Transport phenomena governing nicotine emissions from electronic cigarettes: Model formulation and experimental investigation

Electronic cigarettes (ECIGs) electrically heat and aerosolize a liquid-containing propylene glycol (PG), vegetable glycerin (VG), flavorants, water, and nicotine. ECIG effects and proposed methods to regulate them are controversial. One regulatory focal point involves nicotine emissions. We describe a mathematical model that predicts ECIG nicotine emissions. The model computes the vaporization rate of individual species by numerically solving the unsteady species and energy conservation equations. To validate model predictions, yields of nicotine, total particulate matter, PG, and VG were measured while manipulating puff topography, electrical power, and liquid composition across 100 conditions. Nicotine flux, the rate at which nicotine is emitted per unit time, was the primary outcome. Across conditions, the measured and computed nicotine flux were highly correlated (r = 0.85, p < .0001). As predicted, device power, nicotine concentration, PG/VG ratio, and puff duration influenced nicotine flux (p < .05), while water content and puff velocity did not. Additional empirical investigation revealed that PG/VG liquids act as ideal solutions, that liquid vaporization accounts for more than 95% of ECIG aerosol mass emissions, and that as device power increases the aerosol composition shifts towards the less volatile components of the parent liquid. To the extent that ECIG regulations focus on nicotine emissions, mathematical models like this one can be used to predict ECIG nicotine emissions and to test the effects of proposed regulation of factors that influence nicotine flux.

Copyright © 2017 American Association for Aerosol Research     

Numerical modeling of particle deposition in ferret airways: A comparison with humans

The ferret is commonly used as an animal model for studying human respiratory diseases, but the validation is lacking. The particle deposition patterns in ferret airways was investigated and compared to those in humans. A computational fluid dynamics method was used to simulate particle deposition in the tracheobronchial airway by using the truncated single-path models. The deposition characteristics of particles with diameters of 1, 3, and 5 μm were investigated under various respiratory rates at different activity conditions (i.e., sedentary, light, moderate, and intense activities). For both human and ferret models, deposition increased with both generation and particle size but decreased with respiratory rate. Particles of 1–5 μm deposit more but transport upper in ferrets than in humans, which suggests that ferrets are more likely to be infected in the proximal airways. The results show that the trend of particle deposition in the ferret airways is similar to that in human airways but with different deposition rates and sites. Our findings indicate that ferret for studying human respiratory diseases is suitable for the upper respiratory diseases, such as human influenza, but may not be suitable for studying the lower respiratory diseases, such as pneumonia.

Copyright © 2017 American Association for Aerosol Research     

A comparison of spherical and cylindrical microparticles composed of nanoparticles for pulmonary application

Nano-embedded microparticles represent promising carrier systems to tackle the challenges of nanoparticle delivery into the lungs by inhalation. While spray drying is widely used for the incorporation of nanoparticles into microparticles, the template-assisted technique is a novel method to prepare aspherical, cylindrical microparticles composed of nanoparticles. In this work, both techniques were applied to produce both spherical and cylindrical nano-embedded microparticles. For both geometries particles consisting of gelatin nanoparticles, mannitol and leucine were prepared in three different sizes each. Cylindrical microparticles could be prepared with defined dimensions and narrow size distributions, allowing to target a wide range of aerodynamic diameters. The size of spherical microparticles was influenced by the spraying feed concentration, yielding only small differences in geometric and aerodynamic diameters and broad particle size distributions. Regarding the redispersibility of the nano-embedded microparticles, spherical particles showed better disintegration behavior and higher nanoparticle release in comparison to cylindrical particles upon contact with water. The template-assisted technique yielded higher nanoparticle content in contrast to spray drying. In summary, cylindrical particles represent a promising drug delivery system with high potential for later application. However, further improvements in the preparation method are required to enable higher yields and a possible later scale-up.

