Porous polyurethane foam for use as a particle collection substrate in a nanoparticle respiratory deposition sampler

Porous polyurethane foam was evaluated to replace the eight nylon meshes used as a substrate to collect nanoparticles in the Nanoparticle Respiratory Deposition (NRD) sampler. Cylindrical (25 mm diameter by 40 mm deep) foam with 100 pores per inch was housed in a 25-mm-diameter conductive polypropylene cassette cowl compatible with the NRD sampler. Pristine foam and nylon meshes were evaluated for metals content via elemental analysis. The size-selective collection efficiency of the foam was evaluated using salt (NaCl) and metal fume aerosols in independent tests. Collection efficiencies were compared to the nanoparticulate matter (NPM) criterion and a semi-empirical model for foam. Changes in collection efficiency and pressure drop of the foam and nylon meshes were measured after loading with metal fume particles as measures of substrate performance. Substantially less titanium was found in the foam (0.173 µg sampler^?1) compared to the nylon mesh (125 µg sampler^?1), improving the detection capabilities of the NRD sampler for titanium dioxide particles. The foam collection efficiency was similar to that of the nylon meshes and the NPM criterion (R² = 0.98, for NaCl), although the semi-empirical model underestimated the experimental efficiency (R² = 0.38). The pressure drop across the foam was 8% that of the nylon meshes when pristine and changed minimally with metal fume loading (～19 mg). In contrast, the pores of the nylon meshes clogged after loading with ～1 mg metal fume. These results indicate that foam is a suitable substrate to collect metal (except for cadmium) nanoparticles in the NRD sampler.

Copyright © 2016 American Association for Aerosol Research     

A Cylindrical Thermal Precipitator with a Particle Size-Selective Inlet

We designed a thermal precipitator in a cylindrical configuration with a size-selective inlet, and investigated its performance in experiments using differential mobility analyzer (DMA)-classified particles of sodium chloride (NaCl) and polystyrene latex (PSL). Our investigation was performed in two parts: (1) using the size-selective inlet to determine the best inlet-to-wall distance for optimal impaction of 1 μm particles; (2) using a simple inlet tube to measure particle collection via thermophoresis over a size range from 40 nm to 1000 nm. The results showed that the inlet had a particle cut-off curve, with a 50% particle cut-off Stokes number of 0.238, resulting in removing particles with sizes larger than 1 μm at an aerosol flow rate of 1.5 lpm. The thermophoretic particle collection efficiency in the prototype was measured without the size-selective inlet installed. The size dependence of the collection efficiency was negligible for particles with diameters ≤300 nm and became noticeable for those with diameters >300 nm. An analytical model was further developed to estimate the particle collection efficiency due to thermophoresis of the prototype under various aerosol flow rates and temperature gradients. For particles with diameters less than 400 nm, reasonable agreement was obtained between the measured data and the collection efficiency calculated from the developed analytical model. It was further concluded that the derived formula for the calculation of thermophoretic particle collection efficiency could serve as the backbone for future design of thermal precipitators in any configuration, when combined with the proper formula for the dimensionless thermophoretic particle velocity.

Copyright 2012 American Association for Aerosol Research     

Design and Characterization of a New Coarse Particle Collector Based on Microtrap Impactor Technology

A microtrap inertial impactor has been developed and characterized for use as an area or personal sampler. The microtrap impactor utilizes a high-density multijet plate to direct airflow and a matched multiwell plate to impact and collect particles for extraction with a reduced pressure drop relative to inertial impactors with fewer jets. Reported here is the characterization of the microtrap impactor using a fluidized bed aerosol generator and a small volume nebulizer to generate particles of Arizona Road Dust, potassium chloride, and oleic acid. Collection efficiency was determined by measuring particle size distributions with an aerodynamic particle sizer. Two geometries of the microtrap were tested suitable for a two-stage coarse particle sampler, with 1–4 μm and a 4–10 μm stages. The 1 μm cut-point microtrap stage has a collection efficiency above 97% for particles greater than 2 μm in diameter (at a 10 L/min flow rate and a pressure drop of 0.12 kPa). This stage's collection efficiency was constant for a period of time up to 10 h under typical ambient conditions without any coating on the impaction surface. The microtrap impactor provides an improvement in area sampling due to its high collection efficiency at a low pressure drop across the device, and its use of an uncoated impaction surface allowing for the extraction and analysis of biological samples.

