Removal Of Airborne Particles Research Articles

Electric-field activating on-surface tailored (OST) coarse polyester fibers for efficient airborne particle removal: Interfacial morphologies and electrical response

Fibrous filtration is the most-used method for indoor particulate matter (PM) removal. The filtration performances are governed by filters’ intrinsic geometries, displaying the tradeoff among efficiency, resistance, and lifespan. In this contribution, we provided a chemically-synthesized strategy to improve the performance of coarse filters while preserving their ultralow initial resistances. After elucidating PM-fiber interactions, the fibrous interfacial nano-morphologies were tailored by different dielectric coatings based on commercially-available substrates. Activated by fiber polarizing, the tuned morphologies with ∼100 nm surface roughness and enhanced electrostatic potential are considered the drivers of boosted filtration efficiency. In practice, a 10-mm-thick polydopamine (PDA)-MnOx coated polyester filter possessed an improved efficiency of 97.7 % for 300–500 nm particles, and the ultralow resistance of 11.2 Pa at 0.5 m/s filtration velocity. The strong surface adhesion facilitated long-term efficiency of 95.6 % in a continuous 25-day period without any decay. The nanoscale coatings, which were just one-thousandth in thickness of the fiber gaps, enabled more than 50-fold improvement of the filters’ quality factor. We further established dimensionless factors to evaluate the cost-performance effect. We expect the strategy and techniques can pave the way to better understand electrostatic air filtration, being competitive candidates in the air filtration community.

Fabrication of Poly(Lactic Acid)@TiO2 Electrospun Membrane Decorated with Metal-Organic Frameworks for Efficient Air Filtration and Bacteriostasis.

The development of high-performance filtration materials is essential for the effective removal of airborne particles, and metal-organic frameworks (MOFs) anchored to organic polymer matrices are considered to be one of the most promising porous adsorbents for air pollutants. Nowadays, most air filters are generally based on synthetic fiber polymers derived from petroleum residues and have limited functionality, so the use of MOFs in combination with nanofiber air filters has received a lot of attention. Here, a conjugated electrostatic spinning method is demonstrated for the one-step preparation of poly(lactic acid) (PLA) nanofibrous membranes with a bimodal diameter distribution and the anchoring of Zeolitic Imidazolate Framework-8 (ZIF-8) by the introduction of TiO2 and in situ generation to construct favorable multiscale fibers and rough structures. The prepared PLA/TZ maintained a good PM2.5 capture efficiency of 99.97%, a filtration efficiency of 96.43% for PM0.3, and a pressure drop of 96.0 Pa, with the highest quality factor being 0.08449 Pa-1. Additionally, ZIF-8 was uniformly generated on the surface of PLA and TiO2 nanofibers, obtaining a roughened structure and a larger specific surface area. An enhanced filtration retention effect and electrostatic interactions, as well as active free radicals, can be generated for the deep inactivation of bacteria. Compared with the unmodified membrane, PLA/TZ prepared antibacterial characteristics induced by photocatalysis and Zn2+ release, with excellent bactericidal effects against S. aureus and E. coli. Overall, this work may provide a promising approach for the development of efficient biomass-based filtration materials with antimicrobial properties.

Investigation of the Influence of Data Collection and Analysis Procedures on Aerosol Filtration Model Development

Fibrous air filters are common devices used to remove airborne particles. Their performance is typically measured through their resistance to airflow and captured particle mass. Models describing the evolution of filter performance have been heavily researched; however, the need for improvement remains. Experimental work is irreplaceable in the development of high-fidelity models, yet the estimation of necessary variables is not trivial and may be influenced by selected measurement instruments and analysis methodologies. Therefore, the purpose of this work is to propose a framework to investigate the response of common aerosol measurement instruments, their corresponding analysis methodologies, and the application of their data. A Scanning Mobility Particle Sizer (SMPS) and Laser Aerosol Spectrometer (LAS) were selected for consideration, and their recorded data were compared against baseline measurements. The results of the experiments indicated that the SMPS and LAS yielded a ratio of estimated mass concentrations to the baseline mass concentrations of approximately 1.175 and 0.749, respectively. Regarding the SMPS, it was suggested that the measurable size range, application of a coverage factor, dynamic shape factor, and association between the curve fits and histograms were influential in the final estimates. For the LAS, the application of a curve fit, its association to the histograms, and the selection of the sampling periods were influential. Considering the results, the impact of these factors may not be considered negligible and may skew reproducibility between studies and fossilize confounding factors. Therefore, the proposed methodologies are useful in addressing potential errors in data collection and analysis.

