期刊,Journal of Aerosol Science 2022年165卷期_国家学术搜索

期刊信息/Journal information

Journal of Aerosol Science

Pergamon Press

主办单位：Pergamon Press

国际刊号：0021-8502

Journal of Aerosol Science/Journal Journal of Aerosol ScienceSCIISTPEI

正式出版

收录年代

Internal mixing air-assisted spray nozzle for large droplets: Experimental measurements and numerical simulations

Guang ChenCheng FuBingbing Xu

21页

查看更多>>摘要：In the present study, detailed experimental measurements of a large-droplet spray nozzle under a wide range of operating conditions have been conducted at China Aerodynamics Research and Development Center (CARDC) low-speed vertical wind tunnel facility. The droplet size distributions obtained from these measurements have been modeled using the Rosin-Rammler distribution. A multi-physics multi-phase numerical model for the simulation of the complex spray dynamics associated with the large-droplet spray nozzle has been developed in order to support the performance characterization of this device. More specifically, the primary breakup of liquid (water) in the atomizer-produced spray is modeled using a volume of fluid (VOF) to discrete phase model (DPM) transition representation. The numerical model is validated using the experimental measurements. The small relative error between the numerical predictions and experimental measurements for the droplet size distribution and for a number of characteristic droplet diameters suggest that the numerical model provides accurate high-fidelity predictions of the spray dynamics of the large-droplet spray nozzle. Moreover, it is shown that a simple modification of the spray nozzle (increasing the length of the mixing chamber by 50%) has a significant effect on the performance of the nozzle. In particular, the droplet median volumetric diameter and the spray angle are increased as the air pressure is decreased. Furthermore, an increase in the nozzle mixing chamber length results in a much broader droplet size distribution. The validated VOF-to-DPM transition model developed in this study can be used for a future redesign (involving modifications of some key geometric parameters) of the original large-droplet spray nozzle to generate reliably and robustly larger droplets required to simulate various supercooled large droplet conditions of practical relevance.

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NSTL

Adhesion forces of radioactive particles measured by the Aerodynamic Method-Validation with Atomic Force Microscopy and comparison with adhesion models

Thomas GelainMickael PayetSamuel Peillon

25页

查看更多>>摘要：Median adhesion forces of tritiated tungsten micro-particles deposited on a glass substrate were successfully determined using an aerodynamic method (AM) which is presented in this paper. The original aerodynamic device built for these experiments has been carefully characterized in terms of friction velocities allowing to quantify aerodynamic torque exerted on the particles and to deduce median adhesion forces thanks to a force balance approach. Using the same particle/surface systems (non-radioactive tungsten particles in contact with a glass substrate), distribution of adhesion forces were obtained using AFM for comparison with the AM. The results show a good agreement between the two techniques which allowed to validate the AM. Furthermore, a precise description of the root-mean square roughness (rms) distribution of the glass substrate made it possible to compare the experimental results with different analytical adhesion force models. Integrating the rms roughness distribution of the substrate into the model of Rabinovich et al. showed the best agreement with the present experiments capturing most of the adhesion forces of 10 pm to 18 urn diameter tungsten particles. Moreover, the method developed in this work made it possible to show that the electrostatic image force arising from the self-charging of tritiated tungsten particles has a negligible contribution in the adhesion of the particles for the studied configuration.

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NSTL

Viable SARS-CoV-2 Delta variant detected in aerosols in a residential setting with a self-isolating college student with COVID-19

William B. VassJohn A. LednickySripriya Nannu Shankar

12页

查看更多>>摘要：The B.1.617.2 (Delta) variant of SARS-CoV-2 emerged in India in October of 2020 and spread widely to over 145 countries, comprising over 99% of genome sequence-confirmed virus in COVID-19 cases of the United States (US) by September 2021. The rise in COVID-19 cases due to the Delta variant coincided with a return to in-person school attendance, straining COVID-19 mitigation plans implemented by educational institutions. Some plans required sick students to self-isolate off-campus, resulting in an unintended consequence: exposure of co-inhabitants of dwellings used by the sick person during isolation. We assessed air and surface samples collected from the bedroom of a self-isolating university student with mild COVID-19 for the presence of SARS-CoV-2. That virus' RNA was detected by real-time reverse-transcription quantitative polymerase chain reaction (rRT-qPCR) in air samples from both an isolation bedroom and a distal, non-isolation room of the same dwelling. SARS-CoV-2 was detected and viable virus was isolated in cell cultures from aerosol samples as well as from the surface of a mobile phone. Genomic sequencing revealed that the virus was a Delta variant SARS-CoV-2 strain. Taken together, the results of this work confirm the presence of viable SARS-CoV-2 within a residential living space of a person with COVID-19 and show potential for transportation of virus-laden aerosols beyond a designated isolation suite to other areas of a single-family home.

