Aerosol Flow Research Articles

Post-corona unipolar chargers with tuneable aerosol size-charge relations: Parameters affecting ion dispersion and particle trajectories for charger designs

This paper focusses on the mean charge per particle of monodisperse submicron aerosol, charged by diffusion of unipolar ions in post-corona discharge. It aims to confirm and discuss the limits of considering a single value of Ni$\times$t to describe aerosol charging and then to present methods to control the size-charge relation. Three aerosol chargers, with different mixings of ion and aerosol flows are investigated. Despite comparable ion sources with discharge currents of a few tens of $\mu$A, the size-charge relations differs from one charger to another due to different ion-aerosol mixing conditions and subsequent ion density along particles trajectories. Discrepancies are even more noticeable as the particle size increases. Discharge current, velocities of ion and aerosol flows and electric field control post-discharge ion density in each point of the charging volume. The control of particle trajectory in expanding unipolar ion cloud, leads to tuneable size-charge relations. Aerosol inertia and charging dynamics, that both depends on particle size, affects the Ni$\times$t experienced by the particle and thus the final charge of the particle. Operating conditions to reach a constant mean charge for particles larger than 200 nm are reported. Conclusions provide a basis to design aerosol chargers devoted to electric mobility selection for aerosol deposition, separation or electrical measurements especially to overcome the limits of mobility-to-size data inversion due to multiple charge ambiguity using diffusion chargers.

Synthesis of antibacterial composite coating containing nanocapsules in an atmospheric pressure plasma

Antibacterial coating is an important strategy preventing bacterial colonization and biofilm formation. One-step synthesis of nanocapsule-containing antibacterial coatings with controlled release of Ag+ ions was achieved in the current work by aerosol-assisted atmospheric pressure plasma deposition. The experimental parameters of deposition including the discharge power, silver nitrate concentration, aerosol flow rate, continuous and pulsed mode of operation were studied in order to analyze their effects on surface morphology and chemical composition of the coating. Formation of nanocapsules embedded in the polymeric coating was observed. A core-shell structure was found for nanocapsule with silver in the core and polymer in the shell. Antibacterial coatings on polyethylene terephthalate film were studied in terms of Ag+ ion release, antibacterial properties against Escherichia coli and Staphylococcus aureus, and cytotoxicity with murine fibroblasts. Two-phase release kinetics of Ag+ ions was observed as initially a short-term burst release followed by a long-term slow release. It was revealed that high antibacterial efficiency of the coatings deposited on polyethylene terephthalate films can be coupled with low cytotoxicity. These biocompatible antibacterial coatings are very promising in different fields including biological applications.

The effect of oral and nasal breathing on the deposition of inhaled particles in upper and tracheobronchial airways

The inhalation route has a substantial influence on the fate of inhaled particles. An outbreak of infectious diseases such as COVID-19, influenza or tuberculosis depends on the site of deposition of the inhaled pathogens. But the knowledge of respiratory deposition is important also for occupational safety or targeted delivery of inhaled pharmaceuticals.Simulations utilizing computational fluid dynamics are becoming available to a wide spectrum of users and they can undoubtedly bring detailed predictions of regional deposition of particles. However, if those simulations are to be trusted, they must be validated by experimental data. This article presents simulations and experiments performed on a geometry of airways which is available to other users and thus those results can be used for intercomparison between different research groups. In particular, three hypotheses were tested. First: Oral breathing and combined breathing are equivalent in terms of particle deposition in TB airways, as the pressure resistance of the nasal cavity is so high that the inhaled aerosol flows mostly through the oral cavity in both cases. Second: The influence of the inhalation route (nasal, oral or combined) on the regional distribution of the deposited particles downstream of the trachea is negligible. Third: Simulations can accurately and credibly predict deposition hotspots. The maximum spatial resolution of predicted deposition achievable by current methods was searched for. The simulations were performed using large-eddy simulation, the flow measurements were done by laser Doppler anemometry and the deposition has been measured by positron emission tomography in a realistic replica of human airways. Limitations and sources of uncertainties of the experimental methods were identified.The results confirmed that the high-pressure resistance of the nasal cavity leads to practically identical velocity profiles, even above the glottis for the mouth, and combined mouth and nose breathing. The distribution of deposited particles downstream of the trachea was not influenced by the inhalation route. The carina of the first bifurcation was not among the main deposition hotspots regardless of the inhalation route or flow rate. On the other hand, the deposition hotspots were identified by both CFD and experiments in the second bifurcation in both lungs, and to a lesser extent also in both the third bifurcations in the left lung.

