Most Penetrating Particle Size Research Articles

Comparative Analysis and Evaluation of Modeling Methods for Nuclear-Grade HEPA Filters

High-Efficiency Particulate Air (HEPA) filtration plays a crucial role in maintaining air quality in critical environments such as lean rooms, hospitals, and nuclear facilities. The point of this study is to look into how well nuclear-grade HEPA filters work and behave by looking at the main ways they catch particles using two modeling methods to figure out how well the filters work overall. This study encompasses particles with diameters ranging from 0.05 to 5.00 µm and a density of 1500 kg/m3. The current study systematically examined key parameters such as particle size, fiber diameter, and filtration velocity, which revealed their significant influence on the HEPA filter efficiency. Notably, the most penetrating particle size (MPPS) is identified within the expected range of 0.1–0.3 µm for both approaches. A critical threshold in fiber diameter is discovered when it exceeds 0.85 µm, resulting in a substantial shift in particle penetration and overall collection efficiency. This study also explored the impact of filtration velocity on filter performance, demonstrating increasing deviations as velocity rises, following a polynomial trend. The current study also rigorously validated the model predictions against experimental data from uranine particle filtration tests, confirming the model’s accuracy and applicability. These findings provide essential insights for optimizing the design and operation of nuclear HEPA filters, emphasizing the necessity of considering the particle size, fiber diameter, and filtration velocity. Both modeling approaches exhibit a negligible 0.04% deviation in the MPPS efficiency, which increases polynomially with the filtration velocity. Importantly, both approaches consistently identified the same MPPS regardless of the filtration velocity. Additionally, the model reinforces the substantial impact of fiber size on filter efficiency. A comprehensive comparison with the experimental data yielded closely aligned results with a maximum deviation of 1.14%. This validation strengthens the model’s ability to elucidate the underlying physical phenomena governing the influence of filtration velocity on efficiency, making it a valuable tool in nuclear HEPA filter research and development.

Electrospun carboxylated MWCNTs modified PMIA tree-like nanofibrous membrane with excellent thermal stability and chemical resistance for efficient particulate matter removal

The aim of this study is to fabricate nanofibrous membranes with excellent filtration and mechanical properties for application in the field of flue gas purification. Carboxylated Multiwalled carbon nanotubes (MWCNTs-COOH) were used to enhance the performance of PMIA nanofibrous membranes. The results showed that the average particle size D50 of MWCNTs-COOH in the PMIA electrospining solution was significantly reduced from 644 nm to 361 nm, the stability and dispersibility of MWCNTs-COOH were significantly enhanced. The resultant membranes exhibit a tree-like structure with a bimodal distribution of diameters and interconnected bonding points, where the trunk nanofibers exhibit an average diameter of 134.80 nm, while the branch nanofibers demonstrate an average diameter of 27.19 nm. The MWCNTs-COOH/PMIA nanofibrous membranes exhibited a filtration efficiency of 99.98 % for the most penetrating particle size (MPPS), while maintaining a tensile strength of 46.736 MPa. Notably, they retained significant strength even under harsh conditions, e.g. 56.46 % at 250 °C, 58.26 % with 30 wt% H2SO4, and 82.71 % with 10 wt% NaOH. The filtration efficiency remained at approximately 88.97 % even at 250 °C. These findings expand PMIA's application to harsh environments and offer insights for designing high-performance filters for high-temperature settings.

Submicron PAN and nanofiber CTA air filters: Fabrication, optimization, and performance

