Collection Efficiency Of Filters Research Articles

Investigation of Lubricant Additive Interactions on Gasoline Particulate Filters

<div>To understand how the composition of novel lubricant additives and their ash interact with gasoline particulate filters (GPFs), an accelerated aging protocol was conducted using three lubricant additive formulations and two GPF types. The additive packages (adpaks) consisted of Ca+Mg detergent in a 3:1 or 0:1 ratio and an anti-wear component—either zinc dialkyl dithiophosphate (ZDDP) or a novel phosphonium-phosphinate ionic liquid (IL) substitute. The particulate sampling captured amount/compositions of particulate matter (PM) generated, total particulate number, and size distribution. Five ash loadings were completed. GPF position and adpak composition affected the backpressure, ash composition, ash morphology, and captured mass. The particulate sampling indicated that the ash component consisted primarily of particles less than 50 nm in size and that the Mg-only adpak resulted in more particulate of 50–400 nm in size. Postmortem materials characterization indicated GPFs in the underfloor position had deeper penetration of ash into the walls compared to the close-coupled position. Additionally, the Mg-only adpak had a higher filter collection efficiency (>90%) and the ash particles consisted of a higher concentration of dense ash material. In contrast, four of the 3:1 Ca:Mg lubricant adpaks resulted in a collection efficiency of only 40–50%. Although the collection efficiency was higher with the Mg-only adpak, the ash layer in the GPF was not thicker, nor was the penetration into the wall more significant, and surprisingly the full useful life (FUL) backpressure was lower than with Ca:Mg adpaks. The higher density of the Mg-derived ash was the only detectable difference. A possible explanation of this observation is that Mg ash has a lower melting point and is more susceptible to densification during combustion or GPF regeneration. The substitution of IL in place of the ZDDP did not lead to any notable changes in collection efficiency or location of the ash.</div>

Optimized pleat geometry at specific pleat height in pleated filters for air purification.

The performance of an air purifier is determined by its clean air delivery rate (CADR), expressed as the product of the air flowrate and filter collection efficiency. A high CADR in a commercial air purifier is achieved using a pleated air filter with high filtration performance at a given air flowrate. However, obtaining this high filtration performance depends on the knowledge of the manufacturer, including the optimal pleating design, which remains uncertain to date. In this study, test pleated filters were prepared by folding a flat electrostatically-charged E12 filter medium to obtain different pleating geometries. The proper pleat geometry of the pleated filter, which has a minimum pressure drop at a fixed air flowrate, was dependent on the pleat length (PL ) and pleating ratio (α=pleat height/pleat width), wherein as the PL increases, the α range required to achieve a minimum pressure drop similarly increases. Based on the filter quality factor (qF ), the optimal pleat geometry of a pleated filter was between α values of 6-8, irrespective of the PL . Although both PL and α have certain influences on the qF , α has a greater influence on the pleated filter with no dead zone.

Effect of filter collection efficiency on the clean air delivery rate in an air cleaner.

The performance of an air cleaner is evaluated by the clean air delivery rate (CADR), which is defined as the measure of the delivery of contaminant-free air. Herein, we conducted comparative analyses of various particulate air filters with various collection efficiencies. We installed each filter in identical commercial air cleaners to determine the effects of the collection efficiency on the CADR. Three different filters (E11, E12, and H13 classes) were prepared to determine the effects of the filter collection efficiency and pressure drop on the air cleaner performance (ie, the CADR). Based on experimental data, filters E11 and E12 had similar CADRs and flow rates. However, filter H13, which had the highest collection efficiency and the lowest flow rate, had the lowest CADR. This indicates that even if a filter with higher collection efficiency is installed in an air cleaner, the larger pressure drop causes a reduction in the air flow rate. The CADR value is widely distributed for a flow rate range for commercially available models; however, the collection efficiencies for most air cleaners on the market lie in a narrow range. Therefore, the flow rate has the most direct impact on the performance of a commercial air cleaner.

