Particle Interception Research Articles

Particle-interception properties of high porous metal filter elements for fail-safe function

Abstract The particle interception properties of metal filter elements with a hydraulic pore size of 20–98 μm were investigated in order to evaluate their fail-safe functions. The fail-safe filter element is mounted alongside the main filter element and has to be rapidly plugged when a part of the main filter element is broken in order to prevent particle leakage. This study focused on how fast the filter element was plugged without serious particle penetration during the initial time. The particle leakage and the pressure drop change were measured in two modes in order to simulate a field situation. Mode one operated at a constant high-speed particle-stream flow rate and mode two involved rapid exposure of the filter element to the high-pressure high-speed dust stream. Particle leakage through the filter element increased semi-linearly and the pressure drop decreased exponentially as the hydraulic pore size of the filter element increased. A suitable hydraulic pore size for the metal filter elements lay between 50 and 60 μm in order to intercept particles that were larger than 5 μm within 2 min and without an additional pressure drop of more than 300 Pa under typical operation conditions of filter unit. A selected fail-safe filter element showed a stable base-line pressure drop of less than 3500 Pa for IGCC fly ash with a face velocity of 3 cm/s and 450 °C in a bench-scaled unit (BSU) using hot gas stream from an oil burner.

On the applicability of laser ionization for simulating hypervelocity impacts

In-situ measurements, the direct interception and analysis of dust particles by spacecraft-based instrumentation, provide insights into the dynamical, physical and chemical properties of cosmic dust. The most sensitive detection methods for dust particles in space are based on impact ionization. Laser ionization is used for the test, development, and calibration of impact ionization instruments and to complement laboratory based particle impact experiments. A typical setup uses a 355 nm Nd-YAG laser with a pulse length of about 5 ns. It is necessary to investigate the properties of both processes with respect to their comparability. A study was performed to find out to what extent laser ionization can be used to simulate impact ionization. The findings show that laser ionization and impact ionization show similarities, which can be used to test the functionality of dust impact detectors, especially time-of-flight instruments. Our paper provides information on what extent these similarities hold and where their limits are.

Nanoporous micro-element arrays for particle interception in microfluidic cell separation

The ability to control cell-surface interactions in order to achieve binding of specific cell types is a major challenge for microfluidic immunoaffinity cell capture systems. In the majority of existing systems, the functionalized capture surface is constructed of solid materials, where flow stagnation at the solid-liquid interface is detrimental to the convection of cells to the surface. We study the use of ultra-high porosity (99%) nanoporous micro-posts in microfluidic channels for enhancing interception efficiency of particles in flow. We show using both modelling and experiment that nanoporous posts improve particle interception compared to solid posts through two distinct mechanisms: the increase of direct interception, and the reduction of near-surface hydrodynamic resistance. We provide initial validation that the improvement of interception efficiency also results in an increase in capture efficiency when comparing nanoporous vertically aligned carbon nanotube (VACNT) post arrays with solid PDMS post arrays of the same geometry. Using both bacteria (∼1 μm) and cancer cell lines (∼15 μm) as model systems, we found capture efficiency increases by 6-fold and 4-fold respectively. The combined model and experimental platform presents a new generation of nanoporous microfluidic devices for cell isolation.

On the characterization of nanoparticles emitted from combustion sources related to understanding their effects on health and climate

This work describes the use of well-controlled laboratory flames to produce aerosols of organic carbon (OC) as model particles representative of the OC fraction of combustion-generated particulate matter emissions in fresh exhausts. Water–particle interactions are explored in two specific cases. In the first case, particles are exposed to saturated environments and come into direct contact with liquid water by bubbling flame samples through a column of water. This case is representative of particle–liquid interactions relevant to wet removal routes by particle interception by rain or fog droplets or in biological systems covered with biological fluids composed mostly of water. In the second case, the particles are exposed to sub-saturated vapors with H2O concentrations representative of cloud-forming atmospheres. The particles’ capacity to serve as atmospheric cloud condensation nuclei (CCN) by rapid growth to droplets was measured and compared to NaCl particles, which are highly soluble particles with well known activation diameters. The results show measureable interactions with water in highly saturated conditions. However, in sub-saturated environments, no growth by water condensation was observed, and fresh emissions of OC nanoparticles are not likely to act as CCN in atmospherically relevant humidity.