This study investigates the fabrication, optimization, and performance of submicron polyacrylonitrile (PAN) and nanofiber cellulose triacetate (CTA) air filters produced through electrospinning. PAN fibers with diameters ranging from 379 to 804 nm were generated from PAN/DMF solutions, while genuine CTA nanofibers (65–102 nm) were successfully produced using a recycled CTA polymer and a binary solvent system (DMSO/TCM). The effects of electrospinning parameters, including solution concentration (10–12 wt% for PAN, 8 wt% for CTA), applied voltage (10–16 kV), tip-to-collector distance (16–24 cm), solution supply rate (0.08–0.10 mL/hr), and binary solvent ratio (7:1 to 20:1 DMSO/TCM), on fiber morphology and diameter were systematically examined. Reducing PAN solution concentration and increasing applied voltage effectively decreased fiber diameter, enhancing filtration efficiency. Filtration performance tests revealed that CTA nanofibers outperformed PAN submicron fibers, exhibiting higher quality factors (0.043–0.046 Pa−1) due to their smaller fiber diameters and increased fiber packing density. Decreasing CTA solution supply rate and increasing DMSO/TCM ratio reduced fiber diameter and increased packing density. Longer spinning collection times improved filtration efficiency but increased thickness and pressure drop. The optimization of electrospinning parameters proved crucial for controlling fiber diameter and achieving enhanced filtration efficiency, particularly at the most penetrating particle size (MPPS), which usually covers the ultrafine particle size range. This study provides valuable insights into the development of high-performance air filtration media through the optimization of electrospinning parameters and the utilization of recycled materials.

Fabrication of an amino-modified MWCNTs grafted with chlorosulfonated PMIA nanofibrous membrane via electrospinning for efficient high-temperature dust filtration

The development of nanofibrous membrane with exceptional filtration efficiency, excellent mechanical properties, and high-temperature resistance poses a significant challenge in the field of industrial dust removal. Incorporating multi-walled carbon nanotubes (MWCNTs) into poly(m-phenylene isophthalamide) PMIA enhances the mechanical properties of nanofibrous membrane fabricated via electrospinning. However, the application of MWCNTs is limited due to their poor dispersion and self-aggregation in solvents. Herein, amino-modified MWCNTs (MWCNTs-NH2) grafted with chlorosulfonated PMIA (PMIA-SO2Cl) nanofibrous membrane was fabricated via electrospinning. The results demonstrated that the coupling effect of PMIA-SO2Cl and MWCNTs-NH2 significantly enhanced the stability of MWCNTs in the PMIA electrospinning solution, resulting in a more homogeneous dispersion of MWCNTs and a smaller average particle size (D50 = 198.03 nm). The filtration efficiency of the most penetrating particle size (MPPS) and the tensile strength of PMIA-SO2Cl/MWCNTs-NH2 nanofibrous membrane were 99.990 % and 57.514 MPa, respectively. The tensile strength retention rates in 30 wt% H2SO4 and 10 wt% NaOH were 52.56 % and 80.25 %, respectively. The MWCNTs-NH2/PMIA-SO2Cl nanofibrous membrane exhibited significantly enhanced mechanical property, filtration efficiency and high-temperature resistance (approximately 250 °C) compared to the unmodified nanofibrous membranes. This study was instructive for the application of electrospinning nanofibrous membranes in the field of high-temperature dust removal.

Influence of deposited liquid structures on the separation efficiency of thin oleophilic fiber layers of mist filters

The presence of oil mists constitutes a significant hazard to both, human health and the environment. In industrial applications, the effective separation of these mists typically relies on the utilization of multi-layer nonwoven coalescence filters. The underlying mechanisms governing droplet deposition, liquid transport within the filter matrix, and the evolution of the overall differential pressure have been extensively documented in the existing literature. However, limited and contradictory information is currently available regarding the impact of deposited liquid structures under varying saturation levels on the separation efficiency of coalescence filters.In this study, the influence of an increased liquid saturation at different filtration velocities on the fractional and total separation efficiency of thin porous non-woven fiber layers comparable to the first fiber layers of the first filter layer of commercially utilized coalescence filters are evaluated. As the oil load increases to a saturation of S≤ 0.4, the total separation efficiency (number-based) decreases, for all investigated filtration velocities. In addition, a shift of the most penetrating particle size (MPPS) to smaller droplet sizes and a decrease of the MPPS efficiency is observed. This decrease is attributed to a higher interstitial velocity resulting from the accumulation of liquid within the filter matrix, leading to a lower fractional separation efficiency in the diffusion regime. However, at saturation levels S≥ 0.6, the separation efficiency (meaning both, fractional and total separation efficiency) begins to increase due to the formation of partial oil films, leading to a blockage of void space. These films significantly enhance inertial separation. At the highest investigated saturations (S=0.8), the highest separation efficiencies due to a nearly complete coverage of the filter layers by an oil film are observed. The film formation is confirmed through backlit images of the oil-loaded filter material. Furthermore, an increase of the MPPS efficiency for a saturation of S=0.8 with increasing filtration velocity due to increased diffusional separation is recorded, which cannot yet conclusively answered by the authors. Additionally, the differential pressure across the fiber sheets is presented, revealing a more pronounced influence of the oil film on the differential pressure at increasing filtration velocities.

