Coagulation Process Of Particles Research Articles

ნახშირის წვრილმარცვლოვანი ფრაქციის გაუწყლოების პროცესის ინტენსიფიკაცია ტყიბულის საბადოს პირობებში

Recently, the world is intensively exploiting renewable energy sources, yet coal still remains the main raw material for the energy, ferrous and non-ferrous metallurgy, chemical industries. The main coalfield currently operating in Georgia is the Tkibuli-Shaori minefield. Coals of Tkibuli minefield belongs to the category of difficultto-enrich minerals due to its complex physico-chemical composition. Due to the complexity of the technological process of enrichment, in the process of dehydration of the commodity product, a large amount (20-25%) of finegrained (-0.5 mm) fraction is formed - the so-called silts. These products, which due to the problem of its dehydration and consequently its separation as a separate product, now represent losses. Intensification of the dehydration process of the fine-grained fraction (1515 + 0 μm) clay product, in addition to reducing losses, allows circulating water to be used in the main enrichment process. Experiments have shown that during the treatment of wastewater in a magnetic field, the sedimentation rate of solid particles in the liquid increases dramatically, which is conditioned by the improvement of the particle coagulation process. Accordingly, the number of fine fraction losses in the runoff is reduced by 60-65%.

The Limits of Fine Particle Ultrasonic Coagulation

This paper describes the studies conducted in order to identify the limits of ultrasonic exposure’s effect on the fine particle coagulation process. It has been established as a result of the studies that ultrasonic exposure with a sound pressure level of 160 dB is capable of ensuring coagulation of particles sized 2.5 µm with efficiency δ = 83%. An increase of the coagulation up to 13% is induced with generation of swirling flows. The suggested approach to increasing the coagulation efficiency owing to vortex-type flows between the radiating and reflecting surfaces ensures efficiency of coagulation δ = 96 %. The implementation of this approach has shown that with generation of vortex-type acoustic flows, it makes the most sense for a concentration of particles of 18×10−3 g/m3. Incremental efficiency at such concentrations amounts to 50%.

Coagulation patterns and the impacts on traffic-related ultrafine particle dispersion in road tunnels employing dynamic mesh algorithms.

.In this study, we continue to analyze the diffusion mechanism of ultrafine particles and the particle coagulation phenomenon with a size range of 26-287 nm exhausted from vehicles during the process of passing through a 100-m-long tunnel using the realizable k-ε model and dynamic grid technique. A three-dimensional model consisting of a 100-m highway tunnel and four side-by-side gasoline vehicles (L × W × H = 4.5 m × 1.8 m × 1.5 m) was established in the STAR-CCM+ computational fluid dynamics software. The gasoline vehicles traveled simultaneously under different situations of three driving speeds of 60 km h-1, 40 km h-1, and 20 km h-1 during the simulation. Through data analysis and research, it was found that the coagulation process of particles is very complicated, especially at low speeds. When the vehicle speed is 20 km h-1, the variation in particle concentration at the vehicle wake near the tailpipe (at the vertical plane located 0.1 m behind the exhaust pipe) causes a large error if the coagulation action is not considered. The relative error of the average particle concentration at 0.5 s of the vertical section 0.1 m away from the exhaust pipe is as high as 193.51%. The relative error in the entire tunnel is only 2.82%, which is less than 5%. Thus, it is recommended that particle coagulation should be considered when analyzing particle dispersion in the near-wake region behind the vehicle and the breathing areas, especially when the vehicle travels slowly inside the tunnel. However, when evaluating the particle concentration and exposure levels for the entire tunnel, coagulation can be ignored without significant errors, especially at a high vehicle speeds. This study clarified the importance of coagulation in different areas and its influence on the diffusion of particulate matter. This is conducive to further analysis of the diffusion characteristics of particulate matter and can appreciably reduce the pollution degree in a tunnel by changing the coagulation efficiency of particulate matter in the future.

Global–regional nested simulation of particle number concentration by combing microphysical processes with an evolving organic aerosol module

