High Particle Collection Efficiency Research Articles

Aerodynamic Size-Dependent Collection and Inactivation of Virus-Laden Aerosol Particles in an Electrostatic Precipitator.

Electrostatic precipitators (ESPs) may enable high particle collection efficiency with minimal pressure drop in HVAC systems. However, studies of pathogen collection and inactivation in ESPs at medium to higher flow rates are limited. Here, a single-stage, wire-plate ESP operated at flow rates of 51 and 85 m3 h-1 was used to study the removal of virus-laden aerosol particles for three different airborne viruses: (1) bovine coronavirus (BCoV), (2) influenza A virus (IAV), and (3) porcine reproductive and respiratory virus (PRRSV). Size-resolved measurements of collection efficiency were obtained using Andersen cascade impactors (ACI) sampling upstream and downstream of the ESP. All measurements were analyzed based on three distinctive but complementary methods: (1) fluorimetry to assess physical collection, (2) RT-qPCR to assess viral RNA concentrations and (3) virus titration to assess virus viability. In general, log reductions by virus titration were highest followed by those from RT-qPCR, and last fluorimetry, suggesting that a portion of virus may be potentially inactivated in flight in the ESP. An effective migration (deposition) velocity ranging from 3.10 to 10.05 cm s-1 was also determined using the spatially resolved measurements of virus collection on the ESP plates.

Novel Z-Nanofiber Sheet Mask of High Particle Collection Efficiency, Easy Breathing and Resistant To Water Vapor

Novel Z-Nanofiber Sheet Mask of High Particle Collection Efficiency, Easy Breathing and Resistant To Water Vapor

Improving filtration and pulse-jet cleaning performance of metal web filter media by coating with polytetrafluoroethylene microporous membrane

The metal web filter media has been widely used to purify high-temperature exhaust gas because of its good durability and reliability. Although it has fine high-temperature resistance, its filtration efficiency for fine particles is relatively low. In this study, we developed a new type of composite filter of metal web coated with polytetrafluoroethylene (PTFE) membrane, which combined the high-temperature resistance of the metal web filter and the excellent filtration performance of the membrane-coated filter media. The performance parameters of the composite filter, including pressure drop, filtration efficiency, regeneration efficiency, adhesive force, and high-temperature resistance, were investigated experimentally, and compared with those of the metal web filter and polyester fiber coated with PTFE membrane filter. Although the composite filter yielded a higher pressure drop, it exhibited a high particle collection efficiency. At a face velocity of 10.23cm/s, the filtration efficiency of the composite filter was 99.32 %. This was 1.23 and 0.10 % higher than that of the metal web filter and polyester coated with PTFE membrane filter, respectively. In addition, the composite filter has the characteristics of small cake/fabric adhesion force, low residual pressure drop, high regeneration efficiency, and long cleaning interval. The average cleaning interval and residual pressure drop of the composite filter were 421s and 425.0Pa, respectively, whereas those of the metal web filter were 291s and 658.5Pa, respectively; those of the polyester coated with PTFE membrane filter were 415s and 443.2Pa, respectively. Furthermore, the filtration test at high temperatures and thermogravimetric analysis demonstrated that the composite filter has an excellent thermal stability. At a temperature of 260°C, the average dust emission concentration of the polyester coated with PTFE membrane filter was 2.86 times larger than that of the composite filter (0.532mg/m3).

Deposition of dry particles on a fin-and-tube heat exchanger by a coupled soft-sphere DEM and CFD

In this study, a novel computational model is utilized for investigating fouling of two commonly encountered heat exchanger fin shapes in an air-conditioning application. The computational method utilizes the discrete element method (DEM) coupled with a large-eddy simulation (LES) framework. The fin-and-tube heat exchangers (FTHE) are investigated for three different Reynolds numbers (ReDh=243, 528, 793), three different particle sizes (Dp= 5, 10, 20 µm) and two different adhesive particle types based on the experimental values in the literature. The code is first benchmarked from the CFD and DEM viewpoints. A comprehensive fouling study of the FTHE’s, consisting of altogether 36 simulations, is then carried out. The major numerical findings of the paper consist of the following four features. First, with low adhesive particles, the plain fin shape has a 3.45 higher volume fouling rate with ReDh=793 than at ReDh=264. With the herringbone fin shape, and the low adhesive particles, the volume fouling rate is 1.76 higher with ReDh=793 than at ReDh=264. Second, for the high adhesive particles, the plain fin has a 5.4 times higher volume fouling rate at ReDh=793 than for ReDh=264. The herringbone fin shape has a 3.92 times higher volume fouling rate with the highest Reynolds number of ReDh=793 compared to ReDh=264. Third, high adhesive particles have 3.0 times higher volume fouling rate than low adhesive particles for both fin shapes, all particle sizes and all Reynolds numbers combined. And finally, herringbone fins have 1.74 times higher volume fouling rate than plain fins for low adhesive particles. For high adhesive particles, herringbone has 1.8 times higher volume fouling rate and when both particle types are summed together, herringbone has a 1.78 times higher volume fouling rate than the plain fin shape. As a major finding of the study, the high adhesive particle collection efficiency increases monotonously with the Stokes and Reynolds numbers while low adhesive particle collection efficiency poses a non-monotonous trend.

