Dust Velocity Research Articles

Physical Properties and Concentration of Grain Dust Generated from Post-Harvest Processing of Rough Rice

<abstract><title><italic>Abstract.</italic></title> This research focuses on estimation of the particle size, concentration level, and terminal velocity of grain dust produced during post-harvest processing of rough rice in order to provide critical information for efficient dust collector design. Dust concentration levels were relatively low at indoor processing units, with pre-cleaners, brown rice processes, and milled rice processes indicating 1.3 to 7.7 mg m^-3. Outdoor processing units, such as receiving, drying, and storage, indicated higher dust concentration levels (5.1 to 9.1 mg m^-3). A model of the terminal velocity of grain dust was introduced by two linear regression equations: one for particles smaller than 200 μm, and the other for particles between 200 and 2,000 μm. Coefficients of determination were 0.9266 and 0.9770, respectively, indicating the significance of the model. The particles smaller than 200 μm showed relatively lower terminal velocity (0.15 to 0.26 m s^-1), while the larger particles (200 to 2,000 μm) showed relatively higher terminal velocity (0.9 to 2.2 m s^-1).

Damping and instability of solitons in weakly inhomogeneous dust plasma crystals

By using reductive perturbation method, we derive a Korteweg-de Vries-type equation and a modified Nonlinear Schrodinger equation for dust lattice wave in a weakly inhomogeneous dust plasma crystal. It seems that amplitude and velocity of dust lattice solitary wave decay exponentially. The modulational instability of this dust lattice envelope wave is investigated. It is found that the wave is modulational stable under certain conditions and unstable otherwise.

Modeling of dust air flames

This study analyzes a premixed dust–air flame, under conditions where a homogeneous gas-phase reaction front can exist. Discussion on four possible flame types is provided. A solution is obtained for the burning velocity of a flammable dust–air flame in both fuel and oxygen limiting cases. A sensitivity analysis is used to analyze the features controlling the dust burning. It is shown that vaporization is significant for fuel limiting conditions; however, does not play a major role in oxygen limiting cases. The calculated burning velocity shows good agreement with available experimental data for coal–dust–air flames.

Laboratory testing and data analysis of the Electrostatic Lunar Dust Analyzer (ELDA) instrument

We report the advance development of the Electrostatic Lunar Dust Analyzer (ELDA) instrument for the detection of individual low-velocity micron-size dust particles mobilized near the lunar surface, and the measurement of the dust charge, velocity vector, and mass. The first article (N. Duncan et al., Planet. Space Sci., 2011) described the measurement principle, optimized instrument geometry, and the initial testing performed on air. The full laboratory prototype of ELDA has now been completed and tested under vacuum. The numerical data analysis is improved to include gravitation and the calculation of the particle's mass. The ELDA operation principle is based on sensing a charged dust particle by an array of wire electrodes as it is passing though the instrument. Each wire electrode is connected to a charge sensitive amplifier and the velocity vector is reconstructed from the signal shapes and amplitudes. Within the instrument, a strong electrostatic field is used to deflect the trajectories of the particles. The dust mass is determined from the change in velocity measured before and after deflection. The instrument is tested using particles with 54μm mean radius and a narrow size distribution. The experimental results and the error analyses show that ELDA can measure the mass of individual particle with a factor of two even for very low signal to noise ratio.

Statistical analysis of temporal and spatial evolution of in-vessel dust particles in KSTAR

Images of wide-angle visible standard CCD cameras contain information on in-vessel dusts such as dust creation events (DCEs) that occur during plasma operations, and their velocity. Analyzing the straight line-like dust traces in the shallow cylindrical shell-structured scrape-off layer along the vacuum vessel, a database on the short/long term temporal evolutions, spatial locations of DCEs caused by plasma–dust interaction, and the dust velocity distribution are built. We have studied DCEs of 2010 and 2011 KSTAR campaign.