Abstract. Aerosol microphysical processes are essential for the next generation of global and regional climate and air quality models to determine particle size distribution. The contribution of organic aerosols (OAs) to particle formation, mass, and number concentration is one of the major uncertainties in current models. A new global–regional nested aerosol model was developed to simulate detailed microphysical processes. The model combines an advanced particle microphysics (APM) module and a volatility basis set (VBS) OA module to calculate the kinetic condensation of low-volatility organic compounds and equilibrium partitioning of semi-volatile organic compounds in a 3-D framework using global–regional nested domain. In addition to the condensation of sulfuric acid, the equilibrium partitioning of nitrate and ammonium, and the coagulation process of particles, the microphysical processes of the OAs are realistically represented in our new model. The model uses high-resolution size bins to calculate the size distribution of new particles formed through nucleation and subsequent growth. The multi-scale nesting enables the model to perform high-resolution simulations of the particle formation processes in the urban atmosphere in the background of regional and global environments. By using the nested domains, the model reasonably reproduced the OA components obtained from the analysis of aerosol mass spectrometry measurements through positive matrix factorization and the particle number size distribution in the megacity of Beijing during a period of approximately a month. Anthropogenic organic species accounted for 67 % of the OAs of secondary particles formed by nucleation and subsequent growth, which is considerably larger than that of biogenic OAs. On the global scale, the model well predicted the particle number concentration in various environments. The microphysical module combined with the VBS simulated the universal distribution of organic components among the different aerosol populations. The model results strongly suggest the importance of anthropogenic organic species in aerosol particle formation and growth at polluted urban sites and over the whole globe.

A new weighted fraction Monte Carlo method for particle coagulation

PurposeThe purpose of this study is to investigate the aerosol dynamics of the particle coagulation process using a newly developed weighted fraction Monte Carlo (WFMC) method.Design/methodology/approachThe weighted numerical particles are adopted in a similar manner to the multi-Monte Carlo (MMC) method, with the addition of a new fraction function (α). Probabilistic removal is also introduced to maintain a constant number scheme.FindingsThree typical cases with constant kernel, free-molecular coagulation kernel and different initial distributions for particle coagulation are simulated and validated. The results show an excellent agreement between the Monte Carlo (MC) method and the corresponding analytical solutions or sectional method results. Further numerical results show that the critical stochastic error in the newly proposed WFMC method is significantly reduced when compared with the traditional MMC method for higher-order moments with only a slight increase in computational cost. The particle size distribution is also found to extend for the larger size regime with the WFMC method, which is traditionally insufficient in the classical direct simulation MC and MMC methods. The effects of different fraction functions on the weight function are also investigated.Originality ValueStochastic error is inevitable in MC simulations of aerosol dynamics. To minimize this critical stochastic error, many algorithms, such as MMC method, have been proposed. However, the weight of the numerical particles is not adjustable. This newly developed algorithm with an adjustable weight of the numerical particles can provide improved stochastic error reduction.

Modelling study of emulsion latex coagulation processes in coagulators

AbstractThis paper presents a numerical study of emulsion latex coagulation processes in continuous coagulators based on the full computational fluid dynamics approach. The RANS approach together with the k‐ε turbulence model was used to describe the detailed flow field in the coagulators. The coagulant mixing process was modelled by the convection‐diffusion equation and the emulsion latex coagulation process was formulated by the population balance equation of the particle size with a coagulation kernel including a perikinetic and orthokinetic combined mechanism. The flow and coagulation models were independently validated by means of comparing simulated results to the relevant experimental data from the literature. A series of simulations were carried out to study the effects of coagulator bottom shape, salt solution feeding location, residence time and agitation speed, as well as the influence of four typical scale‐up criteria on the latex particle coagulation process. The presented results would be helpful for the relevant process design, development, and scale‐up of continuous latex coagulators.

Preparation of monodisperse polystyrene nanoparticles with tunable sizes based on soap-free emulsion polymerization technology

Herein, a one-step procedure for the preparation of monodispersed nanoparticles was achieved, with tunable size in range of around 30~300 nm based on soap-free emulsion polymerization using sodium p-styrene sulfonate as ionic comonomer. The polymerization reaction kinetics (i.e., monomer conversion, particle number, and particle size distribution) were investigated in detail. The experimental results indicated that the particle number increased in low ionic comonomer NaSS concentrations (< 10 wt%). The particle number reached maximum value at 10 wt% NaSS concentration, and minimum particle size nanoparticles (22.3 nm) were obtained. The particle size increased when NaSS concentration exceeded 10 wt%. The particle size distribution of latex gradually narrowed as the polymerization reaction was carried out due to the eversible particle coagulation process and competitive growth kinetics of a particle growth period. This method is conventional and practical for the production of nanoparticles.

Facile synthesis of large sized and monodispersed polymer particles using particle coagulation mechanism: an overview

Highly uniform polymer latex particles with controlled particle size have been widely applied in many fields such as nanotechnology, drug delivery, biomedical separation, and material templates. Since the particle size plays a critical role in determining the application fields, various technologies such as two-stage swelling method and dynamic swelling method have been used to control the particle size in the polymerization process. However, these methods usually need a multi-step polymerization reaction and long reaction time. This review focuses on a method of controlling particle size, that is, particle coagulation technology. Particle coagulation technology can be used to produce large sized, monodispersed polymer particles by soap-free emulsion polymerization, macroemulsion polymerization, and dispersion polymerization. In this review article, an overview of the concept of particle coagulation is given, followed by the description of the particle coagulation process in different polymerization systems. Some representative publications about particle coagulation were also reviewed, especially the effect of reaction parameters on the particle coagulation extent and time. Finally, the relationship between the particle coagulation and particle size distribution is reviewed extensively.