Adjustable fiber structure design for precise aerosol filtration

High-efficiency particulate air (HEPA) filters are widely used to filter aerosols. Predicting a HEPA filter's performance is essential to guarantee occupant health and comfort. Traditional cell models do not consider the fiber diameter distribution and spatial orientation, which makes them unable to predict filter performance well. We use the computational fluid dynamics (CFD) method to realize the initial performance simulation of glass-fiber (GF) filter media based on a random 3-D fiber model. In this study, we divided the filter media into multiple independent zones in the thickness direction and generated a fiber structure with the same fiber diameter distribution as the real filter media. Based on this method, we investigated the stability of the model and the effects of parameters such as computational domain width, fiber windward angle, filtration velocity, and fiber diameter distribution on the filtration performance of the filter media. The simulated pressure drop is in good agreement with the experimental values, and the efficiency of the most penetrating particle size (MPPS) of the filter media can be accurately calculated. A fiber model design and performance comparison of different fiber diameter distributions are realized. We believe this method can help us better understand the particle capture process and design a fiber structure for filter media to obtain better performance.

Hierarchical isoporous membrane filters for simultaneous reduction of pressure drop and efficient removal of nanoscale airborne contaminants

Isoporous membranes with well-defined pore architectures offer a unique design approach to achieve a multi-scale porous network. For instance, isoporous membranes with progressively smaller pore sizes can be stacked to create a hierarchical pore network in which each length scale and the gradient of the pore network are deterministic by design. In this paper, we introduce a hierarchically-arranged multilayer isoporous air filter that comprises an ultrathin (thickness <1μm) nanoporous active filtration layer and a microporous support layer. To maximize airflow and thereby reduce pressure drop across the membrane, we engineered a gap between the nanoporous and microporous membranes by designing and fabricating microscale spacer structures akin to feed spacers used in spiral wound reverse osmosis membranes. We demonstrated that such hierarchical isoporous membranes with integrated spacers (HIM-S) can retain high filtration efficiency (>95%) for ultrafine, most penetrating particle size (MPPS) while simultaneously reducing the pressure drop across the membrane (by ∼86%).

A novel slip-velocity model to simulate the filtration performance of nanofiber media

Aerosols such as PM2.5 and PM10 can have an immense impact on human health. With the outbreak of SARS-CoV-2, it is urgent to filter aerosols by media filtration technology. Electrospun nanofibers are a promising material for achieving high efficiency, low resistance, light weight, and environmentally friendly air filtration. But research on filtration theory and computer simulation of nanofiber media is still lacking. The traditional method involving computational fluid dynamics (CFD) and Maxwell’s first-order slip boundary overestimates the slip velocity on the fiber surface. In this study, a new modified slip boundary was proposed, which introduced a slip velocity coefficient on the basis of the no-slip boundary to address the slip wall. Our simulation results were compared with the experimental pressure drop and particle capture efficiency of real polyacrylonitrile (PAN) nanofiber media. The computational accuracy on pressure drop of the modified slip boundary improved 24.6% and 11.2% compared with that of the no-slip boundary and Maxwell’s first-order slip boundary, respectively. It was found that the particle capture efficiency near the most-penetrating particle size (MPPS) was significantly increased when slip effect occurred. This may be explained by the slip velocity on the fiber surface, which would make particles more accessible to the fiber surface and captured by interception.

