Particle Capture Efficiency Research Articles

Dispersion and deposition of particles in a turbulent pipe flow with sudden expansion

Numerical simulations of dispersion and deposition of particles in an axisymmetric turbulent pipe flow with sudden expansion are performed. The cases that particles of different sizes are released from point sources and/or are uniformly distributed are studied. The effects of turbulence diffusion, Brownian dispersion, lift force, and gravity are included in the computational model. A thermodynamically consistent, rate-dependent algebraic stress model is used to simulate the mean velocity and turbulent intensity fields. The instantaneous fluctuating velocity is simulated as a continuous Gaussian random vector field. The Brownian force is modeled as a Gaussian white noise random process. Ensembles of several thousand particle trajectories are evaluated and are statistically analyzed. The effects of particle source location, particle size, and gravity on dispersion and deposition are studied. The particle capture efficiency for an initially uniform distribution is also evaluated. The predicted particle and fluid velocities are compared with the available experimental data and reasonable agreement is observed.

Dispersion and deposition of particles in a turbulent pipe flow with sudden expansion

Numerical simulations of dispersion and deposition of particles in an axisymmetric turbulent pipe flow with sudden expansion are performed. The cases that particles of different sizes are released from point sources and/or are uniformly distributed are studied. The effects of turbulence diffusion, Brownian dispersion, lift force, and gravity are included in the computational model. A thermodynamically consistent, rate-dependent algebraic stress model is used to simulate the mean velocity and turbulent intensity fields. The instantaneous fluctuating velocity is simulated as a continuous Gaussian random vector field. The Brownian force is modeled as a Gaussian white noise random process. Ensembles of several thousand particle trajectories are evaluated and are statistically analyzed. The effects of particle source location, particle size, and gravity on dispersion and deposition are studied. The particle capture efficiency for an initially uniform distribution is also evaluated. The predicted particle and fluid velocities are compared with the available experimental data and reasonable agreement is observed.

Adhesive tapes as capturing surfaces in Burkard sampling

Although pressure‐sensitive adhesive tapes appear to offer many advantages over traditional adhesives in sampling with a Hirst‐type spore trap, their particle capturing efficiency has never been documented. In this paper, the particle capture efficiency of four pressure‐sensitive adhesive tapes was compared to the standard vaseline adhesive in the Burkard 7‐day volumetric spore trap. The capture efficiency was assessed at flow rates of 8 and 101 min−1 over a 16 week period with each tape run alongside the standard. Image analysis was used to count and measure the surface area of individual inorganic and organic particles collected onto each tape. Approximately 230,000 individual particles were analysed, the majority of particles collected on both standard and pressure‐sensitive adhesive tapes had a surface area less than 150 μm2 (approximately diameter 14 μm). Capture efficiency was expressed as a percentage of the counts on the standard and classified by particle size and flow rate. For particles < 1000 μm2(<36 μm in diameter), the best adhesive tape captured 247.6% at 81 min−1 and 132.5% at 101 min−1. For particles > 1000 μm2, the best adhesive tape captured 86.9% at 81 min−1 and 69.8% at 101 min−1. In addition to image analysis, manual counts of pollen grains and Alternaria‐like spore were performed over a four day period for each adhesive and parallel standard at the flow rate of 101 min−1. On the adhesive tapes, pollen grains <20 μm, and pollen grains >20 μm with heavy ornamentation and/or free standing exine elements were captured best. For the best adhesive tape, the capturing efficiency compared to the standard vaseline was 83% for all pollen grains and 60% for Alternaria‐like spores.

Collision Frequencies of Fractal Aggregates with Small Particles by Differential Sedimentation

Two groups of aggregates with fractal dimensions of 1.81 ± 0.09 and 2.33 ± 0.07 were generated by coagulation of latex microspheres (2.84 μm) in a Jar-test (paddle-mixing) device. The collision rates between these fractal aggregates (200−1000 μm) and small (1.48 μm) particles were measured for individual aggregates that had settled through a suspension of the small particles. Aggregate permeabilities calculated from measured settling velocities were 3 orders of magnitude greater than predicted by a permeability model based on a homogeneous distribution of primary particles within the aggregates. Collision frequencies were 1 order of magnitude higher than predicted by a curvilinear model and about 2 orders of magnitude lower than predicted by a rectilinear collision model. The capture efficiencies of small particles by settling aggregates were <0.2% based on the total volume of water swept out by an aggregate. Fluid collection efficiencies, collision frequen cies, and particle capture efficiencies of the fractal ag gregates decreased with the magnitude of fractal dimensions. A fractal permeability model was developed by modifying the Brinkman correlation to describe the permeability as a function of aggregate size. This model was used in conjunction with a filtration model to predict capture rates and capture efficiencies of small particles by settling fractal aggregates. Based on these experiments and models, it is argued that the high aggregate permeabilities and the low overall particle capture efficiencies of fractal ag gregates can be explained by flow through macropores formed between large clusters within the aggregates.