Portable Air Purifiers’ Predicted Efficacy in Mitigating Airborne Pathogen Transmission in an Office Room Featuring Mixing Ventilation

Portable air purifiers have been extensively used to improve indoor air quality and mitigate the transmission of airborne diseases. However, the efficacy of mitigation is strongly affected by the interactions between jet flows of processed air from the air purifiers and the background airflows driven by the ventilation system. Critical factors in this context include the position and capacity of air purifiers and the ventilation rate of the heating ventilation and air-conditioning (HVAC) system. These factors are investigated in this study via computational fluid dynamics (CFD) simulations and the infection probability for different scenarios is quantified using the latest airborne infection predictive model incorporating recent pathological and clinical data for SARS-CoV-2. The results show that the use of air purifiers can significantly reduce the concentration of particulate matter, thus contributing to a generally lower risk of airborne transmission. However, the position of air purifiers affects their overall efficacy remarkably. Comparatively, a central HVAC system is more efficient at removing airborne particles under an equivalent ventilation rate assuming it uses a mixing ventilation scheme.

Numerical investigation of airborne transmission in low-ceiling rooms under displacement ventilation

This study employs computational fluid dynamics (CFD) simulations to evaluate the risk of airborne transmission of COVID-19 in low-ceiling rooms, such as elevator cabins, under mechanical displacement ventilation. The simulations take into account the effects of the human body’s thermal environment and respiratory jet dynamics on the transmission of pathogens. The results of the study are used to propose a potential mitigation strategy based on ventilation thermal control to reduce the risk of airborne transmission in these types of enclosed indoor spaces. Our findings demonstrate that as the ventilation rate (Qv) increases, the efficiency of removing airborne particles (εp) initially increases rapidly, reaches a plateau (εp,c) at a critical ventilation rate (Qc), and subsequently increases at a slower rate beyond Qc. The Qc for low-ceiling rooms is lower compared to high-ceiling rooms due to the increased interaction between the thermal plume generated by the occupants or infectors and the ventilation. Further analysis of the flow and temperature fields reveals that εp is closely linked to the thermal stratification fields, as characterized by the thermal interface height and temperature gradient. When Qv < Qc, hT,20.7 < him (him is the height of infector’s mouth) and aerosol particles are injected into the upper warm layer. As Qv increases, the hti also increases following the 3/5 law, which helps displace the particles out of the room, resulting in a rapid increase of εp. However, when Qv > Qc, hT,20.7 > him and aerosol particles are injected into the lower cool layer. The hti deviates from 3/5 law and increases at a much slower rate, causing an aerosol particle lockup effect and the εp to plateau. In addition, as the Qc increases, the local flow recirculation above the infector head is also enhanced, which leads to the trapping of more particles in that area, contributing to the slower increase in εp. The simulations also indicate that the location of infector relative to ventilation inlet/outlet affects Qc and εp,c with higher Qc and lower εp,c observed when infector is in a corner due to potential formation of a local hot spot of high infection risk when infector is near the ventilation inlet. In conclusion, based on the simulations, we propose a potential ventilation thermal control strategy, by adjusting the ventilation temperature, to reduce the risk of airborne transmission in low-ceiling rooms. Our findings indicate that the thermal environment plays a critical role in the transmission of airborne diseases in confined spaces.

Foliar dust particle retention and metal accumulation of five garden tree species in Hangzhou: Seasonal changes

As particulate matter and heavy metals in the atmosphere affect the atmospheric quality, they pose a threat to human health through the respiratory system. Vegetation can remove airborne particles and purify the atmosphere. Plant leaves are capable of effectively absorbing heavy metals contained by particulates. To evaluate the effects of different garden plants on the particulate matter retention and heavy metal accumulation, the seasonal changes of dust retention of five typical garden plants were compared in the industrial and non-industrial zones in Hangzhou. Results revealed that these species differed in dust retention with the descending order of Loropetalum chinense > Osmanthus fragrans > Pittosporum tobira > Photinia × fraseri > Cinnamomum camphora, which were related to the microstructure feature of the leaf. These species also showed seasonal variation in dust retention, with the highest in summer, followed by winter, autumn, and spring, respectively. The total suspended particle per unit leaf area was higher in the industrial site (80.54 g m−2) than in the non-industrial site (19.77 g m−2). Leaf particles in different size fractions differed among species, while coarse particles (d > ten μm) predominated in most cases. The L. chinense and C. camphora plants accumulated the greatest Pb and Ni compared to other plants. Overall, L. chinense was the best suitable plant species to improve the air quality.