Design and evaluation of a mini-Faraday cup for portable ultrafine particle sizer

In this study, a mini-Faraday cup for portable ultrafine particle sizer was designed, which consisted of a cylindrical metal case, a filter holder, a Teflon insulator, and an internal metal filter. In order to achieve high particle collection efficiency, a disc structure of metal filter was adopted in the proposed Faraday cup. Moreover, a high sensitive weak current amplifier was used and a spring probe electrode instead of the copper wire connecting between the Faraday cup and the weak current amplifier was used to eliminate the noise generated by vibration. The performance of Faraday cup electrometer was evaluated by a series of experiments. The results of the experiments showed that the current values of 220 nm charged particles for different number concentrations measured by the Faraday cup have good linear correlation, since the Adj. R-Square and the Pearson’s correlation coefficient are greater than 0.98 and 0.99, respectively. And the experimental results of the prototype Faraday cup electrometer for particles ranging from 50 to 300 nm agreed well with the theoretical results. The comparative test between the self-developed aerosol electrometer and commercial electrometer were also presented. There was a good linear relationship between the current values measured by the two instruments. The self-developed mini-Faraday cup electrometer had advantages of high particle collection efficiency, small in size and light in weight, which was suitable for the portable measurements of atmosphere ultrafine particle.

Electrostatic Precipitation of Submicron Particles with an Enhanced Unipolar Pre-Charger

A two-stage electrostatic precipitator (ESP) has been developed using an enhanced unipolar pre-charger with dielectric coated ground electrodes. The electrical and particle collection performance was evaluated for particles in the submicron range. By varying the voltage applied to the pre-charger, the particle charging characteristics was compared with that calculated by the theoretical model. The experimental results show that with the adoption of the pre-charger, the charging of the particles at submicron range was enhanced. Further results indicate that the collection efficiency can be improved by about 12.1%–15.9%, compared with the results obtained without the pre-charger. Higher particle collection efficiency can be achieved by increasing the voltage applied to the pre-charger. The unipolar pre-charger studied in this paper proves to be a simple and useful device to improve the submicron particle collection efficiency of conventional ESPs.

PIV Analysis of Particle Behavior in Electrostatic Precipitator

SUMMARYAn electrostatic precipitator (ESP) is a means to collect particulate matter (PM). They are characterized by a high total particle collection efficiency with a low pressure drop. The particle behavior in ESP depends on the particle characteristic, electric field, space charge, and flow pattern. It is important to understand the particle behavior in ESP. Particle image velocimetry (PIV) was used to grasp the particle behavior in ESP. In this paper, results of PIV of the particle flow velocity fields in a wire‐to‐plate type ESP model are presented. The ESP was an acrylic parallelepiped with a wire electrode and plate collecting electrode. The positive and negative dc voltages were applied to the wire electrode, placed at right angles to the main gas flow. The obtained results show that the particle flow velocity was increased with increasing discharge current. This is attributed to increase in ionic wind. The particle velocity right under of the wire electrode was the fastest.

Electrospun Magnetic Nanoparticle-Decorated Nanofiber Filter and Its Applications to High-Efficiency Air Filtration.