Filtration of Nanoparticles with Dimethyldioctadecylammonium Bromide Treated Microporous Polypropylene Filters

Microporous polypropylene membrane filters are modified with a cationic surfactant, dimethyldioctadecylammonium bromide (DDAB), to create a charged surface. Negatively charged nanoparticles can then be filtered by utilizing the electrostatic interaction between the charged particles and the polar heads of the surfactants adsorbed on the filters. The study focuses on particle adsorption and particle filtration. Particle adsorption studies have shown that particle adsorption can be increased significantly with this treatment due to Coulombic attraction. Filtration results for 60 nm negatively charged particles (carboxylate modified copolymer) filtered through DDAB treated filters show a significant increase in particle capture efficiency. Capture efficiency is dependent on the pH of the suspension due to competitive adsorption between the hydroxide ions and the negatively charged nanoparticles. As the mean pore diameter increases, capture efficiency decreases due to the increase in distance between the part...

Cross-flow filtration: cakes with variable resistance and capture efficiency

The cross-flow filtration model of Mackley and Sherman is re-examined with an alternative non-dimensionalization. The particle capture efficiency and cake resistance are assumed to depend on the angle at which particles impact the cake. Predicted filtration rates for all values of the cross-flow velocity may be represented by a single master curve, in reasonable agreement with the experimental results of Mackley and Sherman. The model ignores any concentrated boundary layer of uncaptured particles which flows across the surface of the cake when a final steady state is achieved. Estimates are obtained of the rate of growth of such a layer, and it is found to be negligible in two sets of laboratory experiments.

Prediction of the particle capture efficiency based on the combined mechanisms (turbulent diffusion, inertial impaction, interception, and gravitation) by a 3-D simulation of a wet scrubber

This paper presents results obtained from a computer model which describes the removal of fine particles from gas streams of chemical and metallurgical processes in a wet scrubber. The simulation results show an improvement of the collection efficiency of submicron aerosol particles which is explained by the turbulent diffusion mechanism.

The dynamic variation of particle capture efficiency during ash deposition in coal-fired combustors

Dynamic growth of ash deposits was studied in a carefully controlled environment using high speed video cameras and temperature controlled deposition probes. Deposition data are reported as a function of coal type, extent of particle burnout, and time. Five coals varying in rank from bituminous to lignite were tested. The coals were tested at conditions simulating three locations in a boiler: the near-flame region, the superheater region, and the convection pass. Details of deposit formation were monitored for 90 minutes for each coal at each test condition. A particularly interesting results is that particle capture efficiencies, the fraction of flyash particles that adheres to the probe upon contact, have a strong time dependence, varying from near zero to near unity during deposit formation. Dependence of ash deposition on coal rank and location of the boiler is also discussed.

Sieving Capture of Liquidborne Particles by microporous membrane filtration media

AbstractTest methodology has been developed to measure the particle removal efficiency of microporous membrane filtration media under conditions in which sieving is the dominant particle capture mechanism. The methodology was used to determine the particle capture efficiency of a 0.45 μm membrane filter for removal of submicrometer sized particles from DI water. Particle capture was found to be a strong function of particle diameter, filter media thickness, and filter loading. Particle removal efficiency increased with increasing particle diameter and media thickness. It decreased with increased filter loading when the filters were challenged with the smaller particles used in this study. Removal efficiency initially decreased then subsequently increased during loading with larger particles. Capture was independent of filtration velocity and particle concentration. A sieving model was developed to predict particle capture by the filter media as a function of particle diameter, filter thickness and filter loading. The model was found to accurately predict breakthrough of monodisperse particle suspensions through the media. Particle breakthrough occurred more slowly than predicted when the filters were challenged with a polydisperse particle suspension.

Analysis of particle trajectories of small particles in flotation when the particles and bubbles are both charged

AbstractThe trajectory of a small particle moving to a bubble surface was analyzed by taking into account the effects of surface charges of the bubble and particle and the short range hydrodynamic interaction near the bubble surface, in a flotation process. The particle trajectories obtained theoretically were in good agreement with those obtained by direct observation. Even if the signs of the surface charges of the bubble and particle were the same, the particle adhered to the bubble surface when the net surface force, that is, the sum of the electrostatic force and the van der Waals force, was attractive. Particle capture efficiency, ηS, per bubble was estimated by trajectory analysis and the flotation efficiency, ηT, was calculated. The values of ηT calculated by the particle trajectory analysis were in reasonable agreement with those obtained experimentally. The dependence of particle diameter on ηT was also examined by the particle trajectory analysis.

