Filter Thickness Research Articles

A simple approach to simulate corona-charged electret filters

This paper presents a novel computational model devised to simulate how different ways of corona-charging a fibrous filter can impact its aerosol collection efficiency. The model assigns different bipolar charges to the fibers in the media based on how the corona-generated negative ions impact these fibers they travel from the corona needles towards the grounded surface underneath the media. The charge assignment process is based on observations made from simulating the electrohydrodynamic field around the corona needles. With the fibers virtually charged, the trajectory of positively and negatively charged aerosol particles, ranging in size from 30 to 500 nm, were simulated across the filter thickness to quantify the effect of fiber charge distribution on the filter efficiency. The performance of our virtual filter was found to be better when it was exposed to the corona ions on both the face and back sides. More interestingly, it was found that the filtration efficiency of the filter was dependent on the order by which its face and back sides were charged. The filter was observed to capture smaller particles (less than 150 nm) more efficiently when it was first charged on the face side and then charged on the back side. The opposite effect was observed when the charging order was reversed. This difference in filtration performance was found to arise from the differences in the solid volume fraction of the filter across its thickness.

Use of Low Melting Point Alloy Mcp-96 Filter on Gammagraphic Optimization of Patient Position Verification with Telecobalt 60 Machine

Verification of the patient's position is a stage in external radiotherapy that aims to ensure the accuracy of radiation therapy administration according to plan. Equipment for the patient position verification process that is often used is Electronic Portal Image Devices (EPID) and film portals. However, not all Telecobalt 60 machines are equipped with EPID, so it requires alternative equipment to verify patient positions. One modality that can be utilized is Computed Radiography (CR). The study was conducted to analyze the use of MCP-96 low melting point alloy filters in imaging, verifying patient positions with CR devices on telecobalt 60 machine can calibrate radiation doses and provide good image quality and anatomical information. The study used a posttest-only control group design by comparing radiation dose, image quality, and anatomical information of the patient's position verification image. Imaging was performed using a phantom pelvis as an object and using CR equipment and low melting point alloy MCP-96 as a filter. The results showed that low melting points alloy MCP-96 with a thickness of 1 cm, 2 cm and 4 cm can calibrate the radiation dose output of the telecobalt 60 machine in accordance with recommendations for kilovoltage imaging. There was no significant difference in SNR and CNR images from imaging verification of patient positions with filter thicknesses of 1 cm, 2 cm, and 4 cm. Filter thickness of 1 cm produces images with optimal image quality and anatomical information in gammagraphic imaging verification of patient position using CR on telecobalt 60 machine. Thus, the use of low melting point alloy MCP-96 thickness of 1 cm and CR devices can be used in gammagraphic imaging of patient position verification on a telecobalt 60 machine as an alternative if you do not have EPID.

Spectral performance of two split-filter dual-energy CT systems: A phantom study.

Recently, a second generation of split filter dual-energy CT (SFCT) platform has been developed. The thicknesses of the gold and tin filters used to obtain both low- and high-energy spectra have been changed. These differences in filter thickness may affect the spectral separation between the two spectra and thus the quality of spectral images. To compare the spectral performance of two Split-Filter Dual-Energy CT systems (SFCT-1st and SFCT-2nd ) on virtual monoenergetic images (VMIs) and iodine map. A Multi-Energy CT phantom was scanned on two SFCT with a tube voltage of 120 kVp for both systems (SFCT-1st -120 and SFCT-2nd -120) and 140 kVp only for the second generation (SFCT-2nd -140). Acquisitions were performed on the phantom with a CTDIvol close to 11 mGy. Noise power spectrum (NPS) and task-based transfer function (TTF) were evaluated on VMIs from 40 to 70keV. A detectability index (d') was computed to assess the detection of two contrast-enhanced lesions on VMIs. Hounsfield Unit (HU) accuracy was assessed on VMIs and the accuracy of iodine concentration was assessed on iodine maps. For all keV, noise magnitude values were lower with the SFCT-2nd -120 than with the SFCT-1st -120 (on average: -22.5±2.9%) and higher with the SFCT-2nd -140 than with the SFCT-2nd -120 (on average: 25.0±6.2%). Average NPS spatial frequencies (fav ) were lower with the SFCT-1st -120 than with the SFCT-2nd -120 (-6.0±0.5%) and the SFCT-2nd -140 (-3.6±1.6%). Similar TTF50% values were found for both systems and both kVp for blood and iodine inserts at 2mg/mL (0.29±0.01mm-1 ) and at 4mg/mL (0.31±0.01mm-1 ). d' values peaked at 40keV for the SFCT-2nd and at 70keV for the SFCT-1st . Highest d' values were found for the SFCT-2nd -120 for both simulated lesions. Accuracy of HU values and iodine concentration was higher with the SFCT-2nd than with the SFCT 1st . Compared to the SFCT-1st , with similar spatial resolution and noise texture values, the SFCT-2nd -120 exhibited the lowest values for noise magnitude, the highest detectability index values, and more accurate HU values and iodine concentrations.