Comparison of measurement systems for assessing number- and mass-based particle filtration efficiency

ABSTRACT The particle filtration efficiency (PFE) of a respirator or face mask is one of its key properties. While the physics of particle filtration results in the PFE being size-dependent, measurement standards are specified using a single, integrated PFE, for simplicity. This integrated PFE is commonly defined with respect to either the number (NPFE) or mass (MPFE) distribution of particles as a function of size. This relationship is non-trivial; it is influenced by both the shape of the particle distribution and the fact that multiple practical definitions of particle size are used. This manuscript discusses the relationship between NPFE and MPFE in detail, providing a guide to practitioners. Our discussion begins with a description of the theory underlying different variants of PFE. We then present experimental results for a database of size-resolved PFE (SPFE) measurements for several thousand candidate respirators and filter media, including filter media with systematically varied properties and commercial samples that span 20%–99.8% MPFE. The observed relationships between NPFE and MPFE are discussed in terms of the most-penetrating particle size (MPPS) and charge state of the media. For the sodium chloride particles used here, we observed that the MPFE was greater than NPFE for charged materials and vice versa for uncharged materials. This relationship is observed because a shift from NPFE to MPFE weights the distribution towards larger sizes, while charged materials shift the MPPS to smaller sizes. Results are validated by comparing the output of a pair of automated filter testers, which are used in gauging standards compliance, to that of MPFE computed from a system capable of measuring SPFE over the 20 nm–500 nm range.

Carbon black incorporated electrospun nanofibers for air filtration application

Electrostatic filter media were developed by incorporating various concentrations of Carbon Black (8, 10 and 12 wt%) on Polyvinylidene Fluoride (PVDF) through electrospinning. The prepared nanofibers were characterized for their morphology, phase transformation, wettability, thermal and predominantly electrostatic properties. Three filtration efficiency parameters such as concentration of CB (wt%), electrospinning time (hr) and areal density of substrate (GSM) were fed in Box Behnken design to obtain 15 experimental STATs. The experiments were performed with NaCl solution as the aerosols in the range of 0.1–1 μm and filtration efficiency as the response. Further, other filter media properties such as pore size, air permeability, pressure drop and thickness are investigated. STAT 12 resulted in the highest filtration efficiency of 99.99% with 12 wt% of CB, 3 h of electrospinning time and 60 GSM of substrate. The prepared filter also shows a maximum filtration efficiency of 99.98% at the most penetrating particle size (MPPS), 0.3 μm. The present research thus opens a pathway for hybrid mechanisms of separation improving filtration efficiency in addition to pre-existing mechanisms.

The Applications and Distinctions of Three Different Material Collection Plates in Wet Electrostatic Precipitator

Particle back-corona slows the efficiency of the dry-electrostatic precipitator (dry-ESP), especially during the removal of high resistivity particles. In this study, a new type of wet-electrostatic precipitator (wet-ESP) was designed and built using stainless steel (SS), conductive glass (CG), and original glass (OG) for its collection plates. The objectives of this research included the efficiency characteristics of both the dry-ESP and the wet-ESP, how the materials used in the dust collectors affect the ESP performance including SS, CG, and OG, and the effects on the electric resistivity of the particle of its performance, and the ozone generation rates of the wet-ESP. The experiment results indicated that the wet-ESP could improve the dust-cake phenomenon caused by high electrical resistivity particles that often occurred on dry-ESP in order to prolong its efficiency. Furthermore, the results indicated that during the most penetrating particle size (MPPS) penetration of SSESP and CGESP were both below 6% while OGESP was over 40% under the dry condition. When OGESP was placed and operated under the wet condition, its particle penetration dropped to below 20% under the MPPS. The results confirmed that compared to the dry-ESP, wet-ESP performed at a higher and better efficiency. In addition, as ozone concentration acts on the corona current under the same voltage, the result found that the ozone concentration of OGESP was lower than both CGESP and SSESP under the wet setting.

