Particle Capture Efficiency Research Articles

Model Experiment on Removal of Nonmetallic Inclusions by Bubble Flotation

A new experimental technique, which is based on a kinetic model of particle transport, has been proposed for determination of the capture efficiency of particles by bubble flotation. Cold model experiments by using an aqueous solution and plastic particles are carried out to validate the new experimental technique. Plastic particles having poor wettability tend to adhere to bubbles and they are removed from an aqueous solution by bubble flotation. On the other hand, plastic particles good in wettability are not captured by bubbles. Capture efficiency can be estimated from a difference of transfer rate between the particles having poor and good wettability. The capture efficiency is found to be proportional to the size ratio of particle and bubble, dp/db, and agrees with theoretical results of Sutherland (1948) for a potential flow condition.

Capture efficiency of cooking-related fine and ultrafine particles by residential exhaust hoods.

Effective exhaust hoods can mitigate the indoor air quality impacts of pollutant emissions from residential cooking. This study reports capture efficiencies (CE) measured for cooking-generated particles for scripted cooking procedures in a 121-m3 chamber with kitchenette. CEs also were measured for burner produced CO2 during cooking and separately for pots and pans containing water. The study used four exhaust hoods previously tested by Delp and Singer (Environ. Sci. Technol., 2012, 46, 6167-6173). For pan-frying a hamburger over medium heat on the back burner, CEs for particles were similar to those for burner produced CO2 and mostly above 80%. For stir-frying green beans in a wok (high heat, front burner), CEs for burner CO2 during cooking varied by hood and airflow: CEs were 34-38% for low (51-68 l/s) and 54-72% for high (109-138 l/s) settings. CEs for 0.3-2.0 μm particles during front burner stir-frying were 3-11% on low and 16-70% on high settings. Results indicate that CEs measured for burner CO2 are not predictive of CEs of cooking-generated particles under all conditions, but they may be suitable to identify devices with CEs above 80% both for burner combustion products and for cooking-related particles.

Study on the Design of Venturi Scrubber on Metal Mine

Venturi scrubber is a high-efficiency wet dust collector,and has a high capture efficiency for small solid particles. Applied to metal mines, the venturi scrubber not only eliminate the mine dust in the processes of mining and driving, but also can capture the diesel exhaust particles effectively in theory. Then the air in the mine has been purified and the staff can keep away from the harm of mine dust and diesel exhaust particles. Based on the results of this research from the predecessor, the paper design a reasonable set of pilot programs for mine workers.

Modelling the capture of gasoline engine exhaust particulate matter in three-way catalytic converters

The aim of this work was to numerically model the effect of a three-way catalytic converter on nano-scale particulate matter from a gasoline direct injection engine. The work used a deep bed filtration model to simulate and validate experimental findings. A 1.6L, gasoline direct injection, spark ignition, turbocharged and intercooled Euro IV engine was used for experimentation. The capture efficiency was experimentally determined by measuring pre and post-catalyst particulate matter numbers using a DMS-500 differential mobility spectrometer at different dilution ratio settings. Despite variable experimental results at lower engine speeds and loads, the model was capable of predicting catalytic converter particle capture efficiency in the majority of cases. This indicates that deep bed filtration theory can indeed be used to explain nano-scale particle capture within three-way catalytic converters. The results also suggest that there is no significant agglomeration of particles within the catalytic converter. This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Swimming Speed of Larval Snail Does Not Correlate with Size and Ciliary Beat Frequency

Many marine invertebrates have planktonic larvae with cilia used for both propulsion and capturing of food particles. Hence, changes in ciliary activity have implications for larval nutrition and ability to navigate the water column, which in turn affect survival and dispersal. Using high-speed high-resolution microvideography, we examined the relationship between swimming speed, velar arrangements, and ciliary beat frequency of freely swimming veliger larvae of the gastropod Crepidula fornicata over the course of larval development. Average swimming speed was greatest 6 days post hatching, suggesting a reduction in swimming speed towards settlement. At a given age, veliger larvae have highly variable speeds (0.8–4 body lengths s−1) that are independent of shell size. Contrary to the hypothesis that an increase in ciliary beat frequency increases work done, and therefore speed, there was no significant correlation between swimming speed and ciliary beat frequency. Instead, there are significant correlations between swimming speed and visible area of the velar lobe, and distance between centroids of velum and larval shell. These observations suggest an alternative hypothesis that, instead of modifying ciliary beat frequency, larval C. fornicata modify swimming through adjustment of velum extension or orientation. The ability to adjust velum position could influence particle capture efficiency and fluid disturbance and help promote survival in the plankton.

