Face Velocity Research Articles

Computational Modeling of Multiscale Air Filter Media Consisting of Nano- and Microfibers

With regard to air filtration, computational work has been performed to predict filter performance outcomes in different particulate scenarios, yet comparative verification of different modeling methods is rarely studied. In this study, computational simulations with different modeling techniques are demonstrated for filter media with various fiber diameters, thicknesses, and basis weights. For a microscale meltblown (Micro) filter web, a resolved model reconstructed by X-ray micro-computed tomography (Xμ-CT) is generated. The representative volume elements and the number of voxels are determined by examining the simulation accuracy and the computational time. For a multiscale dual-layer web composed of nanofibers (Nano) and microscale spunbond fibers (SB), a parametric model and a porous plane model are generated. The accuracy of the models is verified in terms of the morphological parameters and flow resistance in comparison, with actual test results. The parametric model and porous plane model suitably predict the characteristics of multiscale filter media. Simulated filtration is conducted for particles of different sizes (0.05–1 μm) in an effort to understand the relationships among the filter morphology, face velocity (71 and 142 mm/s), and particle size. This study presents relevant modeling methods, specifically a resolved model, a parametric model, and a porous plane model for virtualizing filter media on various scales. It provides an informative discussion of various modeling parameters for accurate predictions of filtering behaviors with potential applicability to the reverse-engineering of filter products.

Modeling pressure drop values across ultra-thin nanofiber filters with various ranges of filtration parameters under an aerodynamic slip effect

Computational fluid dynamics simulations of fibrous filters with 56 combinations of different fiber sizes, packing densities, face velocities, and thicknesses were conducted for developing models that predict pressure drops across nanofiber filters. The accuracy of the simulation method was confirmed by comparing the numerical pressure drops to the experimental data obtained for polyacrylonitrile electrospun nanofiber filters. In the simulations, an aerodynamic slip effect around the surface of the small nanofibers was considered. The results showed that, unlike in the case of conventional filtration theory, pressure drops across the thin layers of electrospun nanofiber filters are not proportional to the thickness. This might be a critical factor for obtaining precise pressure drops across the electrospun nanofiber filters with extremely thin layers. Finally, we derived the product of drag coefficient and Reynolds number as a function of packing density, Knudsen number, and ratio of thickness to fiber diameter to get the correlation equation for pressure drop prediction. The obtained equation predicted the pressure drops across the nanofiber filters with the maximum relative difference of less than 15%.

Efficient, Breathable, and Compostable Multilayer Air Filter Material Prepared from Plant-Derived Biopolymers.

State-of-art face masks and respirators are fabricated as single-use devices using microfibrous polypropylene fabrics, which are challenging to be collected and recycled at a community scale. Compostable face masks and respirators can offer a viable alternative to reducing their environmental impact. In this work, we have developed a compostable air filter produced by electrospinning a plant-derived protein, zein, on a craft paper-based substrate. The electrospun material is tailored to be humidity tolerant and mechanically durable by crosslinking zein with citric acid. The electrospun material demonstrated a high particle filtration efficiency (PFE) of 91.15% and a high pressure drop (PD) of 191.2 Pa using an aerosol particle diameter of 75 ± 2 nm at a face velocity of 10 cm/s. We deployed a pleated structure to reduce the PD or improve the breathability of the electrospun material without compromising the PFE over short- and long-duration tests. Over a 1 h salt loading test, the PD of a single-layer pleated filter increased from 28.9 to 39.1 Pa, while that of the flat sample increased from 169.3 to 327 Pa. The stacking of pleated layers enhanced the PFE while retaining a low PD; a two-layer stack with a pleat width of 5 mm offers a PFE of 95.4 ± 0.34% and a low PD of 75.2 ± 6.1 Pa.