An accessible method for screening aerosol filtration identifies poor-performing commercial masks and respirators.

BackgroundThe COVID-19 pandemic has presented an acute shortage of regulation-tested masks. Many of the alternatives available to hospitals have not been certified, leaving uncertainty about their ability to properly protect healthcare workers from SARS-CoV-2 transmission.ObjectiveFor situations where regulatory methods are not accessible, we present experimental methods to evaluate mask filtration and breathability quickly via cost-effective approaches (e.g., ~$2000 USD) that could be replicated in communities of need without extensive infrastructure. We demonstrate the need for screening by evaluating an existing diverse inventory of masks/respirators from a local hospital.MethodsTwo experimental approaches are presented to examine both aerosol filtration and flow impedance (i.e., breathability). For one of the approaches (“quick assessment”), screening for appropriate filtration could be performed under 10 min per mask, on average. Mask fit tests were conducted in tandem but are not the focus of this study.ResultsTests conducted of 47 nonregulation masks reveal variable performance. A number of commercially available masks in hospital inventories perform similarly to N95 masks for aerosol filtration of 0.2 μm and above, but there is a range of masks with relatively lower filtration efficiencies (e.g., <90%) and a subset with poorer filtration (e.g., <70%). All masks functioned acceptably for breathability, and impedance was not correlated with filtration efficiency.SignificanceWith simplified tests, organizations with mask/respirator shortages and uncertain inventories can make informed decisions about use and procurement.

Numerical Simulation and Validation of Aerosol Particle Removal by Water Spray Droplets With OpenFOAM During the Fukushima Daiichi Fuel Debris Retrieval

In the decommissioning of damaged Fukushima Daiichi reactors, the melted and re-solidified fuel debris in the bottom of the reactor pressure vessel and primary containment vessel need to be cut into small pieces before removing them from reactor buildings. During the cutting operations, submicron radioactive aerosol particles are expected to be generated and dispersed into the atmosphere of the primary containment vessel. Those suspended particles must be removed from the air atmosphere inside the containment before escaping to the environment. The water spray system in the upper part of the primary containment vessel is an effective and applicable method to remove airborne radioactive aerosol particles. Computational Fluid Dynamics simulation of aerosol scavenging by spray droplets is complicated but necessary to investigate the aerosol removal process inside the vessel. In this paper, a numerical model was developed and implemented into an open-source computational fluid dynamic code OpenFOAM to simulate the aerosol removal by water spray droplets with considering the collection mechanisms of inertial impaction, interception, and Brownian diffusion. In this model, the dispersed spray droplets were described using the Lagrangian particle tracking method, the continuous particle-laden gas was described using the Eulerian method, and a two-way interaction between dispersed and continuous phases was considered. The polydisperse aerosol particles at different diameters from 0.2 – 1 μm were treated as different gas species of the continuous phase. Continuity equations of each gas specie were solved using a passive scalar transport equation. The numerical model was validated by comparing the simulation results with the experimental data obtained from UTARTS facility. Simulation results agreed well with the experimental results. The simulation results provided more insights to better understand the aerosol removal process, including the time evolution of aerosol mass fraction and flow field of the gas phase.

Simulation Studies on Centrifugal MQL-CCA Method of Applying Coolant during Internal Cylindrical Grinding Process.