A novel multiphase DNS approach for handling solid particles in a rarefied gas

A comprehensive model is proposed for multiphase DNS simulations of gas–solid systems involving particles of size comparable to the mean free path of the gas and to that of the bounding geometry. The model can be implemented into any multiphase Direct Numerical Simulation (DNS) method. In the current work, the Volume of Fluid (VOF) method is used, and it is extended to allow for the incorporation of rarefaction effects. For unbounded flow, the model is in excellent agreement with experimental data from the literature. For flows in closed conduits, the model outperforms the alternate approach of using a slip boundary condition at the particle surface for the most relevant degrees of rarefaction and confinement. The proposed model is also able to correctly handle particle–particle interception. The model is intended for low particle Reynolds number flows, and can be applied to resolve in great detail phenomena in a large number of industrial applications (such as filtration of fine particles in porous media).

Measurement and prediction of filtration efficiency evolution of soot loaded diesel particulate filters

We here present laboratory based experimental and theoretical methods to characterize the filtration efficiency (FE) behavior of diesel particulate filters (DPFs) exposed to soot laden gas streams. Sensitivity of the FE behavior on filter microstructure and geometry properties have been studied, along with the impact of the hydrodynamic and aerosol flow conditions (flow rate, temperature, aerosol characteristics). Evolution of FE with soot load is reported from clean filter FE to maximum efficiency (100%), as the deposited soot in the filter wall itself acts as the filtering medium. The theoretical model considers different mechanisms (Brownian diffusion, particle interception and inertia) of soot capture and their impact on number based and mass based FE. The predictions from the theoretical model are in good agreement with experimental observations over a broad range of filter microstructure. Sensitivity of FE evolution on bare and coated filters has been reported, along with the impact of ash loading of the filters. Methods presented here are useful in determining the performance of DPFs under well-defined laboratory conditions and their extension to dynamic field conditions. These are also useful in determining filter properties for obtaining high FE and low pressure drop.

Capture of Particles by Direct Interception by Cilia During Feeding of a Gastropod Veliger

Ciliary feeders vary in the arrangement of ciliary bands and mechanisms of capture of food. Some larvae use opposed parallel bands of preoral (prototroch) and postoral (metatroch) cilia. Hypotheses for the mechanism of particle capture include filtration by adhesion to a cilium that overtakes a particle (direct interception), but until now unequivocal evidence for this mechanism has been lacking. Here, high-speed video recordings of veliger larvae of the gastropod Lacuna vincta demonstrated direct interception of particles by prototrochal cilia. Adhesion between cilium and particle was seen when a prototrochal cilium tugged a diatom chain into the food groove while in contact with one part of the chain. In several recorded events, a prototochal cilium overtook a particle during its effective stroke and subsequently pulled the particle inward with its recovery stroke; thereupon, the particle was deposited onto the food groove and transported to the mouth. Captures varied, however. In some cases the particle was intercepted multiple times in one capture event; in others, several cilia passed a particle without interception. Particles occasionally remained in the area of recovery strokes, indicating retention without continuing adhesion to a cilium. In three events, a particle lost from prototrochal cilia was intercepted and moved into the food groove by metatrochal cilia. Particles as wide as or wider than the food groove were also captured and transported but were not ingested.

Transport and Deposition of Particles in Turbulent and Laminar Flow

This article reviews the physical processes responsible for the transport and deposition of particles and their theoretical modeling. Both laminar and turbulent processes are considered, emphasizing the physical understanding of the various transport mechanisms. State-of-the-art computational methods for determining particle motion and deposition are discussed, including stochastic Lagrangian particle tracking and a unified Eulerian advection-diffusion approach. The theory presented includes Brownian and turbulent diffusion, turbophoresis, thermophoresis, inertial impaction, gravitational settling, electrical forces, and the effects of surface roughness and particle interception. The article describes two example applications: the deposition of particles in the human respiratory tract and deposition in gas and steam turbines.