Autoclave sterilization and ethanol treatment of re-used surgical masks and N95 respirators during COVID-19: impact on their performance and integrity

SummaryBackgroundAn exceptionally high demand for surgical masks and N95 filtering facepiece respirators (FFRs) during the COVID-19 pandemic has considerably exceeded their supply. These disposable devices are generally not approved for routine decontamination and re-use as a standard of care, while this practice has widely occurred in hospitals. The US Centers for Disease Control and Prevention allowed it “as a crisis capacity strategy”. However, limited testing was conducted on the impact of specific decontamination methods on the performance of N95 FFRs and no data was presented for surgical masks.AimWe evaluated common surgical masks and N95 respirators with respect to the changes in their performance and integrity resulting from autoclave sterilization and a 70% ethanol treatment; these methods are frequently utilized for re-used filtering facepieces in hospitals.MethodsThe filter collection efficiency and pressure drop were determined for unused masks and N95 FFRs, and for those subjected to the treatments in a variety of ways. The collection efficiency was measured for particles of approximately 0.037–3.2 μm to represent aerosolized single viruses, their agglomerates, bacteria and larger particle carriers.FindingsThe initial collection efficiency and the filter breathability may be compromised by sterilization in an autoclave and ethanol treatment. The effect depends on a protective device, particle size, breathing flow rate, type of treatment and other factors. Additionally, physical damages were observed in N95 respirators after autoclaving.ConclusionStrategies advocating decontamination and re-use of filtering facepieces in hospitals should be re-assessed considering the data obtained in this study.

A low-cost particulate matter (PM<sub>2.5</sub>) monitor for wildland fire smoke

Abstract. Wildfires and prescribed fires produce emissions that degrade visibility and are harmful to human health. Smoke emissions and exposure monitoring is critical for public and environmental health protection; however, ground-level measurements of smoke from wildfires and prescribed fires has proven difficult, as existing (validated) monitoring technologies are expensive, cumbersome, and generally require line power. Few ground-based measurements are made during fire events, which limits our ability to assess the environmental and human health impacts of wildland fire smoke. The objective of this work was to develop and validate an Outdoor Aerosol Sampler (OAS) – a filter-based air sampler that has been miniaturized, solar powered, and weatherproofed. This sampler was designed to overcome several of the technical challenges of wildland fire monitoring by being relatively inexpensive and solar powered. The sampler design objectives were achieved by leveraging low-cost electronic components, open-source programming platforms, and in-house fabrication methods. A direct-reading PM2.5 sensor was selected and integrated with the OAS to provide time-resolved concentration data. Cellular communications established via short message service (SMS) technology were utilized in transmitting online sensor readings and controlling the sampling device remotely. A Monte Carlo simulation aided in the selection of battery and solar power necessary to independently power the OAS, while keeping cost and size to a minimum. Thirteen OAS were deployed to monitor smoke concentrations downwind from a large prescribed fire. Aerosol mass concentrations were interpolated across the monitoring network to depict smoke concentration gradients in the vicinity of the fire. Strong concentration gradients were observed (spatially and temporally) and likely present due to a combination of changing fire location and intensity, topographical features (e.g., mountain ridges), and diurnal weather patterns. Gravimetric filter measurements made by the OAS (when corrected for filter collection efficiency) showed relatively good agreement with measurements from an EPA federal equivalent monitor. However, the real-time optical sensor (Sharp GP2Y1023AU0F, Sharp Electronic Co.) within the OAS suffered from temperature dependence, drift, and imprecision.

A simple semi-numerical model for designing pleated air filters under dust loading

In this work, we present a semi-numerical 2-D model for predicting the instantaneous pressure drop and collection efficiency of filters made up of rectangular and triangular pleats in both depth and surface filtration regimes. Inspired from previous CFD simulations, our semi-numerical model adopts appropriate average velocity profiles in the axial and lateral directions to approximate the flow field inside rectangular and triangular pleat channels. The model therefore circumvents the need to obtain a CPU-intensive solution for the partial differential equations governing the flow through a filter, i.e., Navier–Stokes equations. The above-mentioned analytical flow field can then be used to predict the trajectory of the particles flowing through the pleat channels by numerically solving the equation of motion for each particle—a simple set of second order ordinary differential equations. With the particles trajectories obtained, the deposition location and so the dust-cake profile can be approximated. This allows one to predict the instantaneous pressure drop and collection efficiency of a filter (filter’s service life) with a CPU-time of practically zero min. The model developed in this work is aimed at providing the aerosol filtration industry with a fast, but yet fairly accurate method of designing pleated filters. A brief parametric study is presented for model demonstration. In addition, a comparison between the predictions of our model and some experimental data from literature is presented for completeness of the study.

