Coagulation Of Dust Particles Research Articles

Experimental Study on Humidification Coagulation and Removal of Fine Particles Using an Electrostatic Precipitator.

A wet electrostatic precipitator (WESP) has much higher capture rate for fine particulate matter, PM2.5, than a traditional dry type electrostatic precipitator does. In order to make full use of existing dust removal equipment and reduce the emissions of smoke and dust to zero, a combination of chemical coagulation and humidification coagulation is proposed using a WESP. The results show that the addition of chemical coagulant can promote the coagulation of coal-fired dust particles. After the addition of pectin (PG), the median diameter of dust particles increases from 28.19 μm to 45.28 μm. Water vapor humidification can promote the coagulation of dust particles. When the water vapor injection rate increases from 0 kg/h to 3.2 kg/h, the median diameter of dust particles increases from 28.19 μm to 36.45 μm. The synergistic effect of the coagulant and water vapor can enhance the chemical coagulation effect; when 1.0 × 10-2 g/L PG and 3.2 kg/h water vapor synergize, the collection efficiency reaches 98.17%, and when 1.0 × 10-2 g/L polyacrylamide (PAM) and 3.2 kg/h water vapor synergize, the collection efficiency reaches 96.68%. Both chemical coagulation and water vapor humidification can promote the condensation of coal dust, which is beneficial to improve the efficient capture of fine particles using WESP.

Impact of the coagulation of dust particles on Mars during the 2018 global dust storm

Coagulation of particles occurs when two particles collide and stick together. In the Martian atmosphere, coagulation of dust would increase the dust effective particle size, as small particles accrete to larger particles. Murphy et al. (1990) concluded that Brownian coagulation of dust in the Martian atmosphere was not significant, due to the low dust particle mixing ratios, while Montmessin et al. (2002) and Fedorova et al. (2014) showed that it mostly involves dust particle radii smaller than 0.1 μm. However, the effects of coagulation have never been explored in 3D, during a global dust storm, and in presence of larger numbers of small particles. Here we revisit this issue by using the NASA Ames Mars Global Climate Model (MGCM) to investigate the temporal and spatial changes in dust particle sizes during the 2018 global dust storm due to dust coagulation and the overall impact of these processes on Mars' climate. Our parameterization for dust coagulation includes the effect of Brownian motion, Brownian diffusion enhancement, and gravitational collection. We show that Brownian motion and Brownian diffusion enhancement dominate gravitational collection. Coagulation has a significant impact during the global storm, with coagulation rates increased by a factor of 10 compared to non-storm conditions. The mean effective particle radius can be increased by a factor of up to 2 due to coagulation, leading to a 20 K colder atmosphere above 30 km altitude. Overall, our parameterization improves the representation of the decay phase of the storm relative to MCS dust observations. Coagulation also remains a significant process affecting dust outside the storm period if large numbers of submicron-sized particles are involved. As coagulation removes the small sub-micron particles within a relatively short time, it may therefore be possible, in GCMs, to lift larger amounts of submicron-sized particles from the surface without excess dust buildup in the atmosphere, thus improving the agreement with some of the observations without diverging from the observed column opacities.

Coagulation Instability in Protoplanetary Disks: A Novel Mechanism Connecting Collisional Growth and Hydrodynamical Clumping of Dust Particles

Abstract We present a new instability driven by a combination of coagulation and radial drift of dust particles. We refer to this instability as “coagulation instability” and regard it as a promising mechanism to concentrate dust particles and assist planetesimal formation in the very early stages of disk evolution. Because of dust-density dependence of collisional coagulation efficiency, dust particles efficiently (inefficiently) grow in a region of positive (negative) dust density perturbations, leading to a small radial variation of dust sizes and as a result radial velocity perturbations. The resultant velocity perturbations lead to dust concentration and amplify dust density perturbations. This positive feedback makes a disk unstable. The growth timescale of coagulation instability is a few tens of orbital periods even when dust-to-gas mass ratio is on the order of 10−3. In a protoplanetary disk, radial drift and coagulation of dust particles tend to result in dust depletion. The present instability locally concentrates dust particles even in such a dust-depleted region. The resulting concentration provides preferable sites for dust–gas instabilities to develop, which leads to further concentration. Dust diffusion and aerodynamical feedback tend to stabilize short-wavelength modes, but do not completely suppress the growth of coagulation instability. Therefore, coagulation instability is expected to play an important role in setting up the next stage for other instabilities, such as streaming instability or secular gravitational instability, to further develop toward planetesimal formation.