Effect of urban drainage on bioavailability of heavy metals in recipient

Heavy metals comprise one of the most hazardous groups of pollutants entering the aquatic environment. Their behaviour and ecotoxicological effects are not well understood especially if they are occur as a mix of metals. Drawing on data from three Prague creeks, the paper illustrates changes in heavy metals bioavailability resulting from different environmental conditions and related differences in urban drainage types. Heavy metals in sediment from creeks impacted by stormwater drain discharges are more bioavailable and accumulate in organisms to higher concentrations than in organisms from creeks affected by combined sewer overflows. The results also show that bioassay levels of lead in fish from the creeks exceed acceptable concentrations for human consumption (EC 466/2001) and therefore represent a potential health risk for humans. The results demonstrate the importance of providing improved interception efficiency in the drainage system structures. In particular, a higher level of interception of fine particles is critical, because of their higher metal adsorption capacity than for coarser particles.

Epiphytic lichen growth abnormalities and element concentrations as early indicators of forest decline

Thallus morphology and element concentrations (S, Al, Fe, Sr, Mn, Ni, Zn, Cu, Pb, As, F, and Cl) were compared in samples of the fruticose lichen genus Usnea at two heights of the Abies sibirica canopy in the East Sayan Mountains (Krasnoyarsk District, Russia) sampled from three stations at 15, 25 and 35 km from Krasnoyark. Usnea species with an abnormal morphology dominated on branches in the upper canopy, 15–22 m above ground level, and normal thalli on lower tree branches, 2–5 m above ground. Abnormal thalli at the tree-top level contained higher Al, Fe, Zn, F, Sr and Pb concentrations compared with normal thalli growing below, confirming a dust impact. No such clear trend was observed between sampling stations. Crown canopy architecture, surface microtopography and the balance between the processes of deposition and the movement and loss of particles play a major role in particle interception and in pollutant delivery to Usnea.

Lectin binding sites on Euplotes mutabilis (Tuffrau, 1960) and the implications for food particle selection

Seven of the nine lectins tested bound to food vacuolar membranes and/or the cytostome of the filter-feeding ciliate Euplotes mutabilis. Strongest binding to the cytostome was found with concanavalin A, which labelled the cytostomes of more than 90% of cells within 10 s, and quickly labelled progressively more of the food vacuolar membrane material (80% of cells had labelled food vacuoles after 50 s exposure to the lectin). Wheat germ agglutinin specifically labelled the basal halves of a particular group of 8–9 frontal membranelles of every cell within 10 s, as well as labelling the cytostome area and food vacuoles of many cells. The specific areas of the cells which bind these lectins are involved in food capture. The frontal membranelles are involved in the interception of particles from the feeding current. The cytostome membrane bears binding sites to lectins of many types; these binding sites may be involved in the selective capture of food particles destined for ingestion, whilst unbound particles may be rejected.

The Deposition of Aerosol Submicron Particles on Ultrafine Fiber Filters

The diffusion deposition of submicron aerosol particles of a finite size on a model filter composed of parallel ultrafine fibers with a radius comparable with the mean free path of air molecules was considered. The diffusion capture coefficient with allowance made for particle interception ηDRis found by the numerical solution of the elliptic equation of steady-state convective diffusion in the wide ranges of interception parameter R, Peclet (Pe) and Knudsen (Kn) numbers at small Reynolds numbers. It was shown that, at small Kn numbers, the ηDR value exceeds the sum of capture coefficients due to specific deposition mechanisms, interception and diffusion, ηΣ = ηR + ηD, whereas, at Kn > 1, ηDR ≤ ηΣ. Within the range of intermediate Pe, Kn, and R numbers, the radius of the most penetrating particles is higher than the fiber radius.

Time course shift in particle penetration characteristics through capillary pore membrane filters

The time course change in particle penetration through capillary pore membrane filters was investigated for relatively short filtration periods. In the laboratory experiments, penetration efficiencies of the 0.3 and 1.0 μm standard particles through the 2.0 μm capillary filter were continuously monitored. While penetration efficiencies of both 0.3 and 1.0 μm particles decreased, 1.0 μm particles became selectively captured by the filter. Furthermore, even small amount of collected particles (coverage fractions less than 1% of the filter surface) was found to alter particle penetration characteristics possibly because of the intense accumulations around the rims of capillary pores due to significance of particle interception. No distinct effect by addition of clogging particles of 2.0 μm diameter was observed, indicating the change in particle penetration characteristics was initiated even when particle clogs became important. The present study showed the size distribution of collected particles by capillary pore membrane filters could be biased with time even for short sampling duration.