Statistical analysis of temporal and spatial evolution of in-vessel dust particles in fusion devices by using CCD images

Images of wide-angle visible standard CCD cameras contain information on Dust Creation Events (DCEs) that occur during plasma operations. Database on the DCEs can be built by analyzing the straight line-like dust trajectories in scrape-off layer caused by plasma–dust interaction along the vacuum vessel. The database provides short/long term temporal evolution and spatial distribution of origins of DCEs in fusion devices. We have studied DCEs of 2011 KSTAR campaign and compared with that of 2006 Tore Supra (TS) and 2007 ASDEX Upgrade (AUG) campaign. An analysis software, with which the location of dust trajectories in 3D position in the KSTAR vacuum vessel is identified, is developed and the dust velocity distribution in 2011 campaign is measured. ©2001 Elsevier Science. All rights reserved.

Influence of coal dust on premixed turbulent methane–air flames

This study discusses the design of a new experimental platform, the Hybrid Flame Analyzer (HFA) to measure burning velocity of gas, dust, and hybrid (gas and dust) premixed flames. The HFA is used to analyze a particle–gas–air system of coal dust particles (75–90μm and 106–120μm) in a premixed CH4–air (ϕg=0.8, 1.0 and 1.2) flame. Experimental results show that particles usually increase the turbulent burning velocity. Smaller particle sizes and larger concentrations (>50g/m3) increase turbulent burning velocity compared with larger particle sizes and lower concentration ranges. The experimental data is used to develop a correlation similar to turbulent gas flames to help modeling of the complex behavior.

ON THE SECULAR BEHAVIOR OF DUST PARTICLES IN AN ECCENTRIC PROTOPLANETARY DISK WITH AN EMBEDDED MASSIVE GAS GIANT PLANET

We investigate the dust velocity and spatial distribution in an eccentric protoplanetary disk under the secular gravitational perturbation of an embedded planet of about 5 Jupiter masses. We first employ the FARGO code to obtain the two-dimensional density and velocity profiles of the eccentric gas disk exterior to the gap opened up by the embedded planet in the quasi-steady state. We then apply the secular perturbation theory and incorporate the gas drag to estimate the dust velocity and density on the secular timescale. The dust-to-gas ratio of the unperturbed disk is simply assumed to be 0.01. In our fiducial disk model with the planet at 5 AU, we find that 0.01 cm- to 1 m-sized dust particles are well coupled to the gas. Consequently, the particles behave similarly to the gas and exhibit asymmetric dynamics as a result of eccentric orbits. The dust surface density is enhanced around the apocenter of the disk. However, for the case of a low-density gaseous disk (termed "transition disk" henceforth in this work) harboring the planet at 100 AU, the azimuthal distributions of dust of various sizes can deviate significantly. Overall, the asymmetric structure exhibits a phase correlation between the gas velocity fields and dust density distribution. Therefore, our study potentially provides a reality check as to whether an asymmetric disk gap detected at sub-millimeter and centimeter wavelengths is a signpost of a massive gas giant planet.

The Azimuthal Distribution of Dust Particles in an Eccentric Protoplanetary Disk with an Embedded Gas Giant Planet

AbstractWe investigate the dust velocity and spatial distribution in an eccentric protoplanetary disk under the secular gravitational perturbation of an embedded planet of about 5 Jupiter masses. We first employ the FARGO code to obtain the two-dimensional density and velocity profiles of the gas disk with the embedded planet in the quasi-steady state. We then apply the secular perturbation theory and incorporate the gas drag to estimate the dust velocity on the secular timescale. The dust-to-gas ratio of the unperturbed disk is simply assumed to be 0.01. In our fiducial disk model with the planet at 5 AU, we find that for 0.01 cm– to 1 m–sized dust particles well coupled to the gas, the dust behaves similarly to the gas and exhibits non-axisymmetric dynamics as a result of eccentric orbits. However, for the case of a low-density gaseous disk (termed “transition disk” henceforth in this article) harboring the planet at 100 AU, the azimuthal distributions of dust of various sizes can deviate significantly.