Filtration technology has been widely studied due to concerns about exposure to airborne dust, including metal oxide nanoparticles, which cause serious health problems. The aim of these studies has been to develop mechanisms for the continuous and efficient removal of metal oxide dusts. In this study, we introduce a novel air filtration system based on the magnetic attraction force. The filtration system is composed of a magnetic nanoparticle (MNP)-decorated nanofiber (MNP-NF) filter. Using a simple electrospinning system, we fabricated continuous and smooth electrospun nanofibers with evenly distributed Fe3O4 MNPs. Our electrospun MNP-NF filter exhibited high particle collection efficiency (∼97% at 300 nm particle size) compared to the control filter (w/o MNPs, ∼ 68%), with a ∼ 64% lower pressure drop (∼17 Pa) than the control filter (∼27 Pa). Finally, the filter quality factors of the MNP-NF filter were 4.7 and 11.9 times larger than those of the control filter and the conventional high-efficiency particulate air filters (>99% and ∼269 Pa), respectively. Furthermore, we successfully performed a field test of our MNP-NF filter using dust from a subway station tunnel. This work suggests that our novel MNP-NF filter can be used to facilitate effective protection against hazardous metal oxide dust in real environments.

Design and development of an Electrostatic Screen Battery for Emission Control (ESBEC)

Current diesel particulate filters (DPFs) can effectively capture the exhaust particles, but they add to engine backpressure and accumulate particles during their operation, which results in the need to regenerate the DPFs by burning off the collected particles periodically. This regeneration results in aerosol emissions, especially in the 10–30 nm size range and contributes to ultrafine particle pollution. In this research, we designed and developed a prototype of a novel diesel exhaust control device: the Electrostatic Screen Battery for Emissions Control (ESBEC). The device features high particle collection efficiency without adding to the exhaust backpressure and without the need for thermal regeneration of the collected particles. The ESBEC consists of a series of metal mesh screens coated with a superhydrophobic substance and an integrated carbon fiber ionizer to charge the incoming particles. Multiple pairs of screens (e.g., 5 pairs) are arranged in a battery, in which one screen of each pair is supplied with high voltage, and the other is grounded, producing electrostatic field produced across the screens. The application of a superhydrophobic coating onto the screens allows easy removal of the collected particles using liquid without the need for thermal regeneration. The current prototypes of the device were tested with fluorescent polystyrene latex (PSL) particles of 0.2 and 1.2µm in size and at 25 and 105L/min sampling flow rates. The average collection efficiency was ~87% for 0.2µm and ~95% for 1.2µm PSL particles. In addition, the ESBEC was tested with actual diesel exhaust particles; here its performance was verified by visually inspecting deposition of particles on an after-filter with the device ON and OFF. In the next stages of this work, the ESBEC will be challenged with diesel exhaust at different mass concentrations and for different collection time periods.

Pulse-Jet Bag Filter Performances for Treatment of Submicronic and Nanosized Particles from Waste Incineration

The main objectives of this study were to develop an experimental set-up to perform clogging/unclogging tests on a single baghouse fabric filter, and to evaluate its filtration performance regarding submicronic and nanosized particles, for operating conditions as close as possible to those found in real-scale waste incineration facilities in terms of gas flowrate, temperature and humidity, inlet concentrations for both the dust and the sorbent, the pressure and duration of the cleaning pulse-jet. The performances of a bag filter during several clogging/unclogging cycles were evaluated regarding the filtration of a submicronic aerosol whose particle size distribution is representative of nanowaste incineration emissions at the boiler outlet. In order to reproduce the real operating conditions in the flue gas treatment line, the airflow and the bag filter were heated to 150 °C and the filtration unit was insulated. The water content was maintained in the airflow in the range of 10–12% (i.e. 3% relative humidity) by water injection and the filtration velocity throughout the bag filter was 2 cm/s. Moreover, a mix of suspended particles of activated carbon and sodium bicarbonate, used in flue gas treatment lines mainly for dioxin/furan and acid gas removal, were generated simultaneously with the submicronic aerosol. The results showed a high total particle collection efficiency of the bag filter, which increased rapidly with clogging from 98 to 99.99%. Particles with a diameter of 90 nm were the most penetrating across the filter, for which the fractional efficiency reached a minimum value of 97.5%. These results demonstrated the effectiveness of bag filters for submicronic and nanosized particle filtration in industrial conditions for the treatment of waste incineration fumes.

Novel Wire-on-Plate Electrostatic Precipitator (WOP-EP) for Controlling Fine Particle and Nanoparticle Pollution.