Experimental measurements of aspiration efficiency for idealized spherical aerosol samplers in calm air

In a recent previous paper (Su & Vincent, J. Aerosol Sci. 33 (2002) 103) we described a new method by which to investigate the relationships between aspiration efficiency, particle inertia, gravitational effect and sampling orientation for aerosol sampling in perfectly calm air. All previous experimental work to elucidate the basic nature of aerosol sampling in calm air described has been carried out for thin-walled tubes, and none has yet been reported in relation to blunt samplers. To begin to fill this important gap, the present paper describes the application of our new method towards acquiring new measurements of aspiration efficiency for simple blunt samplers. Experiments were carried out to determine the aspiration efficiencies of simple, idealized, spherical blunt samplers for a range of sampling scenarios, for two sizes of blunt samplers and different sampling inlet diameters, and for upwards and downwards sampling scenarios (and hence a range of governing dimensionless physical quantities). It was shown that aspiration efficiency decreased both with increasing inertia (as represented by the Stokes’ number) and with increasing gravitational effect (as represented by the ratio of particle settling velocity to the air velocity at the sampler inlet). The results enabled qualitative physical explanation of the difference between what was observed for upwards and downwards-facing sampling, respectively, in terms of (a) the role of the sampler body in deflecting the air flow in the region close to the body of the sampler (in turn influencing the performance of the sampler), and (b) the interception of particles in the downwards-facing scenario falling within the ‘shadow’ projected upwards by the sampler body. The significant contribution of this work has been the acquisition of a definitive set of new experimental data. These data will be valuable in the future development of understanding of the physics underlying aerosol sampler performance. Such knowledge will be of practical value because (a) blunt samplers are generally the most representative of the types of instruments used in practical occupational, and (b) calm or slowly moving air is characteristic of many indoor situations.

Influence of Impaction Plate Diameter and Particle Density on the Collection Efficiency of Round-Nozzle Inertial Impactors

This study has investigated the influence of impaction plate diameter ( Dc ) and particle density on the particle collection efficiency of single round-nozzle inertial impactors numerically assuming incompressible flow. The study shows that computed St 50 values range from 0.473 to 0.485, which are nearly independent of W/Dc ( W is the nozzle diameter) for the nozzle Reynolds number, Re > 1500, and when W/Dc < 0.32. St 50 values agree quite well with the theoretical values of Rader and Marple (1985), 0.49, and Marple and Liu (1974), 0.477. For a smaller impactor plate diameter such that W/D c > 0.32, St 50 will increase slightly. It increases from 0.483 to 0.507 (Re = 3000) or from 0.479 to 0.495 (Re = 1500) when W/Dc is increased from 0.32 to 0.48. When the nozzle Reynolds number is smaller than 1500, the influence of W/Dc on St 50 is found to be much more pronounced. The effect of particle density on the collection efficiency has also been investigated. When particle gravity is included, the results show that St 50 is not affected by particle density ranging from 0.5 to 10 g/cm 3 , although the particle collection efficiency increases slightly with increasing particle density at high ends of the collection efficiency curves at high nozzle Reynolds number due to an ultra-Stokesian effect. The particle interception effect does not affect the collection efficiency curves at high Reynolds numbers at all, and the effect is negligibly small at low Reynolds numbers.

Particle Deposition in Parallel-Plate Reactors: Simultaneous Diffusion and External Forces

Particle deposition resulting from uniform external forces and Brownian motion is modeled in a parallel-plate reactor geometry characteristic of a wide range of semiconductor process tools: uniform, isothermal, downward flow exiting a perforated-plate showerhead separated by a small gap from a parallel, circular wafer. Particle transport is modeled using a Eulerian approach neglecting particle inertia and interception. Particles are assumed to originate in a planar trap located between the plates, such as would result for particles released from a plasma-induced particle trap after plasma extinction. Flow between infinite parallel plates is described by an analytic quasi-one-dimensional creeping flow approximation, where the showerhead is treated as a porous plate. An analytic, integral expression for particle collection efficiency (fraction of particles that end up on the wafer) is derived as a function of four dimensionless parameters: the flow Reynolds number, a dimensionless trap height, a dimensionle...