Particle capture by a circular cylinder in the vortex-shedding regime

AbstractParticle capture, whereby suspended particles contact and adhere to a solid surface (a ‘collector’), is an important mechanism for a range of environmental processes including suspension feeding by corals and ‘filtering’ by aquatic vegetation. In this paper, we use two- and three-dimensional direct numerical simulations to quantify the capture efficiency ($\eta $) of low-inertia particles by a circular cylindrical collector at intermediate Reynolds numbers in the vortex-shedding regime (i.e. for$47\lt \mathit{Re}\leq 1000$, where$\mathit{Re}$is the collector Reynolds number). We demonstrate that vortex shedding induces oscillations near the leading face of the collector which greatly affect the quantity and distribution of captured particles. Unlike in steady, low-$\mathit{Re}$flow, particles directly upstream of the collector are not the most likely to be captured. Our results demonstrate the dependence of the time-averaged capture efficiency on$\mathit{Re}$and particle size, improving the predictive capability for the capture of particles by aquatic collectors. The transition to theoretical high-Reynolds-number behaviour (i.e. $\eta \sim {\mathit{Re}}^{1/ 2} $) is complex due to comparatively rapid changes in wake conditions in this Reynolds number range.

Simulation of filtration process for multi-fiber filter using the Lattice-Boltzmann two-phase flow model

The particle capture process of fibrous filter depends on not only filtration velocity, packing density of fibers, particle and fiber diameters, but also fiber arrangement (e.g. parallel model, staggered model, and separation ratio). In this work, the Lattice Boltzmann–Cellular Automata (LB–CA) probabilistic model for particle-laden flows was introduced to simulate the filtration process of multi-layer fiber filters with different fiber arrangement, and then the effects of the fiber arrangement on the capture efficiency, pressure drop, quality factor, and capture contribution were investigated. It was found that the staggered model performs better than the parallel model and its capture efficiency is higher than that of the parallel model. In addition, the capture efficiency and pressure drop both increase with the fiber separation ratio, while the quality factor decreases. With respect to the capture contributions of various rows of fibers in the steady and unsteady filtration processes, the fore fibers (especially the first row in the parallel model and the first two rows in the staggered model) play a more important role than the rear ones, especially when inertial impaction is predominant. Furthermore, the dynamic evolution of particle deposition patterns, pressure drop, capture efficiency, quality factor, and capture contribution due to different capture mechanisms in the particle loading of multi-fiber filters were investigated. The key factors to determine the dendritic structures are the shielding effect in the parallel model and the “river diversion” effect in the staggered model. Both the capture efficiency and pressure drop increases with the particle loading, however the pressure drop increases faster, resulting in the decrease of the quality factor. For the loading process of larger particles in the parallel model the pressure drop from the LB–CA model agree well with the predictions of the empirical model, and the interceptive capture efficiency predicted by the empirical model is also in good agreement with the LB–CA results. However, no model considers the fiber arrangement and different capture mechanisms. The LB–CA simulation provides good understanding in the dynamic filtration processes of multi-layer fibrous fibers, which is useful for filter design and arrangement optimization.

Improved Airborne Hot-Wire Measurements of Ice Water Content in Clouds

Abstract Airborne measurements of ice water content (IWC) in both ice and mixed-phase clouds remain one of the long-standing problems in experimental cloud physics. For nearly three decades, IWC has been measured with the help of the Nevzorov hot-wire total water content (TWC) sensor, which had an inverted cone shape. It was assumed that ice particles would be captured inside the cone and then completely melt and evaporate. However, wind tunnel experiments conducted with the help of high-speed video recordings showed that ice particles may bounce out of the TWC cone, resulting in the underestimation of the measured IWC. The TWC sensor was modified to improve the capture efficiency of ice particles. The modified sensor was mounted on the National Research Council (NRC) Convair-580 and its measurements in ice clouds were compared with the measurements of the original Nevzorov TWC sensor, a Droplet Measurement Technologies (DMT) counterflow virtual impactor (CVI), and IWC calculated from the particle size distribution measured by optical array probes (OAPs). Results indicated that the IWC measured by the modified TWC hot-wire sensor as well as the CVI and that deduced from the OAP size distributions agreed reasonably well when the maximum size of ice particles did not exceed 4 mm. However, IWC measured by the original TWC sensor was approximately 3 times lower than that measured by the other three techniques. This result can be used for the retrieval of the past IWC measurements obtained with this TWC sensor. For clouds with ice particles larger than 4 mm, the IWC measured by the modified TWC sensor and CVI exhibited diverging measurements.