Optimization of parameters for portable X-ray diffraction/X-ray fluorescence combined analysis device (P-XRDF-CAD)

This paper aims to optimize the parameters of a portable device that combines X-ray diffraction (XRD) and X-ray fluorescence (XRF) analysis techniques. By using the same X-ray source and detector, the device enables the simultaneous acquisition of two-dimensional XRD and XRF information from a sample with the advantage of high analysis efficiency and consistency in the measurement points. The equipment and slit materials are discussed, including the selection of the X-ray source (Moxtek MAGNUM) and the detector (Andor CCD camera). We also explore two different slit designs (the bottom-hole and side-hole) and optimize their dimensions using rectangular holes instead of inclined trapezoidal holes. Considering the fluorescence X-rays of the filters in the X-ray tube spectra, a theoretical formula is derived for rapid and accurate calculation. The calculated results are compared with the experimental results of Al and Ni filters, demonstrating good agreement across various tube voltages and filter thicknesses. Furthermore, an XRD/XRF comprehensive analysis platform is established. The effects of tube voltage, tube current, exposure time, and pixel-binning on the single-pixel events of the CCD camera are investigated and can be used to guide the selection of appropriate device parameters. The effects of the frame and tube voltage on the XRD/XRF analysis efficiency are examined for several sample materials, including Al, α-Fe, Zn, and ZrO2(Y2O3).

Proposing an intelligent technique based on radial basis function neural network to forecast the energy spectrum of diagnostic X-ray imaging systems

In digital subtraction angiography (digital subtraction total cerebral angiography), cardiac and macrovascular cardiography, anorectal radiology, fluoroscopy, and computed tomography (CT), a prior knowledge to X-ray energy spectrum is crucial for assessing the image quality and also calculating patient X-ray dosage. The present investigation's main objective is to propose an intelligent technique for faster calculating X-ray energy spectrum of medical imaging systems with different exposure settings of tube voltage, filter material, and thickness based on limited specific spectra. In this study, Monte Carlo N Particle (MCNP) simulation code was initially used to generate some limited X-ray spectra for tube voltages of 20, 30, 40, 50, 80, 100, 130, and 150 kV for two different filters of beryllium and aluminum with thicknesses of 0. 4, 0.8, 1.2, 1.6 and 2 mm. Tube voltage, type, and thickness of filter were used as the 3 inputs of 150 Radial Basis Function Neural Network (RBFNN) to forecast point by point of the X-ray spectrum. After training, the RBFNNs could forecast most of the X-ray spectra for tube voltages in the range of 20–150 kV and two various filters of aluminum and beryllium with thicknesses in the range of 0–2 mm.