Development of an equation of state to characterize an electron beam interacting with an aluminum target

The Equations Of State (EOS) of materials under extreme conditions of temperature and pressure can be experimentally studied, thanks to intense electron beam-target experiments. The latter are powerful tools to probe materials in the warm dense matter regime. At CEA/CESTA, we use the CESAR pulsed generator (1 MV, 300 kA). During an experimental shot, a high-power 800 keV, 100 kA, 20 mm-diameter, 100 ns electron pulse produces shock waves in an aluminum target. The behavior of the latter is explored by analyzing the time-history of its rear face velocity, as measured by photon Doppler velocimetry. Using simulations, we can test the accuracy of an EOS over a wide range of densities and temperatures. In addition, an accurate EOS allows for reduction of the uncertainties of the beam parameters that have an impact on beam energy deposition. We have observed that the measurements are not correctly restituted by the simulation codes when they use the available EOS (BLF, SESAME). Thanks to both published data and ab initio calculations, which are valid in the considered thermodynamic regime, we have developed a new EOS describing precisely the thermodynamic (isochoric) regime from one-half to one-third the normal density. The corresponding hydrodynamic simulations appear to be in much better agreement with the measurements. In addition, this new EOS has allowed us to refine the knowledge of the input electron beam parameters that have an impact on beam energy deposition.

Performance evaluation of an electrostatic precipitator with a copper plate using an aerosolized SARS-CoV-2 surrogate (bacteriophage phi 6)

The global spread of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has reminded us of the importance of developing technologies to reduce and control bioaerosols in built environments. For bioaerosol control, the interaction between researchers and biomaterials is essential, and considering the characteristics of target pathogens is strongly required. Herein, we used enveloped viral aerosols, bacteriophage phi 6, for evaluating the performance of an electrostatic precipitator (ESP) with a copper-collecting plate (Cu-plate). In particular, bacteriophage phi 6 is an accessible enveloped virus that can be operated in biosafety level (BSL)-1 as a promising surrogate for SARS-CoV-2 with structural and morphological similarities. ESP with Cu-plate showed >91% of particle removal efficiency for viral aerosols at 77 cm/s of airflow face velocity. Moreover, the Cu-plate presented a potent antiviral performance of 5.4-relative log reduction within <15 min of contact. We believe that the evaluation of ESP performance using an aerosolized enveloped virus and plaque assay is invaluable. Our results provide essential information for the development of bioaerosol control technologies that will lead the post-corona era.

Dynamical modeling of bi-layer Aluminium adhesive tape for laser shock applications

The presented work covers the response of Aluminium tape (Al tape) under high strain rate of deformation (order of 106s−1) using laser shock. High power laser (J) with a short pulse duration (ns) is used to create laser shock within the water confinement regime on two Al tape configurations in order to apply low and high pressure (order of MPa and GPa). Al tape has been modeled using Johnson-Cook (J-C) material model for the Al layer, and Steinberg–Cochran–Guinan (SCG) material model (elastic with pressure dependence) for the adhesive layer, both material models are coupled with Grüneisen equation of state. The Al tape model has been validated by comparing the simulated Back Face Velocity (BFV) of the target with the measured one by the Velocity Interferometer System for Any Reflector (VISAR). In addition, the validated material model is used to conduct the sensitivity studies about the transmitted pressure depending on the acoustical impedance of the target and adhesive thickness. Moreover, location and magnitude of maximum tensile stress within the target are calculated in function of the adhesive thickness of the Al tape. Finally, it has been proved that using one laser beam configuration, maximum tensile zone could appears close to the front face by increasing the adhesive thickness.

Assessment of safety control measures for centralized Chlorine gas system

As a glove manufacturing plant, the chemical is one of the most highly used materials. Some chemicals impact human health, environmental aspects, and physical hazards such as highly flammable gas. Chlorine gas is one of them. Besides the accidental release of chlorine gas incidents, ill-health issues are another aspect that should be taken care of. This study aims to determine the current chlorine concentration at a centralized chlorine gas manifold system in a rubber glove manufacturing plant and evaluate the existing safety control measures. A concept of safety by design, inherently safety, and the fail-safe system was considered during the study. The results show that the chlorine concentration level during drum replacement by the crew is at an average of 1.154 ppm and the standard deviation at 0.3478. The highest concentration was at 1.8 ppm. The wet scrubber assessment was done using the Industrial Ventilation and visual assessments and measurements within the system, including capture velocity, face velocity, and duct velocity or transport velocity. Other assessed parameters are total pressure, static pressure, and velocity pressure. The assessment found that the duct performance for all parameters complies with a minimum requirement of the American Conference of Governmental Industrial Hygienists (ACGIH) guidelines.