Effect of 3D fiber orientation distribution on particle capture efficiency of anisotropic fiber networks

This work examines airborne particle capture by 3D anisotropic fiber networks. A series of virtual 3D anisotropic fiber networks was generated by varying the frequency of fibers oriented along the perpendicular plane of the networks. The Lagrangian formulation of particle transport was studied to obtain the capture efficiency of particles ranging from as low as 0.3 μm diameter to as high as 5.0 μm diameter. It was observed that the particle capture efficiency was decreased with the increase in frequency of fibers oriented along the perpendicular plane of the network. This effect was found to be remarkably higher with larger particles as compared to smaller particles.

Aligned carbon nanotube sheet high efficiency particulate air filters

Aerosol filters, made with conventional micro-fiber fabrics, are designed to efficiently capture small particles from the air. Filters constructed of nano-fiber fabric structures provide even greater filtration efficiency than conventional micro-fiber fabrics due to their higher surface area and smaller pore size. Carbon nanotubes (CNTs) are very small diameter fibers that have the potential to be integrated into filters to further increase particle capture efficiency. In this study, CNT sheets, drawn from millimeter tall CNT arrays, were integrated between traditional micro-fiber fabrics to produce aerosol filters. The filtration performance of the novel filters showed that when the number of CNTs layers increased, the filtration efficiency increased dramatically, while the pressure drop also increased. In order to meet high efficiency particulate air (HEPA) filter requirements with a reasonable pressure drop, CNTs were laid in a cross-plied structure within the filter. The results demonstrated that the three layer cross-ply structure provided 99.98% filtration efficiency at 0.3μm particle size at a 10cm/s face velocity, making it a viable method for producing low basis weight HEPA filters utilizing CNTs as the main filtration component.

Effects of species-specific leaf characteristics and reduced water availability on fine particle capture efficiency of trees

Trees can improve air quality by capturing particles in their foliage. We determined the particle capture efficiencies of coniferous Pinus sylvestris and three broadleaved species: Betula pendula, Betula pubescens and Tilia vulgaris in a wind tunnel using NaCl particles. The importance of leaf surface structure, physiology and moderate soil drought on the particle capture efficiencies of the trees were determined. The results confirm earlier findings of more efficient particle capture by conifers compared to broadleaved plants. The particle capture efficiency of P. sylvestris (0.21%) was significantly higher than those of B. pubescens, T. vulgaris and B. pendula (0.083%, 0.047%, 0.043%, respectively). The small leaf size of P. sylvestris was the major characteristic that increased particle capture. Among the broadleaved species, low leaf wettability, low stomatal density and leaf hairiness increased particle capture. Moderate soil drought tended to increase particle capture efficiency of P. sylvestris.

Modeling of Flow Through a Sandwiched Monolith Filter

The flow field and filtration efficiency was modeled and analyzed for a novel monolith filter, comprised of a series of layers of microchannels. In our simulations, we considered two scenarios: the fluid flowing tangentially across the filter face (cross flow) and fluid flowing normal to the filter face (normal flow). The aim of this article is to study the effect of having two or more layers of filters in series on particle capture efficiency. This will help in understanding the mechanisms of particle capture and provide inputs for studying particle segregation or selective filtration using monolith filters. The influences of particle size, number of filter layers and pressure drop on particle capture efficiency were also investigated.

Exact solution to the inverse Womersley problem for pulsatile flows in cylindrical vessels, with application to magnetic particle targeting

An exact solution to the inverse Womersley problem was derived for the fully-developed, laminar pulsatile flow of a viscous Newtonian fluid, within a circular cylindrical vessel with rigid walls. In particular, given an arbitrary, time-periodic flow rate, the axisymmetric velocity profile was obtained by means of two neat and computable maps relating the corresponding Fourier coefficients. The study of such an inverse problem is motivated by the fact that flow rate is the main physical quantity which can be actually measured in many practical situations. The hypothesis of a fully-developed flow was deliberately introduced, in order to obtain an analytical solution (otherwise hardly achievable). Despite the intrinsic simplifications associated with the adopted position (which restrict the applicability of our results to 3D finite-length complex domains, and non-Newtonian fluids), the obtained solution provides a benchmark – and at the same time an approximation – for the inverse problem of pulsatile flows, it may serve as a debugging tool for more ambitious numerical approaches based on realistic data, and can also be used as an improved source of boundary data. As expected, the main advantage of our analytical solutions (compared to fully numerical approaches) resides in computational efficiency; this was quantitatively assessed through numerical tests. Moreover, the proposed solution was applied in the context of magnetic particle targeting, to highlight some peculiar effects on particle trajectories and capture efficiency due to pulsatility. Such a transport problem is increasingly drawing the attention of an interdisciplinary community, ranging from physicians to biomedical engineers, physicists and roboticists, thanks to its potential for targeted therapy, up to remote guidance of intravascular devices. More in general, the obtained benchmark solution holds potential for effectively exploitation in an interdisciplinary context.