A new wire-on-plate electrostatic precipitator (WOP-EP), where discharge wires are attached directly on the surface of a dielectric plate, was developed to ease the installation of the wires, minimize particle deposition on the wires, and lower ozone emission while maintaining a high particle collection efficiency. For a lab-scale WOP-EP (width, 50 mm; height, 20 mm; length, 180 mm) tested at the applied voltage of 18 kV, experimental total particle collection efficiencies were found as high as 90.9-99.7 and 98.8-99.9% in the particle size range of 30-1870 nm at the average air velocities of 0.50 m/s (flow rate, 30 L/min; residence time, 0.36 s) and 0.25 m/s (flow rate, 15 L/min; residence time, 0.72 s), respectively. Particle collection efficiencies calculated by numerical models agreed well with the experimental results. The comparison to the traditional wire-in-plate EP showed that, at the same applied voltage, the current WOP-EP emitted 1-2 orders of magnitude lower ozone concentration, had cleaner discharge wires after heavy particle loading in the EP, and recovered high particle collection efficiency after the grounded collection plate was cleaned. It is expected that the current WOP-EP can be scaled up as an efficient air-cleaning device to control fine particle and nanoparticle pollution.

Effect of ring shape attached on upper outlet pipe on fine particle classification of gas-cyclone

The effect on particle collection efficiency of a ring attached to the upper part of the outlet pipe of a gas cyclone was examined by experiment and CFD simulation. From a visualization experiment using fine bubble foam and CFD simulation, the rotational recirculation region is at maximum near the upper plate and the region decreases to the lower position. For the tapered shape ring of type Dc, the cyclone pressure drop is minimum, because the rotational recirculation region is almost eliminated by use of this special ring. The 50% cut size of the tapered shape ring of type Dc shows a minimum value and maximum particle collection efficiency is obtained. For the tapered shape ring, the optimum wall thickness ratio of the upper part to lower part is 1.47 and maximum particle collection efficiency and minimum pressure drop is simultaneously realized by use of the type Dc ring. The average downward fluid velocity in the upper part of the cyclone for the type Dc ring is greater than that of the case without the ring. Particles tend to go toward the downward direction easily and high particle collection efficiency is achieved for this special ring. The experimental partial separation efficiency qualitatively agreed with the simulation results.

Filtration performance evaluation of depth filter media cartridges as function of layer structure and pleat count

Abstract Depth filter media are characterized by their multiple-layer structures. Three main parameters indicate the filtration performance of the filter media: initial pressure drop, dust loading characteristics and particle collection efficiency. Four samples of three-layer structure depth filter media with different upstream and downstream layers were prepared to evaluate the effects of layer structure on filtration performance. The filtration performance of these media was closely observed by testing filter cartridges of the same dimensions. The results indicate a slow increase in pressure drop due to uniformly distributed particle loading inside the filter media and a high particle collection efficiency of the cartridge with new depth filter media. This media combines a bulky upstream layer and a final layer of high collection efficiency, giving both satisfactory filtration performance and quality factor values.

The Predictive Method for the Submicron and Nano-Sized Particle Collection Efficiency of Multipoint-to-Plane Electrostatic Precipitators

The multipoint-to-plane electrostatic precipitator (ESP) is one type of ESP devices used for the sampling and control of nanoparticles and sub-micron particles, with the advantage of a low pressure drop and high particle collection efficiency. Several empirical equations for predicting the particle collection efficiency are available in the literature, but most of them are only applicable to wire-in-plate ESPs. For ESPs with different discharge electrodes, the empirical equations are different since the ion concentration and electric fields are different. In this paper, a predictive method is developed to calculate the particle migration velocity and the particle collection efficiency equation η(%) of multipoint-to-plane ESPs in the form of η(%) = {1 – exp{–[β1(NDeβ2) + β3(NDe) + β4]}} × 100%, in which β1, β2, β3 and β4 are regression coefficients and NDe is the Deutsch number determined by the particle migration velocity. Good agreement is obtained between the present model predictions and the experimental particle collection efficiencies obtained from the literature. It is expected that the present model can be used to facilitate the design of efficient multipoint-to-plane ESPs for nanoparticle and sub-micron particles removal in the future.

Usability of cyclone separators as air filters in vehicles

This study deals with the use of cyclone separators as air filters in light or heavy duty vehicles. Cyclone separators were compared with the conventional air filters, which provide low particle collection efficiency with high pressure drop, and these characteristics are made worse by contamination. By taking into account the related studies in the literature, tangential inlet cyclones were considered in this comparison. The pressure drop and particle collection efficiency in the proposed tangential inlet cyclone were computed by using the mathematical models given in the literature. Comparison of the computed results of the cyclone with the conventional air filters demonstrated that the tangential inlet cyclones are advantageous because of low pressure drop and high particle collection efficiency and can be used as main or pre-filters in vehicles.

