Particle Penetration Efficiency Research Articles

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

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

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

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

CFD modeling of black powder particles deposition in 3D 90-degree bend of natural gas pipelines

Black powder deposition is the common problem in the natural gas transmission networks that occurs in some parts of the pipelines, especially in the bends. In this work, the flow of natural gas-particles was simulated within the Eulerian-Lagrangian framework in an industrial 90-degree bend based on the 3D computational fluid dynamics (CFD) tool. The shear stress turbulence (SST) model was applied to simulate the fully developed turbulent gas flow. The size range of the black powder particles was considered within 1–100 μm with Stokes number (Stk) in the range of 0.001–11.25 to include the low and high inertia particles. The results showed that the penetration efficiency of the smaller black powder particles is higher than larger ones and follow the flow streamlines easily without significant deposition on the inner walls. In addition, the particle penetration efficiency in the bend curvature, is considerably less than other straight parts of the pipe, revealing that the particle deposition occurs significantly in those region. It was also observed that the penetration parameter is independent of the number of black powder particles. The effects of the natural gas flow velocity and pipe diameter size on the particle deposition were also investigated. According to the obtained results, increasing the gas flow velocity leads to a decrease in the particles penetration efficiency, consequently increase the particle deposition. The accuracy of the model verified via some available particle deposition data in the literature.

A Sampling and Conditioning Particle System for Solid Particle Measurements Down to 10 nm

<div class="section abstract"><div class="htmlview paragraph">The measurement of vehicle particle number emissions and, therefore, regulation, necessitates a rigorous sampling and conditioning technology able to deliver solid emitted particles with minimum particle losses. European legislation follows a solid particle number measurement method with cutoff size at 23 nm proposed by the Particle Measurement Programme (PMP). Accordingly, the raw exhaust is sampled with constant volume, subsequently passes through a volatile particle remover (VPR), and finally is measured with a particle counter. Lowering the 23 nm cutoff size with current VPR technologies introduces measurement uncertainties mainly due to the high particle losses and possible creation of artefacts.</div><div class="htmlview paragraph">This study describes the development and evaluation of a sampling and conditioning particle system, the SCPS, specially designed for sub-23 nm solid particles measurement. The dilution process is achieved in two stages; the primary dilution is done with a porous tube while the secondary with an ejector diluter that also acts as a pump for the sampling flow. The SCPS offers flexibility in terms of dilution ratio (DR) which is real-time calculated with an algorithm based on a differential pressure measurement across an orifice. Between the two dilution stages, a catalytic stripper removes volatile material with high efficiency. The SCPS evaluation includes the DR calculation algorithm testing, the stability of DR during transient engine conditions, the volatile particle removal efficiency with tetracontane particles, the solid particle penetration efficiency with polydisperse CAST-generated soot particles, and the measurement of sub-23 nm particles emitted by a diesel engine. The high stability of the DR in combination with >99% volatile particle removal and a cutoff size (d<sub>50</sub>) at 7.5 nm suggest that the SCPS may deliver solid emitted particles for robust particle number measurements down to at least 10 nm.</div></div>

Rapid measurement of sub-micrometer aerosol size distribution using a fast integrated mobility spectrometer

Rapid measurement of submicron particle size distributions enables the characterization of aerosols with fast changing properties, and is often necessary for measurements onboard mobile platforms (e.g., research aircraft). Aerosol mobility size distribution is commonly measured by a scanning mobility particle sizer (SMPS), which relies on voltage scanning or stepping to classify particles of different sizes, and may take about 1 minute or longer to obtain a complete size spectrum of aerosol particles. The recently developed fast integrated mobility spectrometer (FIMS) with enhanced dynamic size range separates and detects particles from 10 to ~600 nm simultaneously, allowing submicron aerosol mobility size distributions to be captured at a time resolution of 1 s.In this study, we present a detailed data inversion routine for deriving aerosol size distribution from FIMS measurements of aerosols with a wide size range. The inversion routine takes into consideration the FIMS transfer function, particle penetration efficiency in the FIMS, and multiple charging of aerosols. The accuracy of the FIMS measurement is demonstrated by comparing parallel FIMS and SMPS measurements of stable aerosols with a wide range of size spectrum shapes, including ambient aerosols and aerosols classified by a differential mobility analyzer (DMA). The FIMS and SMPS-derived size distributions show excellent agreements for all aerosols tested. In addition, total number concentrations of ambient aerosols were integrated from 1 Hz FIMS size distributions, and compared with those directly measured by a condensation particle counter (CPC) operated in parallel. The integrated and measured total particle concentrations agree well within 6.5%.