IMPROVING THE EFFICIENCY OF THE VORTEX DUST COLLECTORS

It is proposed to use a modernized “wet” vortex dust collector for cleaning ventilation emissions from non-adhering dust. The design of the vortex dust collector contributes to its effi ciency by installing irrigation nozzles in the primary and secondary air connections made in the form of a Venturi tube, which allows reducing energy consumption during the cleaning of dusty air. Due to the multidirectional movement of dust particles and splashed water, active coagulation of dust particles and water particles occurs, as well as a liquid fi lm is formed on the inner surface of the separation chamber, which prevents the dust particles from rebounding from the separation chamber and facilitates their collection and washing into a collecting bin.

Dust Coagulation Regulated by Turbulent Clustering in Protoplanetary Disks

Abstract The coagulation of dust particles is a key process in planetesimal formation. However, the radial drift and bouncing barriers are not completely resolved, especially for silicate dust. Since the collision velocities of dust particles are regulated by turbulence in a protoplanetary disk, turbulent clustering should be properly treated. To that end, direct numerical simulations (DNSs) of the Navier–Stokes equations are requisite. In a series of papers, Pan & Padoan used a DNS with Reynolds number Re ∼ 1000. Here, we perform DNSs with up to Re = 16,100, which allow us to track the motion of particles with Stokes numbers of 0.01 ≲ St ≲ 0.2 in the inertial range. Through the DNSs, we confirm that the rms relative velocity of particle pairs is smaller by more than a factor of two, compared to that by Ormel & Cuzzi. The distributions of the radial relative velocities are highly non-Gaussian. The results are almost consistent with those by Pan & Padoan or Pan et al. at low Re. Also, we find that the sticking rates for equal-sized particles are much higher than those for different-sized particles. Even in the strong-turbulence case with α-viscosity of 10−2, the sticking rates are as high as ≳50% and the bouncing probabilities are as low as ∼10% for equal-sized particles of St ≲ 0.01. Thus, turbulent clustering plays a significant role in the growth of centimeter-sized compact aggregates (pebbles) and also enhances the solid abundance, which may lead to the streaming instability in a disk.

Using acoustic field energy to decrease dust discharge from the working space of the Vanyukov furnace

To organize in-furnace dust settling in the Vanyukov furnace at OAO SUMZ (Revda, Russia), acoustic emitter technology is used. The emitter design includes a nozzle tube, an air nozzle, a resonator, and a focusing surface. Starting from the surface area of the furnace melt bath and recommended specific acoustic power for in-furnace dust settling, the summary acoustic field sound power is calculated and the optimal amount and arrangement places of acoustic emitters are determined. To form the acoustic field in the Vanyukov furnace for melting copper sulfide zinc-containing feedstock and deplete liquid converter slags, four acoustic emitters are mounted in the end wall through an inspection window, two on the apothecary side and two on the loading side of charge materials. In general, six pilot modes of testing the in-furnace dust settling system with various operational settings of acoustic emitters and one base mode for comparing performance characteristics are implemented. The duration of pilot periods varies from 5 to 18 days, and the total aggregate service time is 68 days. The presence of the acoustic field in the working furnace space at any emitter operation settings promote a decrease in the concentration of dust particles after the chain of gas purifiers (in the commodity point). It is revealed by the experimental data that the minimal summary acoustic field sound power, which decreases the dust concentration due to the coagulation of dust particles inside the furnace space, is 800 W.

Design features of vortex dust collectors

This article states that during the construction of industrial buildings it is necessary to provide engineering communications (including systems of supply and exhaust ventilation) which ensure uninterrupted production, its technological and environmental safety. It is necessary to use cleaning devices to remove pollutants from ventilation emissions in local exhaust systems. As for devices for removing highly disperse non-sticky dust, it is possible to offer vortex dust collectors, the efficiency of which depends on the design and operating mode. A method is proposed to increase the efficiency of a vortex dust collector, to improve the quality of the purified air, and to reduce energy consumption during air purification by installing watering nozzles in primary and secondary air pipes made in the form of a Venturi tube. In consequence of multidirectional movement of dust particles and sprayed water, active coagulation of dust particles takes place, as a result of which the separation increases. Apart from that, watering dusty air flows leads to the formation of a liquid film on the inner surface of the separation chamber, which prevents dust particles from rebounding off the separation chamber and facilitates their capture and flushing into the collecting hopper