Investigation of dust and water ice in comet 9P/Tempel 1 fromSpitzerobservations of the Deep Impact event

Context. The Spitzer spacecraft monitored the Deep Impact event on 2005 July 4 providing unique infrared spectrophotometric data that enabled exploration of comet 9P/Tempel 1’s activity and coma properties prior to and after the collision of the impactor. Aims. The time series of spectra take with the Spitzer Infrared Spectrograph (IRS) show fluorescence emission of the H2O ν2 band at 6.4 μm superimposed on the dust thermal continuum. These data provide constraints on the properties of the dust ejecta cloud (dust size distribution, velocity, and mass), as well as on the water component (origin and mass). Our goal is to determine the dust-to-ice ratio of the material ejected from the impact site. Methods. The temporal evolution of the continuum was analyzed using a dust thermal model which considers amorphous carbon and intimate silicate-carbon mixtures. The water emission was extracted from the spectra and the water columns within the Spitzer extraction aperture were inferred using a fluorescence excitation model. Time-dependent models simulating the development of the ejecta cloud and the sublimation of icy grains were developed to interpret the temporal evolution of both dust and water emissions within the field of view. Results. Both the color temperature of the grains in the ejecta cloud (375 ± 5 K) and their size distribution show that a large quantity of submicron grains were ejected by the impact. The velocity of the smallest grains is 230 m s −1 , with a power index for the size dependence of 0.3−0.5, in agreement with gas loading. The total mass of dust is (0.7−1.2) × 10 5 kg for grain sizes 0.1−1 μ ma nd (0.5−2.1) × 10 6 kg for sizes 0.1−100 μm. A sustained production of water is observed, which can be explained by the sublimation of pure ice grains with sizes less than 1 μm and comprising a mass of ice of (0.8−1.8) × 10 7 kg. The contribution of dirty ice grains to the ice budget is negligible. Assuming that water was essentially produced by icy grains present in the ejecta cloud, our measurements suggest a very high ice-to-dust ratio of about 10 in the excavated material, which greatly exceeds the gas-to-dust production rate ratio of ∼0.5 measured for the background coma. Alternately, if a large amount of material felt back to the surface and sublimated, ice-to-dust ratios of 1−3 are not excluded. A better understanding of the cratering event on 9P/Tempel 1 is required to disentangle between the two hypotheses. Evidence for grain fragmentation in the ejecta cloud is found in the data. The pre-impact water production rate is measured to be (4.7 ± 0.7) × 10 27 mol s −1 .

Study of interaction of entrained coal dust particles in lean methane–air premixed flames

This study investigates the interaction of micron-sized coal particles entrained into lean methane–air premixed flames. In a typical axisymmetric burner, coal particles are made to naturally entrain into a stream of the premixed reactants using an orifice plate and a conical feeder setup. Pittsburgh seam coal dust, with particle sizes in the ranges of 0–25μm, 53–63μm, and 75–90μm, is used. The effects of different coal dust concentrations (10–300g/m3) entrained into the mixture of methane–air at three lean equivalence ratios, ϕ, of 0.75, 0.80 and 0.85, on the laminar burning velocity are studied experimentally. The laminar burning velocity of the coal dust–methane–air mixture is determined by taking high quality shadowgraph images of the resulting flames and processing them using the cone-angle method. The results show that the laminar burning velocity reduces with the addition of coal dust having particle sizes in the ranges of 53–63μm and 75–90μm, irrespective of the equivalence ratio values. However, burning velocity promotion is observed for one case with particle size in the range of 0–25μm at an equivalence ratio of 0.75. Two competing effects are considered to explain these trends. The first effect is due to volatile release, which increases the overall equivalence ratio and thus, the flame temperature and burning velocity. The second is the heat sink effect that the coal particles take up to release the volatiles. This process reduces the flame temperature and accordingly the burning velocity also. A mathematical model is developed considering these effects and it is seen to successfully predict the change of laminar burning velocity for various cases with different dust concentrations and equivalence ratios of the gas mixture. Furthermore, the implication of this study to coal mine safety is discussed.

Diagnostics of mobile dust in scrape-off layer plasmas

Dust production and accumulation pose serious safety and operational implications for the next generation fusion devices. Mobile dust particles can result in core plasma contamination with impurities, and those with high velocities can significantly contribute to the wall erosion. Diagnostics for monitoring dust in tokamaks during plasma discharges are hence important as they can provide information on dust velocity and size, and—in some cases—on dust composition. Such measurements are also valuable as an input for theoretical models of dust dynamics in scrape-off layer plasmas. Existing in situ dust diagnostics, focusing on the range of dust parameters they can detect, are reviewed. Particular attention is paid to the diagnostics which allow us to detect tails of the dust velocity and size distributions, e.g. small and very fast particles. Some of the techniques discussed have been adopted from space-related research and have been shown to be feasible and useful for tokamak applications as well.