© 2013 American Association for Aerosol Research     

Design and development of a self-contained personal electrostatic bioaerosol sampler (PEBS) with a wire-to-wire charger

Here, we present a concept of a personal electrostatic bioaerosol sampler (PEBS), which is an open channel collector consisting of a novel wire-to-wire particle charger and a collection section housing a double-sided and removable metal collection plate and two quarter-cylinder ground electrodes. The charger consists of a tungsten wire (25.4 mm long and 0.076 mm in diameter) connected to high voltage and positioned in the center of the charging section (a cylinder 50.8 mm long and 25.4 mm in diameter); a ring of stainless steel wire 0.381 mm in diameter surrounds the hot electrode at its midpoint and is grounded. The newly designed wire-to-wire charger produces lower ozone concentrations compared to traditional wire-to-plate or wire-to-cylinder charger designs. The particles captured on the collection plate are easily eluted using water or other fluids. The sampler was iteratively optimized for optimum charging and collection voltages, and collection electrode geometry. When tested with polystyrene latex particles ranging from 0.026 µm to 3.1 µm in diameter and 10 L/min collection flow rate, the sampler's collection efficiency was approximately 70%–80% at charging and collection voltages of +5.5 kV and ?7 kV, respectively. The PEBS showed this collection efficiency at sampling times ranging from 10 min to 4 h. Preliminary tests with Bacillus atrophaeus bacterial cells and fungal spores of Penicillium chrysogenum showed similar collection efficiency. The use of a unique wire-to-wire charger resulted in ozone production below 10 ppb. Due to low ozone emissions, this sampler will allow maintaining desirable physiological characteristics of the collected bioaerosols, leading to a more accurate sample analysis.

© 2017 American Association for Aerosol Research     

Thermophoretic Sampler and its Application in Ultrafine Particle Collection

A thermophoretic sampler is designed for the collection of particles smaller than 10 nm. The sampler is composed of heated and cooled surfaces separated by a gap of 0.1 mm; a bypass flow is introduced in the design to minimize the diffusional loss of nanoparticles in the upstream flow channel. Particles may be directly deposited on a 3 mm diameter TEM grid for chemical analysis or on other substrates for other purposes. Calculations show that at an inlet flow rate of 1.5 lpm and thermal gradient of 5 × 10⁵ K/m, a maximum collection efficiency of 41% can be achieved for a particle diameter of 1 nm. Ag particles with median size of 6 nm are used to characterize the thermophoretic sampler collection efficiency. The TEM images show that a sizeable number of particles less than 10 nm in diameter are collected, although they are not uniformly distributed on the grid, and the collection efficiency deduced from these deposited particles is much less than the theoretical estimation. Despite this, the efficiency is orders of magnitude higher than previous designs and it is easier to build.     

颗粒床-旋流耦合分离器不同操作模式下的性能分析

通过实验分别考察了满床/空床操作模式对内置颗粒床-旋流耦合分离器分离性能的影响,获得了两种操作模式下的设备压降和捕集效率。通过改变入口粉尘浓度、入口气速和粉尘颗粒种类,发现满床操作条件下的分离效率比空床操作条件下的分离效率高,且前者压降较低。通过对出口粉尘粒径的分析,含有捕集颗粒的内置颗粒床可有效提高5 μm以下的粉尘颗粒的捕集效率,弥补了离心分离的短板。引入性能指数对不同操作模式进行定量分析,验证了满床操作条件下的耦合分离设备具有更好的综合分离性能。     

Numerical Simulations on Aerodynamic Focusing of Particles in a Wide Size Range of 30 nm–10 μm

Previous designs of conventional aerodynamic lenses have the limitation of a narrow range of focusable particle size, e.g., just one order of magnitude such as 30–300 nm or 3–30 nm. To enlarge the focusable size range to two orders of magnitude (30–3,000 nm), it is necessary to focus small particles and at the same time not to loose the large ones. From numerical simulations of size-resolved particle trajectories, we confirmed that the traveling losses of such large particles could be avoided only when the radial positions of particles approaching the orifice lenses were near the axes of the lenses. Hence, we designed a lens system consisting of seven orifices to fulfill the requirement. In particular, the orifices were aligned in such a way that their diameters would descend and ascend downstream. As a result, 30–2500 nm particles could be focused to produce particle beams with radii of 0.2 mm or less with a transmission efficiency of above 90% 40 mm downstream of the aerodynamic lens exit. Even 10 μm particles could be focused with a transmission efficiency of 80%.

