Concentration Of Dust Particles Research Articles

Optical In Situ Size and Concentration Measurement of Particles Dispersed in Gases at Temperatures up to 1000°C

Based on previous experience, an optical particle counter has been designed which allows the direct measurement of the size and concentration of dust particles in gas flows at high temperatures. The instrument features a new optical measuring volume definition together with a signal control to avoid border-zone error effects. The instrument has a free working distance of 200 mm. Hence it is possible to make true in situ measurements in pipe flows with a cross-section of ca. 60 cm2 and additionally to protect the device against heat and dust precipitation on the optical windows. The instrument was initially used to examine the separation behaviour of cake-forming rigid ceramic barrier filters at temperatures up to 1000 °C. In particular, the fractional efficiencies and the time-related concentration changes on the clean gas side caused by a pulse jet cleaning event could be determined. The results obtained so far demonstrate that ceramic barrier filters show basically the same behaviour as conventional filters, but possess a substantially higher separation efficiency at a corresponding higher pressure drop (fractional penetration values between 10−5 and 10−9 depending on the type of filter material and the cake formation).

Dust build-up on surfaces in the indoor environment

The concentration and the composition of dust in the indoor environment has been associated with reported symptoms of the sick building syndrome. Levels of airborne concentrations of dust particles are well known. However, the relation to dust on surfaces for office environments are not well described. In this study, 662 measurements were performed of surface dust concentrations on hard surfaces in 19 buildings within Harvard University based on a sticking gelatine foil method. The measure is the dust covered area of the surface as a percentage. In three offices, the build-up of dust on surfaces was measured for a period of five days. Close to these surfaces the airborne PM 2.5 and PM 10 particle mass concentrations were measured simultanously. A significant correlation between the dust build-up and the difference between the PM 10 and the PM 2.5 was established. The particle size distribution was measured by means of an Aerodynamic Particle Sizer. The mean dust build-up normalized with the measured PM 10 was approximately four times higher than the equivalent calculated by a deposition model. This may in part be due to the effect of preferred orientation when particles settle to a surface. Different data for dust on surfaces and airborne particles in offices were compared. The levels of airborne particles in offices in Europe seem to be higher than the levels in the US.

Unsteady natural convection of a dusty fluid in an infinite rectangular channel

Natural convection of a dusty fluid in an infinite rectangular channel with differentially heated vertical walls and adiabatic horizontal walls has been studied. The problem has been solved using a combination scheme of central and second upwind differencing. It is seen that the heat transfer rate decreases with an increase of mass concentration of dust particles, but it increases with an increase of the Rayleigh number.

Solar radiation characteristics at Qena / Egypt

Measurements of the hourly global solar radiation (G) and its diffuse component (D) on a horizontal surface have been carried out in Qena / Upper Egypt in the period from June 1992 to May 1993. The corresponding diffuse fraction (DIG) is calculated. Diurnal variations of the results have been studied. Also the daily totals values and its monthly and seasonal averages as well as their frequency distributions were computed and examined. The seasonal and climatic effects on the fluctuation of the results are discussed. These effects were particularly large during spring and Winter months owing to the high fluctuation of the atmospheric conditions with aspect to amount of clouds, water content, and concentration of aerosol dust particles. The influence of clouds is also considered. It shows small effect on the results (4.5%), reflecting the low degree of cloudiness in the study region. The relation between the diffuse fraction and clearness index (G/Go) shows that most of the points lies in the region of the high availability of the incoming solar radiation. In general the study shows clearly the abundance of solar energy in Qena / Egypt, and the suitability of its climate for using it in different applications.

Ordered structures in a nonideal dusty glow-discharge plasma

The formation of ordered structures of charged macroparticles in a constant-current neon glow-discharge plasma is investigated. Experiments were performed with two types of particles: thin-walled glass spheres 50–63 μm in diameter and particles of Al2O3, 3–5 μm in diameter. Formation of quasicrystalline structures is observed in the standing strata and in an artificially created double electric layer. The formation of extended filamentary structures of macroparticles in the absence of visible stratification of the positive column has been observed for the first time. The influence of the discharge parameters on the formation of the ordered structures and their melting is examined. The form of the interaction potential between the charged macroparticles is considered, as well as changes in the conditions for maintaining the discharge in the presence of high concentrations of dust particles.

