flakes formed during the destruction of tungsten layers formed on the walls of the plasma chamber sputtered from the surface of the tungsten target by plasma ions were conducted. The nature of dust degassing at elevated temperatures and the behavior of dust in an electric field were studied. The results obtained are compared with the results of the experiments with dust consisting of crystal particles of simple geometric shapes. The effectiveness of collection of both types of dust using the model of an electrostatic probe is determined.

Effects of gas temperature, pressure, and discharge power on nucleation time of nano-particles in low pressure C2H2/Ar RF plasmas

The formation of dust particles in low-pressure plasmas is a 3-step process. The first one corresponds to nucleation and growth of nanoparticles by chain reactions between ions and gas molecules, the second one is agglomeration of the nanoparticles to form larger particles, and finally, the particles grow by radical deposition on their surfaces. In this work, the nucleation time for carbon dust particles was studied in low pressure acetylene/argon radio frequency (RF) plasmas. Since the self-bias voltage on a powered electrode was drastically affected by the transition from the nucleation to the agglomeration phases, the nucleation time was measured by observing the self-bias voltage time evolution. The nucleation time increases with the gas temperature and decreases when the gas pressure and the RF power are increased. A kinetic model, involving balance between diffusion and charging times of the nanoparticles as well as the chain reactions, is used to explain the exponential dependence of the nucleation time on the gas temperature. The balance between the times was especially indispensable to get good agreement between the model and the experimental results.

A fiery birth of aluminosilica analogs of refractory dust in the upper stratosphere

Following a successful dust collection flight in the upper stratosphere our DUSTER (Dust in the Upper Stratosphere Tracking Experiment and Retrieval) made a safe remote landing at its assigned location on Baffin Island during early June 2009. When the balloon payload that included DUSTER was retrieved it was found part of the payload had experienced a lithium-sparked fire while the payload was being dragged across the landing site. In this process the housing of DUSTER had developed a pin-sized hole that allowed smoke of the fire to enter the collector. Numerous smoke particles were found covering both the DUSTER collection and blank collector surfaces an indication that our experiment to collect upper stratospheric dust had failed! Both collector surfaces were covered by numerous carbon smoke and amorphous, aluminosilica nanoparticles. The compositions of vast majority of these aluminosilica nanoparticles, Al2O3=49wt% and SiO2=51wt%, was both surprising and unique because it was an exact match of the Deep Metastable Eutectic (DME) nanoparticles found in vapor phase condensation experiments. These vapor phase condensation experiments were conducted to explore the formation of extraterrestrial dust particles. We are not claiming an extraterrestrial origin for these particles from this DUSTER experiment. We submit that given the appropriate conditions of high temperature alumina and silica vapors and rapid quenching in a contained natural environment, DME aluminosilica nanoparticles will likely condense. This serendipitous result can be used to explore nanoparticle formation inside incandescent clouds associated with bolides and fireballs.

A facile approach to fabricate superhydrophobic membranes with low contact angle hysteresis

A robust superhydrophobic polyvinyldene fluoride-co-hexafluoropropylene (PVDF-HFP) electrospun membrane was fabricated by using a modest and versatile coating technique. Inspired by the natural phenomenon of thin layer formation of dust particles on the surfaces. Electrospun mats of PVDF-HFP were coated with tetrafluoroethylene oligomers (OTFE) particles. Dust of the OTFE was created in a closed chamber and used to form a thin layer of OTFE particles on the surface of the electrospun PVDF-HFP membranes. Hot pressing was used then to infuse the loose OTFE deposited layer on the surface of the PVDF-HFP membrane. Scanning electron microscopy images indicate that OTFE particles infused ~2–3µm in the electrospun non-woven network. Static contact angle of water on the PVDF-HFP surface improved from 125° ± 2 to 156° ± 2 after OTFE coating. In addition, OTFE coating did not alter the pore size distribution of PVDF-HFP membrane and permeation flux, whereas it significantly helped in improving the water liquid entry pressure. The prepared membranes were tested in direct contact membrane distillation (DCMD) applied to desalination and reported to achieved 99.9% salt rejection with permeation flux of 13–14kg/m2h. In addition to increasing the hydrophobicity of the membranes, OTFE coating significantly reduces the contact angle hysteresis from ~90° ± 2° to ~10° ± 2°. To show the significance of contact angle hysteresis on membrane performance, high fidelity modeling based on computational fluid dynamic in thermal coupled membrane flow was developed. Results of the temperature, polarization coefficient (TPC) and heat transfer coefficient (h) clearly show the favorable impact of the reduced value of hysteresis and its implication of inducing slip. Under total slip, considerable gain in the TCP is observed and reaching as high as 25%.

Influence of a magnetic field on the formation of carbon dust particles in very low-pressure high-density plasmas

Carbon dust particles with radius of a few hundreds of nanometers are formed in a steady-state plasma produced by an electromagnetic surface wave at 200 MHz in very low-pressure conditions. The influence of an applied magnetic field is evidenced by ex situ methods (scanning and transmission electron microscopy, Raman spectroscopy). The observed spherical dust particles are formed of aggregates of graphite nanocrystals embedded in amorphous carbon shells. In addition, the size of the dust particles increases with the magnetic field intensity. Growth occurs as the particles are confined near the sheath edge and their confinement is improved by applying a magnetic field as the corresponding electric field increases in this region. As a consequence, the average dust particle radius is directly related to the magnetic field intensity.

Plasma-enhanced CVD of functional coatings in Ar/maleic anhydride/C2H2 homogeneous dielectric barrier discharges at atmospheric pressure

In this contribution, we focus on the general problems of plasma-enhanced chemical vapor deposition in atmospheric pressure dielectric barrier discharges, i.e. deposition uniformity, film roughness and the formation of dust particles, and demonstrate them on the example of carboxyl coatings prepared by co-polymerization of acetylene and maleic anhydride. Since the transport of monomers at atmospheric pressure is advection-driven, special attention is paid to the gas dynamics simulations, gas flow patterns, velocity and residence time. By using numerical simulations, we design an optimized gas supply geometry capable of synthesizing uniform layers. The selection of the gas mixture containing acetylene was motivated by two of its characteristics: (i) suppression of filaments in dielectric barrier discharges, and (ii) improved film cross-linking, keeping the amount of functional groups high. However, acetylene discharges are prone to the formation of nanoparticles that can be incorporated into the deposited films, leading to their high roughness. Therefore, we also discuss the role of the gas composition, the spatial position of the substrate with respect to gas flow and the deposition time on the topography of the deposited films.