High-Efficiency Air Filter Media with a Three-Dimensional Network Composed of Core–Shell Zeolitic Imidazolate Framework-8@Tunicate Nanocellulose for PM0.3 Removal

Particulate matter (PM) in air has seriously endangered human health. Especially, PM0.3 can easily enter the lungs and blood through breathing. Herein, an air filter with a three-dimensional (3D) network consisting of core-shell structured fibers was designed by in situ growth of zeolitic imidazolate framework-8 on tunicate nanocellulose/glass fiber composite filter media (ZIF-8@TNC/GF). The filtration performance of the obtained ZIF-8@TNC/GF membranes against sodium chloride particles with the MPPS (most penetrating particle size) was investigated. The air filter media at the optimal ratio of ZIF-8 exhibited an ultrahigh efficiency of 99.998% and a quality factor of 0.0308 Pa-1 for PM0.3. Further characterizations showed that the ZIF-8@TNC/GF air filter had a hierarchical and rich pore structure, showing a large specific surface area (50.3 m2 g-1). More significantly, compared with the TNC/GF prepared by the dipping method, TNCs changed from the original two-dimensional (2D) nonuniform network to a uniform 3D network after the ZIF-8 was introduced. Moreover, the ZIF-8@TNC fibers with a core-shell structure inhibited the aggregation of nanocellulose. This study will shed light on the fabrication of high-efficiency TNC composite air filter media with fluffy 3D networks.

Effect of filtration pressure on the particle penetration efficiency of fibrous filter media

• Performance of fibrous filter media tested in the filtration pressure of 0.33–3.0 atm. • Single-fiber efficiency obtained by experiments compared to that by existing models. • A semi-empirical single-fiber efficiency formula for diffusive particles was proposed. The effect of filtration pressure on the particle collection performance of fibrous filter media was systematically investigated. The experiments were carried out in the filtration pressure range of 0.33–3 atm and using test particles in the electrical mobility size range of 20–400 nm. Two fibrous filter media: one made of glass fibers (GF) and the other made of metal fibers (SF), were selected for these tests. Our study shows that, at a face velocity of 0.1 m/s, by increasing the filtration pressure from 0.33 to 3 atm, the most penetrating particle size (MPPS) was slightly decreased, and the particle penetration was increased from 0.8% to 14% for media GF, and from 6.7% to 32.1% for media SF. In comparison to data calculated for existing single-fiber models, it was found that, for diffusive particles, the best fitting of available experimental data (i.e., those collected in this study and reported in others) was found under the assumption that the −1/3 power for the Péclet number is included in the single-fiber efficiency formula. Lastly, a semi-empirical single-fiber efficiency for diffusive particles is proposed to describe the reported experimental data.

Clinical Issues—November 2021

Occupational human papillomavirus vaccination for health care workers Key words: human papillomavirus (HPV), vaccination, occupational exposure, surgical smoke. Respiratory protection during smoke-generating treatment of human papillomavirus lesions Key words: human papillomavirus (HPV), respiratory protection, surgical smoke evacuation, surgical N95 respirator, loop electrosurgical excision procedure (LEEP). Most penetrating particle size in air filtration media testing Key words: most penetrating particle size (MPPS), ultra-low particulate air (ULPA), filtration efficiency, filtration media, surgical smoke evacuation. Smoke evacuation in surgical simulation laboratories Key words: surgical smoke evacuation, simulation laboratories, surgical energy devices, surgical smoke safety.

Optimizing the Packing Density and Chemistry of Cellulose Nanofilters for High-Efficiency Particulate Removal

