An overview of filtration efficiency through the masks: Mechanisms of the aerosols penetration

The masks have always been mentioned as an effective tool against environmental threats.They are considered as protective equipment to preserve the respiratory system against the non-desirable air droplets and aerosols such as the viral or pollution particles.The aerosols can be pollution existence in the air,or the infectious airborne viruses initiated from the sneezing,coughing of the infected people.The filtration efficiency of the different masks against these aerosols are not the same,as the particles have different sizes,shapes,and properties.Therefore,the challenge is to fabricate the filtration masks with higher efficiency to decrease the penetration percentage at the nastiest conditions.To achieve this concept,knowledge about the mechanisms of the penetration of the aerosols through the masks at different effective environmental conditions is necessary.In this paper,the literature about the different kinds of face masks and respiratory masks,common cases of their application,and the advantages and disadvantages of them in this regard have been reviewed.Moreover,the related mechanisms of the penetration of the aerosols through the masks are discussed.The environmental conditions affecting the penetration as well as the quality of the fabrication are studied.Finally,special attention was given to the numerical simulation related to the different existing mechanisms.

Experimental investigation of oil particles filtration on carbon nanotubes composite filter

Due to the lipophilicity of carbon nanotubes (CNTs),the carbon nanotubes composite filter for removing oil particles in cooking fumes is synthesized. The composite filter was fabricated by the chemical vapor deposition (CVD) method. The filtration characteristics of the resultant filter and the influence of the parameters were investigated. The results show that the filtration efficiency of the CNT filter during the saturation period is 99.92%, which satisfies the high efficiency particulate air (HEPA) standard. Pressure drop increases linearly before saturation and the pressure drop at the saturation stage is only two times that of the initial stage, which is far less than that of conventional glass fiber filters. The efficiency increases by enhancing filtration velocity. Pressure drops in the composite filter at the equilibrium stage are equal under different aerosol concentrations. The increase in concentration can improve the efficiency of composite filters. Therefore, the CNT filter is suitable for decreasing oil particle pollution due to its lower increase ratio of pressure drop and higher efficiency.

Relationships between the Processing Parameters of Melt Blown Nonwoven Fabric and Its Structure and Filtration Property

Based on the processing experiment and sodium flame test this paper deals with the relationship between processing parameters, structure, and filtration property of melt blown fabric. Through the image analysis of Questar micro-images in combination with the SEM observation and the measurement of some macrostructure indices, the relationship between the processing parameters and the structure especially the microstructure is emphasized Finally the effect of somestructure factors on filtration properties is discussed theoretically.

Meltblown fabric vs nanofiber membrane, which is better for fabricating personal protective equipments

The coronavirus disease 2019(COVID-19)pandemic has led to a great demand on the personal protection products such as reusable masks.As a key raw material for masks,meltblown fabrics play an important role in rejection of aerosols.However,the electrostatic dominated aerosol rejection mechanism of meltblown fabrics prevents the mask from maintaining the desired protective effect after the static charge degradation.Herein,novel reusable masks with high aerosols rejection efficiency were fabricated by the introduction of spider-web bionic nanofiber membrane(nano cobweb-biomimetic membrane).The reuse stability of meltblown and nanofiber membrane mask was separately evaluated by infiltrating water,75%alcohol solution,and exposing under ultraviolet(UV)light.After the water immersion test,the filtration efficiency of meltblown mask was decreased to about 79%,while the nanofiber membrane was maintained at 99%.The same phenomenon could be observed after the 75%alcohol treatment,a high filtration efficiency of 99%was maintained in nanofiber membrane,but obvious negative effect was observed in meltblown mask,which decreased to about 50%.In addition,after long-term expose under UV light,no filtration efficiency decrease was observed in nanofiber membrane,which provide a suitable way to disinfect the potential carried virus.This work successfully achieved the daily disinfection and reuse of masks,which effectively alleviate the shortage of masks during this special period.

Performance of N95 elastomeric respirators in high humidity and high coal dust concentration environment

High humidity and high dust concentration in deep coal mines may severely challenge the performance of respirators worn by coal miners.This paper aims at quantitatively evaluating the respirators used in deep coal mines and providing scientific guidance for the respiratory protection of miners.Based on the self-designed in-situ PM2.5 collector,controllable PM2.5 generator,human breathing simulator,and respirator simulation testing system,under the simulated deep mine working condition,this study investigated the effects of dust loading,wearing time,and dust concentration on the filtration efficiency,breathing resistance,and quality factor of N95 elastomeric respirators.With the increase of dust loading,the respirator filtration efficiency firstly decreased,then increased(minimum value 97.5%).The breathing resistance increased exponentially from 120 to 180 to 1020-1530 Pa,and the quality factor decreased logarithmically from 0.051 to 0.076 to 0.0058-0.0085 Pa^(-1).As the PM2.5 coal dust concentration increased from 5 to 50 mg/m^(3),the wearing time for the respirator breathing resistance to exceed 300 Pa reduced from 7 h to less than 1 h.One N95 elastomeric respirator is not able to perform an 8-h work shift.To avoid the excessive breathing resistance caused by dust loading,more filter cartridges are needed for coal miners.