Copyright © 2018 American Association for Aerosol Research     

Inactivation of aerosolized surrogates of Bacillus anthracis spores by combustion products of aluminum- and magnesium-based reactive materials: Effect of exposure time

Targeting bioweapon facilities may release biothreat agents into the atmosphere. Bacterial spores such as Bacillus anthracis (Ba) escaping from direct exposure to the fireball potentially represent a high health risk. To mitigate it, reactive materials with biocidal properties are being developed. Aluminum-based iodine-containing compositions (e.g., Al·I₂ and Al·B·I₂) have been shown to inactivate aerosolized simulants of Ba effectively, i.e., by factors exceeding 10⁴ when the spores are exposed to their combustion products over a short time (～0.33 s). This follow-up study aimed at establishing an association between the spore inactivation caused by exposure to combustion products of different materials and the exposure time. Powders of Al, Al·I₂, Al·B·I₂, Mg, Mg·S, and Mg·B·I₂ were combusted, and viable aerosolized endospores of B. thuringiensis var kurstaki (a well-established Ba simulant) were exposed to the released products for relatively short time periods: from ～0.1 to ～2 s. The tests were performed at two temperatures in the exposure chamber: ～170°C and ～260°C; both temperatures are lower than required for quick thermal inactivation of the spores. The higher temperature and exposure times above 0.33 s generated distinctively higher inactivation levels (as high as ～10⁵) for iodine-containing materials. We also observed inactivation levels of up to ～10³ at very short exposure times, 0.12s, in the presence of condensing MgO. However, the effect of MgO at longer exposure times became negligible. The biocidal effect of sulfur oxides was found to be weak. The study findings are crucial for establishing strategies and developing reaction models that target specific bioagent inactivation levels.

Copyright © 2018 American Association for Aerosol Research     

Aerosol deposition in 3D models of the upper airways and trachea of rhesus macaques

Abstract

Little is known about aerosol deposition in macaques, variability in deposition between animals, or how deposition in macaques and humans compare. This is despite the use of macaques in assessments of toxic aerosols that are often translated to estimates of human exposure. We used three dimensional (3D) physical models of the upper airways and trachea (UAT) of Rhesus macaques to begin to fill in this information gap. Models of the UAT of five, living rhesus macaques were produced from CT scans, using 3D printing technology. Models were exposed to a polydisperse aerosol containing 0.54 to 9.65 micron particles, during constant flowrates of 2, 4, and 6 liters per min. Percent deposition in UAT models was quantified using an Aerodynamic Particle Sizer and was compared to in vivo upper airway deposition in ten, adult human subjects. Deposition in the UAT models increased as Stokes number increased. Deposition also varied significantly between models, but intermodel variability was reduced when plotted as a function of Stokes number. Using Stokes number, deposition in four of the five UAT models overlapped with each other and also overlapped with human upper airway deposition. These models could be used to explore the relationship between factors that affect toxic aerosol deposition in the UAT in vitro and pathology following toxic aerosol exposure in Rhesus macaques in vivo. Results from those experiments could also be applicable to humans because of deposition similarities.

Copyright © 2020 American Association for Aerosol Research     

Experimental investigations of particle formation from propellant and solvent droplets using a monodisperse spray dryer