3-D microscale simulation of dust-loading in thin flat-sheet filters: A comparison with 1-D macroscale simulations

In this work, a microscale approach is undertaken to simulate the instantaneous pressure drop and collection efficiency of fibrous media exposed to particle loading, i.e., filter aging. The air flow field through 3-D disordered geometries representing the internal microstructure of a fibrous filter is obtained by numerically solving Stokes' equations. A Lagrangian approach is used to track the trajectory of particles through our virtual filter media and determine the filter's collection efficiency under different dust-load conditions. The calculations were conducted using the ANSYS CFD code enhanced with a series of in-house C++ subroutines. To better illustrate the value of such CPU-intensive 3-D microscale modeling, we compared the results of our simulations with those obtained from a 1-D macroscale model developed based on some of the pioneering studies reported in the literature. It was found that while the 1-D macroscale models can provide fast predictions for the pressure drop and collection efficiency of a given filter, they require a series of empirical correction factors or case-specific assumptions that limit their usage for design and development of new filter media. The 3-D microscale simulation methods, in contrast, are self-sufficient as they are developed based on first principles. With the current rate of progress in developing high-speed computers, it is expected that 3-D microscale simulations will be the preferred method of filter design in the near future.

Single-Fiber Diffusion Efficiency for Elliptical Fibers

Fibers with elliptical cross-sections have higher surface to volume ratios than those with circular cross-sections and may therefore lead to increased filter collection efficiency. Single-fiber theory and velocity flow fields developed for elliptical fibers can be used to predict collection efficiency by diffusion for elliptical fibers. Utilizing the convective diffusion equation in elliptical coordinates, single-fiber diffusion efficiency was calculated for 4,312 combinations of cross-section aspect ratio, filter solidity, orientation of the cross-section to the air flow, and Peclet number. An empirical expression was developed from the results of these model runs to predict single-fiber diffusion efficiency for any combination of conditions. The equation indicates that diffusion efficiency is most strongly influenced by the Peclet number because decreases in particle size and increases in air velocity affect diffusion substantially. Increases in aspect ratio and solidity also increase the diffusion effi...

Collection Efficiency for Filters with Staggered Parallel Y and Triple Y Fibers: A Numerical Study

A numerical study is performed to determine the collection efficiency of filters composed of staggered parallel Y and triple Y fibers. By employing the Lattice Boltzmann method, the Navier–Stokes equations are solved for flow fields in a two-dimensional domain with periodic boundary conditions. Trajectories of particles with different diameters arranging from 0.02 μm to 5 μm are then computed by solving the particle motion equation hence obtaining the collection efficiency of single Y and triple Y fibers. The effects of fiber orientation, Brownian motion, particulate size and Reynolds number on the collection efficiency of these two types of fibers are also evaluated numerically. Y and triple Y fibers have low packing density and relatively large area to volume ratio, and the latter property helps enhance the Brownian diffusion collection mechanism for smaller particles. The large void zone of these fibers can accommodate more particles, which improves the particle loading capacity. It is also found out that the flow field and collection efficiency of triple Y fiber is less susceptible to different fiber orientations due to its geometric symmetry. The numerical results obtained in this work provide helpful information in designing high efficiency filters.