Size-specific filtration efficiency and pressure drop of school-aged children's woven and nonwoven masks at varying face velocities

BackgroundDifferences in physiology and breathing patterns between children and adults lead to disparate responses to aerosols of varying sizes. No standardized method exists for measuring the filtration efficiency (FE) of children's masks to reflect such differences. MethodsUsing an adult N95 mask as a control and two different face velocities (vf) (9.3 cm/s representing adults and 4.0 cm/s representing school-aged children), we tested the pressure drop (ΔP) through children's nonwoven masks (surgical and KN95) and children's woven masks (100% cotton and partially-cotton-based masks), as well as their size-specific FE between aerodynamic particle diameters of 0.02 and 2.01 μm. ResultsAll three types of mask showed a 1 to 9% absolute increase in minimum FE at the lower vf and a significant decrease in ΔP. For children's surgical masks the increase in FE was significant for most of the examined particle sizes, but for children's woven masks the increase was limited to particles smaller than 0.04 μm. ConclusionsLower vf for children is likely to lead to a higher FE, lower ΔP, and consequently higher filter qualities in children's masks. For woven masks, the FE for particles larger than 0.04 μm was low (typically <50%) for both vf‘s studied.

Variety-duty Characteristic Analysis and Optimal Operation of Cold-End System of 600MW Direct Air-cooled Thermal Power Unit

The operating backpressure of the direct air-cooled unit is a significant economic parameter, and the optimal backpressure is corresponding to the best efficiency of the unit, which is mainly affected by ambient temperature, steam turbine exhaust flow, and face velocity in the operation of the cold-end system. A calculation model of the condenser of a 600MW direct air-cooled unit using the ε-NTU method was established to analyze the off-design performance. Compared with the characteristic curve provided by the manufacturer, the maximum error of the calculation results is 1.68%, meeting the engineering accuracy requirements. In order to obtain the optimal backpressure and optimal face velocity under off-design conditions, a cold-end optimization calculation model based on genetic algorithm is established with the maximum net power output as the objective function. The influence of the exhaust steam flow, ambient temperature and face velocity on the pressure of condenser is analyzed. In addition, the changing rules of the net power output with face velocity and backpressure under different conditions are studied. The results indicated that the working pressure of the condenser increases with the increment in ambient temperature and exhaust steam flow, and decreases with the rise of face velocity. The net power output of unit increases first and then decreases with the increment in backpressure and face velocity. Moreover, the higher the ambient temperature, the larger optimal face velocity and optimal backpressure of the unit, as well as the more cooling air volume is required under the optimal air face velocity. Keywords: Direct air-cooled unit, Off-design condition, Characteristic analysis, Optimal backpressure, Genetic algorithm DOI: 10.7176/JETP/13-1-02 Publication date: January 31 st 2023

Face Masks and Prevention of Respiratory Viral Infections: An Overview

Airborne transmission of respiratory viruses consists of three sequential steps: (1) release of respiratory fluids in the form of droplets from the nose and mouth of an infected person, (2) transport of the droplets through air, and (3) entry of the droplets into the nose and mouth of an uninfected individual. Talking, coughing, and sneezing emit droplets across a spectrum of sizes. The water in exhaled droplets begins to evaporate in air and, as a result, the droplets are reduced in size shortly after being emitted. Face masks are effective for capturing droplets just released from the nose and mouth. Studies indicate that more than 50% of community transmission of SARS-CoV-2 is from asymptomatic and pre-symptomatic cases. Use of face masks by the public can effectively reduce the chance of infected individuals unknowingly spreading the virus. In addition to being an effective device for source control, face masks can protect the wearers from inhaling virus-laden droplets. Cloth masks and disposable masks provide reasonable protection for the public, while surgical masks and N95 respirators give higher levels of protection as needed in healthcare settings. Made with varied materials, these masks have different structural characteristics. The collection efficiency of a face mask depends on droplet size, face velocity, and the structural characteristics of the mask. For a given mask, capturing droplets is more effective during exhalation than during inhalation. Pressure drop across the mask should be taken into consideration when selecting a face mask. The best face mask is the one that gives the highest collection efficiency with the least pressure drop. For an effective protection, a mask should fit the face properly. While face masks have proven adequate in reducing airborne transmission of SARS-CoV-2 infections, continuous improvement is needed to better prepare for future respiratory viral threats.

Denitrification activity test of a V modified Mn-based ceramic filter.

