Dispersion Of Fine Particles Research Articles

Improving the performance of air purification efficiency from fine-dispersed particles by ultrasonic exposure in swirling flow

The article presents the results of a research of the process of removing particles in range 2.5 µm that are most dangerous to human health using ultrasonic coagulation. The two-stage gas clearing system consisting of the agglomerator and the cyclone dust collector (supplemented by an ultrasonic radiator) was proposed and made. The carried out investigations have revealed the optimal conditions for the formation of a swirling flow, providing high efficiency coagulation of fine-dispersed particles. The formation of a swirling gas-dispersed flow in the conditions of ultrasonic exposure provides an increase in the average particle size 2.5 µm by 4.5 times due to particles convergence and the formation of local areas with high concentration. In this case, the ultrasonic effect on a rectilinear flow with 2.5-μm particles allows increasing particles size of only 1.6 times. The ultrasonic exposure has increasing 2.5-µm particle clearing efficiency from 46 to 85% by optimal conditions for gas-dispersed flow.

Aggregation characteristics of fine hematite and siderite particles in aqueous suspension

Siderite-bearing hematite is a type of refractory iron ore, where fine particle aggregation or dispersion behavior is of importance for the separation efficiency. Hence, the aggregation characteristics of fine particles (hematite and siderite) using sodium oleate (NaOl) as a flocculant were investigated through FBRM particle size analysis (a real-time particle characterization tool), zeta potential analysis, adsorption tests, contact angle measurements, and X-DLVO theoretical calculations. The results showed that NaOl could interact with hematite and siderite when the pH value ranged from 5.0 to 9.0, in which the hydrophobic interaction played a leading role in inducing homo-aggregation and hetero-aggregation in the mineral particles. However, in the strong alkaline solution environment (pH = 11.0), NaOl could only interact with siderite and scarcely adsorbed onto the hematite surface, which was mainly covered with ferric hydroxyl compound (Fe-OH). This largely prevented the formation of hematite-hematite and hematite-siderite aggregates in the suspension.

Spatial distribution, mobility and potential health risks of arsenic and lead concentrations in semiarid fine top-soils of Durango City, Mexico

Significant amounts of mining wastes containing Fe-oxide rich phases (i.e., hard rock dumps, tailing impoundments) have been historically deposited in semiarid soils within Durango City. Urban mapping along with mineralogical and geostatistical analyses were carried out to determine levels of concentration, spatial distribution, and relationships between As-bearing and Pb-bearing phases and their mobilities for different sites around this city. It was found that fine As-bearing particles (<5–10 μm) comprised of Pb3(AsO4)2-like, FeAsS, and complex structures were the main phases in urban sprawl soil, while PbO2-like, PbS, and (Ba, Pb)SO4-like were the main Pb-bearing phases (<5 μm). Levels of As and Pb vary in urban sprawl soil from 4.37 to 42 and 8.3 to 82.5 mg kg−1, respectively, and are higher in the soil adjacent to Cerro de Mercado, where the mining area is conurbated, from 55.1 to 221 and 21.6 to 107.3 mg kg−1, respectively. Most of these concentrations were associated with the finest soil fraction (<10–250 μm), enhancing health risks due to inhalation or incidental intake. The spatial distribution patterns of these elements were mainly related to high traffic density and mining waste for Pb, and eolic dispersion of fine soil particles for As. A low mobility was found for Pb (up to 3%), indicating a low environmental risk if released, whereas As mobility changes from a low to a medium risk level (0.1–37.1%). Geostatistical analysis suggested correlations between soil pollution and distance regarding hard rock and tailing impoundment sources.