Fabrication of a High-Performance and Reusable Planar Face Mask in Response to the COVID-19 Pandemic

The coronavirus disease 2019(COVID-19)pandemic has caused a surge in demand for face masks,with the massive consumption of masks leading to an increase in resource-related and environmental con-cerns.In this work,we fabricated meltblown polypropylene(mb-PP)-based high-performance planar face masks and investigated the effects of six commonly used disinfection methods and various mask-wearing periods on the reusability of these masks.The results show that,after three cycles of treatment using hot water at 70℃ for 30 min,which is one of the most scalable,user-friendly methods for viral disinfection,the particle filtration efficiency(PFE)of the mask remained almost unchanged.After mask wearing for 24 h and subsequent disinfection using the same treatment procedures,the PFE decreased to 91.3%;the average number of bacterial and fungal colonies was assessed to be 9.2 and 51.6 colony-forming units per gram(CFU∙g^(-1)),respectively;and coliform and pyogenic bacteria were not detected.Both the PFE and the microbial indicators are well above the standard for reusable masks after disinfection.Schlieren pho-tography was then used to assess the capabilities of used and disinfected masks during use;it showed that the masks exhibit a high performance in suppressing the spread of breathed air.

An improved CFD model of gas flow and particle interception in a fiber material

An improved CFD model of gas flow and particle interception in a fiber material which fiber size is Y-shape was developed in this work. The porous medium model was used to build the model of the whole size of fiber filter medium. Mixture model was adopted. The algorithm of particle interception in the whole size of fiber filter medium was derived and UDF(User Defined Function) that described kinds of particle filtering mechanisms in filter fibrous media was added to the Fluent default conservation equation as source term for simulation. The inertial resistance of the filter was taken into consideration, which provided a more precise measurement of the smoke flow and the particle interception in the filter under higher smoke speed conditions. The commercial software, Fluent 6.3, was used to simulate the smoke flow and particle interception in the filter in a single suction. The velocity and pressure profiles of smoke or nicotine particle in the filter, as well as nicotine particle volume fraction profile were well simulated. Finally, the comparisons of nicotine particle filtration efficiency between Fluent simulation results in this work and experimental results, as well as the model prediction in the literature were made to validate the simulation model. The comparisons showed that the particle entrapment model from simulation results was in good agreement with that from the experimental results. In addition, the Fluent simulation results are closer to reality both at the beginning and the end of the smoke process comparing with the model predicted results in the literature.

Preparation of High-precision Electrospun Nanoair Filter Paper for Air Purification

Electrospinning technology has become a research hotspot becauseof its advantages, such as simple operation, low cost, large specific surfacearea, high porosity, and good fiber continuity. Here, a new type of compositenanoair filter paper was prepared using electrospinning technology. Toimprove the practicability of air filter base paper, phenolic resin was used as acuring agent to improve the strength. The results show that the electrospunnanoair filter paper with air filter paper as the receiving substrate andpolyvinyl alcohol (PVA) solution as the spinning solution excellentlyperformed in all aspects. The influence of the thickness (spinning time) of thePVA nanofiber membrane on the micromorphology, physical properties, andfiltration performance of the electrospun nanoair filter paper was analyzed.According to the ISO 5011-2014 standard, the initial resistance, filtrationefficiency, mean pore size, and dust capacity of the electrospun nanoair filterpaper were 77.3 Pa, 99.9941%, 3.50 μm, and 146 g/m^(2), respectively, when thespinning time was 15 min.

An indoor air aerosol model for outdoor contaminant transmission into occupied rooms

The paper presents a simple model for outdoor air contaminant transmission into occupied rooms. In the model, several factors such as filtration, ventilation, deposition, re-emission, outdoor concentration and indoor sources are included. The model results show that the air exchange rate plays an important role in the transmission of outdoor contaminants into the indoor environment. The model shows that increasing the value of the filtration efficiency decreases the mass concentration of indoor particles. In addition, if outdoor aerosol particles have a periodic behaviour, indoor aerosol particles also behave periodically but smoother. Indoor sources are found to be able to increase indoor concentrations greatly and continuously.