Differentiating Between Physical and Viable Penetrations When Challenging Respirator Filters with Bioaerosols

AbstractThe feasibility of a novel testing protocol that allows differentiating between the physical (total) and viable bioaerosol penetrations through respirator filters was investigated. Three respirator models – two conventional N95 filtering‐facepiece respirators (FFR) used as controls and one P95 iodinated polymer FFR with antimicrobial properties – were challenged with aerosolized MS2 bacteriophage virus. Physical (Pphysical) and viable (Peviabl) filter penetrations were simultaneously measured with the FFR sealed on a manikin at a constant inhalation flow rate of 85 L/min. Separate testing was performed on specially‐manufactured P95 filter swatches with (i) no iodinated resin additive and (ii) “high” amount of the additive to determine whether it influenced filtration behavior of the P95 respirator. Bioaerosol collection on the N95 FFR filters fell in the range consistent with previous studies featuring about 2% penetration for MS2 and a peak around ∼︁5%. The P95 iodinated polymer respirator was found to be highly efficient, attributed in part to the iodinated resin powder which in separate swatch tests was found to increase the filter collection efficiency. No statistically significant differences were observed between penetration values obtained for total and culturable viruses for the two control respirators. Similarly, no difference was observed for the iodinated respirator, which suggested that the microbial inactivation effect was of insufficient magnitude to be detected or was not present for viral particles that penetrated the filter. Possible “long‐term” inactivation effect of the iodine‐based additive on the viable viruses, which were captured on the filter over time, was beyond the scope of this study. The novel testing protocol appears to be an adequate tool for evaluating respirators designed to protect against bioaerosol particles. Further improvement may be considered with respect to the aerosolization method for viable microorganisms.

Low-temperature filtration of gases using multilayer cermet filters

The performance characteristics of highly efficient cermet filters with a multilayer membrane structure used for the treatment of nitrogen, argon, helium, methane, carbon monoxide and dioxide at temperatures up to 75 K are studied. It is shown that as the temperature decreases, their collection efficiency with respect to a finely dispersed aerosol decreases. At low Reynolds numbers, the variation of the gas-flow pressure drop through the filters is determined by the gas viscosity. The multilayer nickel-based membrane structure is stable to substantial temperature gradients and can be regenerated by blowing and heating. It is found that the filter collection efficiency for liquid gases is determined by the pore size of the fine-pore selective layer of the filters according to the sieving mechanism of collecting dispersed particles.

Development of a double-layered ceramic filter for aerosol filtration at high-temperatures: The filter collection efficiency

The performance of double-layered ceramic filters for aerosol filtration at high temperatures was evaluated in this work. The filtering structure was composed of two layers: a thin granular membrane deposited on a reticulate ceramic support of high porosity. The goal was to minimize the high pressure drop inherent of granular structures, without decreasing their high collection efficiency for small particles. The reticulate support was developed using the technique of ceramic replication of polyurethane foam substrates of 45 and 75 pores per inch (ppi). The filtering membrane was prepared by depositing a thin layer of granular alumina–clay paste on one face of the support. Filters had their permeability and fractional collection efficiency analyzed for filtration of an airborne suspension of phosphatic rock in temperatures ranging from ambient to 700 °C. Results revealed that collection efficiency decreased with gas temperature and was enhanced with filtration time. Also, the support layer influenced the collection efficiency: the 75 ppi support was more effective than the 45 ppi. Particle collection efficiency dropped considerably for particles below 2 μm in diameter. The maximum collection occurred for particle diameters of approximately 3 μm, and decreased again for diameters between 4 and 8 μm. Such trend was successfully represented by the proposed correlation, which is based on the classical mechanisms acting on particle collection. Inertial impaction seems to be the predominant collection mechanism, with particle bouncing/re-entrainment acting as detachment mechanisms.