Collecting finely-dispersed particles from the gas flow in a centrifugal separator with coaxially arranged pipes

The article deals with the problem of increasing the efficiency of dedusting the gas flow from the finely dispersed particles smaller than 10 μm. In order to solve this problem, a design of centrifugal separator with coaxially arranged pipes is proposed. The described principle of operation includes the large values of centrifugal forces, which take place inside the device when the flow is swirled, and these forces throw the finely dispersed particles to the walls of device. This scientific paper shows a numerical simulation of gas flow dedusting process by means of ANSYS Fluent software package. The efficiency of dedusting the gas from the finely dispersed particles of up to 10 μm in the device is on average within the range of 53.8–76.7%. The exponential function, describing the changes in the pressure loss from the input gas rate, is obtained. In the course of studies, it was found that the pressure loss in the device is not more than 800 Pa at the input gas rate from 3 to 19 m/s.

Variations of atmospheric aerosol parameters in periods of seismic activity in Tien–Shan

Combination of numerical modeling (MERRA) and ground based (AERONET) monitoring of atmospheric aerosol parameters were used to discover a possible connection to seismic activities within the territory of Tien-Shan. The obtained results demonstrated consistent behavior between increase of aerosol optical thickness (AOT) and powerful earthquakes, epicenters of which were located within 200 km from the “Issyk-Kul” station (AERONET). Thereat, the dominant role was played by fine-dispersed particles, which virtually determined the nature of AOT evolution. We also observed well-defined changes of the ratio between mass fraction PM1.0 (particles less than 1.0 μm aerodynamic diameter) and optical thickness of aerosol scattering several days before an earthquake of M &gt; 5.0 magnitude.

Effect of surface mechanical attrition on microstructure and mechanical properties of hypoeuctectoid steel

Effect of ultra-fine structure obtained by surface mechanical attrition treatment(SMAT) on microstructure, yield strength (YS), ultimate tensile strength (UTS) and microhardness of hypoeuctectoid steel have been studied in this paper. Surface alteration has been obtained by vibratory SMAT equipment with particular parameters for similar class of material. The SMAT has been carried out for different time periods such as 10, 20, 30 min. The pearlite and ferrite geometry present has been found intermixed after SMAT process. The microstructure shows a composite structure consisting of fiber/angular cementite particulates dispersed in a ferrite matrix. Thus, these structure obtained at 30 min of SMAT has significantly affected the mechanical properties. The SMAT affected layer has found to be 300μm which shows an increased Young’s modulus from 140 GPa to 246 GPa. The yield stress (YS) and ultimate tensile strength (UTS) has been increased about 6% and 22% , respectively. The surface microhardness of the material has been changed from 226±5 HV0.3 to 405±7 HV0.3 by SMAT, which is attributed to the grain refinement and dispersion of fine carbide particles within the matrix.

A novel Mg(OH)2 binding layer-based DGT technique for measuring phosphorus in water and sediment.

Diffusive gradients in thin films (DGT) have gained wide attention for in situ measurement of reactive phosphorus species (PO4) in natural water, sediments and potentially soils. In this study, a novel Mg(OH)2 binding gel was formed using magnesium hydroxide obtained by in situ hydration of calcined magnesium oxide. Laboratory scale experiments showed that the novel Mg(OH)2 gel had a homogeneous dispersion of fine particles of Mg(OH)2 with a particle size of 2-5 μm. With 10 mL of 2.0 mol L-1 NaOH as the eluting agent, the optimal elution efficiency of PO4 on the Mg(OH)2 gel was 72 ± 5%. There were linear relationships between the accumulated PO4 mass and the applied PO4 concentration (0.1 to 20 mg P per L), time (0 to 24 h) and temperature (22 to 40 °C). The capacity of the Mg(OH)2 binding layer was determined to be 99.5 μg P per disc. Tests in synthetic seawater, Chaohu Lake and Yihai Pond confirmed that Mg(OH)2-DGT was able to accurately measure phosphorus up to 10 days. This was indicated by the good agreements between the concentrations measured by DGT (CDGT) technology and by an ex situ chemical method in solution (Csoln), with a CDGT/Csoln ratio between 0.91 and 1.09.