Deposition of SiO2 nanoparticles in heat exchanger during combustion of biogas

Experimental results are presented on silica deposition in a typical domestic heat exchanger during combustion of siloxane-containing gas as a model of biogas that is produced naturally during the anaerobic degradation of organic material in landfills and waste water treatment plants. A model of silica deposition is developed. The main objective is to demonstrate that the mass flux of silica to heat exchanger surfaces is not sensitive to details of particle coagulation process and particle size distribution. It is shown that the deposition flux of silica depends linearly on siloxane concentration in input air/gas mixture.

Measurements of mercury speciation and fine particle size distribution on combustion of China coal seams

The percentage of mercury that is removed in currently used air pollution control devices (APCDs) depends on the speciation in the flue gas exhausting from the coal combustor. Bench-scale measurements were carried out in the flue gas from combustion of different types of coal in a drop-tube furnace set-up to better understand the formation process of three mercury species, i.e. Hg0, Hg2+ and Hgp, in gaseous phase and fine particles. It was observed that due to chemical reaction kinetics limitations, higher mercury concentrations in flue gas lead to lower Hg2+ proportions. The concentration of chlorine has the opposite effect, not as significantly as that of mercury though. With the chlorine concentration increasing, the proportion of Hg2+ increases. Combusting finer sized coal powders results in the formation of more Hg2+. Mineral composition of coal and feed coal particle size has a great impact on fine particle formation. Increased Al in coal results in more finer particle formation, while Fe in coal increases concentration of larger particles. The coexistence of Al and Si can enhance the particle coagulation process. This process is also enhanced at higher coal feed rates, and when feed coal particle sizes are smaller. Results from oxy-coal and conventional air combustion were compared.

Brownian Dynamics Simulation of the Influence of Hydrodynamic Interaction on Particle Coagulation

采用布朗动力学模拟方法,研究了流体动力学作用对稀溶液中悬浮粒子聚集过程的影响.模拟中忽略了一个粒子同时与多个粒子碰撞聚集的可能,引入了前人有关两粒子间流体动力学作用影响的研究成果.模拟结果证实了流体动力学的作用在比较大的幅度上减缓了粒子的聚集过程,是导致粒子聚集速率的实验值低于Smoluchowski理论值的重要原因之一.另外,在分别加入和排除重力作用,以及考虑和忽略粒子间流体动力学作用在内的各种...

Research on nucleation and coagulation of nanoparticles in parallel twin jets

The large eddy simulation method has been used to simulate the diffusion of H2SO4 vapor in the parallel twin jets. The distributions of number concentration and size of nanoparticles produced by nucleation and coagulation in sulfuric acid/water system are given. The functions of the sulfur content, relative humidity and jet Reynolds number are evaluated according to the distributions of number concentration and size of nanoparticles. The results show that the nucleation in sulfuric acid/water system produces large number of nanoparticles, and gas-to-nanoparticle conversion mostly takes place in the middle and interface of the twin jets. The coagulation process of particles reduces the number concentration, while increases the mean particle size. For the case with higher sulfur content, more number and smaller size nanoparticles are produced by nucleation and coagulation. There is also a larger number of nanoparticles for the cases with higher relative humidity and jet Reynolds number.

Single-particle method for stochastic simulation of coagulation processes

A Monte Carlo stochastic simulation algorithm based on a single-particle method is suggested to describe steady-state particle coagulation processes. The method does not require any information on nearby particles; instead a fictitious coalescence partner with a given size is generated. The main drawback that limited applicability of this method in the past was that for each control volume the particle size distribution function had to be sampled and stored. In the present study we applied a discrete representation of the distribution function that requires only small memory resources and allows fast updating.

Self-Preserving Size Distribution of Fire Soot Fractal Coagulation in Flaming Combustion

In this work, by carefully calculating the different Knudsen numbers, the free molecular and continuum regimes of flaming combustion were first explicitly defined as the soot particle growth zone low in the flame and the upper zone near the ambient air in the plume respectively, and the fractal coagulation theory was applied to analyze the soot particle agglomeration in the two cluster–cluster aggregation-dominating regions. The accurate analytical simplicity solution obtained proved that self-preserving size distribution (SPSD) exists in the two regions. Additionally we got the relation between the normalized number concentration of the total particle aggregates and the dimensionless time as well as the actual lag-time from monodisperse distribution to SPSD. The results indicate that the fractal morphology of the soot particles affects the particle coagulation process to a large extent, especially has a great influence on soot particle SPSD, total aggregates number concentration in the growth region and the time needed from monodisperse distribution to SPSD above the flame region near the air conditions. The validation of our theoretical results was verified in comparison with previous work and our experimental results.

