Journal of Aerosol Science最新文献

Radiological dispersal devices (RDDs) have a potential to disperse radioactive aerosols into the atmosphere through explosions. Accurately estimating the respirable fraction of these aerosols through experiments presents a considerable challenge. Also, the modeling of aerosol particle evolution stemming from an RDD explosion is inherently complex, involving the interplay of various physical processes operating at different time scales. In this study, we propose a comprehensive numerical model to estimate the respirable fraction of aerosols generated during RDD explosions, integrating the thermodynamic properties of detonation products with microphysical aerosol processes. The model assumes particles are spherical and ignores charge effects. It is also assumed that the thermodynamic properties of the cloud are uniform within its volume and that thermal equilibrium exists between particles and the surrounding medium. Numerical simulations are conducted for diverse experimental scenarios, and performance of the model is assessed by comparing its predictions with experimental data pertaining to Carbon and Cobalt particles. Notably, the model predicts the average particle diameter of Carbon particles within the detonation front of TNT at 13.8 nm, closely matching the experimental observation of 13 nm (Rubtsov et al., 2019). Additionally, the model captures the peak value of the cobalt particle mass fraction distribution, approximating it to be around $0.7\mu m$, in agreement with experimental findings (Di Lemma et al., 2016). These findings indicate that the proposed model is capable of predicting the behavior of both radioactive and non-radioactive aerosols. Also, this study underscores the potential of modeling approaches in addressing existing knowledge gaps related to RDDs, thereby contributing to enhanced impact assessment and management strategies for incidents involving RDDs.

In this work, the oxide nanopowders of Al₂O₃, ZrO₂, Y₂O₃, Gd₂O₃, CeO₂, and SiO₂ were synthesized by CW CO₂ laser vaporization technique with controlled gas condensation in an inert atmosphere. Methods for controlling the size of the resulting nanoparticles by adjusting the gas composition and pressure during the vaporization process have been demonstrated. The potential for producing ultrasmall oxide nanoparticles with dimensions less than 5 nm has been shown. The size distribution of nanoparticles taken from different parts of the evaporation-condensation tract was studied using scanning (SEM) and transmission (TEM) electron microscopy methods. The effect of synthesis conditions (pressure and composition of the inert gas) on characteristics of the nanoparticles is discussed. Using a wide class of simple oxides as the example, it is shown that the powders synthesized by the laser method consist of three types of particles: target spherical particles with a diameter of 3–20 nm (more than 98%), larger spherical particles with a diameter of 50–200 nm, and shapeless large particles with sizes more than 200 nm. The possibility of separating large particles from the main particles using the original labyrinth system for gas pumping is shown. The obtained particles with controlled sizes can be effectively used in various applications, in particular, for the preparation of catalysts and adsorbents.

A light-emitting-diode (LED) based optical technique is developed to measure the surface area per unit volume of particles in aerosols and liquid sprays. The technique uses path-integrated measurements of transmittance, T, from two angles to produce a tomographic reconstruction of the local extinction coefficients, K, in the region of interest, using the Beer-Lambert law and a deconvolution algorithm. When the particles in the flow have sufficiently large diameters (existing in the Mie scattering regime), these extinction coefficients can be related to the surface area per unit volume of the particles. The technique has the potential to be applied to a wide range of two-phase flows. In the present study, it is applied to flows through a pharmaceutical inhaler device, where two powders with different particle size distributions are considered.

Safe reactor decommissioning, especially for damaged Fukushima Daiichi (1F) nuclear power plants, is vital for environmental safety. Key challenges include remotely cleaning radiation hotspots and cutting fuel debris within the damaged primary containment vessel. However, submicron radioactive Aerosol Particles (APs) can be generated, thus necessitating effective aerosol control and removal to avoid radioactive environmental pollution and reduce radiation exposure risks during 1F decommissioning. Flue gases containing submicron APs that result in environmental pollution can also generated from other industrial works, e.g., coal, mining and chemical sectors. Conventional water spray is difficult to scavenge these small APs. Although previous studies showed the effectiveness of charged droplets on accelerating aerosol removal, the charging configuration is also important to scavenging performance. Hence, this study performs aerosol scavenging experiments in our UTARTS facility with varying induction electrode designs. Experimental results show the saturation of scavenging efficiency at high voltage and indicate the importance of charging polarity. Moreover, proper configurations of electrode position, geometry and material are studied and discussed. Our findings can be beneficial for the improvement of spray system for aerosol removal to mitigate radioactivity release and minimize contaminated water production and have implications for gas purification in various environmental and chemical industries.

Inhalation has become widely accepted as the optimal drug delivery mechanism for respiratory diseases, which often requires targeting a particular region of the lung. Mathematical models are key to understanding the factors that influence drug transport and deposition in the lung. This study proposes a simple zero-dimensional typical path model that couples respiratory mechanics and particle deposition over multiple oscillatory breathing cycles. Respiration is modeled using an RLC (resistance–inductance–capacitance) circuit analog framework to capture airflows, lung pressures, and volumes. The model is validated against experimental deposition fractions reported in the literature. The model is used to explore the effects of oscillatory respiration and multiple breaths on particle deposition in different regions of the lung. The results indicate that oscillatory dynamics are important in compliant airways. Deposition increases over multiple breaths as the concentration of suspended particles increases in the respiratory airways.