Design of an in-tank thermal neutron beam for PGNAA application at Isfahan MNSR

Calculations have been done in order to achieve a thermal neutron beam for Prompt Gamma Neutron Activation Analysis (PGNAA) applications using Miniature Neutron Source Reactor (MNSR) as neutron source. The MNSR is a 30 kW tank-in-pool reactor and there are ten small occupied in-tank irradiation positions. Also, there are four positions in order to install or remove aluminum Regulating Rod Tubes (RRTs) that are bigger than that ten irradiation positions. In this study, the eastern RRT has been selected for more simulations of thermal neutron beam. Thermal neutron flux (φth), the ratio of thermal neutron flux to gamma dose rate (φthDγ), and the ratio of thermal neutron flux to total neutron flux (φthφtot) have been considered in calculations as important neutron beam parameters. Some designs have been done and simulated using MCNP code. The effect of the height of beam inlet, the effect of the different materials and thickness of moderators, and the effect of different thickness and height of gamma filters on the beam parameters at the beam outlet have been investigated. The results of different designs showed that using appropriate heights and thicknesses, by using bismuth as gamma filter and heavy water as moderator, φth, φthφtot and φthDγ, are 1.64E + 06n.cm−2.s−1, 0.789, and 4.36E + 05n.cm−2.μSv−1 respectively. Also, by using bismuth as gamma filter and graphite as moderator, these parameters are 1.57E + 06n.cm−2.s−1, 0.761, and 4.69E + 05E + 05n.cm−2.μSv−1, respectively.

Effect of varying X-ray tube voltage and additional filtration on image quality and patient dose in digital radiography system

This study investigated the effect of varying x-ray tube voltage and additional filtration thicknesses on radiation dose and image quality in digital radiography system. The polymethylmethacrylate (PMMA) phantoms of different thicknesses simulating both the adult chest and abdomen and the pediatric patient's chest examinations were used. X-ray tube voltage range of 70–125 kVp was used for adult patient chest radiography, 70–100 kVp for adult patient abdominal radiography, and 50–70 kVp for pediatric 1-year-old chest examination. 0.1–0.3 mm Cu and 1.0 mm Al filters were used as additional filters. Patient doses were measured with an ionization chamber, considering the irradiation parameters recommended for radiographic examinations performed in radiology clinics in the EUR 16260 protocol. The Entrance Skin Dose (ESD) was calculated from the air kerma value measured at the entrance surface of the PMMA phantoms. Effective dose values were calculated by employing PCXMC 2.0 program. For image quality evaluations, CDRAD, LCD-4, Beam stop and Huttner test object used together with PMMA phantoms and Alderson RS-330 Lung/Chest phantom were used. Figure of Merit (FOM), which allows quantitative assessment in terms of image quality and patient dose, has been calculated. Based on the calculated FOM values were evaluated at the tube voltages and additional filter thicknesses recommended in the EUR 16260 protocol. Entrance Skin Dose and Inverse Image Quality Figure (IQFinv) value obtained from contrast detail analysis decreased with increasing filter thickness and tube voltage. Decrease in ESD and IQFinv with increasing tube voltage without additional filter was 56% and 21% for adult chest radiography, 69% and 39% for adult abdominal radiography and 34% and 6% for 1-year-old pediatric chest radiography. When calculated FOM values are examined, it can be recommended to use a 0.1 mm Cu filter at 90 kVp and a 0.1 mm Cu + 1.0 mm Al filter at 125 kVp for adult chest radiography. For adult abdominal radiography, 0.2 mm Cu filter at 70 and 80 kVp and 0.1 mm Cu filter at 90 and 100 kVp were found to be appropriate. It was determined that the appropriate additional filter at 70 kVp for 1-year-old chest radiography was 1.0 mm Al+0.1 mm Cu.

Performance Evaluation of High Efficiency Particulate Filters for The Removal of Sub-Micrometer Radioactive Aerosols in Nuclear Power Reactors. Simulation Study

The removal of radioactive aerosols has always been one of the key issues of air decontamination in a nuclear power plant to reduce both the exposure of the radiation workers inside the NPP and environmental radiation impact. Radioactive aerosols may be removed using nuclear grade High Efficiency Particulate Air filters. The thickness of the particulate filter is function of many parameters like the particle size, the fiber diameter, the face velocity and the ratio volume of fiber/volume of filter. In this work we evaluated, by using a semi empirical model, the effect of different parameters (fiber diameter, particle size, face velocity) on the performance of the HEPA filters to reach an efficiency removal above 99.99%. The results suggest that thin layers of fiber, can work as an efficient and cost-effective filter. This study revealed that the thickness of the filter showed a positive correlation with the face velocity, but negative correlation with fiber diameter and particle diameter. It is also found that the efficiency removal is higher for lower particle velocities in air stream.