Effect of Ozone Gas on Removal of Airborne Particles.

Objective Airborne particles are one of the most important factors in the spread of infectious pathogens and must be monitored in healthcare facilities. Viable particles are living microorganisms, whereas non-viable particles do not contain microorganisms but act as transport for viable particles. The effectiveness of ozone in reducing these particles in a non-controlled room and a controlled cleanroom using high-efficiency particles air (HEPA) filter was analyzed in this study. Materials and Methods Viable particles and non-viable particles sized 0.5 and 5 μm were quantified before and after ozonation in two different health environments: non-controlled (group 1) and controlled area, which was associated with a HEPA filtering system (group 2). Active air sampling using a MAS 100 was used to count the number of viable particles, while the number of non-viable particles/m 3 was obtained following the manufacturer's recommendations of the Lasair III 310C system. Results Our results of the viable particles counting were not quantifiable and analyzed using statistical tests. Both groups showed a slight tendency to reduce the number of viable particles after ozonation of the environmental air. A statistically significant reduction of non-viable 5 μm particles after ozonation was observed in both groups (G1: p = 0,009; G2: p = 0,002). Reduction in the non-viable 0.5 μm particles after ozonation was observed only in group 2, associated with the HEPA filter. In group 1, after ozonation, a significant increase in 0.5 μm particles was observed, probably due to the breaking of 5 μm particles by ozone gas. Our results suggest that ozone gas can break 5 μm particles and, when associated with a HEPA filter, increases its effectiveness in removing 0.5 μm particles. Conclusion Considering that 5 μm particles are important in the air transport of microorganisms, their reduction in the environment can be a relevant parameter in controlling the dissemination of infections.

Diffusion characteristics of the industrial submicron particle under Brownian motion and turbulent diffusion

The industrial release of submicron aerosol particles at workplace could cause undue health effect on workers. To effectively capture and remove airborne particles, we need to study the characteristics of various interactive particle motion forces (drag force, Brownian force, Saffman lift force, etc.) and the dispersion of these aerosol particles in indoor air. In this study, the dominant force of submicron particles was determined by calculating the acting forces with different particle sizes. Then, a Discrete Particle Model (DPM) was used to calculate the trajectory of particle movement in turbulent thermal plume flow. Horizontal dispersity ( DH) was defined to evaluate the horizontal diffusion of the particulate matter. The impact of different particle diameters, heat source temperatures and initial relative velocities on DH was investigated. This study showed that the main acting forces for submicron aerosol particles were drag force, Brownian force, Saffman lift force and thermophoresis force. Brownian force cannot be ignored when the particle diameter was below 0.3 µm, which would promote the irregular movement of particles in space and enhance their diffusion ability. The smaller the particle size, the higher the heat source temperature and the lower the particles' initial velocity would lead to the increase of DH.

Visualisation and numerical analysis of laser powder bed fusion under cross-flow

As well as preventing oxidation, a cross-flow of inert gas over the powder bed extracts process by-products, making it critical for process repeatability and build quality during the additive manufacturing of metallic parts. In this study, high-magnification schlieren imaging was employed to visualise the interactions between the cross-flow, laser plume and individual powder particles for the first time. Novel 3D multiphysics simulations of the cross-flow, including the vapour jet and laser plume, were used to calculate energy, momentum and species transport over the processed area in order to understand and quantify the observed interactions. During processing, metallic fumes as well as a significant number of airborne powder particles and agglomerates were observed to remain close to the powder bed, over the scanned area. These particles interact in a range of stochastic collisions that affect the build consistency. Refractive index gradients were formed in the atmosphere above the island scans, which extended many tens of mm beyond the processing area. The rate of extraction of these by-products, regulated by the velocity of the cross-flow, was related to the quality of the builds. A cross-flow perpendicular to the laser scan direction was observed to remove airborne particles from adjacent laser scans most effectively, limiting laser-particle and particle-particle interactions. The model demonstrated that the refractive index gradients away from the vapour jet are due to the metal concentration rather than the temperature of the heated gas.