Deposition rates from polydispersed particle populations of arbitrary spread

AbstractFor particle deposition from log‐normal polydispersed aerosol streams by one or more of several mechanisms described by piecewise‐power‐law mass transfer coefficients, we derive useful relations between actual total mass deposition rates and the ‘reference’ rate one would calculate by imagining that all particles in the mainstream population had the average particle volume v(=ϕp/Np). Included here are diffusion or inertial mechanisms for laminar‐ or turbulent‐boundary layers, free‐molecular or continuum diffusion at high Peclet numbers of dense spherical particles, or fractal agglomerates. The mainstream particle volume distribution is considered to be log‐normal with arbitrary ‘spread’ parameter, thereby generalizing earlier results for “coagulation‐aged” (self‐preserving) distributions. Further generalizations include transitions between important particle transport mechanisms, opening the way to efficient, finite‐analytic methods for predicting mass deposition rates for arbitrary, size‐dependent particle capture efficiencies.

Effects of flow velocity, food concentration and particle flux on growth rates of juvenile bay scallops Argopecten irradians

Feeding rates, and hence growth, of suspension-feeding organisms are determined by many interacting factors including efficiency of particle capture, food-particle concentration, and ambient flow regimes. Studies in a recirculating seawater flume were conducted to examine the growth rates of juvenile bay scallops Argopecten irradians irradians (L.) (3–10 mm in shell height) in four flow velocities (0, 1, 6, and 15 cm · s −1) over a range of food concentrations (0–75 000 cells · ml −1) in a four-by-four factorial design. Particle flux (algal cells · cm −2· s −1) encountered by the scallops is the product of food concentration (cells · ml −1) and flow velocity (cm · s −1). The experimental levels of food concentration and flow velocity were chosen to produce a wide range of fluxes. Several treatments with equal flux derived from different flows and food concentrations were used to decouple the effects of each factor. Within a given flux of particles, growth rates were not significantly different between flows or particle concentrations. Growth was only weakly correlated to flux of particles over the range of fluxes tested. The effects of algal concentration were more pronounced than the effects of flow velocity suggesting that differences in growth were a result of differences in algal concentrations. Additional experiments were run to determine the clearance rates of scallops at different food concentrations. These experiments support the findings of the flume experiments; clearance rates were seen to decrease with increasing food concentrations. Flux of food particles is not a predictor of growth, rather it is the combination of the effects due to food concentration and flow velocity which determine the response of the individual juvenile bay scallop.

Gut‐Passage, particle selection and ingestion of filter‐feeding Blackfly (Dipt., Simuliidae) larvae inhabiting a waterfall in Tahiti (French Polynesia)1

Field experiments were carried out to study larval feeding parameters of Simulium cataractarum Craig 1987 (Diptera, Simuliidae) at the Trois Cascades de Faarumai (Tahiti, French Polynesia). Most larvae were attached to submerged moss on spring‐wetted rock walls beside the main waterfall. 1 I suspensions of red cellulose powder and two different mixtures of latex beads of various diameter were dispensed into the stream flow passing the larval colony. Gut‐passage time was calculated by the gut‐throughput of the red cellulose band. Particle ingestion was analyzed for artificial particles (latex beads and cellulose particles) as well as for natural food supply (diatoms and other algae). Particle capture efficiency was estimated calculating an absolute selectivity index IE∗ based on ingestion efficiency. By introducing this index estimation errors can be avoided if relative indices are used as demonstrated for Jacobs’ electivity index D which compares relative proportions of food categories or particle sizes i...

Mechanism of fabric filtration by electrostatic augmentation

Experimental studies on precharged particle filtration and a mechanism for the electrostatic effects of fabric filtration are described. The residual pressure drop and the rate of pressure drop are reduced and the capture efficiency of submicron particles is improved, possibly because of the repellent force between the charged particles and the charge on the dust cake, which is more loosely packed and porous. By heating the ground electrode of the precharger, a higher removal efficiency is obtained for a high resistivity fly ash (i.e., about 19 13 ohm cm and above).

Diffusive capture of ultrafine particles by spheres

We present a theory for the capture of ultrafine particles by spheres for the case where magnetically driven diffusion is dominant. A variational principle is used to study the particle concentration field and capture efficiency of a representative collecting sphere as a function of magnetic field strength and flow rate for small Peclet numbers. The study is intended to complement earlier work on cylindrical collectors and our own recent calculations for spherical collectors in the realm of large Peclet numbers.