Copyright 2013 American Association for Aerosol Research     

Focused Deposition of Nanoparticles on Polymer Film with an Improved TSI-Nanoparticle Sampler (Model 3089)

A two-dimensional array of spots of deposited nanoparticles as small as 7 × 7 μm was fabricated on a polymer film using a modified commercial nanometer aerosol sampler (NAS; TSI-model 3089) coupled with a surface-discharge microplasma aerosol charger (SMAC). The charged aerosol particles were electrostatically focused by a metal mesh (electrically grounded) on the polymer film (insulator) and electrode (3 kV). The effect of mesh geometry on the concentration ratio (focusing ratio × collection efficiency) was evaluated using monodisperse polystyrene latex particles with diameters of 48, 100, and 300 nm. The electrostatic focusing effect was also analyzed by a numerical simulation of the electrostatic field. The two-dimensional patterning of nanoparticles is an effective method in concentrating particles for the subsequent observation and chemical analysis of aerosol particles. In our experiments, the SMAC-NAS system achieved a net concentration ratio of more than 20 times for 48- and 100-nm particles, which would significantly shorten the aerosol-sampling time. The particle deposition patterns formed on a transparent polymer film may provide samples for analyzing the transmittance, luminescence, and other optical characteristics of deposited nanoparticles.

Copyright 2015 American Association for Aerosol Research     

Experimental Investigation of Electrostatic Separators of Plastic Particles using Different Charging Devices

Tribo-electrostatic separation is a clean technology that enables the recycling of plastics contained in granular waste of electric and electronic equipment (WEEE). The granules are first charged using a tribocharging device and then separated in a horizontal intense electric field generated between two vertical electrodes energized with two high-voltage supplies of opposite polarities. The aim of this paper is to perform a comparison between three different tribocharging devices commonly used: the fluidized bed, the static charger, and the tribo-cyclone. The study was carried out using the same granular sample comprising 50% PVC (Polyvinyl chloride) and 50% HDPE (High-density polyethylene) particles of 1–2 mm average granulometric size. In spite that particles acquire higher electric charge using the cyclone device, separation efficiency is better with the fluidized bed device.     

气固错流移动颗粒床过滤器除尘效率

研究了气固错流移动颗粒床过滤器除尘效率与表观过滤气速、颗粒层移动速度、过滤气体粉尘含量的关系,并进一步探讨了粉尘在颗粒层内的沉积对除尘效果的影响.结果表明,颗粒层内粉尘沉积量较低时,沉积的粉尘有效地促进了颗粒层除尘效率的提高,但随粉尘沉积量增大,沉积粉尘的二次飞扬变得严重,其促进效应逐渐减小.在考虑了沉积粉尘对除尘效率影响和颗粒层内粉尘沉积不均匀性的基础上,基于捕集单元的收缩管模型,建立了计算移动颗粒层除尘效率和床层内粉尘沉积分布的数学模型.模型计算结果和实验数据比较表明,在操作气速0.1～0.3m•s^-1范围内,计算值与实验结果吻合较好.据此对除尘效率和床层内粉尘沉积的变化趋势进行了模拟分析.     

Role of bed height and amount of dust on the efficiency of sound‐assisted fluidized bed filter/afterburner

A 40‐mm sound‐assisted fluidized bed filter/afterburner for hot gas clean‐up has been characterized in terms of bed saturation time, total amount of collected particles, fraction of fine particles permanently adhered on the coarse bed particles, and efficiency of using a regeneration strategy based on mechanical (attrition) and/or chemical (combustion) action. Experiments have been carried out at ambient temperature as well as at 850°C, with and without application of sound and varying bed height and amount of dust in the gas flow. The controversial effect of the application of sound: not only enhancement of particles interactions but also increase of fines permanently adhering on bed coarse particles is presented and discussed. A simplified model has been developed to obtain rough predictions of bed height which maximize fine particles capture, bed saturation time, total amount of particles collected in the bed, fraction of fine particles loading present as adhered particles on bed particles. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Surface-collection efficiency of Nuclepore filters for nanoparticles

The flat surface of Nuclepore filters is suitable for observing collected particles with a scanning electron microscope (SEM). However, experimental data on surface-collection efficiency are limited because surface-collection efficiencies cannot be measured directly using aerosol measuring instruments. In this study, the surface-collection efficiencies of Nuclepore filters were determined by establishing the ratio of the number of particles deposited on the surface of the filter visually counted with an SEM to the number of inflow particles counted by a condensation particle counter, using monodispersed polystyrene latex particles (30–800 nm) and silver particles (15–30 nm). Because Nuclepore filters with smaller pore sizes would be expected to produce higher minimum surface-collection efficiency and a higher pressure-drop, 0.08 and 0.2 µm Nuclepore filters were chosen as the test filters in view of both collection efficiency and pressure drop. The results showed that the minimum surface-collection efficiencies of the 0.08 µm pores at face velocities of 1.9 and 8.4 cm·s^?1 were approximately 0.6 and 0.7, respectively, and those of the 0.2 µm pores at face velocities of 1.5 and 8.6 cm·s^?1 were approximately 0.8 and 0.6, respectively. Because the pressure drop of the 0.2 µm pore filter was lower than that of the 0.08 µm pore filter under the same flow-rate conditions, the 0.2 µm pore filter would be more suitable considering the pressure drop and collection efficiency. The obtained surface collection efficiencies were quantitatively inconsistent with theoretical surface-collection efficiencies calculated using conventional theoretical models developed to determine the collection efficiency of filters with larger pores.