On the nanoparticulate flow

Nanoparticulate flows occur in a wide range of natural and engineering applications hence have received much attention. The purpose of the present paper is to provide a brief review on the research on the nanoparticulate flow in some aspects which consist of the method of moment for solving the particle population balance equation, penetration efficiency, pressure drop and heat transfer in the turbulent nanoparticulate pipe flow, fluctuating-lattice Boltzmann model for Brownian motion of nanoparticles.

A model for evaluating the particle penetration efficiency in a ninety-degree bend with a circular-cross section in laminar and turbulent flow regions

Understanding particle penetration losses in a bent section is useful for quantitatively evaluating the aerosol sampling error in a sampling system. This study intended to examine the physical factors that contribute to sampling error in a 90° bend installed in a sampling line and to evaluate current models that are used to predict penetration losses in continuous emission sampling (CPS).·The particle penetration characteristics of seven size groups (0.1, 0.5, 1.0, 5.0, 10 and 20μm) were numerically investigated via a Lagrangian particle-tracking model in a 90° bend with a circular cross-section. A particle–wall collision model was adopted to consider the particle–wall collision effect. Good agreement was achieved between gas mean velocity and particle penetration efficiency predictions and experimental data in the literature. An analysis was performed to study the particle penetration characteristics in pipes with different bend curvature ratios, geometries and various Re numbers. Our results indicated that approximately 20% particle losses for ≥5μm particles occur if the sampling line is bent. In addition, particle losses can typically be reduced by lowering the air velocity in the sampling line or by using a sampling line with a larger inner diameter. Models based on numerical data were developed as a function of related parameters to further predict the particle penetration efficiency. In a laminar flow, the model η=α⋅e−λ⋅St is given with an error of 2.6%–4.3%. In a turbulent flow system, however, the St and the Dean Number (De) both affect the particle penetration efficiency and the corresponding model η=α⋅e−λ⋅St+κ⋅De is suggested. In comparison to the EPA recommended model, which may contain approximately 3.9%–16.95% sampling error, the new models show better agreement with the experimental data.

Simulations of aerosol filtration by vegetation: Validation of existing models with available lab data and application to near-roadway scenario

ABSTRACTConcentrations of ultrafine particles (UFP) are generally elevated in the near-roadway environment due to traffic-related pollution. Exposure to UFP has been linked to adverse health effects for communities living near major roadways. Strategies to mitigate near-roadway air pollution include vehicle emission regulations, as well as installation of physical barriers such as walls, tree stands, and shrubs. Numerical simulation tools can be very useful to investigate the effectiveness of these barriers in mitigating air pollution. In the present work, a Reynolds-Averaged Navier–Stokes (RANS) based computational fluid dynamics (CFD) solver is used to predict filtration of UFP by vegetation. The RANS equations for turbulent flow are combined with a dry deposition velocity model and three different wake turbulence models. Reasonably good predictions of pressure drop across the vegetation and particle penetration efficiency are obtained when compared with available wind tunnel experiments for high leaf a...

Performance comparison of two thermodenuders in Volatility Tandem DMA measurements

Volatility Tandem Differential Mobility Analysers (VTDMAs) are widely used for determining the volatile and refractory fractions and thus the mixing state of aerosols particles. A three-channel VTDMA consisting of two thermodenuders (TDs) with distinct designs (i.e., the NanoTD, having a straight tube design, and a coiled TD; cTD) and a by-pass line was built and fully characterized. Both TDs were tested using laboratory-generated aerosol particles (single compound and core–shell particles) as well as atmospheric aerosols observed at an urban background station. The NanoTD exhibited high particle penetration efficiency and negligible thermophoretic losses, making it advantageous for ultrafine particle analysis, especially in environments with low particle concentration. The cTD allows longer particle residence time for the same flow rate, resulting in higher particle volatilization in some cases. Higher particle losses in this TD, both thermophoretic and diffusional, pose a limitation when dealing with low particle concentrations.The difference in the performance between the thermodenuders was only noticed at intermediate temperatures, at which particle volume loss becomes more pronounced. These temperatures vary among aerosols, since the volatilization rate depends on the chemical complexity and size of the particles sampled. Differences in the aerosol volume fraction remaining after heating with the two TD designs exhibited a maximum of 20% for single-compound particles and 12% for urban background aerosols. Measurements using core–shell particles yielded differences of up to 21% in particle volatilization, independently of particle size, when comparing the system using either of the two TD designs. Similar results were obtained with the two TD designs at higher operating temperatures (e.g., 230°C), indicating that at this temperature most of the material on the particles was evaporated.