Improvement approach for determination of cadmium at trace levels in soils by handheld X-ray fluorescence analyzers

Determining trace levels of cadmium in soils by the handheld X-ray fluorescence analyzer is severely hampered by the spectrum baseline. To improve the peak-to-background ratio of the characteristic Cd-Kα X-ray, the filter structure, material, and thickness were optimized; to find the most informative variables for the PLS analysis of trace Cd, the related information enhancement competitive adaptive reweighted sampling (rieCARS) was proposed as a variable selection approach, which contains correlated spectral selection (CSS), double logarithmic processing(DLP), competitive adaptive reweighted sampling (CARS). To eliminate the interference of the K-series line of the Ag anode target on trace Cd, the X-ray tube was used with the Tungsten anode target. One combined filter containing a 0.4 mm thickness Cu and a 0.5 mm thickness Fe was selected, which was placed between the X-ray tube and the sample. The instrumental limit of detection for the Cd descended from 32 mg/kg to 0.02 mg/kg . Sixty-four soil samples were used to establish the model for the filtered signal. The model was compared with PLS, CARS+PLS, DLP + CARS+PLS, CSS + PLS, and CSS + CARS+PLS. The application of rieCARS improved the performance of the calibration model for trace Cd. The coefficient of determination R2 of the rieCARS+PLS model on the calibration set was 0.990; the RMSEP on the test set was 0.28 mg/kg; the average of the relative error in the Poyang Lake soil samples was 0.18; the relative standard deviation for the thirteen replicates of the GSD17 was 0.07. The developed analytical procedure will lay the foundation for the analysis of heavy metal pollution sources in soils and ecological sustainability assessment.

Enhancing air filtration efficiency with triboelectric nanogenerators in face masks and industrial filters

The removal efficiency of traditional air filters decreases with decreasing particle size, requiring the use of highly compact filter layers to achieve high efficiency, resulting in high-pressure drops and power consumption. To address this issue, this study proposes a novel approach by combining triboelectric nanogenerator (TENG) properties with industrial air filters and face masks to improve removal efficiency while maintaining low-pressure drop. The study investigates the impacts of key parameters, such as airflow velocity, particle size, and applied voltage, on filter performance through a developed mathematical model. The optimal voltage range required to remove specific particle sizes is also modeled, and suitable triboelectric materials for producing the optimal voltage are suggested. Results show that the use of the suggested triboelectric-based filter, generated using a polypropylene (PP)-polyurethane (PU) TENG pair, with a 300 µm filter thickness, 30 µm pore size, and 30 µm fiber diameter, enhances the removal efficiency of particles from 23.0 % to 99.0 %. Specifically, a 10 V voltage on the fiber surface enables the removal of particles in the range of 10 nm to 100 µm with an efficiency of 99.0 %, which is 4 times higher than a traditional filter. The study demonstrates the potential of utilizing various antibacterial and polymer-based triboelectric materials in different applications, including self-powered smart face masks and industrial air filters.

Automated extraction of orientation and stratigraphic thickness from geological maps

Geological maps are available for almost every region of the world and, therefore, represent the most commonly used source of information for earth scientists. Advances in computing power and the availability of digital elevation data have opened new possibilities to automatically extract quantitative information from geological maps, especially in regions with topographic relief and good bedrock exposure. We present an innovative approach to automatically extract orientation (dip direction/dip) and stratigraphic thickness from a 1:25′000 geological map vector data set of the Swiss Alps. The approach allows a rapid spatial overview on the orientation and thickness of a given geological unit over large areas. Key improvements of the approach with respect to commonly used 3D modelling approaches are its objectivity, rapidity and the possibility to classify and/or filter orientation and thickness model output after five numeric reliability parameters. The approach is designed to support authorities and the industry in performing a rapid screening of a given region and to early identify promising areas for potential mineral extraction projects. Large-scale spatial overviews on the orientation and thickness of geological units are of large interest in many other disciplines such as tectonic and stratigraphic reconstruction, hydrogeological or geotechnical analyses. Therefore, the approach will be widely applicable also beyond the evaluation of potential mineral resources.