This paper describes simulation studies regarding the application of the centrifugal minimum quantity lubrication (MQL) method simultaneously with the delivery of a compressed cooled air (CCA) stream in the internal cylindrical grinding process. The idea of a new hybrid cooling and lubrication method connecting centrifugal (through a grinding wheel) lubrication by MQL with a CCA stream is described. The methodology of computational fluid dynamics (CFD) simulation studies, as well as the results of numerical simulations, are presented in detail. The aim of the simulations was to determine the most favourable geometrical and kinematic parameters of the system in the context of air-oil aerosol and CCA flow, as well as heat exchange. In the simulation, the variables were the grinding arbor geometrical parameters, the angle of CCA supply line outlets, and the grinding wheel and workpiece peripheral speed. As a result of the simulation studies, the most favourable geometrical parameters were designated, determining the orientation of the ends of the two CCA supply line outlets before and after the grinding zone, the number of openings in the drilled-out grinding arbor, and the influence of the grinding speed on the parameters of the coolant flow and temperature of objects in the grinding zone. In addition, the results of simulation tests made it possible to visualise the velocity vectors of the two-phase coolant flow in a complex system of air-oil aerosol delivery centrifugally through an open structure of a very fast rotating porous layer (grinding wheel), with an additional supply of CCA using an external cold air gun (CAG).

Pharmacokinetic Analysis of Epithelial/Endothelial Cell Barriers in Microfluidic Bilayer Devices with an Air-Liquid Interface.

As the range of applications of organs-on-chips is broadening, the evaluation of aerosol-based therapies using a lung-on-a-chip model has become an attractive approach. Inhalation therapies are not only minimally invasive but also provide optimal pharmacokinetic conditions for drug absorption. As drug development evolves, it is likely that better screening through use of organs-on-chips can significantly save time and cost. In this work, bio-aerosols of various compounds including insulin were generated using a jet nebulizer. The aerosol flows were driven through microfluidic bilayer devices establishing an air–liquid interface to mimic the blood–air barrier in human small airways. The aerosol flow in the microfluidic devices has been characterized and adjusted to closely match physiological values. The permeability of several compounds, including paracellular and transcellular biomarkers, across epithelial/endothelial cell barriers was measured. Concentration–time plots were established in microfluidic devices with and without cells; the curves were then utilized to extract standard pharmacokinetic parameters such as the area under the curve, maximum concentration, and time to maximum concentration. The cell barrier significantly affected the measured pharmacokinetic parameters, as compound absorption through the barrier decreases with its increasing molecular size. Aerosolizing insulin can lead to the formation of fibrils, prior to its entry to the microfluidic device, with a substantially larger apparent molecular size effectively blocking its paracellular transport. The results demonstrate the advantage of using lung-on-a-chip for drug discovery with applications such as development of novel inhaled therapies.

Simulation of the Interaction of Ice Crystals with the Surface of a Flying Vehicle

A physical and mathematical model of the movement of nonspherical particles in the two-phase flow over an aerodynamic body, allowing one to estimate the area of wetting of the body surface by these particles depending on their stochastic orientation in the flow, is proposed. On the basis of the heuristic model developed earlier, the coefficients of restoring the velocity components of the ice crystals colliding with the surface of a blunt-nosed body were calculated for values of the governing parameters of the collision process varying within a wide range. It is shown that the initial orientation of these crystals in the aerosol flow over the body influences the trajectories of their movement in the vicinity of the body.

DMA 내 막대형 시스 유동 층류화 장치에 의한 샘플 유동 정렬 및 입자 분류 효율 향상

DMA 내 막대형 시스 유동 층류화 장치에 의한 샘플 유동 정렬 및 입자 분류 효율 향상

Heterogeneous Chemistry of CaCO3 Aerosols with HNO3 and HCl.