The global spread of COVID-19 as well as the worsening air pollution throughout the world have brought tremendous attention to the development of materials that can efficiently capture particulate matter. We suggest that the high porosity of electrospun filters composed of nanofibers could provide minimal obstruction to air flow, while their high tortuosity and surface area-to-volume ratio present an excellent platform to capture particulates. In this study, the removal of nanoscale particles via in-house fabricated cellulose nanofilters is significantly enhanced by chemically functionalizing the fibers’ surface via the deposition of the bioinspired glue polydopamine (PDA) or the polycation poly(diallyldimethylammonium chloride) (PDADMAC). The effects of filter packing density, layering thickness, and chemistry on their performance, i.e., their filtration efficiency, most penetrating particle size (MPPS), particle fractional penetration percent, and performance in a high relative humidity environment, were investigated. When evaluated in an extremely hazardous environment (PM concentration ∼ 2000 μg m–3), the filtration efficiency, pressure drop, and quality factor for the cellulose nanofilters were measured to be >98.0%, <200 Pa, and ∼0.03 Pa–1, respectively. When we evaluated the performance of a composite hydrophobic/hydrophilic filter in an 80% relative humidity environment, a 99.8% filtration efficiency was achieved. We have demonstrated that the removal of nanoscale particulates can be effectively captured using cellulose-based nanofilters, even in a nonideal high humidity environment. These fundamental investigations into the structure–property-chemistry relationships of in-house electrospun nanofilters on nanoscale particulate removal hold the potential to help drive the future engineering of nanofilters for air purification applications, which is a timely and extremely important concern.

Size-Specific Filtration Performance of N95 Respirators After Decontamination by Moist Heat Incubation

Background: Decontamination and reuse of respirators have been proposed to mitigate the shortage of respirators during pandemics. The U.S. National Institute for Occupational Safety and Health (NIOSH)'s respirator filtration efficiency (FE) test has been used to confirm that decontamination procedures maintain minimum FE above 95% for N95s and similar respirators. However, it was hypothesized that the limited range of test particle sizes may not include the most penetrating particle size (MPPS) for all respirators, especially after decontamination by moist heat incubation (MHI). Materials and Methods: A custom-designed apparatus was used to measure size-specific FE for respirators across particle size bins between aerodynamic diameter of 0.07 and 1.97 μm using an electrical low-pressure impactor. FEs were measured for two N95 respirator models before and after 10 cycles of MHI. In addition, pressure drop through the respirator materials and scanning electron microscope (SEM) images of respirator layers were obtained before and after MHI. Results: For Kimtech™ brand N95 respirators, FE was not reduced at any size after MHI. For Safe Life brand N95s, FE was below 95% before MHI and decreased significantly after MHI. The MPPS for this respirator was outside the range defined in NIOSH test protocol, and increased after MHI. There was no appreciable change to the pressure drop through the two respirator models after MHI, nor was any deterioration in fiber integrity visible in SEM images. Conclusions: Based on the results of the present study and other studies in the literature, MHI can be used to decontaminate respirators without significant decrease in FE. However, potential effects of MHI on FE need to be assessed for each respirator model. The ability to evaluate size-specific FE across a wide range of particle sizes is important in identifying the MPPS and associated FE of respirators before and after MHI.

Filtration performance of glass fibrous air filter media under sinusoidal flow condition

Air filter is one of the key equipments for sustainable built environment. However, the variation of incoming air velocity is usually neglected in previous studies. Therefore, we applied computational fluid dynamics techniques at micro-scale to study the filtration performance of a glass fibrous media under sinusoidal flow condition. The effects of different flow rates, fluctuation frequencies, fluctuation amplitudes and particle sizes on filtration performance were investigated. Results show that changing the incoming flow field can weaken the Brownian diffusion of particles, resulting in reduced capture efficiency for particles smaller than 0.1 μm. The ratio of particle penetration between sinusoidal flow condition and constant flow condition is calculated. When the fluctuating frequency of the airflow changes for particles less than 0.1 μm, the smaller the particle size is, the larger the ratio of particle penetration is. When the particle size is near the Most Penetrating Particle Size (MPPS), the fluctuating airflow with large amplitude makes the particles more easily trapped by the fiber. The fluctuating airflow with large amplitude will result in a significant reduction in the capture efficiency for particles larger than 1 μm, and the penetration ratio will be greater than that under constant flow condition by three times. For particles with size smaller than 0.1 μm and larger than 1 μm, the amplitude of 0.4 u‾ and smaller has little effect on the capture efficiency. The capture efficiency of particles with size near MPPS value is less susceptible to changes in sinusoidal gas velocity with small amplitude.