Application of InP Quantum Dot film by Photolithography Technology on a Micro-LED Display

The technical of realizing full-color display by monochromatic integrated 100 × 100 blue Micro-LED array exciting InP quantum dot color conversion layer is researched in this study. Using photolithography technology to prepare color film on a separate glass cover glass has the advantages of better accuracy and display resolution. The optimum thickness 12 μm of the quantum dot photoresist (QDPR) was verified and 10 μm black matrix (BM) was proposed to reduce the light crosstalk between different sub-pixels. The thickness of color filter 1 ± 0.4 μm was made successfully between the QDPR and the cover glass, which can greatly can significantly increase the display color gamut from 78.7% to 100.8% NTSC. The red and green brightness conversion efficiency reach up to 78.1% and 296.5% respectively. Representative RGB monochromatic pictures with 100% high yield were displayed successfully.

Application of bio-slow sand filters for drinking water production: Linking purification performance to bacterial community and metabolic functions

Bio-slow sand filters (BSSFs) are widely employed in rural drinking water treatment ascribing to its economic applicability, easy operation and high efficiency. This study investigated the influence of particle size, filter thickness, water quality and filtration rate on decontamination performance, bacterial community and metabolic function of BSSFs. The effluent ammonia nitrogen during stable operation period basically met the standards for drinking water quality in China (0.5 mg/L). The average removal efficiencies of fine sand were about 4 % higher than those of coarse sand, and thick filter layer showed more stable performance. Schmutzdecke removed most turbidity and organic pollutants, playing an overwhelming role in water purification. Filtration rate was a key factor in shaping bacterial community structure. Proteobacteria and Cyanobacteria were dominant phyla, whose relative abundance significantly decreased and increased as filtration rate increasing, respectively. Co-occurrence patterns were dominant within bacterial communities. Function bacteria (e.g. Hyphomicrobium and Methylophilus) and rare genera (Curvibacter and Simplicispira) were identified as hub genera in the networks. The bacterial communities exhibited a metabolic versatility. Several pathways for secondary metabolism significantly shifted under different conditions, such as xenobiotics biodegradation and metabolism. Moreover, filtration rate and dominant genera greatly affected pollutant removal performance. Many species of Proteobacteria and Bacteroidota were closely related to carbohydrate metabolism, energy metabolism and nucleotide metabolism, and metabolic functions corresponded more cohesively to conditional abundant taxa, conditional rare or abundant taxa, conditional rare taxa. This study highlights the adaptability and bacterial community characteristics of BSSFs, and provides references for their practical application.

Low-dose whole-spine imaging using slot-scan digital radiography: a phantom study

BackgroundSlot-scan digital radiography (SSDR) is equipped with detachable scatter grids and a variable copper filter. In this study, this function was used to obtain parameters for low-dose imaging for whole-spine imaging.MethodsWith the scatter grid removed and the beam-hardening (BH) filters (0.0, 0.1, 0.2, or 0.3 mm) inserted, the tube voltage (80, 90, 100, 110, or 120 kV) and the exposure time were adjusted to 20 different parameters that produce equivalent image quality. Slot-scan radiographs of an acrylic phantom were acquired with the set parameters, and the optimal parameters (four types) for each filter were determined using the figure of merit. For the four types of parameters obtained in the previous section, SSDR was performed on whole-spine phantoms by varying the tube current, and the parameter with the lowest radiation dose was determined by visual evaluation.ResultsThe parameters for each filter according to the FOM results were 90 kV, 400 mA, and 2.8 ms for 0.0 mm thickness; 100 kV, 400 mA, and 2.0 ms for 0.1 mm thickness; 100 kV, 400 mA, and 2.8 ms for 0.2 mm thickness; and 110 kV, 400 mA, and 2.2 ms for 0.3 mm thickness. Visual evaluation of the varying tube currents was performed using these four parameters when the BH filter thicknesses were 0.0, 0.1, 0.2, and 0.3 mm. The entrance surface dose was 59.44 µGy at 90 kV, 125 mA, and 2.8 ms; 57.39 µGy at 100 kV, 250 mA, and 2.0 ms; 46.89 µGy at 100 kV, 250 mA, and 2.8 ms; and 39.48 µGy at 110 kV, 250 mA, and 2.2 ms, indicating that the 0.3-mm BH filter was associated with the minimum dose.ConclusionWhole-spine SSDR could reduce the dose by 79% while maintaining the image quality.