Calcite (CaCO3) aerosols often serve as an idealized proxy for calcium-rich mineral dust. Their use has also previously been proposed for stratospheric solar radiation management (SSRM). Little is known about the heterogeneous chemistry of calcite aerosols with trace gases HNO3 and HCl and therefore their potential impact on stratospheric ozone (O3). Here we report the results of an experimental study of the uptake of HNO3 and HCl onto submicron CaCO3 particles in two different flow reactors. Products and reaction kinetics were observed by impacting aerosolized CaCO3 onto ZnSe windows, exposing them to the reagent gases at a wide range of concentrations, at 296 K and under dry conditions, and analyzing the particles before and after trace gas exposure using Fourier transform infrared spectroscopy (FTIR). A Ca(OH)(HCO3) termination layer was detected in the form of a HCO3- peak in the FTIR spectra, indicating a hydrated surface even under dry conditions. The results demonstrate the reaction of HNO3 with Ca(OH)(HCO3) to produce Ca(NO3)2, water, and CO2. HCl reacted with Ca(OH)(HCO3) to produce CaCl2 and also water and CO2. The depletion of the Ca(OH)(HCO3)/Ca(CO3) signal due to reaction with HNO3 or HCl followed pseudo-first-order kinetics. From the FTIR analysis, the reactive uptake coefficient for HNO3 was determined to be in the range of 0.013 ≤ γHNO3 ≤ 0.14, and that for HCl was 0.0011 ≤ γHCl ≤ 0.012 within the reported uncertainty. The reaction of HCl with airborne CaCO3 aerosols was also studied in an aerosol flow tube coupled with a quadrupole chemical ionization mass spectrometer (CIMS) under similar conditions to the FTIR study, and γHCl was determined to be 0.013 ± 0.001. Following previous modeling studies, these results suggest that the reactions of HCl and HNO3 with calcite in the stratosphere could ameliorate the potential for stratospheric solar radiation management to lead to stratospheric ozone depletion.

Observation and quantification of aerosol outflow from southern Africa using spaceborne lidar

Biomass burning in Africa provides a prolific source of aerosols that are transported from the source region to distant areas, as far away as South America and Australia. Models have long predicted the primary outflow and transport routes. Over time, field studies have validated the basic production and dynamics that underlie these transport patterns. In more recent years, the advancement of spaceborne active remote-sensing techniques has allowed for more detailed verification of the models and, importantly, verification of the vertical distribution of the aerosols in the transport regions, particularly with respect to westerly transport over the Atlantic Ocean. The Cloud-Aerosol Transport System (CATS) lidar on the International Space Station has detection sensitivity that provides observations that support long-held theories of aerosol transport from the African subcontinent over the remote Indian Ocean and as far downstream as Australia.&#x0D; Significance:&#x0D; &#x0D; Biomass burning in Africa can have impacts as far away as Australia.&#x0D; Flow of aerosols from Africa towards Australia has long been postulated by transport models, but has been poorly characterised due to a lack of measurements.&#x0D; The CATS instrument on the International Space Station has detection sensitivity that captures aerosol transport from Africa over the Indian Ocean to Australia.&#x0D; &#x0D; Open data set: &#x0D; https://cats.gsfc.nasa.gov/

MOF-derived nano-popcorns synthesized by sonochemistry as efficient sensitizers for tumor microwave thermal therapy

Microwave (MW) thermal therapy has been vigorously developed in recent years because of its better therapeutic efficiency and smaller side effects compared with traditional tumor treatment methods. In order to promote the tumor cell apoptosis under MW irradiation and achieve better therapeutic effect and prognosis, various microwave sensitizers have been developed. Metal organic frameworks (MOFs) have become one of the most popular materials for microwave sensitization due to their diverse morphology, porous surface and good biodegradability. However, the harsh preparation conditions and long growth time are insurmountable shortcomings of MOFs. Besides, the spongy porous structure of MOFs is not conducive to the retention of ions, leading to insufficient friction and collision between ions under MW radiation. Herein, we synthesized a kind of open-mouthed Zr MOF-derived nano-popcorns (ZDNPs) with the size of about 250 nm by a rapid sonochemical aerosol flow strategy. Compared with UIO-66, the open-mouthed ZDNPs have a better ability to entrap more ions due to their big cracks on the surface, thus improving their MW sensitization performance. The MW heating experiments in vitro present that the net temperature change value of ZDNP was 120% higher than UIO-66 at the same concentration, proving that ZDNP had a higher MW-thermo conversion efficiency than UIO-66, which provided an unprecedented direction for the exploration of more diversified MW sensitizers.