In view of the characteristics of high temperature denitrification and low water and sulfur resistance of single manganese-based catalysts, a vanadium-manganese-based ceramic filter (VMA(14)-CCF) was prepared by the impregnation method modified with V. The results showed that the NO conversion of VMA(14)-CCF was more than 80% at 175-400 °C. At 225-300 °C, the conversion of NO can reach 100%. High NO conversion and low pressure drop can be maintained at all face velocities. The resistance of VMA(14)-CCF to water, sulfur and alkali metal poisoning is better than that of a single manganese-based ceramic filter. XRD, SEM, XPS and BET were further used for characterization analysis. The introduction of V protects the MnOx center, promotes the conversion of Mn3+ to Mn4+, and provides abundant surface adsorbed oxygen. The development of VMA(14)-CCF greatly broadens the application range of ceramic filters in denitrification.

Construction of Pt@CNTs/SiC Catalytic Membrane for High-Efficiency Removal of Formaldehyde and Dust

Catalytic membranes can achieve the simultaneous purification of particulate matter (PM) and gaseous pollutants, and their performance depends on the design of a catalyst and its combination with a membrane material. Herein, a novel Pt@CNTs/SiC catalytic membrane composed of a Pt@CNTs (carbon nanotubes) membrane layer and a porous SiC support was developed for the simultaneous removal of formaldehyde and PM at room temperature. The CNT membrane layer underwent vertically integrated growth on a porous SiC support, which provided the catalytic membrane with a pore size of 7.4 μm and a high gas permeance of 240.2 m3·m–2·h–1·kPa–1. The loading of Pt particles on CNTs slightly decreased the gas permeance of the catalytic membrane (219.9 m3·m–2·h–1·kPa–1) but endowed the membrane with catalytic formaldehyde degradation performance. The obtained Pt@CNTs/SiC catalytic membrane with a 240 μm thick CNT layer and 0.8% Pt loading exhibited 99.999% filtration efficiency for 300 nm SiO2 (face velocity = 1 m/min) and 72.1% formaldehyde degradation (gas flow = 49 mL/min), implying that the Pt@CNTs/SiC membrane has good application potential in the collaborative removal of various air pollutants.

Nanofibrous aerosol sample filter substrates: Design, fabrication, and characterization

The manuscript demonstrates the application of nanofibrous filtration technology to aerosol sampling, by suggesting the fabrication sequence and laboratory validation of sampling filters. Four multilayer composite filters were developed from polymers Polyc[ε]aprolactone (PCL), Cellulose acetate (CA), Poly(1-acrylonitrile) (PAN), and Poly(hexano-6-lactam) (PA6) by two modifications of electrospinning process. The layered structure provided a fibre and pore gradient from the microfibrous base layer, the mesofibrous middle layer, and the nanofibrous upper layer, acting as a 2D collection surface for aerosol particles. The sampling filters were characterized for their morphology, wettability, weight stability, filtration efficiency, and pressure drop. The fibre diameter of the nanofibrous layer ranged from 0.42 ± 0.21 μm (PCL) to 0.086 ± 0.02 μm (PA6), while pore size ranged from 2.83 ± 0.35 μm (CA) to <0.4 μm (PA6). Such a morphology allowed for reaching a consistent particle collection efficiency ranging between 99.4 and 99.9% at a particle size of 0.3 μm, and at a reasonable pressure drop, such as 0.5–2.2 kPa at a face velocity of 10 cm/s. The fabrication sequence and obtained indicate a suitability for the preparation of bespoke filtering substrates to suit a specific subsequent physical, chemical, or toxicological analysis of collected particles.

Performance evaluation of an architecturally-designed vertical high capacity linear slot diffuser in a tropical atrium

This paper proposed a new approach for the efficient air conditioning of large tropical buildings. The current study has two objectives: the design and numerical investigations of the performance of vertically oriented high capacity linear slot diffusers (HCLSD) in an atrium building and the verification and validation of the different turbulence models through laboratory-scale experiments. The HCLSD was investigated with varying angles of inclination of the blades (ϕ = 0o to 25o) for the in-depth performance analyses. The performance was evaluated by monitoring and comparing the velocity and temperature profiles along the vertical lines drawn at different locations in the studied domain. A relatively longer jet throw was noticed through quantitative analysis at ϕ = 0o. Note that more than 33% increment in the face velocity was recorded at this angle. The corresponding terminal velocity of 0.225 m/s was observed at 8 m distance from the diffuser face. The detailed investigations at 0o deflector angle (case-1) were carried out for velocity, temperature field, and thermal comfort indices, i.e. PMV and PPD models. For the occupied zone, the thermal comfort indices were found within the acceptable ranges (i.e. PMV = + 0.1 to +0.9 and PPD = 4% to 20%). Abbreviations: ACMV: Air conditioning and mechanical ventilation; CFD: Computational fluid dynamics; CMH: Cubic meter per hour; DV: Displacement ventilation; HCLSD: High capacity linear slot diffuser; IAQ: Indoor air quality; MV: Mixing ventilation; PMV: Predicted mean vote; PPD: Predicted percentage dissatisfied; RANS: Reynolds-Averaged Navier – Stokes; RNG: Re-Normalization Group; SST: Shear-Stress Transport: SIMPLE: Semi-implicit method for pressure linked equations; VAV: Variable air volume; VSD: Variable speed drives