Effects of simultaneous acoustic and electric fields on removal of fine particles emitted from coal combustion

Traditional electrostatic precipitation has a relatively low collection efficiency of fine particles emitted from coal combustion due to insufficient particle charging. This paper establishes an experimental system combining travelling sound waves with wire-duct electrostatic precipitation in order to measure the separated and simultaneous effects of an electric and acoustic field on fine particle penetration efficiency. The ranges of the main physical parameters are as follows: discharge voltage, V=8–12kV; acoustic frequency, ƒ=800–2400Hz; sound pressure level (SPL), SPL=130–148dB; residence time, t=2–6s; initial fine particle concentration, N0=6.5×105–4.99×106/cm3. The application of acoustic waves in an electric field is proven as an advisable method to remove fine particles with the lowest total penetration efficiency of 4.4%. Although the sound does not change the current–voltage curves of negative corona, it can distort the motion trajectory of the particles leading to a positive result for fine particle removal. The effectiveness of sound on the improvement of fine particle removal diminishes as the voltage increases. For a given discharge voltage, there exists an optimal frequency and SPL. The optimal frequency slightly increases, while the optimal SPL decreases as the applied voltage increases. The influence of residence time and initial fine particle concentration in combined fields are also studied.

Accessing the Influence of Hess-Murray Law on Suspension Flow through Ramified Structures

The present study focuses on fluid flow and particle transport in symmetric T-shaped structures formed by tubes with circular and square cross-section. The performances of optimized structures (i.e., structures designed based on constructal allometric laws for minimum flow resistance) and not optimized structures were studied. Flow resistance and particle penetration efficiency were studied both for laminar and turbulent flow regimes, and for micrometer and submicrometer particles. Optimized structures have been proven to perform better for fluid flow but they have a similar performance for particle transport.

Experimental investigation on charging characteristics and penetration efficiency of PM2.5 emitted from coal combustion enhanced by positive corona pulsed ESP

The electrostatic precipitator (ESP) has been extensively used for collecting aerosol particles emitted from coal combustion, but its collection efficiency of PM2.5 (Particulate matter whose aerodynamic diameter is less than 2.5 μm) is relatively low due to insufficient particle charging. The positive pulsed ESP is considered to enhance particle charging and improve collection efficiency. A laboratory-scale pulsed ESP with wire-plate electrode configuration was established to investigate the particle charging and penetration efficiency under controlled operating conditions of different applied impulse peak voltages, impulse frequencies, dust loadings and residence times. The results show that most particles larger than 0.2 μm are negatively charged, while most particles smaller than 0.2 μm are positively charged. For a given operating condition, the particle penetration efficiency curve has the highest penetration efficiency for particles with a diameter near 0.2 μm, and there is always a negative correlation between the particle penetration efficiency and the average number of charges per particle. Under the same operating conditions, the particle penetration efficiency decreases with increasing impulse peak voltage and impulse frequency, but increases as the dust loading increases. The results imply that residence time of 4 s is optimum for particle charging and collection. PM2.5 number reduction exceeding 90% was achieved in our pulsed ESP.

Three-Dimensional Simulation of Brownian Motion of Nano-Particles In Aerodynamic Lenses

A computer code for analyzing nano-particle motions in an aerodynamic particle beam focusing system was developed. The code uses an accurate three-dimensional model for the Brownian diffusion of nano-particles in strongly varying pressure field in the aerodynamic lens system. Lagrangian particle trajectory analysis was performed assuming a one-way coupling model. The particle equation of motion used included drag and Brownian forces. The prediction of the 3-D model for penetration efficiency, beam divergence angle, beam diameter and radial cumulative fraction were evaluated and were compared with those of the axisymmetric models. The simulation results showed that for particle diameters less than 30 nm in helium gas, the Brownian force could significantly affect the beam focusing and particle penetration efficiency. Some potential errors in the naive usage of axisymmetric model were discussed. It was shown that the earlier axisymmetric models lead to the incorrect mean square radial displacement of Browni...