Heat transfer of a spherical element with air-water aerosol in a cylindrical channel

The heat transfer from a single sphere suspended in a cylindrical channel with finely dispersed air-water (aerosol) flow is experimentally studied. Under stationary heating conditions, the values of the heat-transfer coefficients are obtained as dependent on the Reynolds number and the water mist rate. A physical model of heat transfer from the sphere surface with water mist-air flow is proposed, which allows evaluating the processes proceeding at the various stages of droplet evaporation in the flow near a heated surface and formation of a water film on the surface itself. The relative mass of the droplet moisture deposited on the sphere surface is estimated depending on the water mist rate and Reynolds number of the flow. A criterial equation is obtained that generalizes the experimental data in the form of the dependence of Nusselt number on the regime parameters of Reynolds, Weber, and the water-to-steam phase transition parameter is obtained.

Модели процессов, сопровождающих кристаллизацию переохлажденных капель

The creation of high-performance methods for calculating the interaction of aerosol flows with a solid is of great practical interest in the problems of preventing surfaces from icing, predicting climatic phenomena, metallurgy and astronomical processes. One of the methods of icing diminishing is the use of hydrophobic coatings, which, as a rule, work effectively with insignificant ratios of inertial forces to the forces of surface tension of a liquid near the relief of the streamlined body. However, when the surface density of the kinetic energy of the supercooled drop exceeds a certain critical value, the ice-phobic properties lead to negative effects due to the penetration of the supercooled liquid into the depressions and solidification in them. A method is developed for calculating the interaction of supercooled drops with a relief solids, which have various degrees of hydrophobicity. Basic criteria for corresponding the results of molecular modeling to physical reality are formulated. The need to develop algorithms for numerical simulation is due to the fact that significant computational resources are required even for calculating small droplets which are several tens of nanometers in size. Numerical estimates of the parameters of the relief of a hydrophobic surface of a solid are obtained depending on the dimensionless dynamic parameters of the impact of supercooled drops. Moving interface – the crystallization front in supercooled metastable liquid droplets has specific properties. On the basis of previously carried out experimental studies, theoretical estimates, analytical and experimental data of other researchers, in present work mathematical models of the crystallization features of a supercooled metastable liquid are developed. Estimates of the parameters of the processes accompanying the movement of the crystallization front in supercooled metastable water droplets are obtained with application to the problem of icing of aircraft.

CFD modeling of aerosol flow through a granular filter with porous granules

In this work, we made a comparative calculation of a granular filter with different shapes of the granules. We created granular filter models with solid and porous granules. The diameter of the granules was 5 mm, and the porosity was ε = 0,8. A comparison was made on the deposition efficiency, pressure drop, porosity, and filter quality parameter. We have found that for a filter with porous granules, the particle deposition efficiency is slightly lower than for a filter with solid granules. However, the pressure drop is an order of magnitude higher for a filter with solid granules, which ensures the maximum value of the filter quality.

Enhancing Single Channel MQL through Bypass Controlled Design for Deep Hole Drilling with Small Diameter Tool

Because of significant energy savings, enablement of higher machining speed as well as environmentally friendly features, Minimum Quantity Lubrication (MQL) has been efficiently used for many machining processes. However, in deep hole drilling with small tools (tool diameter D< 5 mm and length L>25 D) there is a bottleneck for the single-channel MQL system. The single-channel MQL, based on the Venturi principle, has difficulty generating the required oil quantity due to dropped air pressure difference during the deep hole drilling process. In this paper, a system concept based on a bypass design is proposed and investigated in static and dynamic laboratory tests. In the static test, the oil volume with and without bypass control was measured. Through the spray pattern test, the aerosol distribution and the reaction time are analyzed. A dynamic machining trial with a drill tool (D=4.5 mm, L= 40 D) was carried out with the proposed system. The tool wear was tracked and analyzed up to 100 meters in drilling distance. The result shows that the single-channel MQL with a bypass control is able to overcome this limitation and enables a uniform and continuous aerosol flow to tooltips.