Large scale PIV-measurement to evaluate the flow isolation device (FID) efficiency in the stocker room of wafer masks

Silicon chip demand increased in recent years while the linewidth of the integrated circuits (ICs) has decreased. Improvement of the wafer process yield has become a key factor in chip manufacturing. The yield of the wafer process is closely related to the quality of the mask in the lithography process. The environmental conditions of the mask stocker room need to be carefully monitored and controlled to maintain the mask quality. The moist air invasion from the stocker room when the mask box exchange door is open can significantly increase the internal ambient humidity. This humidity leads to mask defects. Therefore, the moist air invasion from the stocker room should be minimized. In this study, an innovative flow isolation device (FID) is designed and manufactured. This device is used to block the flow of air through the mask exchange door. Smoke flow visualization and particle image velocimetry (PIV) were performed to evaluate the FID performance. The experimental results show that when the pressure of the stocker room is 0.3 Pa and the face velocity of FID is 2.0 m/s, the isolation efficiency is around 83.03%. The newly designed FID can significantly reduce the volume of CDA used during manufacturing. This can significantly reduce waste and energy cost.

Evaluation of ozone removal devices applied in ventilation systems

Applying ozone removal devices in ventilation systems is an effective way to reduce building occupant exposure to ozone. However, little is known about the performance of commercially-available ozone removal devices under realistic usage conditions, especially for technologies that have recently emerged for general ventilation such as ultraviolet photocatalytic oxidation (UV–PCO) and catalysis (without UV). A total of 14 ozone removal devices that are representative of products on the market were selected: 11 activated carbon filters, 2 UV-PCO devices, and 1 catalyst filter without UV. We tested these devices with an “ozone stress test” by exposing them to 70 ppb, 107 ppb, and 500 ppb of ozone at 25 °C, 50% RH, and 2.5 m/s face velocity. The device performance was evaluated by the average efficiency at each ozone level, degradation rate at 500 ppb, pressure drop, and a quality factor that combines efficiency and pressure drop. Results show a wide range of single-pass removal efficiency from 3% to 93% at 70 ppb. All devices degraded at a slow rate; at 500 ppb, most devices degraded at 1.5%/h relative to their efficiency at the beginning of this period. The catalyst (no UV) and three 12″ activated carbon devices achieved high efficiency at the least cost of pressure drop. The loading and source of carbon had a significant impact on the efficiency of activated carbon filters. A two-fold increase in carbon loading led to nearly a two-fold higher single-pass removal efficiency. Coal-based carbon degraded 20 times faster than coconut shell-based carbon.

Performance of Textile Mask Materials in Varied Humidity: Filtration Efficiency, Breathability, and Quality Factor

During the COVID-19 pandemic, reusable masks became ubiquitous; these masks were made from various fabrics without guidance from the research community or regulating agencies. Though reusable masks reduce the waste stream associated with disposable masks and promote the use of masks by the population, their efficacy in preventing the transmission of infectious agents has not been evaluated sufficiently. Among the unknowns is the effect of relative humidity (RH) on fabrics’ filtration efficiency (FE) and breathability. This study evaluates the FE and breathability of several readily accessible mask materials in an aerosol chamber. Sodium chloride aerosols were used as the challenge aerosol with aerodynamic particle diameter in the 0.5 to 2.5 µm range. To mimic the variability in RH in the environment and the exhaled-breath condition, the chamber was operated at RH of 30% to 70%. The face velocity was varied between 0.05 m/s and 0.19 m/s to simulate different breathing rates. The FE and pressure drop were used to determine the quality factor of the materials. Among the tested materials, the 3M P100 filter has the highest pressure drop of 140 Pa; the N95 mask and the 3M P100 have almost 100% FE for all sizes of particles and tested face velocities; the surgical mask has nearly 90% FE for all the particles and the lowest pressure drop among the certified materials, which ranks it the second to the N95 mask in the quality factor. Other material performance data are presented as a function of relative humidity and aerosol size. The quality factor for each material was compared against reference filtration media and surgical masks. Multiple layers of selected materials are also tested. While the additional layers improve FE, the pressure drop increases linearly. Additionally, the certified materials performed approximately three times better than the highest performing non-certified material.