Growth mechanism of cadmium sulfide ultrafine particles in water-in-oil microemulsion.

The growth mechanism of CdS ultrafine particles in water-in-oil microemulsions was investigated. The growth occurs via a irreversible particle coagulation process. Its rate constant is dependent on the agglomeration number of a particle n. At small agglomeration numbers, the rate constant k is about 107 dm3mol–1s–1. It decreases dramatically to about 103 dm3mol–1s–1 at a critical agglomeration number nc followed by a further decrease in k above 2nc. This causes sharpening of the size distribution near nc and 2nc. A simple model based on the coagulation process with n-dependent rate constants is proposed, which explains well the experimental results. The effects of initial mixing and the feed ratio of Cd2+ to S2– are understood well by the proposed model. The relationship between nc and the stable supramolecules composed of CdS particles was discussed.

Mechanism of formation of silver halide ultrafine particles in reverse micellar systems.

The mechanism of formation of silver halide ultrafine particles in sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/isooctane reverse micellar systems has been studied. The particle formation process was followed by a change in the UV-visible absorption spectra. The effects of the concentrations of reactants and water content of reverse micellar solution on the size of formed particles were investigated. The size of AgCl particles decreased with increasing water content or reactant concentration, whereas the size of AgBr and AgI particles increased. A possible interpretation is the dissolution of AgCl, which is caused by some impurities in the AOT. Particle coagulation processes of AgBr and AgI particles are found to be dominated by the concentration of micellar droplets containing two or more particles.

Rate of soot growth in atmospheric premixed laminar flames

The process of soot formation, the growth of the soot mass, of the soot particles and the change in their number density has been measured in laminar premixed fuel-air flames. The following fuels have been used: acetylene, benzene, n -hexane, n -heptane, cyclohexane, cyclohexene, naphthalene, pyridine, thiophene, and furane. In addition, mixtures of ethylene with hydrogen have been investigated for C/H ratios from 0.48 to 0.30. The various mixtures have been tested for different C/O ratios and flow velocities on a capillary burner with shielded flame and on a porous plate burner. In some cases the initial temperature was varied. Two lasers were used to measure the soot aerosol absorption and scattering; temperatures were measured by the Na-line reversal and the Kurlbaum methods. The experiments show that the particle coagulation process is practically the same for all flames (flame temperatures from 1500 K to 200 K). The growth of the soot volume fraction f c in the later phase (after about 10% of the final volume fraction f M has been reached) can be approximated by df v /dt=k(f M -f v ). The “rate constant ( k )“ for the growth of f v has been found to depend on temperature, but not on the type of fuel, the C/O ratio or the C/H ratio. The amount of soot finally present ( f M ) varies greatly with C/O ratio, approximately with 3rd to 4th power of the carbon surplus (C/O-(C/O) crit ). Moreover, it depends considerably on temperature above 1500 K. Its total value for a given C/O is typical of the type of fuel.

Calculation of coagulation of particles of the condensate in a laval nozzle

The article presents a method for calculating the process of the coagulation of particles, resulting from different degrees of velocity lag in a nozzle, and the results of calculations carried out by the methods of Euler and Lagrange. Both methods ensure a good degree of accuracy in a numerical calculation of the change in the degree of dispersion of particles in a nozzle. The process of the collision and coalescence of the drops of a condensate, resulting from different velocity lags of particles of different sizes, with the nonequilibrium flow of a two-phase stream in nozzles, is discussed in [1–5], There are two possible approaches to a description of the change in the degree of dispersion of a system of particles, i.e., the Euler and Lagrange methods [6]. The Euler method postulates a jumpwise growth of the particles, with the collision and coalescence of two drops. In this case, for particles of a definite fraction with a mass mi (i=1, ⋯, n), determinations are made of the decrease in the number of these particles in a unit of volume n(mi) due to entrainment of the particles resulting from their coalescence with drops of other fractions, and of the increase of n(mi) due to the formation of particles mi, with the coalescence of particles of the fractions m and (mi−m), where m=mi. This type of model was used in [2–5] for calculating the coagulation process of particles in a nozzle. In a more complete statement, nonequilibrium flow in a nozzle, taking account of collisions, coalescence, and of the exchange of energies and momentum between particles, is discussed in [3]. The Lagrange method for fixed i-particles considers a continuous increase in the mass mi as the result of coalescence with smaller j-drops (j=1, ⋯, i−1) and a decrease in the number of particles in unit volume ni, resulting from their absorption by larger particles (j=i+1,⋯, n). This approach is discussed in [1]. The present article gives below a method for calculating the coagulation process of particles in a nozzle using the Lagrange method, and analyzes the results of electronic-computer calculations, carried out using both of the above-discussed methods.