© 2016 American Association for Aerosol Research     

Fluidization Characteristics of a Fine Magnetite Powder Fluidized Bed for Density-Based Dry Separation of Coal

Gas-solid fluidized bed separation technique is very beneficial for saving water resources and for the clean utilization of coal resource. The hydrodynamics of 0.15–0.06 mm fine Geldart B magnetite powder were experimentally and numerically studied to decrease the lower size limit. The results show that the static bed height should be controlled near 300 mm (e.g., 300–350 mm). The bubble size, amount, and frequency of the fine particle bed are smaller than those of the bed containing 0.3–0.15 mm large Geldart B particles, thus leading to a higher bed activity. The pressure drop and density of the fine particle bed are uniform and stable, which indicates a good fluidization quality. Furthermore, simulated results are consistent with experimental data, which indicates the correctness and effectiveness of the simulations. The superficial gas velocity should be adjusted to not more than 1.8U _mf for the fine particle bed. Additionally, wide size range magnetite powder, which contains 94.23 wt% < 0.3 mm particles with a 0.3–0.06 mm particles content of 91.38 wt%, was used in an industrial scale modularized demonstration system for 50-6 mm coal density separation. The ash content of feed coal was reduced from 55.35% to 14.67% with a probable error, E, value of 0.06 g/cm^3.     

Improvement of the Nanoparticle Charging Efficiency of a Single-Wire Corona Unipolar Charger by Using Radial Sheath Airflow: Numerical Study

A single-wire corona unipolar charger with radial sheath air was proposed to enhance the nanoparticle charging efficiency. The charger consists of an insulated Teflon tube (inner diameter = 6.35 mm) with a 6 mm-long grounded porous metal tube placed at its center from which radial sheath air is introduced, and a discharge gold wire of 50 μm in the outer diameter and 6 mm in the effective length. The performance of the charger was evaluated and optimized numerically. The effect of the position of the sheath air opening on reducing charged particle loss was found to be important and two designs were studied. In design 1, both ends of the 6 mm wide sheath air opening are aligned with the ends of the 6 mm-long discharge wire, while in design 2 the sheath air opening is shifted 2 mm toward the left of the leading edge of the wire. At the same operating condition, design 2 was found to have less electrostatic loss than design 1 because of its smaller deposition region for charged particles. Compared to two unipolar chargers with the highest extrinsic charging efficiency for particles smaller than 10 nm in diameter, design 2 operated at the applied voltage of +3.5 kV, aerosol flow rate of 0.5 L/min, and sheath airflow rate of 0.7 L/min has a comparable extrinsic charging efficiency of 17.2%–70.5% based on particle number for particles ranging from 2.5 to 10 nm in diameter.

Copyright 2013 American Association for Aerosol Research     

Experimental Study of Aerosol Filtration by the Granular Bed Over a Wide Range of Reynolds Numbers

The collection performance of granular bed filters consisting of uniform spheres with diameters of 0.5–2.0 mm was experimentally studied by using monodisperse aerosol particles ranging from 0.02 to 2 μm in diameter at superficial velocity from 0.4 to 120 cm/s. Based on the experimental data, prediction equations of collection efficiency due to individual mechanical collection mechanisms were obtained, elucidating the influence of the Reynolds number on the particle collection. Furthermore, by assuming the additivity of the individual mechanical collection efficiencies, a prediction equation applicable to the wide range of filtration conditions is proposed.     

Development and Optimization of the Electrostatic Precipitator with Superhydrophobic Surface (EPSS) Mark II for Collection of Bioaerosols

We recently developed an electrostatic collector for bioaerosols that electrostatically deposits biological particles onto a 3.2 mm electrode covered by a superhydrophobic substance. The deposited biological particles are removed and collected by rolling water droplets (20 or 40 microliter) which results in high concentration rates. The collector has been improved further by integrating it with an electrical charger. Here, we describe the development and optimization of the charger and collection chamber, while maximizing collection efficiency and minimizing particle loss. The resulting sampler is made of static dissipative material (e.g., Delrin), is shaped as a closed half cylinder, and is integrated with a charger. The sampler's round top section contains eight carbon fiber brushes (ion sources to charge particles), while its flat bottom section holds a rectangular collection electrode (254 × 3.2 mm) made of pressed carbon fiber and coated with a superhydrophobic material.