Performance of mechanical filters used in general ventilation against nanoparticles

With an equal mass, nanoparticles (NP) have a higher toxicity than particles with the same chemical composition but with larger surface area. However, the toxicological knowledge concerning NP is still insufficient to establish limit values of exposure. To seek the lowest exposure level, filtration is a simple and effective way to capture particles, including NP. According to ANSI/ASHRAE 52.2 standard, ventilation filters efficiency is tested for particles ranging from 0.3 to 10.0 μm. Performances of entire filters for NP are still very limited and particle size of 300 nm (0.3 μm) is commonly used as the most penetrating particle size (MPPS) for mechanical media. To evaluate the filter performance for NP, five type of filters were investigated to measure their performance for particles smaller than 300 nm including NP. The performance of these filters was evaluated in terms of penetration and pressure drop. Experimental data permit to evaluate the MPPS for these mechanical filters. Nevertheless, 150–500 nm range provides a better estimation of the MPPS in the conditions which were tested. Also, filtration velocity influences efficiency for nanoparticles at 50 nm but no effect was observed for MPPS.

Comparative Performance of the NanoScan and the Classic SMPS in Determining N95 Filtering Facepiece Efficiency Against Nanoparticles

Nanoparticles are defined as particles with at least one dimension in the range of 1–100 nm. Due to the special properties of nanoparticles, they are used in many workplaces, thus leading to occupational exposure. Filtering facepieces (FFPs) are generally used in these workplaces to reduce the exposure. Many studies have measured FFP efficiency in laboratories using a scanning mobility particle sizer (SMPS). The aim of this study was to determine whether a NanoScan could be used to measure FFP efficiency against nanoparticles in workplaces for one type of N95 FFP. The results showed that the NanoScan gave maximum penetration and most penetrating particle size (MPPS) data for all configurations tested. Observations were consistent with those of previous studies: low penetration, MPPS smaller than 100 nm, and penetration increased as the airflow rate increased. The NanoScan gave a less precise MPPS and a slightly overestimated maximum penetration. These results confirm that the classic SMPS is a more precise instrument considering these two devices, whereas the NanoScan is faster to provide general information about the overall behaviour, which make it easy to use for a workplace environment. A NanoScan can thus be used as a first approach in workplaces.

Fine/ultrafine particle air filtration and aerosol loading of hollow-fiber membranes: A comparison of mathematical models for the most penetrating particle size and dimensionless permeability with experimental data

Hollow-fiber membranes (HFMs) have widely been applied to many liquid treatment applications such as wastewater treatment, membrane distillation and membrane contactor/bioreactor applications. However, they have rarely been used for aerosol filtration thus far. In this work, we tested air filtration performance of air filter modules composed of polypropylene HFMs. The experimental results of most penetrating particle size (MPPS) and permeability were then compared with theoretically predicted values. Filtration efficiency and MPPS were measured using a monodisperse (20, 35, 50, 70, 100, 140, 280 and 400 nm) and a polydisperse aerosol (15–594 nm). Dimensionless permeability was predicted using models assuming isotropic 3D pore structure and compared with permeability measured using capillary flow porometry. Finally, an experiment to observe pressure drop with long-term particle loading was carried out. In the experiments with the monodisperse aerosol, no penetration was observed regardless of particle size. Therefore, face velocity was increased and high concentrations of the polydisperse aerosol were used to increase the penetration. The MPPS was then found to be 333 and 250 nm at a flowrate of 10 and 40 L/min, respectively. The MPPS model for diffusion and interception dominant regime proposed by Lee and Liu (1986) was closest to these results. Dimensionless permeability varied depending on the conditions for which the individual models were derived. For example, the RUC (representative unit cell) model underestimates the results while the results predicted using the empirical formula of Davies (1953) differ significantly from the measured values. The loading experiments have shown significantly prolonged fouling by high concentrations of submicron particles compared to conventional fibrous filters.