Use of Tracer Gas Techniques for Industrial Exhaust Hood Efficiency Evaluation — Application of Sulfur Hexafluoride for Hood Controlling Particulate Emissions

One of the most commonly used controls of harmful industrial contaminants is a local exhaust hood. The efficiency of this system is defined as the ratio of air contaminant quantity captured by the system per unit time to the total contaminant quantity produced by the process per unit time. A tracer gas technique, using sulfur hexafluoride (SF6), has been developed for the efficiency estimation of hoods controlling gaseous or vaporous contaminants. To extend the applicability of this method to hoods controlling particulate contaminants, a relationship between the hood particle capture efficiency and the hood efficiency determined by the tracer gas technique was studied. A particulate tracer was used for the hood efficiency and the data were compared with those obtained by the SF6 technique. Both tracers were discharged under the same conditions. Based on a statistical data analysis, described in detail in this paper, a mathematical relationship between the efficiency obtained by both particulate and SF6 was obtained for different velocity ratios (discharge velocity to capture velocity). For a hood controlling particles' of 3 µm in diameter, no correction of the hood efficiency data estimated by the SF6 technique is required. For larger particles, a corrective factor should be used for modification of the efficiency results obtained by the SF6 technique.

Use of Tracer Gas Techniques for Industrial Exhaust Hood Efficiency Evaluation — Application of Sulfur Hexafluoride for Hood Controlling Particulate Emissions

One of the most commonly used controls of harmful industrial contaminants is a local exhaust hood. The efficiency of this system is defined as the ratio of air contaminant quantity captured by the system per unit time to the total contaminant quantity produced by the process per unit time. A tracer gas technique, using sulfur hexafluoride (SF6), has been developed for the efficiency estimation of hoods controlling gaseous or vaporous contaminants. To extend the applicability of this method to hoods controlling particulate contaminants, a relationship between the hood particle capture efficiency and the hood efficiency determined by the tracer gas technique was studied. A particulate tracer was used for the hood efficiency and the data were compared with those obtained by the SF6 technique. Both tracers were discharged under the same conditions. Based on a statistical data analysis, described in detail in this paper, a mathematical relationship between the efficiency obtained by both particulate and SF6 was obtained for different velocity ratios (discharge velocity to capture velocity). For a hood controlling particles' of 3 µm in diameter, no correction of the hood efficiency data estimated by the SF6 technique is required. For larger particles, a corrective factor should be used for modification of the efficiency results obtained by the SF6 technique.

The efficiency of particle capture by an infinite array of ferromagnetic wires at low reynolds numbers

A new theoretical model is presented to describe the capture and retention of weakly magnetic particles carried by a viscous fluid past an infinite array of ferromagnetic wires in the HGMS transverse configuration. While the forces involved in the capture process are expressed analytically, the equations of particle motion are solved numerically yielding the trajectories, singular points and capture efficiencies. The capture efficiencies, determined for a wide range of values of operational parameters, are calculated on the basis of a laminar flow model, which by contrast to the potential flow model used in previous studies, gives a very good description of fluid motion at low Reynolds numbers. The effect of particle buildup upon the capture efficiencies is also calculated and shown to decrease with increasing λ V m/ V oλ.

Morphological Study of Sieve Efficiencies and Mandibular Surfaces in the Antarctic Krill, Euphausia superba

The filtering basket of Euphausia superba is a complex comb filter with a wide range of mesh intervals. Intersetal distances range from approximately 15–95 μm between primary setae to 4–18 μm between secondary setae (setules). Microsetules with spacing of 1–2 μm thicken boundary layers surrounding secondary setae. Reynolds numbers for setules and microsetules, ranging from 0.006 to 0.95, limit the feeding modes available to E. superba for suspension feeding. Relative efficiency of particle capture, estimated from intersetule mesh size and grazing experiments with small phytoplankton (&lt; 30 μm), show an asymptotic efficiency for particles 12–28 μm. Setule frequency distribution conservatively characterizes particle size selection for these small particles. The fine structure of the mandibular pars molaris varies between krill species and shows specialized surfaces that can split diatom chains, cut or fracture hard tests, and grind particles smaller than 10 μm.

Some hydrodynamic aspects of fitter feeding with rectangular-mesh nets

The maximum particle-capture efficiencies of rectangular-mesh nets have been estimated for cases where the net is set up in running water. The pressure drop due to fluid flow through a plane, rectangular network of cylindrical fibres at low Reynolds number was derived from equations published for an array of parallel, equally-spaced cylinders. Expressions were assumed for the pressure drop across a plane, porous disc of finite extent in a high Reynolds-number flow, so as to find the average flow speed through the disc as a function of the flow speed in its absence. This information was used to estimate the speed of water flow through particular examples of Trichoptera larval filter nets, and from this, their efficiencies of particle capture due to direct interception and to diffusional deposition, in terms of the flow approaching the mouth of the filter system from far upstream. The Stokes number, which governs the contribution of inertial impaction to the capture process, was also found for various particle sizes. Diffusional deposition and inertial impaction were estimated to be negligible except for particles smaller than 0·3 μm and larger than 50 μm respectively. It is suggested that coarse-net spinners, Hydropsyche and Arctopsyche, are potentially highly efficient at capturing large particles, whereas Macronema and the philopotamids are better adapted to the capture of particles smaller than 3 μm.