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NSTL

Minimizing the coincidence error in particle size spectrometers with digital signal processing techniques

Lukas OeserNakul SamalaLars Hillemann

12页

查看更多>>摘要：Aerosol quantification is highly coveted for many applications ranging from quality monitoring to healthcare. Optical particle size spectrometers are one of the popular measurement devices used in aerosol characterization, which provide information about the size distribution and concentration of the particles. One drawback of this method is that the spectrometers are limited to applications with relatively low concentrations. At high concentrations, the number concentration is underestimated, while the size distribution is shifted towards larger particles. This phenomenon is commonly referred as coincidence error. However, the counting efficiency, above the lower detection limit, depends i. a. on the detector dead time. In order to minimize the probability of coincidence events, the dead time of the detector has to be as small as possible. The contribution of this work is to minimize the coincidence error by purposefully reducing the detector dead time. Therefore, various digital signal processing methods, to minimize dead time, are investigated and experimentally verified. Wavelet and derivative-based peak detection algorithms were found to be able to separate even strongly overlapping scattered light pulses from each other. The results show that the detector dead time can be reduced by 65% with digital signal processing techniques. Allowing the quantification of aerosols with more than 2.9 times the maximum concentration of current optical aerosol spectrometers, without increasing the coincidence error.

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NSTL

Fluid-structure interaction of human nasal valves under sniff conditions and transport of inhaled aerosols: A numerical study

Hadrien CalmetAlfonso SantiagoJuan Carlos Cajas

16页

查看更多>>摘要：The nasal valve is the narrowest part of the nasal airway which is responsible for the largest part of the nasal resistance. Even little changes in the aperture can affect the flow downstream through the nose significantly. Its principal function is to limit airflow for example during a rapid and short inhalation, also called a sniff. Coupling Computational Fluid Dynamics (CFD) with Fluid-Structure Interaction (FSI) allows solving and exchanging force and displacement between the solid and fluid domains and offers a more accurate representation of the physical system in confined flow cases. Furthermore, particle transport and deposition are performed in this study to reveal the effect of the complex coupling on the nasal cavity deposition of inhaled aerosols. Two different configurations are used to model the nasal valve and differences in magnitudes in deformations are observed during the sniff. A comparison between FSI results and the in-vivo evaluation of the deformation shows an acceptable agreement as to the first step of validation. In addition, the results demonstrated that FSI increases significantly the particle deposition in the nasal cavity and the micro-particle diameter is the critical range parameter to enhance deposition with nasal valve deformation during a sniff.

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NSTL

On-line compositional measurements of AuAg aerosol nanoparticles generated by spark ablation using optical emission spectroscopy

Markus SnellmanPer SamuelssonAxel Eriksson

11页

查看更多>>摘要：Spark ablation is an established technique for generating aerosol nanoparticles. Recent demonstrations of compositional tuning of bimetallic aerosols have led to a demand for on-line stoichiometry measurements. In this work, we present a simple, non-intrusive method to determine the composition of a binary AuAg nanoparticle aerosol on-line using the optical emission from the electrical discharges. Machine learning models based on the least absolute shrinkage and selection operator (LASSO) were trained on optical spectra datasets collected during aerosol generation and labelled with X-ray fluorescence spectroscopy (XRF) compositional measurements. Models trained for varying discharge energies demonstrated good predictability of nanoparticle stoichiometry with mean absolute errors <10 at. %. While the models utilized the emission spectra at different wavelengths in the predictions, a combined model using spectra from all discharge energies made accurate predictions of the AuAg nanoparticle composition, showing the method's robustness under variable synthesis conditions.

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NSTL

A quantitative criterion to predict atomic disordering during high velocity nanoparticle impact

T.V. ChitrakarMichael F. BeckerDesiderio Kovar

13页

查看更多>>摘要：Particle deformation at impact is a critical parameter for film formation using aerosol deposition processes for sub-micron particles. Here we study the necessary criteria to initiate atomic disorder during particle impact that can lead to deformation via viscous flow. Molecular dynamics simulations were conducted to test the hypothesis that disordering of individual silver atoms occurs under non-uniform, high strain rate loading when a critical potential energy/atom (PE/atom) of -2.72 eV is exceeded. To test this hypothesis, simulations of Ag nanoparticles impacting a flat Ag substrate were conducted for impact velocities of 100, 300, and 600 m/s, and the PE/atom and the atomic configurations for atoms positioned at different locations within the nanoparticles were tracked over time. The results showed that atoms that disorder or do not disorder could be correctly predicted by the PE/atom. A statistically varying time differential was observed between the time amorphization was predicted and when it occurred. For the small fraction of the atoms that were borderline cases, the PE/atom and two measures of atomic disorder did not agree. The physical causes for the time differentials between predicted and observed disordering and the accuracy of prediction of disordering are discussed.