Soft-X-Ray-Enhanced Electrostatic Precipitation for Protection against Inhalable Allergens, Ultrafine Particles, and Microbial Infections

Protection of the human lung from infectious agents, allergens, and ultrafine particles is difficult with current technologies. High-efficiency particulate air (HEPA) filters remove airborne particles of >0.3 μm with 99.97% efficiency, but they are expensive to maintain. Electrostatic precipitation has been used as an inexpensive approach to remove large particles from airflows, but it has a collection efficiency minimum in the submicrometer size range, allowing for a penetration window for some allergens and ultrafine particles. Incorporating soft X-ray irradiation as an in situ component of the electrostatic precipitation process greatly improves capture efficiency of ultrafine particles. Here we demonstrate the removal and inactivation capabilities of soft-X-ray-enhanced electrostatic precipitation technology targeting infectious agents (Bacillus anthracis, Mycobacterium bovis BCG, and poxviruses), allergens, and ultrafine particles. Incorporation of in situ soft X-ray irradiation at low-intensity corona conditions resulted in (i) 2-fold to 9-fold increase in capture efficiency of 200- to 600-nm particles and (ii) a considerable delay in the mean day of death as well as lower overall mortality rates in ectromelia virus (ECTV) cohorts. At the high-intensity corona conditions, nearly complete protection from viral and bacterial respiratory infection was afforded to the murine models for all biological agents tested. When optimized for combined efficient particle removal with limited ozone production, this technology could be incorporated into stand-alone indoor air cleaners or scaled for installation in aircraft cabin, office, and residential heating, ventilating, and air-conditioning (HVAC) systems.

Submicron particle filtration in monolith filters – A modeling and experimental study

With over a million micron-sized channels per square centimeter arranged in a regular pattern on a thin film, monolith filters have significant potential for submicron aerosol particle filtration, even though the filtration process with this class of filters has not been well studied. In order to better understand the capture mechanisms and the main factors that affect the capture efficiency, so as to build predictive numerical models and to improve the design of monolith filters, the filtration process in monolith filters was investigated both experimentally and numerically. Using an electrostatic particle classifier (EPC) and a condensation particle counter (CPC), the experimental platform measured the capture efficiency of salt particles with diameters ranging from 50–300 nm on two monolith filter samples. Based on the filtration process and the repeating geometric structure, a single unit model was proposed. The drag force, electrostatic force, and Brownian motion are considered as the major forces affecting particle motion. Published theories underestimated the capture efficiency compared to the experimental results. The Brownian motion model and the capture criterion were then empirically modified to gain better agreement with the experiment.

Modeling of Cross-Flow Across an Electrostatically Charged Monolith Filter

The flow field and filtration efficiency of electrostatically charged micro-channel filters under cross-flow conditions were modeled. In our simulations, the fluid flows tangentially to the filter face (cross-flow). Particles with diameters larger than 2 μm were considered in this study, hence, the effects of Brownian motion were not included in the simulations. The influence of particle size, pressure drop, and electrostatic charge on the filtration efficiency was investigated. Measurements from performing electrostatic force microscopy (EFM) on the monolith sample confirmed the presence of charge and gave a qualitative measurement of the charge distribution. Results from the flow simulations indicate that the electrostatic forces increased the particle capture efficiency only at lower pressure drop. At higher pressure drops, electrostatic forces did not significantly increase the capture efficiency of the particles. Also, the capture efficiency of relatively small particles is found to be more dependent on the pressure drop across the filter than that of larger particles.

High Performance Air Filters Produced from Freeze-Dried Fibrillated Wood Pulp: Fiber Network Compression Due to the Freezing Process

High efficiency air filters to capture submicrometer particles have been produced from fibrillated pulp fiber by a wet beating and freeze-drying procedure. Under appropriate conditions, air permeability and particle capture efficiency meeting the N95 standard can be achieved. Pulp type, beating time, and the freezing process were examined. Particle capture efficiency improved with increased beating, but excessive beating resulted in the formation of a low permeability layer (LPL). This LPL was the result of fiber network compression induced by the freezing process and formed farthest from the cold source. Adding a formation aid commonly used in paper making prevented compression of the fiber network, resulting in higher quality filters.