Investigation of the local oil distribution on oleophilic mist filters applying X-ray micro-computed tomography

Nonwoven coalescence filter media are often used in real-world applications to separate droplet aerosols from a gas stream. While mechanisms like droplet deposition, liquid transport and the evolution of the pressure drop are well understood, information on separated liquid structures formed during filtration is scarce. However, this information is important to understand the initial state of the coalescence filtration process, more specifically, the transition from individual deposited droplets to larger oil structures and subsequently the effect of these oil structures on the separation efficiency.In this work, deposited oil structures in the micrometer region of an oleophilic filter medium of different oil loading stages (saturations) are presented for the first time by utilizing micro–computed tomography (μ-CT) and several post-processing steps. The local (determined via μ-CT) and global (determined gravimetrically) porosities as well as local and global saturations are compared and evaluated. While local (Φlocal=0.9575) and global (Φglobal=0.9588) porosities are in good accordance, significant deviations in the saturation are observed. The local saturation fluctuates significantly at the highest investigated oil loading stage. Especially at high global saturations, local areas are completely saturated with oil. Other areas are weakly saturated, which are particularly relevant for the gas flow to pass through the filter media. Furthermore, a novel routine to distinguish between different coalesced oil objects (e.g. oil droplets or oil sails) is developed and presented. It is shown, that the majority of the deposited oil (>80%) is stored in oil sails between adjacent fibers. Oil droplets surrounding fibers are found to be growing in size with increasing oil loading time. In addition, the volume fraction of the deposited oil in the direction of filter thickness shows, that most of the oil is deposited on the upstream side at the first 80% of the filter.

Optical filter wavefront distortion: out-of-band to in-band predictions and the effect of the illumination source bandwidth.

The wavefront distortion (WFD) of a surface with an optical filter coating is ideally measured at the operating wavelength (λ) and angle of incidence (θ) of the filter. However, this is not always possible, requiring that the filter be measured at an out-of-band wavelength and angle (typically λ=633n m and θ=0∘). Since the transmitted wavefront error (TWE) and reflected wavefront error (RWE) can depend on the measurement wavelength and angle, an out-of-band measurement may not give an accurate characterization of the WFD. In this paper, we will show how to predict the wavefront error (WFE) of an optical filter at the in-band wavelength and angle from a WFE measurement at an out-of-band wavelength and different angle. This method uses (i)the theoretical phase properties of the optical coating, (ii)the measured filter thickness uniformity, and (iii)the substrate's WFE dependence versus the angle of incidence. Reasonably good agreement was achieved between the RWE measured directly at λ=1050n m (θ=45∘) and the predicted RWE based on an RWE measurement at λ=660n m (θ=0∘). It is also shown through a series of TWE measurements using a light emitting diode (LED) and laser light sources that, if the TWE of a narrow bandpass filter (e.g.,an 11nm bandwidth centered at λ=1050n m) is measured with a broadband LED source, the WFD can be dominated by the chromatic aberration of the wavefront measuring system-hence, a light source that has a bandwidth narrower than the optical filter bandwidth should be used.

Effect of micro-CT acquisition parameters and individual analysis on the assessment of bone repair.

This study aimed to investigate whether two acquisition parameters, voxel size and filter thickness, used in a micro-computed tomography (micro-CT) scan, together with the examiner's experience, influence the outcome of bone repair analysis in an experimental model. Bone defects were created in rat tibiae and scanned using two voxel sizes of 6- or 12-µm and two aluminum filter thickness of 0.5- or 1-mm. Then, bone volume fraction (BV/TV) and trabecular thickness (Tb.Th) were analyzed twice by two groups of operators: experienced and inexperienced examiners. For BV/TV, no significant differences were found between scanning voxel sizes of 6 and 12 µm for the experienced examiners; however, for the inexperienced examiners, the analysis performed using a 12-µm voxel size resulted in higher BV/TV values (32.4 and 32.9) than those acquired using a 6-µm voxel size (25.4 and 24.8) (p < 0.05). For Tb.Th, no significant differences between the analyses performed by experienced and inexperienced groups were observed when using the 6-µm voxel size. However, inexperienced examiners' analysis revealed higher Tb.Th values when using the 12-µm voxel size compared with 6 µm (0.05 vs. 0.03, p < 0.05). Filter thickness had no influence on the results of any group. In conclusion, voxel size and operator experience affected the measured Tb.Th and BV/TV of a region with new bone formation. Operator experience in micro-CT analysis is more critical for BV/TV than for Tb.Th, whereas voxel size significantly affects Tb.Th evaluation. Operators in the initial phases of research training should be calibrated for bone assessments.