Thermal conduction anisotropy of a magnetic functional fluids utilizing cluster formation of dispersed fine particles (in the case of micron-sized graphite particles)

The thermal conductivity of a magnetic fluid is expected to enhance by adding micron-sized particles with high thermal conductivity. The thermal conductivity of the magnetic fluid containing micron-sized graphite particles was investigated experimentally. The shapes of the graphite particles were sphere and flake-like. As the results of visualization experiments using the dark field microscope, the spherical graphite particles form chain-like clusters under applied magnetic field, while the fibrous structure is formed by the flake-like graphite particles, however, chain-like cluster formation cannot be clearly observed. The experiments using the transient hot-wire method showed that the thermal conductivity of magnetic fluid containing graphite particles is enhanced by applying magnetic field and by increasing the volume fraction of graphite particles.

Dependence of viscosity and transition temperatures of a thermal rheological fluid system on the molecular weight of the side-chain crystalline block copolymer dispersant

Stimuli-responsive materials are promising intelligent materials because of precise and easy control of their various properties simply by providing external stimuli. Herein, we developed a temperature-responsive thermal rheological (TR) fluid, consisting of a solution of polyethylene (PE) fine particle dispersion and a side-chain crystalline block copolymer (SCCBC). The viscosity of the TR fluid was reduced significantly depending on the degree of polymerization of SCCBC; the viscosity was minimized by using a stearyl acrylate15-n-butyl acrylate59 (STA15-nBA59) which has a low total molecular weight and whose functional unit has larger molecular weight than the side-chain crystalline unit. In addition, the TR fluids changed from liquid to almost-solid state, depending on temperature, and the transition temperature of TR fluid was increased using SCCBC with a higher total molecular weight. This result implied that the transition temperatures and viscosity of the TR fluids could be controlled simply by changing the molecular weight of SCCBCs.

화학 수송 모델과 기상 모델을 이용한 석탄 화력 발전소에서 배출되는 미세먼지의 거동 분석

A coal-fired power plant is considered as one of the main sources for fine particulate matters. Particulate matter generated from the power plant can be classified into the primary particulate matter (PM) and the secondary PM. The primary PM is ejected as a solid-state and the secondary PM is ejected as a gaseous state called a precursor and becomes a solid-state by chemical reactions in the atmosphere. Since the size of the secondary PM is smaller than 2.5 micrometers, it can cause severe health problems. Therefore, accurate prediction of advection and diffusion of PM generated from a coal-fired power plant is highly necessary. In the present study, the WRF-Chem (Weather Research and Forecasting–Chemistry) model is used to simulate air quality near a coal-fired power plant. The Carbon-bond mechanism version Z (CBMZ), is used to predict formation of the secondary PM. An aerosol model, which simulates aerosol interactions and chemistry (MOSAIC), is used to predict the transport of fine particles. The meteorological model WRF is used to predict dispersion of fine particles and gaseous components.

SINTERING AND DURABILITY OF CLAYAND DIOPSIDE-CONTAINING CERAMIC AND FAIENCE WALL MATERIALS

The paper summarizes the research results of sintering and durability of wall ceramic materi-als modified by diopside-containing raw products and based on low-melting-point clays and loams, and kaolinand high-melting-point clay faience. Mechanical-and-physical properties of ceramic materials are identified and studied after annealing, depending on the diopside content. It is shown that depending on the content and introduction of clay minerals in the ceramic mixture, both coarse (0.5–1 mm) and fine (0.06 mm, dominating particle size of 0.01–0.015 mm) dis-persed diopside particles can be used. It is found that for loams with the clay mineral content of less than 10 wt.%, the addition of finely-dispersed diopside particles is more efficient. The latter provides ceramic sintering at 1000–1100 °С and increases its strength by 1.5–2 times. The intro-duction of dispersion diopside particles in the faience mixture lowers the annealing temperature from 1250 to 1150 °С with a simultaneous increase in its strength.