Spectropolarimetry of the Superwind Filaments of the Starburst Galaxy M 82: Kinematics of Dust Outflow

Spectropolarimetry results for the starburst galaxy M 82 are presented. The optical emission lines of the filaments in the energetic outflow (``superwind'') from the nuclear starburst region of M 82 are substantially polarized. The H$\alpha$ polarization degrees and angles measured by our study are consistent with previous narrowband imaging polarimetry data. The polarized emission lines are redshifted with respect to the emission lines in the total light and systemic motion of the galaxy. The emission line intensity ratios [N II]$/$H$\alpha$ and [S II]$/$H$\alpha$ in the polarized light are similar to those of the nuclear star-forming region. In addition, the electron density $N_{\rm e}$ derived from the [S II]$\lambda$6731$/\lambda$6717 line ratio of the polarized light is $\sim\ $600–1000 cm$^{-3}$ at a distance of more than 1 kpc from the nucleus, whereas the $N_{\rm e}$ derived from the total light are less than 300 cm$^{-3}$. These facts strongly suggest that the emission from the nuclear starburst of M 82 is scattered by dust grains entrained and transported outward by the superwind. A simple hollow biconical outflow model shows that the velocity of the outflowing dust grains, $v_{\rm d}$, ranges from 100 to 200 km s$^{-1}$ near the nucleus, decreases monotonically with the distance from the nucleus, and reaches $\sim\ $10 km s$^{-1}$ at around 1 kpc. The motion of the dust is substantially slower than that of both ionized gas ($v_{{\rm H}\alpha}$$\sim\ $ 600 km s$^{-1}$) and molecular gas ($v_{\rm CO}$$\sim\ $ 200 km s$^{-1}$) at the same distance from the nucleus of M 82. This indicates that dust grains in the superwind are kinematically decoupled from both gas components at large radii. Since the dust velocity $v_{\rm d}$ is much less than the escape velocity of M 82 ($v_{\rm esc}$$\approx$ 170 km s$^{-1}$ at 1.5 kpc from the nucleus), most of the dust entrained by the superwind cannot escape to intergalactic space, and may fall back into the galaxy disk if there is no additional acceleration mechanism (such as radiation pressure).

Structure of the magnetized sheath of a dusty plasma

A three-component fluid model for a dusty plasma-sheath in an oblique magnetic field is presented. The study is carried out for the conditions when the thermophoretic force associated with the electron temperature gradient is one of the most important forces affecting dust grains in the sheath. It is shown that the sheath properties (the sheath size, the electron, ion and dust particle densities and velocities, the electric field potential, and the forces affecting the dust particles) are functions of the neutral gas pressure and ion temperature, the dust size, the dust material density, and the electron temperature gradient. Effects of plasma-dust collisions on the sheath structure are studied. It is shown that an increase in the forces pushing dust particles to the wall is accompanied by a decrease in the sheath width. The results of this work are particularly relevant to low-temperature plasma-enabled technologies, where effective control of nano- and microsized particles near solid or liquid surfaces is required.

Fluid simulation of an electrostatic plasma sheath with two species of positive ions and charged nanoparticles

One-dimensional fluid simulations are used to study the dynamics of an electrostatic plasma sheath containing nanosized dust grains and two species of positive ions, i.e., He+ and Ar+. The impacts of the concentration of each species, the velocity at the sheath edge of the ions, and the bias voltage of the substrate, on the spatial distribution of the velocity and number density of the plasma particles, and the incident fluxes of the ions on the substrate, are investigated. The numerical results show that the sheath thickness increases with increasing σ, the density ratio of He+ ions to Ar+ ions at the sheath edge. For nanosized dust particles considered in this work, the dominant forces are the ion drag and the electric force and the effects of the neutral drag and gravity are negligible. Due to enhancement of the ion drag force and the electric force, the dust velocity increases and, consequently, the dust number density decreases as the concentration at the sheath edge of Ar+ ions is increased. For the same velocity and number density at the sheath edge, the number density of Ar+ ions near the wall is larger than that of He+ ions, but their incident fluxes are the same. The maximum in the dust number density increases with the velocity of Ar+ ions at the sheath edge, but it weakly changes with the Mach number of He+ ions, except for large values of σ. The position of the maximum dust number density initially decreases very quickly with increasing the velocity at the sheath edge of the ions from small values, but then at larger values it changes quite slowly. The differences in the sheath parameters for different values of σ disappear at some values of the velocity at the sheath edge of the ions and dust particles. The incident flux of the ions are independent of the bias voltage of the substrate, but their kinetic energy is equal to the bias potential.