Impact of multilayering on the filtration performance of clean air filter media

AbstractFibrous filter media are commonly used to remove airborne particles that are harmful to human health and the environment. Although filter media are often multilayered for various reasons, no systematic study of the impact of multilayering on filter media performance has been reported. In this paper, direct numerical simulations with the lattice Boltzmann method are used in order to shed light on the impact of multilayering on the performance of clean bimodal fibrous filter media in a Stokes flow regime. Virtual model clean filter media with up to eight layers and various fibre formulations are compared in terms of permeability or pressure drop, capture efficiency, and quality factor. A careful analysis of the results revealed that multilayering had no statistically significant impact on the performance of the clean filter media. At best, the impact of multilayering was similar to that of the inherent variability of such random structures. Fibre formulation was found to be a more efficient way of improving the performance of the filter media. Placing interlayered air gaps between fibrous layers also slightly improved the quality factor by facilitating the flow at the interfaces of the fibrous layers. These findings will guide future studies on the performance of multilayered filters with more complex flow conditions, such as those encountered with inertial or nanofibre‐made filter media and with the fouling of filter media.

The nasal tent: an adjuvant for performing endoscopic endonasal surgery in the Covid era and beyond.

PurposeTo propose a cost-effective reproducible barrier method to safely perform endoscopic endonasal surgery during the Covid-19 pandemic.MethodsThis manuscript highlights the use of a clear, cost-effective disposable plastic sheet that is draped as a tent over the operating area to contain aerolization of particles. This is then connected to a suction to remove airborne particles and thus reduce transmission of the virus.ConclusionThe use of a nasal tent is a simple and affordable method to limit particle spread during high-risk aerolisation procedures during the Covid era and beyond.

Characteristics of dust-collection efficiency and ozone emission by high-voltage electrode shape of electrostatic precipitator for subway tunnel environment

The air pollution level of particulate matters in subway tunnel environments is severe. The present study conducted experimental measurements and analyses on dust-collection efficiencies and ozone emission rates in a lab-scale wind tunnel to determine a high-voltage electrode shape suitable for an electrostatic precipitator to remove airborne particles in subway tunnels. Six high-voltage electrode shapes (saw-type, few-saw-type, short-saw-type, tree-type, wave-type, and spike-type) were tested. The results indicate that while breakdown voltage of the spike-type high-voltage electrode was 66 % of other electrode shapes, its dust-collection efficiency per unit voltage was similar to that of other electrode shapes. However, the dust-collection efficiency per unit of power in the spike-type high-voltage electrode was significantly low. Moreover, the wave-type high-voltage electrode shape had 20 % lower dust-collection efficiency than the saw-type and tree-type high-voltage electrode shapes under conditions of low voltage and high flow velocities. Ozone emission rates for all shapes increased proportionally to the electric current. However, ozone emission rates for each high-voltage electrode shape are varied as 12–23 μg/s per mA. The saw-type and tree-type high-voltage electrode shapes were superior in terms of dust collection, 90 % collection efficiency was shown at about 1.5 W/(m/s)2. The saw-type had a lower ozone emission rate (16.4 μg/s per mA) than the tree-type (19.6 μg/s per mA). Thus, the saw-type shape was the most suitable as a high-voltage electrode in the electrostatic precipitator for removing airborne particles in a subway. The results also indicate that both dust-collection efficiencies and ozone emission rates should be evaluated concurrently when evaluating electrostatic precipitator high-voltage electrodes.