Electrostatic Enhancement of Collection Efficiency of the Fibrous Filter Pretreated with Ionic Surfactants

A study of the electrostatic enhancement of collection efficiency of filters pretreated with ionic surfactants has been carried out in controlled conditions with monodisperse aerosols. Cationic surfactant (dimethyl dioctadecylammonium bromide [DDAB]) and anionic surfactant (sodium oleate [SO]) were used to pretreat polypropylene fibrous filters as the positively and negatively charged filters, respectively. The effects of aerosol size, aerosol charge state, face velocity, aerosol type, and relative humidity (RH) were considered to elucidate their influence on the aerosol penetration. Results indicate that penetration through surfactant-pretreated filters was lower than that through untreated filters, and pretreatment of the filter with surfactant was observed not to affect the structure of the filter. The electrofieldmeter direct-measured the very clear electric field of filter when treating ionic surfactants. The results proved that pretreatment with surfactant caused filters to become charged. Comparing penetration through surfactant-pretreated filters with that through untreated filters with neutral aerosol, the penetration reduction factor of the surfactant-pretreated filters was in the range 1.3–2.2. Comparing aerosol penetration through the surfactant-pretreated filters with singly charged aerosol with that through untreated filters with uncharged aerosol indicates that the former decreases by a factor of 1.8–48.8. The surface fiber charges of the DDAB- and SO-pretreated filters were calculated to be 2.02 × 1−10 C/m and −1.53 × 10−10 C/m. Moreover, the aerosol penetrations through the surfactant-pretreated filters increased with the face velocity. Surfactant-pretreated filters performed better against solid aerosol than against liquid aerosol. RH has no effect on aerosol penetration through the surfactant-pretreated filters. Regression equations for Coulombic and dielectrophoretic single-fiber efficiencies in terms of the dimensionless parameters could be fitted by the experimental measurements of surfactant-pretreated filters in this work.

Inertial impaction-dominated fibrous filtration with rectangular or cylindrical fibers

Fibrous filter, being simple in structure and low cost in material, is widely used in fine particulate removal. The collection efficiency of a fibrous filter is heavily dependent on the collection efficiency of a single fiber. Despite the availability of a reasonable formulation for single fiber collection by diffusion, most expressions of collection efficiencies by interception and impaction are empirically based and few simple analytical formulations are available, especially for impaction-dominated collection. In this paper, impaction-dominated fibrous filtration with rectangular fibers for particulate size much smaller than that of the collecting fibers are both numerically and analytically investigated. The effects of fiber aspect ratio, filter packing density, particulate size and Stokes number on the collection efficiency of a rectangular fiber in the impaction-dominated filtration are numerically determined. In addition, simple analytical expressions of single fiber collection efficiencies due to interception and inertial impaction of fine powders are derived based on Kuwabara flow analysis around a cylinder. Hence, using the equivalent hydraulic diameter concept for rectangular fibers with moderate fiber aspect ratios, the effect of particulate polydispersion on the filter collection efficiency is investigated based on presumed mass-based Gaussian size distribution and log-normal size distribution, respectively. Differences between overall size-averaged collection efficiency and mean size collection efficiency can, thus, be estimated.

COLLECTION OF FUNGAL SPORES ON AIR FILTERS AND SPORE REENTRAINMENT FROM FILTERS INTO AIR

The collection of fungal spores on ventilation filters and their potential for subsequent reentrainment were compared with the collection and reentrainment of standard test particles. Potassium chloride (KCl) particles were selected as the standard test particles, as recommended by the ASHRAE standard 52.2. Penicillium brevicompactum and Penicillium melinii were selected to represent common fungal spores in indoor air. Two commonly used filters were tested: medium-efficiency filter medium A from a prefilter and higher efficiency medium B from a fine filter. The collection efficiencies of filters were determined at a face velocity to the pleated filter assembly of 2.54 m s −1 , which is typical for both filters. The collection efficiency was found to be slightly lower for fungal spores than for KCl particles of the same aerodynamic size. When the reentrainment velocity was the same as the loading velocity through the filter medium (0.56 m s −1 for A, 0.09 m s −1 for B), the reentrainment rate was less than 0.4%. When the reentrainment velocity was increased to 3.00 m s −1 , the reentrainment of fungal spores was higher than that of KCl particles: 2–6% for P. brevicompactum, 5–12% for P. melinii, and 0.2–0.6% for KCl particles. The differences in behaviour between fungal spores and KCl particles were attributed to aggregation and deaggregation of fungal spores. The higher reentrainment rate of P. melinii compared to that of P. brevicompactum can be explained by the different surface structure of these spores. The results suggest that during the startup of a ventilation system or during other operations, when the air velocity may suddenly increase, reentrainment of fungal spores can be significant. Furthermore, if fungal spores grow on the ventilation filters, the reentrainment rate may become even higher than measured in this study.