Integral field spectroscopy of H2 and CO emission in IRAS 18276−1431: evidence for ongoing post-AGB mass-loss

We present K-band integral field spectroscopy of the bipolar post-AGB object IRAS 18276-1431 (OH 17.7-2.0) using SINFONI on the VLT. This allows us to image both the continuum and molecular features in this object from 1.95-2.45{\mu}m with a spatial resolution down to 70 mas and a spectral resolution of approx. 5000. We detect a range of H2 ro-vibrational emission lines which are consistent with shock excitation in regions of dense (approx. 10^7 cm^-3) gas with shock velocities in the range 25 - 30 km/s. The distribution of H2 emission in the bipolar lobes suggests that a fast wind is impinging on material in the cavity walls and tips. H2 emission is also seen along a line of sight close to the obscured star as well as in the equatorial region to either side of the stellar position which has the appearance of a ring with radius 0.3 arcsec. This latter feature may be radially cospatial with the boundary between the AGB and post-AGB winds. The first overtone 12^CO bandheads are observed longward of 2.29 {\mu}m with the v = 2-0 bandhead prominently in emission. The CO emission has the same spatial distribution as the K-band continuum and therefore originates from an unresolved central source close to the star. We interpret this as evidence for ongoing mass loss in this object. This conclusion is further supported by a rising K-band continuum indicating the presence of warm dust close to the star, possibly down to the condensation radius. The red-shifted scattered peak of the CO bandhead is used to estimate a dust velocity along the bipolar axis of 95 km/s for the collimated wind. This places a lower limit of approx. 125 yr on the age of the bipolar cavities, meaning that the collimated fast wind turned on very soon after the cessation of AGB mass loss.

Comet 67P/Churyumov-Gerasimenko: the GIADA dust environment model of the Rosetta mission target

Context. The ESA Rosetta spacecraft will reach the short-period comet 67P/Churyumov-Gerasimenko in 2014. Orbiting strategy, orbiter safety conditions, landing scenarios and expected results from dust collectors depend on models of the 67P dust environment. Many papers already tackled this matter, analysing a limited set of observations, and therefore often reaching conflicting conclusions. Aims. We consider a set of observations representative of all ground-based and IR (thermal infrared) Spitzer data collected over the last three perihelion passages, to determine the 67P dust environment after the end of the gas drag on dust (at about 20 nucleus radii) consistent with available 67P gas and dust coma photometry, images of the dust coma, tail and trail, at optical and IR wavelengths. Methods. In order to obtain the best fit to 67P data, we consider three independent tail and trail simulation codes (developed by three independent groups), which parametrise cometary dust by the quantity β, the ratio between solar radiation pressure and gravity forces. GIADA, the dust monitor instrument of the Rosetta orbiter, will provide an experimental determination of the β-dust mass relation. Results. A 67P environment model based on a perihelion-symmetric dust velocity and on a perihelion-asymmetric dust size distribution, is consistent with all available data. During most Rosetta operations, the dust cross-section is dominated by mm to cm-sized grains, while the ejected dust mass is dominated by grains larger than a few mm, with a dust-to-gas ratio of 3 around perihelion. Conclusions. 67P onsets its activity at Sun-distances rh ≥ 3.4 AU; the dust geometric albedo is 0.04 ± 0.02; at 3.0 AU, 10 g grains escape the nucleus gravity field (10 kg grains at perihelion) with a dust mass-loss rate of 10−40 kg s −1 (500 kg s −1 at perihelion); 67P’s activity depends on seasons, with the northern heminucleus (rich in large grains and CN depleted) active before perihelion.