A new pin-to-plate corona discharger with clean air protection for particulate matter removal

Abstract High concentration particulate matter (PM) has been a serious environmental problem in China and other developing countries. Electrostatic-based purification technology is a method to remove airborne particles, and can reduce the energy consumption of ventilation fans in buildings because of its low pressure drop. In this study, we developed a new pin-to-plate corona discharger with particle-free external air protection to prevent particles polluting the surface of discharge pins. By using an optical microscope, we observed a certain number of particles deposited on the non-protected (exposed pins) and few particles deposited on the protected pins after they operating for 3 weeks. We experimentally studied the long-term performances of the exposed and protected pins in single-pass PM removal efficiency and ozone production. The results showed that the protected pins produce less ozone and have higher breakdown voltage than the exposed pins. Experimental results indicated that the improved pin-to-plate corona discharger has better long-term performance and is safer than the exposed one. The results of the research can give an understanding of how to improve electrostatic-based purification technologies toward stable discharging for high removal efficiency of particles.

Enhancement of Airborne Particles Removal in a Hospital Operating Room

This article presents the results of a numerical study to examine the transport of particles in an operating room equipped with an Econoclean ventilation system. Its aims are to reduce the number of particles falling onto the operating table. A simplified CFD model of the operating room was developed and validated based on the measured air velocity distribution. An SST k-ω turbulent flow model was used to simulate the airflow, while a discrete phase model was used to simulate the movement of the airborne particles. The effects of the standing posture of the surgical staff on the settlement of the particles on the operating table were examined. Results show that under the present ventilation system, when the surgical staff bend forward at an angle of 45°, the number of airborne particles that tend to fall onto the operating table increased by 1.4-fold. Adding an exhaust grille to the operating room does not have any significant effects on the distribution of the airborne particles. However, when a larger air supply diffuser is also used, the number of airborne particles that settled on the operating table was reduced 4-fold. More airborne particles are transported towards the exhaust grilles, and more airborne particles accumulate below the operating table. The present study shows that the usage of large air supply diffuser in the operating room is capable of reducing the number of airborne particles fall onto the operating table. Also, it enhances the efficiency of airborne particle removal.

Experimental and numerical investigation of submicron particle deposition enhancement by patterned surface

Exposure to inhaling airborne particles in indoor and outdoor environments is a threat to public health. Indoor air passes through ventilation ducts and continuously circulates with the air outdoors, resulting in a higher concentration of suspended particles in indoor environments when compared to outdoor environments. Thus removing airborne particles in ventilation ducts becomes essential, especially in large buildings. Repeated surface ribs have been reported to greatly enhance the particle collection efficiency while it also causes a significant pressure drop, leading to higher energy consumption. In this study, an overall efficiency ratio is defined, taking into consideration the particle removal rate and the associated pressure drop, to evaluate the overall performance of different surface patterns in a ventilation duct. After the design and optimization processes, the semi-circular patterns are shown to have the best overall efficiency, i.e. a 1137 times increase when compared with having no patterned surface. The deposition velocity on the semi-circular surface found in simulation results were validated with a fully-developed wind tunnel experiment. This study shows that semi-circular surface patterns with a pitch-to-height ratio of 4 are recommended for the overall enhancement in the ventilation duct, especially for capturing submicron particles.

Filtration of airborne particles by a trickle granular bed: a modelling approach

ABSTRACT The removal of airborne particles was investigated using a trickle granular bed. This filtration process maintains a constant pressure drop during particles loading, which makes it an interesting alternative for aerosol filtration. In order to establish mathematical models for the design of the process, a modelling approach that takes into account the changes of the bed characteristics due to the liquid hold up is undertaken. This approach allows predicting the pressure drop and the filtration efficiency of the trickle granular bed, based on the assumption that the bed porosity decreases and the collectors diameter increases with increasing the liquid flow rate. The model predictions are in agreement with experimental data. For particles with diameters around 100 nm the collection efficiency presents a minimum. For smaller particles the collection efficiency increases as the dominating collection mechanism is Brownian diffusion. In the micronic range the collection is governed by inertial and interception mechanisms and consequently increases with increasing the particle size.