Experimental studies of particle formation from solution droplets were conducted using a newly developed monodisperse spray drying process. Solutes beclomethasone dipropionate and caffeine were dissolved in ethanol, pressurized hydrofluoroalkane propellant 134a, and mixtures thereof. Solutions were atomized into monodisperse microdroplets using a custom droplet generator installed in a laboratory scale spray dryer, enabling drying and collection of the resulting monodisperse microparticles. The effects of droplet diameter, solution concentration, solvent composition, and drying rate on the physical properties of the dried particles were evaluated. Particle morphology and size were assessed using ultramicroscopy and image analysis of micrographs. Extent of crystallinity and polymorphism were investigated using Raman spectroscopy. The drying temperature was found to have a large effect on the morphology of amorphous beclomethasone dipropionate particles. Particles dried near room temperature were spheroidal to ellipsoidal with prevalent surface concavities and evidence of shell buckling; increasing the drying temperature for fixed droplet size and composition resulted in a transition to more spherical, smooth-surfaced particle morphologies. Crystalline caffeine microparticles were made up of assemblies of multiple crystallites. The measured length and breadth of these crystallites was found to be correlated with the time available for crystal nucleation and growth as calculated using a particle formation model. The results highlight the abilities and limitations of currently available particle formation models in elucidating the relationships between the size, composition, and evaporation rate of drying solution droplets and the physical properties of the resulting particles. The work demonstrates the suitability of monodisperse spray drying as an experimental technique for investigating the fundamentals of particle formation from solution droplets.

© 2018 American Association for Aerosol Research     

A review of microfluidic concepts and applications for atmospheric aerosol science

Microfluidics is used in a broad range of applications, from biology and medicine to chemistry and polymer science, because this versatile platform enables rapid and precise repeatability of measurements and experiments on a relatively low-cost laboratory platform. Despite wide-ranging uses, this powerful research platform remains under-utilized by the atmospheric aerosol science community. This review will summarize selected microfluidic concepts and tools with potential applications to aerosol science. Where appropriate, the basic operating conditions and tunable parameters in microfluidics will be compared to typical aerosol experimental methods. Microfluidics offers a number of advantages over larger-scale experiments; for example, the small volumes of sample required for experiments open a number of avenues for sample collection that are accessible to the aerosol community. Filter extraction, spot sampling, and particle-into-liquid sampling techniques could all be used to capture aerosol samples to supply microfluidic measurements and experiments. Microfluidic concepts, such as device geometries for creating emulsions and developments in particle and droplet manipulation techniques will be reviewed, and current and potential microfluidic applications to aerosol science will be discussed.

Copyright © 2018 American Association for Aerosol Research     

Investigation of airflow and particle behavior around a subway train running in the underground tunnel

Airflow around an eight-passenger-car subway train running in the underground tunnel at a cruise speed of 70 km/h was numerically simulated, and the trajectories of the particles that were assumed to be re-suspended from the ground or generated at the contact points between the wheels and rails were predicted. In addition, field experiments were conducted to measure airflow velocity and PM₁₀ mass concentration under a T-car (trailer car without a driving cab) during the running of a subway train in straight sections of the underground tunnel of the Seoul Subway Line 5. The numerically predicted airflow velocities agreed well with the experimental data with the error of less than 30%, and the predicted particle distribution showed a similar tendency to the experimental results. The airflow under the T-car was predicted to be relatively uniform compared to the airflow under other passenger cars. Both numerical results and experimental data signified that a lot of particles could drift under the T-car by showing a higher particle concentration in the central area of the space under the T-car than in the edge area. As a result, the space underneath the T-car is anticipated to be a good place for installing a dust-removal system.

© 2016 American Association for Aerosol Research     

Effect of electric charge convection on the rate of mass transfer from a droplet in a constant electric field

We consider mass transfer in a system comprising a stationary fluid dielectric sphere embedded into an immiscible dielectric liquid under the influence of a constant uniform electric field. The partial differential equation of convective diffusion is solved by means of a similarity transformation, and the solution is obtained in a closed analytical form. For small electric Reynolds numbers the obtained solution recovers the solution found by Morrison [1].     