The Influence of Laser Sintering Modes on the Conductivity and Microstructure of Silver Nanoparticle Arrays Formed by Dry Aerosol Printing

The demand for the development of local laser sintering of nanoparticle arrays is explained by the expanding needs for printed electronics for functional microstructure formation, on heat-sensitive substrates in particular. This work is based on the research into the sintering of arrays of silver nanoparticles synthesized in a spark discharge and deposited on a substrate by focused aerosol flow. The sintering was done by continuous and pulsed lasers with wavelengths 527, 980 and 1054 nm. Sintered samples were studied by measuring the resistivity, cross-section profile area and microstructure features. The highest average conductivity, equal to the half of the bulk silver conductivity, was achieved when sintering by continuous radiation with a wavelength 980 nm. The results showed that when using pulsed radiation the direct heating of nanoparticles in the sample surface layer dominates with the formation of a pore-free conductive layer of around 0.5 μm thick and crystallite of 70–80 nm size. It was found that laser sintering by radiation with a wavelength 527 nm required an order of magnitude lower specific energy costs as compared to the longwave laser radiation. The high energy efficiency of laser sintering is explained by special conditions for radiation absorption at plasmon resonance.

Determination of the Mean Mobility and Estimation of the Mobility Distribution of Aerosols with a Concentric-Cylindrical Electrostatic Precipitator

Concentric-cylindrical electrical condensers, commonly employed in laboratory research work to precipitate charged aerosol particles (electrostatic precipitator, ESP), can also be used to measure the mean electric mobility of the aerosol and to estimate its mobility distribution. A theoretical research has been carried out to describe the performance of an ESP and its application to the determination of aerosol mobility distribution. Two main equations have been derived: the transfer function, i.e. the probability that a particle of a given mobility is transmitted through the ESP; and, from it, the basic equation describing the performance of the precipitator, the penetration–voltage equation. These equations are valid for whatever shape of the flow velocity profile. MonteCarlo simulations have been carried out to compute the penetration–voltage curve and found to be in excellent agreement with the analytical equations. The parameters (geometric mean and standard deviation) of aerosols with lognormal mobility distributions can be estimated with certain accuracy as long as the distribution width is not too large. Finally, the effect of Brownian diffusion (not taken into account in the theoretical model) has been considered in the MonteCarlo simulations and found to be negligible provided that proper ESP geometric dimensions and aerosol flow rate are used.

Evaluation of the efficiency of prefilter models using numerical simulation

In this work, we estimate the contribution of the prefilter to the operation of the filter-prefilter system and propose two models of prefilters with curved plates. Numerical calculations of the aerosol flow in various combinations of filters and prefilters are carried out. We calculate the particle deposition efficiency of different filter models. The prefilter in the case of five and ten plates increases the limit of deposition efficiency for open cell foam material. A prefilter with five curved plates with parameters l=0.33 mm and h=4 mm is more preferably in comparison with ten plates with parameters l=0.33 mm and h=2 mm.

Experimental Investigation of the Suppression of Crown and Ground Forest Fires

Results of experimental investigations on the suppression of the flame combustion and thermal decomposition of forest combustible materials by aerosol flows of a pure water and aqueous solutions are presented. The characteristics of some sprayers were determined and the densities of wetting of a fire hotbed, provided by them, were calculated. The times of extinguishing hotbeds of model crown and ground forest fi res were measured, and distributions of temperatures and heat flows in them were determined. It is shown that the efficiency of extinguishing a forest fire is mainly determined by the sizes of the aerosol droplets acting on it.