ACOUSTIC FIELD ENERGY UTILIZATION FOR LOWERING DUST REMOVAL FROM THE VANYUKOV FURNACE

The acoustic generator technology was used to arrange in-furnace dust deposition in the Vanyukov furnace, OJSC SUMZ (Revda, Russia). The generator design included a nozzle tube, an air nozzle, a resonator and a focusing surface. The total acoustic power of the acoustic field and the optimum number and location of the acoustic generators were determined based on the surface area of the furnace molten pool and the recommended values of specific acoustic power for in-furnace dust deposition. To create an acoustic field in the Vanyukov’s furnace for melting the sulfide copper zinc-containing raw material and depleting the liquid converter slag, four acoustic generators were installed in the end wall through the inspection window: two on the uptake side and two on the charge material loading side. In total, six pilot modes of in-furnace dust deposition system testing at different operation settings of acoustic generators were implemented with one basic mode to compare performance. The duration of test periods ranged from 5 to 18 days, and the total operation time of the unit using acoustic generators was 68 days. It should be noted that the presence of an acoustic field in the furnace body at any operation settings of generators in one way or another helped to reduce the concentration of dust particles downstream the chain of gas purifiers (at the commodity point). According to test data, it was found that the minimum total acoustic power of the acoustic field, which reduces the dust concentration due to the coagulation of dust particles within the furnace space, is 800 W.

SPIRAL STRUCTURE AND DIFFERENTIAL DUST SIZE DISTRIBUTION IN THE LkHα 330 DISK

ABSTRACT Dust trapping accelerates the coagulation of dust particles, and, thus, it represents an initial step toward the formation of planetesimals. We report H-band (1.6 μm) linear polarimetric observations and 0.87 mm interferometric continuum observations toward a transitional disk around LkHα 330. As a result, a pair of spiral arms were detected in the H-band emission, and an asymmetric (potentially arm-like) structure was detected in the 0.87 mm continuum emission. We discuss the origin of the spiral arm and the asymmetric structure and suggest that a massive unseen planet is the most plausible explanation. The possibility of dust trapping and grain growth causing the asymmetric structure was also investigated through the opacity index (β) by plotting the observed spectral energy distribution slope between 0.87 mm from our Submillimeter Array observation and 1.3 mm from literature. The results imply that grains are indistinguishable from interstellar medium-like dust in the east side ( ) but are much smaller in the west side , indicating differential dust size distribution between the two sides of the disk. Combining the results of near-infrared and submillimeter observations, we conjecture that the spiral arms exist at the upper surface and an asymmetric structure resides in the disk interior. Future observations at centimeter wavelengths and differential polarization imaging in other bands (Y–K) with extreme AO imagers are required to understand how large dust grains form and to further explore the dust distribution in the disk.

A possible mechanism for overcoming the electrostatic barrier against dust growth in protoplanetary disks

The coagulation of dust particles under the conditions in protoplanetary disks is investigated. The study focuses on the repulsive electrostatic barrier against growth of charged dust grains. Taking into account the photoelectric effect leads to the appearance of a layer at intermediate heights where the dust has a close to zero charge, enabling the dust grains to grow efficiently. An increase in the coagulation rate comes about not only due to the lowering of the Coulomb barrier, but also because of the electrostatic attraction between grains of opposite charge due to the non-zero dispersion of the near-zero charge. Depending on the efficiency of mixing in the disk, the acceleration of the evolution of the dust in this layer could be important, both in the quasi-stationary stage of the disk evolution and during its dispersal.

Ice condensation as a planet formation mechanism

We show that condensation is an efficient particle growth mechanism, leading to growth beyond decimeter-sized pebbles close to an ice line in protoplanetary discs. As coagulation of dust particles is frustrated by bouncing and fragmentation, condensation could be a complementary, or even dominant, growth mode in the early stages of planet formation. Ice particles diffuse across the ice line and sublimate, and vapour diffusing back across the ice line recondenses onto already existing particles, causing them to grow. We develop a numerical model of the dynamical behaviour of ice particles close to the water ice line, approximately 3 AU from the host star. Particles move with the turbulent gas, modelled as a random walk. They also sediment towards the midplane and drift radially towards the central star. Condensation and sublimation are calculated using a Monte Carlo approach. Our results indicate that, with a turbulent alpha-value of 0.01, growth from millimeter to at least decimeter-sized pebbles is possible on a time scale of 1000 years. We find that particle growth is dominated by ice and vapour transport across the radial ice line, with growth due to transport across the atmospheric ice line being negligible. Ice particles mix outwards by turbulent diffusion, leading to net growth across the entire cold region. The resulting particles are large enough to be sensitive to concentration by streaming instabilities, and in pressure bumps and vortices, which can cause further growth into planetesimals. In our model, particles are considered to be homogeneous ice particles. Taking into account the more realistic composition of ice condensed onto rocky ice nuclei might affect the growth time scales, by release of refractory ice nuclei after sublimation. We also ignore sticking and fragmentation in particle collisions. These effects will be the subject of future investigations.