Soot particles are known to be harmful to health and the environment, and reducing their production in industrial systems is a crucial task in the pursuit of green energy production. Characterization and accurate modeling of these particles are essential yet complex. In particular, information on aggregate sizing remains limited. Angular light scattering is an established in-situ method for precise, spatially resolved, non-intrusive characterization of soot aggregates. However, the associated post-processing is prone to various error sources. Specifically, signal trapping during light scattering is suspected to lead significant errors. Moreover, current techniques for reconstructing the line-of-sight integrated scattering signal (Abel inversion) are inherently noisy. This work addresses both issues by implementing a noise-free Abel inversion method based on piecewise spline functions. This method accounts for signal trapping and can be applied to any axisymmetric and spatially continuous flame. The correction for the signal trapping effect relies on extinction measurements from the line-of-sight attenuation (LOSA). The technique is tested on a canonical laminar diffusion ethylene flame at five different angles. The impact of this correction is evaluated on the equivalent monodisperse radius of gyration, denoted as $R_g^{\ast }$, and the forward scattering coefficient, represented as ${\kappa }_{vv}\left(0^{\circ }\right)$. The results show that the calculation of $R_g^{\ast }$ is robust regarding signal trapping effect. However, correcting for this effect significantly increases ${\kappa }_{vv}\left(0^{\circ }\right)$.

In the present paper, we studied the forces on a spherical particle of radius R moving in the vicinity of the plane wall in a shear flow of free molecular regime. We consider that the distance ratio between the plane wall and the particle (L) and the particle radius (R) is large (e.g., L/R > 5), and the gas molecular mean free path (λ) is much higher than the particle size (λ/R ≫1). An analytical formula for the forces is obtained based on gas kinetic theory and certain simplifying assumptions, and is verified by using Direct Simulation Monte Carlo Method. It is found that the forces acting on the particle can be affected by the momentum accommodation coefficients (σ) of the wall and particle surfaces, the wall/gas temperature ratios (T_w/T), and the velocity gradient (G) of the gas flow. In the cases of specular reflections (σ = 0), the near-wall effect can be neglected. With the increase of the momentum accommodation coefficients, the near-wall effect can be enhanced. When near-wall particles move in the direction parallel to the plane wall, there is a lift force which is perpendicular to the wall due to the near-wall effect and the shear flow. For T_w/T < 1, the lift force for the near-wall particles is in the direction against the wall. While for T_w/T > 1, the force is in the direction away from the plane wall. The findings presented in this paper can provide theoretical guidance for the application of near-wall particles in shear flows.

This is the third of a series of papers dealing with the behavior of Brownian aerosol particles immersed in a laminar fluid flow. The evolution along the tube of the distributions of particle radial positions (RPD), particle residence time (RTD), and particle mean axial velocity (MAVD) were determined by Monte Carlo (MC) simulation of particles trajectories. The RPD and particle penetration was also determined by numerical solution of the advection-diffusion equation (ADE) with negligible particle axial diffusion. The fairly good agreement shown between the results obtained by these two methods justifies our confidence on the use of the MC technique to determine other particle properties, as MAVD and RTD, for which the corresponding differential equation is yet unknown. Flow-related properties of the aerosol, such as penetration and residence time, are mainly determined by its MAVD. The MAVD is intimately related to the RPD; the latter evolves in such a manner that the surviving particles tend to accumulate nearer the tube axis and farther from the wall. When the fluid local velocity depends on the spatial location, the mean particle axial velocity increases as the aerosol flows downstream the tube, and its value can be considerably larger than the mean fluid velocity, in spite that no external force is acting on the particle. A direct consequence of this counterintuitive fact is that the mean aerosol residence time in the tube can be much smaller, by a factor of ∼0.65, than that of the fluid for even moderate values of the particle diffusion coefficient. This asymptotic value of the aerosol mean residence time can be predicted using the ADE in conjunction with a simple estimation model proposed here. If the fluid velocity is constant within the tube (uniform or plug flow), the mean particle axial velocity is everywhere equal to the fluid velocity, and particles and fluid spend the same time to traverse the tube. The larger the departure of the fluid velocity profile from uniformity, the larger the difference of mean axial velocity and mean residence time between particles and fluid.

This study presents a microscale simulation method that allows one to study the impact of particle loading on the aerosol capture efficiency of an electrostatically charged filter. This was done by considering a bipolarly charged fiber loaded with different amounts of neutral and charged particles with a diameter of 300 nm. The simulations predicted the deposition pattern of the aerosol particles as well as their impact on the electrostatic field of the bipolar fiber. The particle-loaded fiber was then challenged with aerosol particles in the range of 50 nm to 1 μm and with different charge polarities to study how the electrostatic field of the deposited particles interacts with that of the fiber to attract or repel the incoming airborne particles. More specifically, our simulations revealed that particle deposition can enhance the capture efficiency of a bipolar fiber when it is challenged with small particles (smaller than about 400 nm) regardless of the charge polarity of the airborne or deposited particles. The numerical simulations reported in this paper were conducted using the ANSYS CFD code enhanced with in-house subroutines to superimpose the electrostatic field of the deposited particles to that of the bipolar fiber and to include Brownian, polarization, and Coulomb forces in particle trajectory calculations.

The influence of background pressure on electrospray plume evolution is observed by simulating the emission and propagation of an electrospray particle population into an electric field at a range of relevant background pressures. Differences in plume evolution from atmospheric pressure to one hundredth of atmospheric pressure are evident from plume characteristics such as (1) the overall domain of the resulting plumes and (2) the terminal angle at a downstream terminus of one standard deviation and three standard deviations of particle number density. Plume divergence and terminal angle are shown to correlate strongly with background pressure for pressures above which plume-background collision rates are significant, consistent with experimental observations of increased plume divergence with increased background pressure. The results suggest a simple expression for the pressure below which a system achieves minimum plume divergence: $P_{th}=kT/7.7299{\sigma }_{fl}d$ for a system of temperature $T$, background fluid molecules with cross-section ${\sigma }_{fl}$, and plume species of diameter $d$.