Ventilation and air quality in an office building

The aim of this study is to assess the performance of the mechanical ventilation system and air quality in an office building. The perfluorocarbon tracer (PFT) technique was used to measure air flow in an air handling unit and to estimate flow rates supplied to the office. In order to validate the PFT technique as a viable means of measuring air flow in the mechanical ventilation system, the PFT measurements were compared with measurements made using a pitot-static tube. Air exchange range, ventilation effectiveness and age of air were examined. The concentrations of carbon dioxide (CO2), carbon monoxide (CO), formaldehyde (HCHO) and dust particles were monitored. In addition, a questionnaire was completed by the staff in order to provide a subjective assessment of indoor air quality.

Experimental investigation of altitude dependence of size distribution and concentration of dust particles within the city of Budapest

Experimental investigation of altitude dependence of size distribution and concentration of dust particles within the city of Budapest

Electrical characterization and modeling of a dust forming plasma in a radio frequency discharge

In this article we focus on the time evolution of macroscopic and microscopic properties of a dust forming plasma in a silane–argon low pressure radio frequency (rf) discharge. The time evolution of electron density, ion density, dust particle concentration, and the current density were recorded in a low pressure (0.1 Torr) rf Ar–SiH4 discharge. From these data and optical emission spectroscopy simultaneous measurements, the time evolution of the electron mean energy and the particle mean charge are determined. Together with previous experimental data concerning the nucleation and growth of dust particles, a complete experimental set of microscopic and macroscopic data is available and it is compared to a theoretical model including both particle growth and dusty discharge parameters. A clear representation of this closely coupled time evolution of the particles’ formation and plasma properties is given. It includes the nucleation and coagulation phenomena for particles, and the strong increase of the rf electric field in the plasma volume and the increase of the excitation rates of electrons.

Modelling of a new crossflow moving-bed heat-exchanger/filter (MHEF)

A new crossflow moving-bed heat-exchanger/filter (MHEF) is presented, which is theoretically shown to have very good collection capabilities. This device allows for gas filtration and heat exchange at the same time. The MHEF is constructed on the basis of computer modelling, which from first principles has made it possible to calculate the dust deposit, particle concentration and pressure drop.

Dust accumulation in the canopy: A potential cause of dental microwear in primates

Dental microwear researchers consider exogenous grit or dust to be an important cause of microscopic wear on primate teeth. No study to date has examined the accumulation of such abrasives on foods eaten by primates in the forest. This investigation introduces a method to collect dust at various heights in the canopy. Results from dust collection studies conducted at the primate research stations at Ketambe in Indonesia, and Hacienda La Pacifica in Costa Rica indicate that 1) grit collects throughout the canopy in both open country and tropical rain forest environments; and 2) the sizes and concentrations of dust particles accumulated over a fixed period of time differ depending on site location and season of investigation. These results may hold important implications for the interpretation of microwear on primate teeth.

Self consistent low pressure RF (radiant flux) discharge modelling: Comparisons with experiments in clean and dusty plasmas

Abstract

Ventilation and air quality in a library building

Measurements of air flow were carried out in a library building. The constant-injection and pulse-injection tracer-gas techniques were used to measure air flow in air handling units and to estimate flow rates supplied to each floor. Tracer-gas measurements were compared with measurements made using a Pitot-static tube. Air exchange rate, ventilation efficiency and age of air were examined. The concentrations of carbon dioxide (CO2), carbon monoxide (CO), formaldehyde (HCHO) and dust particles were monitored. In addition, a questionnaire was completed by library staff and users in order to provide a subjective assessment of indoor air quality.