Effect of two-step tempering treatment on microstructure and impact toughness of bainitic steel for heavy wall thickness reactor pressure vessels

SA508 Gr.3 steel is widely applied for the fabrication of reactor pressure vessels, which require high impact toughness to ensure the safety of nuclear power plants. In this work, a two-step tempering treatment is proposed to manufacture the SA508 Gr.3 steel with high toughness. A pre-tempering at 400 °C was added before the ultimate tempering of intercritical heat treatment process. The ductile-brittle transition temperature of the steel processed with the new heat treatment is significantly decreased by 26 °C. The scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy characterizations show that the decomposition of M-A constituents into dispersed fine carbide particles and the increase of high-angle grain boundaries contribute to the decrease in ductile-brittle transition temperature. The results suggest that the modified two-step tempering treatment is effective to enhance the impact toughness of SA508 Gr.3 steel.

Influence of ventilation strategies on dispersion and removal of fine particles: An experimental and simulation study

In this study, effect of inlet/outlet configurations on the dispersion and removal of fine particles are examined experimentally and numerically. Ten different inlet/outlet configurations are tested for three different contaminant release cases as by incoming air, from breathing level and close to the outlet. Air velocity and contaminant distributions, air change efficiency, contaminant removal effectiveness and particle decay are investigated for each case. Results revealed that both inlet and outlet opening positions have a strong impact on the performance of the ventilation system. The highest air change efficiency is achieved for the inlet/outlet positioned on the same vertical wall. In terms of particle removal, ventilation performance changes up to the particle source position and the area of interest. The most proper inlet/outlet positions should be decided by considering the source position and the main region of concern of the ventilation system. Moreover, close relation of particle source and outlet opening is found most likely to remove the contaminants effectively.

Концептуальное исследование задач разработки метода ликвидации разливов нефти в ледовых морях с помощью тонкодисперсных твердых частиц

Концептуальное исследование задач разработки метода ликвидации разливов нефти в ледовых морях с помощью тонкодисперсных твердых частиц

Dispersion of Fine Particles Using High-Speed Mixers

Dispersion of Fine Particles Using High-Speed Mixers

Microstructure, hardness and corrosion behaviour of friction-stir processed AA5083

PurposeThe purpose of this study is to refine the microstructure and improve the corrosion behaviour of aluminium alloy AA5083 by subjecting it to friction stir processing (FSP).Design/methodology/approachFSP trials are conducted as per central composite design, by varying tool rotation speed, tool traverse speed and shoulder diameter at three levels. The microstructure is examined and the hardness is measured for both the base material and the processed workpieces. The corrosion behaviour of the base material and processed workpieces is studied using potentiodynamic polarization technique for three different testing temperatures, and the corrosion current and corrosion rate are calculated.FindingsThe results reveal that FSP refined the grains, dispersed secondary phases, increased the hardness and improved the corrosion resistance of most of the friction stir processed specimens than the base material at all the three testing temperatures. Grain refinement and fine dispersion of ß phase improves the hardness and corrosion resistance of most of the FSPed specimens. However partial dissolution of ß phase decreases the hardness in some of the specimens. Most of the FSPed specimens displayed more positive potential than the base material at all the testing temperatures representing a higher nobility than the base material, as a result of fine dispersion of secondary phase particles in the matrix. Large pits formed on the surface of the base specimen indicating a higher corrosion rate at all three testing temperatures. The SEM image of FSPed specimens reveals the occurrence of very few pits and minimal corrosion products on the surface, which indicates lower corrosion rate.Originality/valueThe corrosion mechanism of the friction stir-processed AA5083 specimens is found to be a combination of activation and concentration polarization.