Numerical study on the filtration characteristics of fine particles in granular bed filter at high temperature

Granular bed filter(GBF)has become one of the current research hot topics due to its excellent performance in removing fine particles.In this paper,a three-dimensional fixed bed GBF filtration model was established and its accuracy was verified.Then,the GBF filtration performance at high temperature were studied.The results demonstrate that elevating the temperature diminishes the filtration efficiency,albeit to a limited extent.The increasing of inlet gas velocity can significantly improve pressure drop for GBF and the filtration efficiency for fine particles of sizes larger than 5μm.As the diameter of stacked granular particle diameter grows,the filtration efficiency and pressure drop drops.The density of fine particles almost does not affect the filtration efficiency for fine particles of 1∼7μm,but a higher density leads to a higher filtration efficiency for fine particles of sizes bigger than 9μm.Additionally,as the fine particles size increases,the change of the filtration efficiency roughly goes through three stages:Stage 1:the filtration efficiency is basically unchanged;Stage 2:the filtration efficiency increases rapidly;Stage 3:the filtration efficiency increases steadily,but the rate of increase slows down.With the increase of the fine particles Stokes number,the filtration efficiency of GBF will pass through two phases of stabilization and rapid increase.

Filtration characteristics of granular bed with layered drawers for removing dust from gas streams

Filtration tests were conducted on a granular bed filter with layered drawers filled with corundum particles with sizes between either 1 mm and 1.5 mm or 2 mm and 3 mm or with quartz sand particles with sizes between 0.125 mm and 1.5 mm.Filtration velocity,filter particle thickness,and filter particle size were all found to influence the filtration efficiency and the pressure drop of both the fixed granular bed and the layered-drawer granular bed.Granular strata with different thickness ratios also strongly influenced the filtration efficiency and pressure drop.For a granular bed with two sizes of filter particles,the coarse granules in the upper layer capture dust with large particle sizes,while the fine granules in the lower layer capture dust with smaller particle sizes that passes through the filter cake and upper layer.Optimal operating conditions were determined at which the filtration efficiency was found to be 99.42%with a bed pressure drop of 320 Pa.

Charged ultrafine particle filtration through vehicular cabin air filters

Understanding the effectiveness of cabin air filters is important for assessing human exposure to ultra- fine particles （UFPs） of vehicular origin. The filtration efficiency of vehicular UFPs with electric charges was investigated for different electric charge characteristics （charge state, charge polarity）. The average filtration efficiency increased ~10% as the electric charge state on the particles changed in distribution from lightly charged to highly charged. The enhancement of filtration efficiency due to electric charge was different at various filter-face air velocities. As electric charges increased, the filtration efficiency increased 12% and 9% at low air velocity （0.1 m/s） and high air velocity （0.S m/s）, respectively. The filter fiber material poses somewhat effect on the filtration efficiency change due to the electric charge. The effects of filter usage and charge polarity on filtration efficiency due to the electric charge were negligi- ble. A coefficient was empirically derived and successfully accounts for the electric charge effect on UFP filtratinn efficiency.

Modeling the performance of air filters for cleanrooms using lattice Boltzmann method

Air filters with a low resistance,high filtration efficiency,and long lifetime are important to ensure good indoor air quality.In this study,the lattice Boltzmann method is applied on six types of fibrous filter media with lognormal-distribution models,which consider the influence of the solid fraction,number of fibers,and average fiber diameter.The influences of the filtration velocity and fiber layout on the resistance,efficiency,and quality factor are discussed.The resistance is found to be relatively low when the solid fraction inside the filter media is uniformly distributed.The filter media with a random lognormal-distribution model demonstrated the best filtration performance in terms of quality factor.However,when the solid fraction is uniform along the thickness of the filter media,the comprehensive filtration performance is the best when a small fiber is near the inlet and a large one is close to the outlet.This study provides a viable numerical method for performance optimization of air-filtration devices for the next-generation cleanroom industry.

Experimental Investigation of a Cryogenic Filter for Separating Solid Carbon Dioxide Particles from Liquid Nitrogen

This paper presents an investigation of a new method of purifying cryogenic liquid using sintered metallic wire-mesh filter, which has the advantages of high purifying efficiency and preferred strength at absolutely low temperature. Experiments are conducted to purify solid CO2 particles from liquid nitrogen. Temperature and pressure in the upstream and downstream of the filter, and the flow rate of carbon dioxide （CO2） gas and liquid nitrogen are measured, with the gas content of filtrate analyzed using a CO2 concentration detector. It is illustrated that after filtration, the purity of liquid nitrogen （volume fraction） is higher than 99.99%, which means that the volume fraction of CO2 is less than 0.01%. Effects of operation parameters on the performance of the filter, such as pressure drop Ap and filtration efficiency E are analyzed quantitatively. The present conclusions will provide a guideline to the optimumal design and operation of sintered metallic wire-mesh filter in cryogenic application.

Design of a Low Respiratory Resistance Mask for COVID-19

Observational evidence suggests that mask-wearing mitigates transmission of COVID-19;at the same time high respiratory resistance leads to an unwillingness to wear masks.This paper proposed a respiratory drive structure to reduce the air resistance of a mask.This structure provides different shapes during expiration and inspiration while focusing on filtering dust,bacteria,or viruses.Meanwhile,the assembled system on the mask can be disassembled and replaced.Then porous media simulation is used to verify the model effect.Experimental results of a new mask show that the ventilation resistance is reduced by 20%,and the bacterial filtration efficiency meets the requirements of YY 0469–2011.