The optimized configuration of the EPSS Mark II had a collection efficiency of up to 84% when sampling airborne Escherichia coli at 10 L/min and for 10 min. The bacteria were accumulated in rolling water droplets as small as 20 microliters, and the sampler achieved sample concentration rates of up to 4.2 × 10⁵/min. When the sampler was operated for a longer time period (60 min), its collection efficiency was 72%. The efficiency decrease was most likely due to a reduced particle removal from the electrode, but the difference was not statistically significant. Since the EPSS Mark II shows satisfactory collection efficiency and high sample concentration rate, it could serve as a basis for developing a field-deployable version of the sampler.

Copyright 2015 American Association for Aerosol Research     

Numerical analysis of the dynamics of aerosol inertial collection and aggregation on raindrops

A three-dimensional stochastic model is developed for predicting atmospheric aerosol collection and aggregation on the surface of a falling raindrop at its terminal velocity. Potential flow and viscous flow are assumed as the flow fields in the vicinity of the large and the small raindrops, respectively. The results show that hydrophobic coarse mode aerosols collected by either small raindrops (d_c < 100 μm) or large drops (d_c > 100 μm) form aggregations on the surfaces of drops, and accumulation mode aerosols tend to be captured by the aggregations or hydrophobic coarse particles which have been collected by the drops, and this may significantly enhance the capability of the raindrop for fine aerosol collection. When the aggregation effect is considered in the calculation, fine aerosol efficiency can be promoted by one to two orders of magnitude. Therefore, fine particle collision efficiency by raindrops is underestimated by employing the classical dynamic theory which neglects the particle aggregation effect. However, the collection efficiency of coarse particles remains almost constant with the increase in the amount of particles collected by large drops, while there is only a slight increase in efficiency by small raindrops upon increasing in particle concentration. This implies that the traditional limiting trajectory method can still be used for the calculation of coarse particle collection efficiencies by either small or large raindrops.

Copyright © 2018 American Association for Aerosol Research     

FILTERS AND FILTRATION HANDBOOK 4th Edition (1997) By T. Christopher Dickenson Publisher: Elsevier Advanced Technology The Boulevard,Langford Lane,Kidlington, Oxford OX5 1GB,U.K.

Abstract

Revolving air flow was generated by oblique holes on air distribution board in a fluidized bed dryer. Such a revolving air flow shows a large scale velocity fluctuation in radial as well as tangential directions. This turbulent flow of air can fluidize the inert particles with superior performance than vibrated fluidized bed. The revolving fluidized bed is simpler in fabrication and easier in operation. For two types of inert particles tested, 4 mm glass beads and 4 mm × 5 mm Teflon cylindrical extrudates, the volumetric heat transfer coefficients were found to increase with the liquid feed flowrate and air flow velocity but decrease with the air inlet temperature, height of static bed, and liquid concentration. The revolving fluidized bed gives an increase of volumetric heat transfer coefficient by 1 kW/m³ K, and represents a 15–25% enhancement from ordinary fluidized bed operated at a bed height of 60 mm, bed diameter of 140 mm, superficial air flow velocity of 3.5 m/s, liquid feed (Soya milk) flowrate of 20 mL/min at a concentration of 6.7%, and a temperature ranges of 80–140°C using Teflon extrudates as inert particles.     

A Novel Particle Trap Impactor for Use with the Gas-Quenching Probe Sampling System

A novel particle trap impactor has been developed for use with the gas-quenching probe in order to exclude solid particles from entering into the probe during sampling of gaseous metallic species in fluidized bed combustion conditions. The impactor must be small in size (Ø_impactor ≤ Ø_probe = 45 mm) but capable of collecting a relatively large amount of particles at elevated temperatures. As the first step, the impactor was designed, constructed, and tested at room temperature for KCI aerosol particles. The impactor with a nozzle of 0.95 mm in diameter, in combination with the orifice-to-jet diameter ratio of 1.5 and the ratio of the jet-to-plate spacing to jet diameter at 1.4 yielded a sharp cutoff curve with a maximum collection efficiency of about 0.9 and a √Stk₅₀ value of about 0.22. In addition, the collection efficiency of the impactor was compared with the particle removal efficiency of a filter of the same type as the filter previously used with the gas-quenching probe. The difference from the comparison is very small, indicating that the impactor can be used to replace the filter to prevent fly ash particles from entering the gas-quenching probe in fluidized bed combustion conditions.