COLLECTION OF SUBMICRON AEROSOL PARTICLES BY FILTERS COMPOSED OF NANOFIBERS

The deposition of aerosol particles from a Stokes flow in filters composed of nanofibers has been considered at Knudsen numbers Kn ∼ 1. The efficiency of particle collection by model filters with 2D and 3D structures has been determined by numerical simulation as depending on particle radius rp , filter parameters (nanofiber radius a, packing density α and filter thickness), and filtration conditions taking into account the gas slip at the fibers.It has been shown that the efficiencies of particle collection by nanofibers in model 2D and 3D filters are almost equal at the same low packing density 0.02. It has been found that the dependence of the penetration of particles on their radius at a constant velocity on the order of several centimeters per second and at Kn ∼ 1 passes through a maximum, which corresponds to particle radius rp ∼ a. The calculated sizes of the most penetrating particles agree with experimental data. The results obtained will be used when selecting aerosols for testing nanofibrous filters.

Recent developments in design criteria for granular and geotextile filters

Granular and geotextile filters are commonly provided in several hydrological infrastructures to limit soil erosion and allow unimpeded water seepage. The success of a filter depends on forming a bridging structure, which is governed by the grain size distribution of soil and the constriction size distribution of filter. Currently, the retention requirement is satisfied considering representative grain and opening size, whereas the hydraulic conductivity requirement is satisfied considering empirical factors for avoiding excessive clogging. In this paper, the design criteria for granular and geotextile filters are reviewed, and improved design criteria are presented. A probabilistic retention criterion is developed, considering the grain size and constriction size as random variables. The influence of filter thickness is incorporated into the criterion by considering the number of constrictions in a filtration path. A hydraulic conductivity criterion is developed theoretically based on governing flow equations and the expected partial clogging of geotextiles. The limit states for the developed criteria are evaluated based on the wide range of experimental data. The developed design criteria are applicable to granular and nonwoven geotextiles, which offers an improvement in design compared to the existing criteria in practice.

Efficacy of Do-It-Yourself air filtration units in reducing exposure to simulated respiratory aerosols

Many respiratory diseases, including COVID-19, can be spread by aerosols expelled by infected people when they cough, talk, sing, or exhale. Exposure to these aerosols indoors can be reduced by portable air filtration units (air cleaners). Homemade or Do-It-Yourself (DIY) air filtration units are a popular alternative to commercially produced devices, but performance data is limited. Our study used a speaker-audience model to examine the efficacy of two popular types of DIY air filtration units, the Corsi-Rosenthal cube and a modified Ford air filtration unit, in reducing exposure to simulated respiratory aerosols within a mock classroom. Experiments were conducted using four breathing simulators at different locations in the room, one acting as the respiratory aerosol source and three as recipients. Optical particle spectrometers monitored simulated respiratory aerosol particles (0.3–3 μm) as they dispersed throughout the room. Using two DIY cubes (in the front and back of the room) increased the air change rate as much as 12.4 over room ventilation, depending on filter thickness and fan airflow. Using multiple linear regression, each unit increase of air change reduced exposure by 10%. Increasing the number of filters, filter thickness, and fan airflow significantly enhanced the air change rate, which resulted in exposure reductions of up to 73%. Our results show DIY air filtration units can be an effective means of reducing aerosol exposure. However, they also show performance of DIY units can vary considerably depending upon their design, construction, and positioning, and users should be mindful of these limitations.