Development of a calibration reference device for use with test standard ANSI/ASHRAE 52.2-2007 (RP-1466)

Theoretical and experimental work has been conducted to develop a calibration reference device that could be used in test facilities that conform to ANSI/ASHRAE Standard 52.2 2007. After exploring alternative concepts, including electrostatic precipitators, cyclones, and wire mesh screens, a three-stage parallel flow inertial impactor using round orifices as flow nozzles was selected. Small-scale versions were fabricated and tested for flow rate versus pressure drop and particle capture efficiency versus size. The full-scale prototype was fabricated from aluminum and stainless steel and tested in a wind tunnel configured according to ANSI/ASHRAE Standard 52.2 2007. Oleic acid and potassium chloride aerosols were introduced, and the upstream and downstream particle concentrations were measured with optical particle counters with the channels as required in the standard. Results show a pressure drop of 950 Pa (3.8 in. water) at 0.944 m3/s (2000 cfm) rather than the 750 Pa (3.0 in. water) used in the design. Particle collection efficiency for liquid oleic acid particles nearly agrees with the design theory and provides a minimum efficiency reporting value value of 9. However, solid KCl particles larger than about 3 microns are not captured well, perhaps caused by particle bounce from the porous, oil-impregnated impaction plates. Additional theoretical work is required on pressure drop and solid particle capture for impactors of this design before theoretical predictions agree well with the measured results.

Development of a magnetic bead fluorescence microscopy immunoassay to detect and quantify Leptospira in environmental water samples

Climate change, world population growth, and poverty have led to an increase in the incidence of leptospirosis. Leptospirosis is caused by pathogenic spirochaete bacteria that belong to the genus Leptospira. The bacteria are maintained in the renal tubules of the reservoir hosts (typically a rodent), then shed into the environment via the urine. Water is key for environmental survival and transmission, as leptospires can survive for several weeks in a moist environment. Therefore, environmental epidemiological studies are needed to study the contamination of environmental water sources. However, few such studies have been performed using cultivation of the isolates and PCR assays. But, leptospira cultivation can be easily contaminated by other organisms and takes usually several weeks. Moreover, PCR is a complex and costly analysis for the underdeveloped countries that have the highest incidence of leptospirosis. In this study, we describe two modifications of a fluorescence microscopy assay based on immuno-magnetic separation (IMS) to detect leptospires in environmental water samples that mainly differ in fluorescent dye staining. The first type uses acridine orange fluorescent dye staining combined with multiplexed IMS for sample screening. The detection limit ranged from 102 to 103 organisms per mL and largely depended on the capture efficiency (CE) of the immuno-magnetic particles. The second type uses serogroup-specific immuno-particles and direct fluorescence antibody staining (DFA) to detect leptospires; the detection limit of this second assay was approximately 101 cells per mL. Both assay types were applied to natural and experimentally infected water samples, which were also analysed with DFM and real-time PCR. Our data show that the fluorescent microscopy immunoassay successfully identified experimental leptospire contamination and was as sensitive as PCR. This modified immune-fluorescence assay may therefore enable epidemiological studies of leptospirosis.

Enhanced Filter Performance by Fluidized-Bed Pretreatment with Al(OH)3(am): Observations and Model Simulation

Fluidized-bed pretreatment of a rapid sand filter with alum (Al2ðSO4Þ3 · 14H2O) has been shown to significantly improve performance during the initial portion of filter operation. Two alternative mechanisms are hypothesized by which alum pretreatment acts to improve particle removal: (1) AlðOHÞ3ðamÞ coats the sand filter medium, and alters its porosity. (2) Precipitated AlðOHÞ3ðamÞ embedded within the media pores acts as an additional filter medium that increases the particle capture efficiency. Conceptual models for these two mechanisms are developed and compared with experimental data for particle removal and head loss. Model predictions indicate that particle removal by filtration through AlðOHÞ3ðamÞ flocs is the mechanism that significantly enhances the filter performance. DOI: 10.1061/(ASCE) EE.1943-7870.0000493. © 2012 American Society of Civil Engineers. CE Database subject headings: Fluidized bed technology; Filters; Waste treatment; Simulation. Author keywords: Fluidized-bed pretreatment; Alum; Rapid sand filter; Ripening.