Potential for Selective, Controlled Biofouling by Dreissena Species to Intercept Pollutants from Industrial Effluents

Dreissenid mussels (Dreissena polymorpha and Dreissena bugensis) are typically cited as troublesome invasive biofoulers, but their high productivity and filtration capacity offer promise for water quality management. Described here is a design that has evaluated the potential for flow-through mussel filters to clear bioavailable contamination from effluents before discharge. Fine resuspended natural sediments (to which many pollutants readily adsorb) were intercepted by a cascading series of three 16 l filters with a residence time of less than 10 mintankm 1. The inexpensive design cleared up to 96% of suspended particles, and allowed removal of mussels and pseudofaeces as needed. More than 80% of particle interception resulted from mussel filtering, with little attributed to blockage by the apparatus and/or mussel shells. Scale-up, treatment and disposal of by-products, and practical filter applications are recommended.

Interception of small particles by flocculent structures, sessile ciliates, and the basic layer of a wastewater biofilm.

We investigated attachment processes of hydrophobic and hydrophilic particles (diameter = 1 microm) to mature biofilms grown on clay marbles in a sequencing batch biofilm reactor. During a treatment cycle with filtered wastewater containing different fluorescent beads, the progression of particle density in various biofilm compartments (carrier biofilm, basic biofilm layer, biofilm flocs, and sessile ciliates) was determined by flow cytometry, confocal laser scanning microscopy and automated image analysis. Particles were almost completely removed from wastewater by typical processes of particle retention: up to 58% of particles attached to clay marbles, up to 15% were associated with suspended flocs, and up to 10% were ingested by sessile ciliates. Ingestion of particles by ciliates was exceptionally high immediately after wastewater addition (1,200 particles grazer(-1) x h(-1)) and continued until approximately 14% of the water had been cleared by ciliate filter feeding. Most probably, ciliate bioturbation increases particle sorption to the basic biofilm. Backwashing of the reactor detached pieces of biofilm and thus released approximately 50% of the particles into rinsing water. Clay marbles in the upper part of the reactor were more efficiently abraded than in the lower part. No indications for selective attachment of the applied hydrophobic and hydrophilic beads were found. As a consequence of interception patterns, organisms at elevated biofilm structures are probably major profiteers of wastewater particles; among them, ciliates may be of major importance because of their highly active digestive food vacuoles.

簡易型塩分飛散予測モデルの構築と評価

A simple numerical model, which is based on an atmospheric diffusion model considering the vertical subsidence of sea salt particles and the semitheoretical estimation of their generation and vertical distribution, is proposed to estimate the amount of wind-driven sea salt or sea salt damage at any point along the coastal area under strong onshore wind conditions. The performance of the model was evaluated through sensitivity studies of the calculation methods for the deposition, adsorption and on the vertical distribution pattern of sea salt particles over the ocean used as initial data. The results were compared to data observed under typhoon conditions in Okinawa Prefecture. The estimated initial vertical distribution pattern of sea salt particles for each size class reproduced well the observed pattern under the strong onshore wind conditions. The atmospheric concentration, deposition and adsorption of sea salt particles observed under strong onshore wind conditions over a platform-like topography near the coast can be reproduced by the model when the interception of sea salt particles by the cliff and the observation efficiencies are considered. In the model, the deposition and adsorption of sea salt particles over the coastal area are proportional to the wind speed to the third or fourth power, and they are most sensitive to the wind speed near the coast. These features are reasonably consistent with the results of studies reported in the literature. Through a series of evaluations, it was suggested that this model is useful for the simple evaluation of sea salt damage over a coastal area under a flat or simple topography.

Dry deposition of particles to wave surfaces: II. Wind tunnel experiments

Wind tunnel measurements of particle dry deposition to wavy and flat surfaces were made to estimate the enhancement of deposition rates due to waves on water surfaces. Measurements were made of 4.0 and 6.7 μm uranine particles at wind speeds of 5 and 10 m s −1 to sinusoidal waves with height to length ratios 2 a/ λ=0.1 and 0.03 and to flat surfaces. Results showed that deposition was greatest to the upslope portion of the wave, accounting for 40–45% of the total mass, followed by the trough (30%), downslope (15%), and crest (10–15%). These results generally agreed within experimental variability with modeling predictions ( Zufall et al., 1999). Deposition was enhanced at the upslope due to the effects of particle interception and impaction on the wave. Total deposition to the wave surfaces was greater than deposition to the flat surface for a large majority of the cases. The average increase in deposition to both wave surfaces for both particle sizes and wind speeds over deposition to the flat surface was 80%.