The influence of monomer shape on aggregate morphologies

Context. The coagulation of dust particles is the initial step in planetary formation, with the precursors to planetesimals believed to form via the collisions of micron and submicron sized dust particles in the disk surrounding a newly formed protostar. One of the usual assumptions in numerical models of aggregation is that of spherical monomers. However, the polarization of light in the interstellar medium (ISM) indicates that dust particles may not necessarily be spherical. Aims. This study investigates the influence of monomer shape (ellipsoidal vs. spherical) on the morphology of aggregates. The ellipsoidal grains used are prolate with an axis ratio of 3:1:1, which current evidence suggests as a possible shape for instellar dust grains. Methods. Populations of aggregates are built from ellipsoidal monomers and spherical monomers using both particle-cluster aggregation (PCA) and cluster-cluster aggregation (CCA) regimes incorporating the rotation of particles. The morphology of the resulting aggregates is compared using the maximum radius, porosity, fractal dimension, compactness factor and friction time. The last two factors indicate how the dynamics of a population of dust may be altered depending on monomer shape. Results. The results of this study indicate that monomer shape plays an important role in determining the final morphology of aggregates. Comparing ellipsoid grains with 3:1:1 axis ratio to spheres, the greatest difference is seen in compactness factors: (∼18%) for the PCA regime, reaching a maximum of (∼80%) for the CCA regime. The influence on porosity is also appreciable, (∼8%) and (∼15%) for PCA and CCA regimes respectively. The resulting differences for the friction times depend on the collision regime employed, yet show a marked difference for the different monomer shapes, (∼12%) for PCA and (>50%) for CCA at large sizes. It is concluded that the effect of monomer shape in the hit-and-stick aggregation model may produce appreciable structural variation in the final aggregate. Present models of fluffy aggregates made up of only spherical monomers therefore may not be the best representation for grains in some astrophysical environments.

Aggregate dust connections and emissivity enhancements

Context. Observations of cold condensed clouds in the interstellar medium show an enhancement in the dust emissivity at long wavelengths. Model calculations with the discrete-dipole approximation (DDA) can explain this enhancement with the coagulation of dust particles into aggregates. Aims. We study the nature of grain-grain contacts and their effects on the aggregate optical properties. Methods. We use DDA and the T-matrix method (TMM) to calculate the absorption properties of aggregate dust grains and analyse where and why the enhancement in the emissivity occurs. Results. We find that the absorption coefficient changes with material composition and with the contact area between monomers. A larger contact area, with DDA, compared to a zero-point contact with TMM, results in an enhancement of the absorption coefficient for wavelengths where the considered material has a large value n (the real part of the refractive index). Conclusions. DDA seems to be the most realistic way of taking into account “real” inter-particle contact effects in aggregate particles.

On a mathematical model of dust coagulation in interstellar clouds

AbstractWe consider a kinetic model that takes into account the phenomena of coagulation of dust particles inside interstellar nebulae. After a detailed modeling of the system, the main aim of the paper consists in studying, for the proposed model, a Cauchy problem in an unbounded domain under rather general conditions. Copyright © 2010 John Wiley & Sons, Ltd.

On the role of dust in the cometary plasma

The cometary coma consists of neutral gas, plasma, and dust grains. The dust grains can influence both the neutral and charged coma’s constituents. Usually, the presence of dust particles in a plasma results in additional losses of both electrons and ions due to the plasma recombination on the particle surfaces. Solar radiation makes the impact of dust even more complicated depending on the solar flux, the dust number density, the photoelectric properties of the dust particles, the dust particle composition, the distribution of the sizes, etc. We propose a simple kinetic model evaluating the role of dust particles in the coma plasma chemistry and demonstrate that this role can be crucial, resulting in a nontrivial behavior of both the electron and ion densities of the plasma. We show that a coma’s dust particles can be negatively as well as positively charged depending on their composition. These opposite charges of the grains can result in fast coagulation of dust particles, thus, forming complex aggregate shapes of cometary grains.