The impact of the gulf war on the Arabian environment—I. Particulate pollution and reduction of solar irradiance

This paper investigates some of the air pollution problems which have been created as a result of the Gulf war in early 1991. Temporary periods of increased dust storm activity have been observed in Saudi Arabia. This is presumably due to disturbance of the desert surface by the extremely large number of tanks and other war machines before and during the war. The concentrations of inhalable dust particles (<15 μm) increased during the months just after the war by a factor of about 1.5 of their values during the same months of the previous year, 1990. The total horizontal solar energy flux in Riyadh has been significantly reduced during dry days with no clouds. This is attributed to the presence of soot particles, which have been generated at an extremely high rate from the fired oil fields in Kuwait. The direct normal solar insolation were also measured at the photovoltaic solar power plant in Riyadh during these days and significant reductions were observed due to the effective absorption of solar radiation by soot particles. The generated power from the plant has been reduced during days with a polluted atmosphere by about 50–80% of the expected value for such days, if the atmosphere were dry and clear.

Characteristics of a dusty nonthermal plasma from a particle-in-cell Monte Carlo simulation.

Nonthermal dusty plasmas can be found in plasma-processing applications as well as in space phsyics. A model based on a particle-in-cell Monte Carlo simulation has been developed to study the physical properties of such plasmas and the plasma-dust particle interactions. Assuming a uniform dusty plasma with a given size and concentration of dust particles, the model provides self-consistently the average electric field necessary to sustain the plasma for a given current density flowing through it, the charge and floating potential of the dust particles, the potential distribution, and the velocity distribution functions of electrons and positive ions. The model has been applied to situations where the distance between dust particles is much smaller than the electron Debye length (particulates interact electrostatically with each other) as well as situations where the distance between dust particles is larger than the Debye length (particulates are isolated electrostatically from each other). Questions concerning the momentum and energy transfer from electrons and ions to dust particles are also discussed. Simple scaling laws are also derived and compared with the numerical results.

Numerical analysis of dust particles motion inside gas bubbles for flue gas desulfurization in a jet bubbling reactor

The motion of dust particles in a rising air bubble is governed by the inertial force due to the internal flow inside the bubble and the diffusion process due to the nonuniform distribution of the dust particles concentration. The circulating flow inside a bubble has a considerable effect on both phenomena. The dust removal efficiency under the influence of the circulating flow is analyzed numerically. Comparison of the calculated results with the experimental data in a pilot plant with respect to the removal efficiency shows that the phenomena are well described by this analysis, and that inertial motion and diffusion play important roles in determining the motion of particles inside a bubble in a jet bubbling reactor.

Endotoxin, ammonia, and total and respirable dust in swine confinement buildings: the effect of recirculated air and respiratory protective masks (1992)

Caretakers and pigs in dusty environments with particles and toxic gases may sustain health consequences. We studied concentrations of ammonia, endotoxin, and total and respirable dust particles in four mechanically ventilated swine nurseries and two grower facilities using an ammonia sampler, filter, and British cyclone. In two of the nursery facilities, we determined the protection offered by respiratory masks that were mounted on glass funnels with filters or British cyclones and sampled for dust. In response to the increasing summer ventilation, large, nonrespirable particle concentrations in swine building atmospheres were reduced more completely by ventilation air movement than smaller respirable particles or ammonia. Total airborne endotoxin concentrations were similar to those eliciting pulmonary reactions. Total airborne endotoxin correlated with total suspended particles rather than respirable particles. Smaller respirable fecal particles enriched in endotoxin apparently stick to larger nonrespirable particles or are agglomerated before they became airborne. Internal recirculated air partially limited the mass concentration of respirable particles in the breathing zone of swine caretakers at lower but not higher ventilation rates. Respiratory protection limited the potential total dust exposures of swine caretakers in such atmospheres (<25 %, 2-tie masks; <50%, I-tie masks of the total suspended particles). Respirable particles were reduced to <55% by 2-tie masks. Properly worn 2-tie masks protect against both large and small respirable particles in swine confinement facilities.; Swine Day, Manhattan, KS, November 19, 1992

Hypotheses to explain the higher symptom rates observed around hazardous waste sites.