A self-triggered dust trajectory sensor

A self-triggered dust trajectory sensor not only determines the trajectories of charged dust particles but also acts as a highly sensitive dust detector. The objective of a dust trajectory sensor (DTS) is to measure charges Q≥100aC and trajectories of submicron-sized grains with accuracies of ∼1° in direction and ∼1% in speed in the range v=1–100km/s. It determines the trajectories from the signals induced in an array of wire electrodes. Most signals are weak and distorted by amplifier noise. Transient recorders continuously store them until a trigger signal indicates the presence of a dust particle. A trigger signal was previously available only after the particle had passed through the DTS and was detected externally by impact ionization. In certain important applications, however, an external trigger is not available or too late. In this paper we discuss a method of generating a trigger from noisy DTS signals before the dust grain exits the sensor. Specifically, we use seven parallel, double-triangle-shaped velocity filters on each sensor electrode to cover the velocity range v=1–128km/s. Each velocity filter feeds into four parallel amplitude filters, two for single large signals and two for pairs of smaller but coincident signals from adjacent wires. We demonstrate by computer simulation that the probability of generating at least one trigger is high, typically pt≥0.99 at v=20km/s, charge-to-noise ratio QNR≥6.25, and angle of incidence from 0° to 27°. The minimum QNR required to derive a trigger varies with dust velocity as ∼v1/2. The false event rate, caused by amplifier noise, is estimated to be on the order of one per year.

Dynamical Simulations of the Planetary System HD 69830

The planetary system of HD 69830 is uniquely constrained by observations of (i) an infrared excess indicative of a debris disk with warm dust and (ii) radial velocity variations indicative of three planets. This presents a valuable opportunity to test planet formation models by integrating dynamical models of planetary formation and migration with those for the sculpting of a dust-producing planetesimal disk. We perform n -body simulations and investigate the excitation of both planet and planetesimal eccentricities, the accretion of planetesimals onto the planets, and the clearing of a planetesimal disk by the planets as they grow in mass and migrate through the disk. In simulations tuned to closely follow previous semi-analytic models for the growth and migration of the planets, we find that the inner planet accretes significantly more planetesimals than previously estimated. We find that eccentricity excitation due to mutual planetary perturbations during and after the migration do not naturally produce the observed eccentricities. Our simulations suggest that this discrepancy may be reduced or possibly reconciled if the planets are significantly more massive than expected (possible if the planetary system's angular momentum were nearly parallel to our line of sight). Even if the planets are significantly more massive than previously assumed, we find that the migrating planets are inefficient at clearing the outer planetesimal disk and that a significant fraction of the planetesimal population beyond 1 AU remains bound on moderately eccentric and inclined orbits. While much of the remaining planetesimal belt would have eroded via a collisional cascade and radiation pressure, we explore whether some of the highly excited planetesimals may be able to persist over the age of the central star, producing the dust observed in the HD 69830 system.

The return of activity in main-belt comet 133P/Elst-Pizarro

Comet 133P/Elst-Pizarro is the first-known and currently best-characterised member of the main-belt comets, a recently-identified class of objects that exhibit cometary activity but which are dynamically indistinguishable from main-belt asteroids. We report here on the results of a multi-year monitoring campaign from 2003 to 2008, and present observations of the return of activity in 2007. We find a pattern of activity consistent with the seasonal activity modulation hypothesis proposed by Hsieh et al. (2004, AJ, 127, 2997). Additionally, recomputation of phase function parameters using data in which 133P was inactive yields new IAU parameters of H_R=15.49+/-0.05 mag and G_R=0.04+/-0.05, and linear parameters of m_R(1,1,0)=15.80+/-0.05 mag and Beta=0.041+/-0.005 mag/deg. Comparison between predicted magnitudes using these new parameters and the comet's actual brightnesses during its 2002 and 2007 active periods reveals the presence of unresolved coma during both episodes, on the order of ~0.20 of the nucleus cross-section in 2002 and ~0.25 in 2007. Multifilter observations during 133P's 2007 active outburst yield mean nucleus colours of B-V=0.65+/-0.03 mag, V-R=0.36+/-0.01 mag, and R-I=0.32+/-0.01 mag, with no indication of significant rotational variation, and similar colours for the trail. Finally, while 133P's trail appears shorter and weaker in 2007 than in 2002, other measures of activity strength such as dust velocity and coma contamination of nucleus photometry are found to remain approximately constant. We attribute changes in trail strength to the timing of observations and projection effects, thus finding no evidence of any substantial decrease in activity strength between 2002 and 2007.