Particle Deposition

The aim of this study was to investigate the deposition of particles in three types of synthetic fabric filter by scanning electron microscope (SEM) and to determine the experimental adhesive force of filter cakes in fabric filters. The fabrics used were acrylic, polypropylene and polyester. The particulate matter was phosphate rock. The particles were deposited in the filters during 10 filtration cycles, with a superficial filtration velocity of 0.10 m/s and maximum pressure drop of 980 Pa across the filter. The cleaning technique used was reverse air flow at 0.12 m/s. The results showed that the deposition depth of particles in the polypropylene filter was lower than those observed in the polyester and acrylic filters. Nevertheless, the residual pressure drop of the polypropylene at the beginning of the filtration assays was highest, owing to the greater accumulation of particles at the surface of the filter and the characteristics of the filter itself. It was also observed that the adhesion force was higher in the polypropylene filter than in the other filters, making it hard to remove the filter cake from that filter.► The behavior of the particle deposition and adhesion forces can improve the understanding of the cycles of filtration. ► The polypropylene filter exhibited the highest number of particles retained on the surface of the filter. ► The acrylic and polyester filters trapped greater numbers of particles internally than the polypropylene filter. ► The adhesion force was higher in the polypropylene filter, making it difficult to remove the cakes from the filter.

The plasma spray process is widely used to produce thick coatings by the successive pilling of particles deposited in a molten or semi-molten state on a prepared substrate. However, this process includes time-dependent phenomena that affect the reliability of the process and reproducibility of coating. These phenomena are principally linked to the continuous movement of the electric arc root on the anode wall in the plasma gun. Such a movement leads to arc length variations resulting in fluctuations in arc voltage, enthalpy input to the flow and instabilities in the plasma jet. This paper presents an attempt to develop a time-dependent and 3-D model of the plasma spray process that can provide a useful insight in the time-evolution of the performance of the process. The effect of the transient behaviour of the arc on the gas flow is modelled with a time dependant heat source located inside the nozzle and evolving with the arc voltage. The first stage of the study consisted in the validation of the flow model thanks to the comparison of steady-state computed results with experimental data. The second dealt the time-dependant simulation of the flow.

The invention of uniformly sized, polymer micro-spheres in 1950s provided the possibility for a direct optical observation of various equilibrium structures and dynamic processes in two dimensions (2D). These include 2D-phase transitions, particle aggregation, deposition on solid surfaces, fracture of 2D particulate layers, and many others. The initial interest was driven mainly by the possibility for direct observation and precise quantitative analysis of these complex phenomena, which include many-body interactions and are of great interest for the condensed matter physics. The optical observations have been often combined with computer experiments, in which the collective properties of the particles are simulated. During the last decade, the research interest shifted to a large extend towards the mechanisms and procedures for controlled fabrication of new 2D-structured materials, which possess unique optical properties and has a potential for various applications in nanotechnolog...

Trees are effective in the capture of particles from urban air to the extent that they can significantly improve urban air quality. As a result of their aerodynamic properties conifers, with their smaller leaves and more complex shoot structures, have been shown to capture larger amounts of particle matter than broadleaved trees. This study focuses on the effects of particle size on the deposition velocity of particles (Vg) to five urban tree species (coniferous and broadleaved) measured at two field sites, one urban and polluted and a second more rural. The larger uptake to conifers is confirmed, and for broadleaves and conifers Vg values are shown to be greater for ultra-fine particles (Dp < 1.0 microm) than for fine and coarse particles. This is important since finer particles are more likely to be deposited deep in the alveoli of the human lung causing adverse health effects. The finer particle fraction is also shown to be transported further from the emission source; in this study a busy urban road. In further sets of data the aqueous soluble and insoluble fractions of the ultra-fines were separated, indicating that aqueous insoluble particles made up only a small proportion of the ultra-fines. Much of the ultra-fine fraction is present as aerosol. Chemical analysis of the aqueous soluble fractions of coarse, fine and ultra-fine particles showed the importance of nitrates, chloride and phosphates in all three size categories at the polluted and more rural location.

We have shown that pulmonary exposure to fine particulate matter (PM) impairs endothelium dependent dilation in systemic arterioles. Ultrafine PM has been suggested to be inherently more toxic by virtue of its increased surface area. The purpose of this study was to determine if ultrafine PM (or nanoparticle) inhalation produces greater microvascular dysfunction than fine PM. Rats were exposed to fine or ultrafine TiO2 aerosols (primary particle diameters of ~1 mum and ~21 nm, respectively) at concentrations which do not alter bronchoalveolar lavage markers of pulmonary inflammation or lung damage. By histopathologic evaluation, no significant inflammatory changes were seen in the lung. However, particle-containing macrophages were frequently seen in intimate contact with the alveolar wall. The spinotrapezius muscle was prepared for in vivo microscopy 24 hours after inhalation exposures. Intraluminal infusion of the Ca2+ ionophore A23187 was used to evaluate endothelium-dependent ar...

Seasonal differences in the particle size fractions and mass loadings of household dust deposited on indoor surfaces were examined in four New Jersey homes. Housedust was collected during a 30-day period on non-electrostatic polyethylene sample plates on which a glass slide had been placed. In each home two samples were collected at a height of 1.5 m and two were collected at a height of 0.3 m above the floor. Dust samples were obtained from each home during a summer and winter collection period. Particle size measurement was completed using an adaptation of a Meridian ACAS 570 Interactive Laser Cytometer. Results indicated that the dust mass deposited on household surfaces during the summer was greater than during the winter. The arithmetic mean mass deposition rate for all houses was 0.37 +/- 0.13 microgram/cm2/day during the summer and 0.22 +/- 0.13 microgram/cm2/day during the winter. The total number of particles deposited, however, was greater during the winter than during the...

The effect of the addition of chlorine and/or sulfur to the fuel on fly ash composition, deposit formation, and superheater corrosion has been studied during biomass combustion in a circulating fluidized-bed boiler. The chlorine (HCl (aq)) and sulfur (SO2 (g)) were added in ...