Five studies were carried out around hazardous waste sites in California in which the main route of exposure was to low-level parts per billion concentrations of either gaseous emissions or airborne dust particles. Although there was no evidence suggesting excesses in cancer or birth defects, the total number and the prevalence of many of subjective symptoms were higher in areas near the site than in control neighborhoods. We discuss a number of causal processes that could explain these results. We conclude that a classical toxicological response and mass psychogenic illness are not valid explanations. Recall bias may explain part of the pattern. We present data from situations where stress alone from environmental anxiety has produced a similar magnitude of excess symptoms in populations. The fact that excess symptoms in waste site neighbors is found primarily in those who complain of odors or who are worried about environmental chemicals suggests the possibility that autonomic, stress-mediated mechanisms or behavioral sensitization are active in the genesis of these symptoms. A variety of confounders were controlled for. The hypothesis that chemically "acquired immune deficiency" can cause subtle symptomatology as a prodrome to subsequent serious disease has been raised in testimony at several toxic tort trials about waste sites. Although this hypothesis seems unlikely, particularly at sites such as the ones we studied with low airborne exposures, if true it would have profound regulatory implications.

Linear flow induced in fluid particle suspension by an infinite differentially rotating disk

The steady, axisymmetric laminar flow of a homogeneous incompressible fluid with suspended particles occupying the half-infinite space over a differentially rotating rigid plane boundary is analyzed in this paper. The effect of suspended particles is described by two parametersf and τ. The mass concentration parameterf is a measure of the concentration of suspended dust particles. The interaction parameter τ is a measure of the rate at which the velocity of dust particles adjusts to changes in the fluid velocity and depends upon the size of the individual particles. Due to Ekman suction, the particle density remains no longer a constant in the boundary layer but varies with the axial coordinate ξ. Flow characteristics and density variations are studied as functions off, τ and ξ. Possible limiting cases for τ≪1 and τ≫1 which correspond to the case of fine dust and coarse dust respectively are derived and discussed.

Note on axis-symmetric jet mixing of compressible dusty fluid

Laminar jet mixing of a compressible dusty fluid issuing from a circular opening has been considered. Assuming that the jet mixing is under full expansion, the governing equations have been linearised and solved by successively using Hankel and Laplace transform techniques. Numerical computations of the integrals giving velocity, temperature and density of both the fluid and particle phase have been made to discuss results. The increase in the concentration of dust particles results in width of the jet is greater for compressible flow. The compressible dusty jet does not cool as fast as a compressible jet of clear fluid. The particle concentration decreases along the axial direction but increases towards the free jet boundary.

In Vitro cytotoxic effects of cobalt-containing dusts on mouse peritoneal and rat alveolar macrophages

"Hard metal disease" is a chronic lung disease characterized by the presence of interstitial fibrosis; the role of cobalt in the development of this entity is still debated. Indeed, most cases have been observed in some workplaces (grinding) of the hard metal industry and in the diamond polishing industry whereas no similar cases have been reported from workers exposed to pure cobalt powders in cobalt refineries. This study was designed to assess the in vitro toxicity (LDH release, morphology) of different cobalt-containing dusts toward murine peritoneal and alveolar macrophages. The results clearly demonstrate that, both in terms of dust particle and cobalt concentrations, the reactivity of the tungsten carbide-cobalt mixture is quite different from that of cobalt metal powder. The ground tungsten carbide-cobalt mixture prepared by the hard metal industry is almost as toxic as crystalline silica whereas, when tested separately, tungsten carbide has no effect and pure cobalt metal powder slightly impairs cell viability. The uptake of cobalt by macrophages in the presence of tungsten carbide was found to be increased. These observations may have some practical implications in industrial hygiene; they suggest that the acceptable exposure level to cobalt metal should be different when handled alone or in association with other powders such as tungsten carbide.