Dust coagulation in equilibrium molecular gas

We study coagulation of dust particles immersed in equilibrium molecular gas. The dissipative grain interactions are modeled by a constant coefficient of restitution, while for the adhesive interactions the model of Johnson, Kendall and Roberts is applied. We formulate the Boltzmann-type master equation for the mass–velocity distribution function of aggregates and use the Kramers–Moyal expansion for the grain–gas collision integral. We derive coagulation equations and kinetic coefficients for these equations and analyze different regimes of the system evolution.

Energy loss of charged projectiles in a self-gravitating Lorentzian dusty plasma

The energy loss of a pair of test charge projectiles passing through a multicomponent, self-gravitating, dusty plasma with a generalized Lorentzian distribution is presented. Analytical and numerical results are obtained for the shielded potential and for the slowing down of a pair of test charge projectiles. The correlation and interference effects of two collinear and noncollinear projectiles on the shielded potential as well as on the energy loss are presented. An interference contribution of these projectiles to the potential and energy loss is observed that depends upon their orientation and separation distance. It is found that the energy loss of collinear projectiles decreases with the increase of the dust Jeans frequency for any separation distance. On the other hand, with small values of κ (the generalized Lorentzian distribution case), the test charge projectile gains energy instead of losing for projectile velocity greater than the thermal velocity of the dust, and this gain is increased as we increase the dust Jeans frequency. These results are helpful to understand the energy loss mechanism, which plays an important role in explaining the coagulation of dust particles in molecular clouds as well as in dust plasma crystal formation.

Effect of self-gravitation on the energy loss of pair of projectiles in dusty plasma

The effect of self-gravitation of massive dust grains is investigated on the shielded potential and the energy loss of pair of charged projectiles passing through a dust-contaminated plasma. Analytical general expressions are derived for the shielded potential and for the energy loss by incorporating two-body correlation effects. An interference contribution of these projectiles to the shielded potential and energy loss is observed that depends upon their orientation and separation distance. It is found that for two collinear projectiles the potential is enhanced by increasing dust Jeans frequency for separation less than Debye length and the energy loss versus projectile velocity decreases with the increase of Jeans frequency for arbitrary separation. The effect of inclination of two noncollinear projectiles on energy loss is also investigated for a fixed value of Jeans frequency ωjd=4×10−4ωpd. The contribution to the energy loss due to the interference term has been separately calculated for a typical Jeans frequency. The present investigation would be useful to explain the coagulation of dust particles in the molecular clouds and in the ion-beam-driven inertial confinement fusion approach.

Effect of grain-size distribution on the energy loss of a pair of charged projectiles in a dust-contaminated plasma

Analytical and numerical results are presented for the slowing down of a pair of heavy test charge projectiles through a multicomponent, dust-contaminated plasma. The correlation and interference effects of two collinear and noncollinear projectiles on electrostatic potential and energy loss are studied for a Maxwellian distribution and a special class of physically reasonable size distributions. The energy loss behavior versus projectile velocity of noncollinear projectiles is also examined for various orientations. It is found that the energy loss for Maxwellian distribution (for large value of spectral index κ) is larger compared to that for generalized Lorentzian distribution. It is also observed that for smaller values of κ, the test charge projectile gains energy instead of losing. These results would be useful for the understanding of the energy loss mechanism, which might be responsible for the coagulation of dust particles in molecular clouds, in the ion-beam driven inertial confinement fusion scheme and in dust plasma crystal formation, etc.

Modeling chondrule melting using a resizing box_tree code

Current theories hold that chondrule formation results from the melting of clusters of relict grains in the protoplanetary nebula. Although it is possible to simulate the coagulation of dust particles in the protoplanetary nebula, the accuracy of such a simulation is dependent on the number of particles used. A larger number of particles yields a more accurate simulation, but comes at the expense of considerably longer CPU times. On the other hand, once the number of particles used by the simulation drops below a certain threshold, the model begins to lose relevance. box_tree is a program that divides the protoplanetary disk into self-similar patches or boxes. Boundary conditions on a box are imposed using twenty-six “ghost” boxes. box_tree utilizes tree code to deal with gravitational and electrostatic forces between particles within the ring. This paper introduces a scheme whereby the box_tree model can significantly enlarge its simulation parameters allowing for more realistic data generation.