A study of ionization and collection efficiencies in electrospray-based electrostatic precipitators

Ozone-free electrostatic precipitators incorporating an array of electrospray wick charged aerosol ionization sources were built and tested. The particle ionization and collection efficiencies were independently measured for airborne particles as a function of air flow rate, electric field magnitude, and particle size. The results indicate that, while particle ionization efficiencies near 100% can be achieved using the electrospray ionization method, the number of elemental charges deposited onto a given particle depends strongly on the particle diameter and for submicron particles is very low. High overall particle collection efficiency, therefore, requires a carefully designed precipitation region where the maximum particle collection time, associated with the particles with the lowest mobility, is less than the residence time within the collector.

Influence of leaks in surface filters on particulate emissions

Compliance with severe limit values of dust emissions is a main characteristic of surface filters. This characteristic is due to the high particle collection efficiency of surface filters. Beside regular operation it is necessary to consider phenomena such as a “pinhole” bypass through leaks in surface filters to ensure the above mentioned compliance with the limit values at all times. Experimental research has been carried out to observe and understand the “pinhole” bypass through leaks and the behaviour of pinholes over filtration time. To work out the influence of different filtration conditions the parameters pinhole diameter, filter face velocity and dust cake thickness were varied. The results can be explained by formulas usually used to calculate volumetric flow rates of orifice gauges. The experiments and the calculations lead to the conclusions that bigger pinholes decrease the collection efficiency and higher filter face velocities increase the collection efficiency of pinholed filter media.

Collection characteristics of low-pressure impactors with various impaction substrate materials

The effects of types of low-pressure impactors (DLPI; Dekati; referred to hereinafter as “LPI”; and NanoMOUDI-II; MSP) and impaction substrate materials (aluminum foils, quartz fiber filters, and polycarbonate filters) on mass size distribution were studied for diesel exhaust particles from dynamometer test (DEP) and roadside atmospheric particles for a better understanding in terms of chemical analysis of impactor sample. Particle mass size distribution measured with LPI using aluminum foils and polycarbonate filters was distorted toward smaller mode diameters than those measured with NanoMOUDI using aluminum foils in sampling DEP and roadside atmospheric particles. This difference is explained by the occurrence of particle blow off in LPI. Heavy loading due to high concentrations in a specific size range results in greater particle loading height, from which particles are easily blown off by high jet velocities. Mass size distribution of DEP measured with LPI using a quartz fiber filter was modified to larger mode diameter than that measured with NanoMOUDI using aluminum foils. Higher particle collection efficiency than the ideal condition and smaller particles than the calibrated size, collected on upper stages, resulted in larger mode diameter, owing to the occurrence of filtration as well as impaction, and a shorter jet-to-plate distance, owing to the thickness of the filter. On the other hand, mass size distribution of roadside atmospheric particles measured with LPI using quartz fiber filters was similar to that measured with NanoMOUDI using aluminum foils. It is possible that the artifact of filtration is not important because of lower particle concentrations in the roadside atmosphere than in DEP. This experimental study of mass size distributions with various impactor types and substrate materials will enhance our understanding of the size distribution of chemical components, because impaction substrate material is restricted from methods of chemical analysis even though each substrate material has different collection characteristics.

The effect of a new method of fluid flow control on submicron particle classification in gas-cyclones

The purpose of this paper is to study the effects of a secondary flow injection method on submicron particle separation in a cyclone. It is found that particle collection efficiency increased with an increased secondary flow rate in the upper cylindrical section of the cyclone.In order to achieve a high particle collection efficiency, the location of the secondary flow injection should be close to the upper plate and a high injection velocity should be used.The use of a newly developed cyclone (type A) resulted in a high particle collection efficiency. Nearly all particles are collected by the secondary injection fluid flow. Three-dimensional simulation results are qualitatively agreed with the experimental data.

乾式サイクロンの局所的な流動制御による分級性能の向上

The present work studied the effectiveness of secondary flow injection into a cyclone on the separation performance of sub-micron particles. The particle collection efficiency increased with the secondary flowrate when injected in the upper cylindrical section of the cyclone. It was found that high particle collection efficiency is attained when the injection location of the secondary flow is close to the upper plate at a high flow velocity. A new type of cyclone developed based on these results achieved a high collection efficiency, which was in qualitative agreement with the three-dimensional simulation results.