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NSTL

Modeling of the electrical interaction between desert dust particles and the Earth's atmosphere

Sotirios A. MalliosVasiliki DaskalopoulouVassilis Amiridis

29页

查看更多>>摘要：In the current work, the two distinct charging mechanisms of spherical dust particles settling in the Earth's atmosphere, i.e. ion attachment and contact electrification, are studied in parallel. A novel ID numerical model has been developed that parametrizes the charging processes in the presence of a large scale electric field, under stagnant atmospheric conditions where wind contribution is neglected. The model is able to self-consistently calculate the modification of atmospheric ion densities and the subsequent alteration of the large scale electric field, when dust particles are present and atmospheric ions attach to them, and is further updated to account for the particle charging due to the efficient collisions between particles of sizes ranging from fine (less than 1 祄 in radius) to giant mode (larger than 50 祄 in radius). Due to a lack of a rigorous mathematical expression for the quantification of the particle collision process, the mechanical and electrostatic effects are modeled independently, based on works in the past literature, and then are combined by a simple superposition principle. Additionally, the electrostatic effects are studied in the presence of weak external electric fields (less than 1-2 kV/m). Moreover, for the same reasons a simple superposition principle has been applied for the quantification of the ion attachment process. All these assumptions lead to an approximation of the actual mechanisms quantification, but this method can lead to physically reasonable results, highlighting the impact of several processes to the eventual charging of the dust particles. By binning integration of a realistic particle size distribution in the model, the acquired electrical charge on the dust particles is calculated in the range of 0.5 to 2000 elementary charges. The particles become on average negatively charged, but under specific conditions giant mode particles can be locally and temporarily positive, congruently to previously reported laboratory experiments. Moreover, the electrical force that is applied on the particles by each mechanism individually and through the superposition of both, is extracted and compared to the gravitational force acting on each particle. However, the ID results indicate that the electrical force is not enough to significantly influence the gravitational settling of the charged particles, as it is more than one order of magnitude less than gravity. This designates that although the electrical processes alone are accounted for, significant meteorological processes such as updrafts, wind shears, or horizontal winds need to be included in the model to accurately represent the modulation of particle electrification and so as to represent the impact of electricity on particle dynamics in a more realistic way.

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NSTL

Single-pass wind tunnel testing for recirculating virus aerosol control technologies

Hui OuyangYuechen QiaoMy Yang

13页

查看更多>>摘要：A number of recirculating flow aerosol control technologies have been commercialized to mitigate aerosol-transmitted virus infections. Many of these technologies incorporate filters for particle collection and some may also incorporate technologies for virus inactivation. Given the wide variety of commercially available aerosol control technologies to consumers, it is extremely important to develop standardized methods to characterize their performance in bioaerosol removal and inactivation, such that technologies can be compared on an 'equivalent-test' basis. However, no standard procedures have been established to evaluate the effectiveness of bioaerosol removal and inactivation in recirculating aerosol control technologies. We propose the use of a single-pass tunnel to assess the performance of bioaerosol control technologies, as single-pass wind tunnels can be sealed with well-controlled velocity and particle concentration profiles. Here, we specifically describe the construction of a single-pass wind tunnel and apply it to three recirculating aerosol control technologies, incorporating UV-C sources, filters, and electrostatic precipitators, respectively. We utilize a porcine respiratory coronavirus (PRCV) challenge aerosol, generated via pneumatic nebulization of a high titer (~10~7 TCID_(50) mL~(-1)) viral suspension. Following guidelines similar to those used in the ANSI/ASHRAE Standard 52-2 test procedure for HVAC filters, in single-pass wind tunnel tests, velocity uniformity and particle uniformity are first monitored across the cross-section of the tunnel. The size distribution of viable particles is additionally determined in advance of tests by the collection of particles in the wind tunnel using a cascade impactor, with both RT-qPCR and titration used to quantify viruses collected on each impaction stage. We show that the viable particle size distribution follows the volumetric size distribution of the nebulized virus-laden suspension, and that this distribution can be tuned to be similar in shape to the observed distribution of aerosol from human respiratory activities. Following tunnel and virus aerosol characterization, for each tested technology, using triplicate tests, the single-pass log reduction based on RT-qPCR and viable virus titration is determined by simultaneously collecting virus aerosol particles upstream and downstream of the control technology. The tested technologies in this study have titration-based single-pass log reductions in the 1.5-4.0 range. Overall, design and testing suggest that the single-pass wind tunnel approach is a tractable method to examine the efficacy of aerosol control technologies in removing and inactivating viruses in aerosols, and suggest that such technologies should be described by their single-pass log reduction and operating flow rate, with the test virus size distribution reported alongside test results. In addition, we examine the limits of detection in single-pass wind tunnel tests in comparison to chamber tests, and in doing so find that for most control technologies, the wind tunnel test will yield higher concentrations downstream or during sampling, and hence clearer results for the log reduction.

原文链接:

NSTL