Impact of activated carbon contents on cabin air filter performance at different fume flow rates

The present study has been undertaken to analyze the filtration performance of two different nonwoven polypropylene filter media, viz. needle felt and spun-bonded sandwiched with granular activated carbon of varying concentration under different face velocities. The materials are studied on a laboratory based cabin air filter test rig. Spun bonded material reveals relatively lower emission and pressure drop. Interestingly, lower face velocity reveals relatively improved filter behavior in case of both the filter materials. Further, a reduction in downstream emission in terms of PM 2.5 &amp; PM 10 , number concentration and peal pressure drop is observed at higher concentration of activated carbon.

Metal-organic framework decorated polyimide nanofiber aerogels for efficient high-temperature particulate matter removal

Particulate matter (PM) originated from high temperature (200–300 °C) does great harm to public health, could be effectively removed via high-temperature air filters. Nevertheless, a mass of obstacles still remain in the way of exploiting a high-temperature air filter with simultaneously high mechanical strength, excellent air filtration performance and good thermal stability. Herein, we report a robust and efficient nanofiber aerogel-based air filter fabricated by compounding zeolite imidazole framework-8 (ZIF-8) nanoparticles with polyimide (PI) nanofiber aerogels. As the matrix material, the robust and porous PI nanofiber aerogel endows the filter with satisfactory air permeability, outstanding adsorption capacity, great thermal stability and favorable mechanical performance. Moreover, the dispersed ZIF-8 provides a good deal of active sites, which is beneficial to capture finer PMs by electrostatic attraction. As a result, ZIF-8/PI composite nanofiber aerogel (ZIF-8/PI NFA) exhibits great high-temperature filtration performance. At 300 °C, ZIF-8/PI NFA is able to remove 96.2 % and 99.5 % of PM0.3 and PM2.5 with slight pressure drop of 88.5 Pa (air face velocity of 5.3 cm s−1), and it can continuously work under 300 °C without any performance attenuation. This ZIF-8/PI NFA with high efficiency, good thermal stability and great mechanical properties displays a broad application prospect in industrial and automotive air purification fields.

Ultrafine nanofiber-based high efficiency air filter from waste cigarette butts

Air and water pollution caused by particulate natters (PM) and waste cigarette butts (WCBs) have wreaked havoc across the globe in last several years, where the latter is subtle in nature. This work aims to tackle both the concerns by recycling WCB into air filter, a value-added product, to remove PMs from air. The air filters consist of ultrafine nanofibers extruded from WCB solution in acetone using supersonic solution blowing (SSB). The ultrafine nanofiber layer, sandwiched between two spunbond polyester membranes, demonstrated remarkable particle filtration efficiency (PFE) of 99.99% at PM2 and 99.7% at PM0.1 when tested at face velocity of 0.96 m/s (i.e., 90 L per minute). The ultrafine nanofiber membrane demonstrated unique architectural feature with 94% volumetric porosity and mean fiber diameter of 92.4 ± 1.2 nm. The structural characterization confirmed its identity as cellulose acetate (CA), free of nicotine and various heavy metals which WCBs generally have. The ultrafine fiber diameter and highly porous structure allowed the 3-ply arrangement to operate at high efficiency with a pressure drop (ΔP) of 50.4 Pa at 0.96 m/s, compared to 41.8 Pa of 2-ply spunbond layers, and PFE of 69.2% at PM2. A laboratory-scale multi-layer prototype filter was developed to mimic a commercial HEPA filter which demonstrated a PFE >99.99% at face velocity of 2.12 m/s and PM0.1. The membrane containing ultrafine nanofibers demonstrated enhanced hydrophobicity (contact angle- 132.8°), which could repel water drops of mean size 256 ± 92 μm when impacted at a velocity of 10 m/s, mimicking a sneezing pattern.