Microorganism-ionizing respirator with reduced breathing resistance suitable for removing airborne bacteria

In this paper, we have demonstrated the feasibility of using microorganism-ionizing respirators with reduced breathing resistance to remove airborne bacteria. Using a miniaturized corona ionizer and two pairs of separator electrodes, airborne bacteria were ionized and removed from the airflow. Two microorganism-ionizing respirator designs were experimentally evaluated with flow rates ranging from ∼10 to 20 L/min and yielded airborne bacterial removal efficiencies of ∼75%–100%. Further, they were in close agreement with the analytical airborne particle removal efficiencies, at a similar range of flow rates. These flow rates also correspond to the breathing rates of standing and walking adults. More importantly, the breathing resistance could be reduced by more than 50% for flow rates of ∼200 L/min. Using manganese (IV) oxide coated mesh, the ozone concentration in the air outflow was reduced to less than 0.1 ppm, at a flow rate of ∼20 L/min, thus enabling safe use. The power consumption was less than 1 W.

Al-Coated Conductive Fiber Filters for High-Efficiency Electrostatic Filtration: Effects of Electrical and Fiber Structural Properties

Through the direct decomposition of an Al precursor ink AlH3{O(C4H9)2}, we fabricated an Al-coated conductive fiber filter for the efficient electrostatic removal of airborne particles (>99%) with a low pressure drop (~several Pascals). The effects of the electrical and structural properties of the filters were investigated in terms of collection efficiency, pressure drop, and particle deposition behavior. The collection efficiency did not show a significant correlation with the extent of electrical conductivity, as the filter is electrostatically charged by the metallic Al layers forming electrical networks throughout the fibers. Most of the charged particles were collected via surface filtration by Coulombic interactions; consequently, the filter thickness had little effect on the collection efficiency. Based on simulations of various fiber structures, we found that surface filtration can transition to depth filtration depending on the extent of interfiber distance. Therefore, the effects of structural characteristics on collection efficiency varied depending on the degree of the fiber packing density. This study will offer valuable information pertaining to the development of a conductive metal/polymer composite air filter for an energy-efficient and high-performance electrostatic filtration system.

Efficiency of ionizers in removing airborne particles in indoor environments

Air ionizers are increasingly being used to clean indoor environments of particle pollution. We tested the efficiency of a small negative ion generator (Aironic AH-202) in removing ultrafine particles from indoor environments. A high-flow air filter fitted with a HEPA filter was used to compare the removal efficiencies. We estimated the percentage of particles removed when the ionizer was operated within a closed chamber of volume 1 m3, in a closed unventilated room of volume 20 m3 and in three force-ventilated rooms of volume 32, 45 and 132 m3. The closed chamber studies were conducted with ambient particles and with smoke at particle number concentrations of 5 × 103 and 7 × 104 cm−3, respectively. In both cases, 70% of the particles were removed by the ionizer in 15 min. In general, the particle removal efficiency of both the ionizer and the air filter decreased as the room size increased. Both devices were also more effective in unventilated rooms than in ventilated rooms. The most important finding in this study was that, while the air filter was more effective than the ionizer in the two small rooms, the ionizer was clearly more effective than the air filter in the three largest rooms. We conclude that air ionizers are more suited than high-flow air filters in removing ultrafine particles from rooms larger than about 25 m3. The investigation also showed that small ions produced by the ionizer, placed in one room, were carried through the air conditioning system into other rooms, effectively removing particles from the air in these rooms in the process.

Performance evaluation of mobile downflow booths for reducing airborne particles in the workplace

ABSTRACTCompared to other common control measures, the downflow booth is a costly engineering control used to contain airborne dust or particles. The downflow booth provides unidirectional filtered airflow from the ceiling, entraining released particles away from the workers' breathing zone, and delivers contained airflow to a lower level exhaust for removing particulates by filtering media. In this study, we designed and built a mobile downflow booth that is capable of quick assembly and easy size change to provide greater flexibility and particle control for various manufacturing processes or tasks. An experimental study was conducted to thoroughly evaluate the control performance of downflow booths used for removing airborne particles generated by the transfer of powdered lactose between two containers. Statistical analysis compared particle reduction ratios obtained from various test conditions including booth size (short, regular, or extended), supply air velocity (0.41 and 0.51 m/s or 80 and 100 feet per minute, fpm), powder transfer location (near or far from the booth exhaust), and inclusion or exclusion of curtains at the booth entrance. Our study results show that only short-depth downflow booths failed to protect the worker performing powder transfer far from the booth exhausts. Statistical analysis shows that better control performance can be obtained with supply air velocity of 0.51 m/s (100 fpm) than with 0.41 m/s (80 fpm) and that use of curtains for downflow booths did not improve their control performance.