Evaluation of the efficiency of rectangular separators to collect the particles from the gas flows

Analysis of the separation devices’ operation and improvement of efficient gas mixture purification processes is relevant issue and is a great interest for the specialists of different industrial brunches. Modernization of internal devices in the cases of existing separators is the main goal in the field of increasing the efficiency of fine dispersed particles’ collection process. Design of a rectangular separator with a number of I-beams has been developed. Operation principle of the device is described. When the multiphase flow moves between the device elements, the centrifugal force appears, that ensures the coagulation of finely dispersed liquid drops, facilitating their uniform settling on the entire surface of I-beams. The advantage of these separators is noted. High values of centrifugal force are achieved at relatively low gas flow rates that allows to carry out the separation processes at low energy costs. Numerical study of the gas mixture flow through the rectangular separator is shown at different values of the flow rate and different diameter of particles. The results of separation efficiency are shown for different designs of I-beams. Increase in the rate leads to efficiency increase. Ranges of efficient operation of the separator have been determined. Studies showed the advisability of using the rectangular separators to purify the gases from finely dispersed particles.

Evaluation of air change rates for estimating particle dispersion on a reduced scale model

Similarity between a model and a prototype is important for scale model experimental studies. Proper scaling by considering similarity parameters can lead to valuable results. The objective of this study is to investigate dispersion of fine particles under different air change rates by experimental and numerical techniques. Experimental studies are performed on a 1:5 reduced scale model. Similarity parameters are considered for kinematic and particle dispersion similarities. The RNG k – ε turbulence model is used in the numerical predictions. It is shown that the average room and outlet concentrations get similar values with the removal of accumulation as the air velocity increases. Moreover, it is disclosed that the advantages of the increasing air change rates may have limits in reducing contaminant level.

Investigations on the corrosion behaviour and biocompatibility of magnesium alloy surface composites AZ91D-ZrO2 fabricated by friction stir processing

ABSTRACTIn the current study, friction stir processing was applied as a methodology to produce surface composites of AZ91D magnesium alloy with ZrO2 particles. Microstructural evolution, microhardness profile and corrosion behaviour of the developed surface composite were analysed. The results indicate that the combined effect of friction stir processing and reinforcement of ZrO2 reduced the grain size, and fragmented and dispersed the secondary phases. The fine dispersion of ZrO2 particles contributed to the enhancement of cumulative surface potential, and hence the corrosion resistance of the developed surface composite. The analysis of post-corrosion test specimens revealed the formation of corrosion products that had similar composition to that of hydroxyapatite. The formation of such corrosion products is beneficial, as it contributes to corrosion resistance (stable and adherent layer) and biocompatibility.

Role of Sr on microstructure, mechanical properties, wear and corrosion behaviour of an Al–Mg2Si–Cu in-situ composite

The influence of Sr additions on the microstructure of primary and eutectic Mg2Si phases, wear and corrosion behaviour of Al–Mg2Si–Cu in-situ composite was investigated. The results showed that addition of 0.01 wt% Sr modified the primary Mg2Si morphology but exceeding this level of Sr induced a loss of modification as the primary phase morphology coarsened again. The Al–Mg2Si eutectic phase, on the other hand, still exhibited a refined structure even with higher levels of Sr additions. Thermal analysis results revealed that both modification of the primary Mg2Si and refinement of the eutectic Mg2Si are most likely related to nucleation and growth stages respectively. The results of 0.01 wt% Sr addition showed that the mean size and mean aspect ratio decreased by about 30% and 6% respectively, but the mean density increased by 185% respectively. The highest UTS, El%, impact toughness and hardness were measured at 101.57 MPa, 1.1%, 1.31 J and 81 VHN respectively. Fractography of tensile and impact specimens from the Sr-treated composite revealed that Mg2Si particles suffered cracking with few decohesion indicating higher ductility. The results of wear testing also showed that composites treated with Sr have higher wear resistance compared with those of without Sr. The highest resistance to wear was observed in the composite containing 0.01 wt %Sr which is likely the result of good dispersion of fine Mg2Si particles in the Al matrix. This fine morphology and uniform distribution of Mg2Si particles also contributed to better corrosion resistance by reducing the propagation of corrosion pits.