Evaluation of the pDR-1200 Real-Time Aerosol Monitor

The objective of this research was to characterize the ability of the pDR-1200 real-time aerosol monitor to measure aerosols of varying size, composition, and origin. Particle aspiration and transmission efficiency was characterized at airflow rates of 2 L/min, 5 L/min, and 10 L/min in a wind tunnel in both static and orientation-averaged configurations. At 10 L/min, the particle cut point for 50% penetration of particles through the device (d 50 ) was approximately 6 μ m, while at 2 L/min and 5 L/min the d 50 was significantly larger, about 9 μ m (p = 0.01). There was no significant difference in particle penetration efficiency between facing-the-wind and orientation-averaged configurations (p avg = 0.66). The pDR-1200 response factor, which is defined as the ratio the time-averaged, monitor-reported concentration to a gravimetric filter concentration measured directly downstream of the sensing zone, was evaluated for four aerosol types: Arizona road dust, background ambient aerosol, environmental tobacco smoke, and diesel particulate matter. These aerosols, each of varying refractive index and particle size distribution, produced significant changes in the measured response factor (p < 0.01). The pDR-1200 both overestimated and underestimated (up to a factor of 7) the gravimetrically determined aerosol concentration. These discrepancies further reinforce the need to calibrate the instrument in situ for each aerosol of interest. Inter-instrument variability was generally low for co-located monitors.

Balloon-Based In Vitro MDI Aerosol Deposition Experiments on the Effects of Mouthpiece Diameter

For this article, we studied the effects of mouthpiece diameter and flow rate on aerosol penetration efficiency for metered-dose inhaler (MDI) applications. Measurements show that increasing the mouthpiece diameter has a moderate and positive influence on the particle penetration efficiency of the MDI. The particle penetration efficiency increases monotonically with the increase of the mouthpiece diameter from 16 mm to 20 mm. Second, the experiments show that airflow rate has an apparent and significant effect on particles deposition in the oral airway. The reduction of the airflow rate from 90 L/min to 30 L/min tripled the penetration efficiency of the MDI. A new experimental system has been employed to measure the particles deposition in the human airways. Expansion balloons were used to induce airflow as well as to collect the penetrated particles through an airway cast. The potential advantages of the balloon-based experimental system are simplicity, accuracy, and cost-effectiveness.

Determining the infiltration of outdoor particles in the indoor environment using a dynamic model

As people spend a significant portion of their time indoors, it is desirable to determine the fraction of outdoor particles that reach the indoor environment and the associated inter- and intra-home variability. This fraction depends on particle penetration efficiency and deposition rate. An alternative method for calculating the dynamic infiltration factor using time-dependent concentrations and air-exchange measurements is presented. We discuss the limitations of calculating the penetration rate and deposition velocity independently and find that the indoor/outdoor ratio often overestimates penetration efficiency. The dynamic infiltration factors are calculated for seven houses, for generally seven nights per house, for 17 particle size fractions. For the smallest particle size fraction (0.02–0.03 μ m), the mean infiltration factor across homes was 0.49, increasing up to 0.76 for the 0.2–0.3 μ m size fraction, and then decreasing steadily to 0.32 for the largest size fraction (4–6 μ m). The coefficients of variation between nights and homes were determined and are comparable, ranging between 0.07 and 0.18 for all the size fractions up to 1 μ m, with values up to 0.48 for larger size fractions.

Filtering Efficiency of N95- and R95-Type Facepiece Respirators, Dust-Mist Facepiece Respirators, and Surgical Masks Operating in Unipolarly Ionized Indoor Air Environments

The emission of unipolar air ions in the vicinity of a filtering facepiece respirator has been recently shown to considerably enhance its respiratory protection efficiency. The effect is driven by the electric repelling forces that develop between the unipolarly charged mask and the aerosol particles, thus creating a shield for the incoming particles and consequently decreasing the penetration efficiency through the filter. The manikin-based preliminary evaluation of this concept has been performed with a very limited number of variables. In this study, four types of half-mask facepiece filtering devices (N95, R95, and dust-mist respirators, as well as surgical masks), operating at two different breathing flow rates, were tested with unipolar air ion emitters exhibiting different emission rates and polarities. The particle penetration efficiency through the facepiece filter was determined in a room-size indoor test chamber by a real-time particle size selective aerosol monitoring performed inside and outside of the mask, which was face-sealed onto a manikin. Three commercially available ionic air purifiers were utilized as air ion emitters. For the targeted particle size range of ~0.04 – 1.3 μm, a 12- minute air ionization in the vicinity of a manikin enhanced the respiratory mask performance by a factor ranging from 1.61 to 3,250, depending on the respirator type, breathing flow rate, and the ion emission rate. The effect was achieved primarily within the first 3 minutes.