Sub 0.1 Micron Particle Detection and Analysis Using High Sensitivity Nephelometry

This article describes the principles of operation of a novel approach to liquid nephelometry. The use of a modulated laser diode light source in combination with the liquid cell design allows measurements with a sensitivity of 0.00001 NTU, one to two orders of magnitude more sensitive than previous designs. Data presented indicate the instrument response to sub 0.1 micron PSL spheres as well as sensitivity to colloidal silica to 6.3 parts per billion (ppb). Illustrative examples will be given for the application of two simultaneous liquid nephelometers for filter collection efficiency testing as a function of challenge particle size, filter loading, and flow rate.

Fine mist filtration by wet filters—II: Efficiency of fibrous filters

Stainless steel fibrous filters of 4–22 μm wire diameter have been studied as collectors for dense mists of approx. 1 μm particles. The liquid collected in the filter in the steady state when equilibrium has been reached with the aerosol stream is found to increase the filter collection efficiency, sometimes very greatly, under most conditions studied. Only in the diffusional collection regime at very low fibre volume fractions (packing densities) or large fibre diameters does collected liquid diminish the efficiency. These findings are explained in terms of the effect of the liquid distribution on the collection mechanisms. In particular, collected liquid usually increases the efficiency of all significant single fibre collection mechanisms by increasing the effective packing density of the fibres, i.e. by adding to the distortion of a single fibre's flow field caused by neighbouring fibres. An existing model for dry fibrous filters has been modified to take account of the liquid distribution and provides good quantitative prediction of the relative collection efficiency of wet and dry filters having packing densities over 0.04.

Filter Collection of Airborne Permethrin with Determination by HPLC

Abstract Glass microfiber filter was evaluated for the collection of perrrethrin aerosols. Determination and quantification of collected permethrin isomers by high performance liquid chroratography was developed on an octadecyl bonded phase column with an aqueous acetonitrile solvent and ultra-violet detection. Sampling of a test atmosphere of permethrin aerosol indicated a filter collection efficiency greater than 96%. The detection limit of the method for permethrin in air was estimated to be 8 μg/m3 for a 20 L air sample.

Filtration of diesel particles

Pressure drops and collection efficiency have been determined for two Teflon-coated glass fiber filters: Pallflex T60A20 and TX40HI20-WW, and two Teflon membrane filters: Ghia Zefluor 2.0 and 3.0 μm pore size. The T60A20 filter gave the lowest pressure drops but had a clean filter collection efficiency of less than 80%. This efficiency rose quickly as the filter loaded, exceeding 95% for loadings greater than 0.03 mg cm −2. The other filters tested had efficiencies greater than 94% for all of the conditions tested, but had significantly higher pressure drops. The pressure drop produced by the collected particles was examined in some detail. The pressure drop divided by the product of face velocity and mass loading was found to be a constant which depended upon particle size and collection conditions. A relationship between this normalized pressure drop and particle size has been established. It may be used to estimate the mass mean diameter of diesel or diesel-like particles from relatively simple pressure drop measurements.

Assessment of stack gas emitted trace metals from incineration: Determination of filter collection efficiency by condensational enlargement of penetrating submicron particles

A method for collection of trace metals on the surface of submicron particles as well as metal vapour is described. The method and the proposed device are based on particle enlargement by condensation of acidic vapour and subsequent collection by an impactor. The device is intended for use as calibration standard for testing high load sampling systems in stack gas emission measurements. As an example, the collection efficiency of coarse quarts fibre filters towards Zn, Cd, Pb and Cu has been assessed during stack gas sampling from waste incinerators. The filter penetration is discussed in relation to sampling precision, and requirements in the selection of trace metal sampling systems are considered. Less than 13% (in average) of emitted Zn, Cd, Pb and Cu penetrates the commonly used quarts fibre filters.