电场参数对高频脉冲水滴电聚结行为的影响

文章在高频高压脉冲电场条件下,研究了电场强度、电场频率、占空比等电场参数对水滴靠近过程中的变形及运动特性的影响。结果表明:在水滴靠近过程中,自开始施加电场到聚并时比为0.8时,平均变形度和靠近速率变化甚微,在此之后水滴由于偶极作用力和偶极极化变形效应的增强而发生大幅度变形和加速靠近,直至开始聚并。当E=1.071—1.813 kV/cm,f=2—6 kHz,n=12.8%—87.5%时,随电场参数的增大,水滴靠近时间呈现不同趋势的缩短,平均变形度明显加剧,靠近速率小幅增大,且后两者具有相近的变化规律,说明水滴间的极化力和本身的变形性具有一致性。本研究为高频脉冲电场下水滴电聚结和新型动态电聚结设备的优化提供理论基础。     

Deformation and breakup of a second-order fluid droplet in an electric field

The effects of elastic property on the deformation and breakup of an uncharged drop in a uniform electric field are investigated theoretically using the second-order fluid model as a constitutive equation. Two dimensionless numbers, the electric capillary number (C) and the Deborah number (De), the dimensionless parammeters governing the problem. The asymptotic analytic solution of the nonlinear free boundary problem is determined by utilizing the method of domain perturbation in the limit of small mathcal C and small De. The asymptotic solution provides the limiting point of C above which no steady-state drop shape exists. The linear stability theory shows that the elastic property of fluids give either stabilizing or destabilizing effect on the drop, depending on the deformation mode.     

The effect of electric field on droplet formation and motion in a viscous liquid

The formation and initial motion of distilled water droplets injected into a viscous oil were studied in the absence of an electrical field and under the influence of a high voltage (up to 10 kV) field. The droplets were formed at a stainless steel nozzle in a rectangular cell (38 × 10 × 10 cm) equipped with grounded parallel plate electrodes along two sides of the cell. As the voltage applied to the nozzle was increased, the formed droplets were reduced in size and showed repulsion and some upwards scattering; the droplet velocity near the nozzle was greatly increased by the field, with the droplets decelerating as they moved away from the nozzle. Droplet formation and motion with and without electric field have been compared with predictive models, showing qualitative agreement and partial quantitative agreement.     

Space charge and internal electric field distribution in poly(2,5-pyridinediyl)

We present measurements of the spatial distribution of space charge and the internal electric field in 3-4 μm thick films of a luminescent conjugated polymer by means of the laser intensity modulation method. The internal electric field is spatially modified by the existence and persistence of space charge layers induced by the external bias. We observe a double layer of homo-charges and hetero-charges, which is explained by a trapping model that implements the presence of traps near the surface of the film. Within this model, space charge layers are built up by a combination of carrier injection from the electrodes, not into the valence or conduction bands, but directly into intra-gap traps near the interface, as well as the separation of bulk electrons and holes in the external field and subsequent trapping. A trap density of about 10²³ m⁻³ is concluded from the results. In addition, the conjugated polymer poly(2,5-pyridinediyl) is found to have strong electret properties with local charge storage of up to 500 C/m³.     

Effect of an external electric field on the charge distribution of electrostatic coagulation

This article analyzes the effect of an external electric field on the charge distribution of bipolar and unipolar charged particles numerically by solving the coagulation equation for charged particles, based on the analytical expression for the coagulation coefficient [Wang, L. Z., Zhang, X. R., & Zhu, K. Q. (2005). An analytical expression for the coagulation coefficient of bipolarly charged particles by an external electric field with the effect of Coulomb force. Journal of Aerosol Science, 36, 1050–1055]. For symmetric bipolar charged particles, the external electric field does not change the symmetry of the initial charge distribution as the coagulation time increases. In addition, the particle number concentration decays monotonically during coagulation regardless of the magnitude of the particle charge. For asymmetric bipolar charged and unipolar charged particles, however, the particle number concentration does not decay monotonically for each value of charge during coagulation, due to the effect of an external electric field.     

自激振荡脉冲清洗射流研究及应用现状

自激振荡脉冲射流的发展是一个理论研究和试验研究相结合的发展过程.首先概述了国内外有关自激脉冲射流的理论研究现状和实验研究现状,而后主要介绍了它的应用现状,特别是在油罐清淤方面的应用,最后对下一步研究的方向和应用的领域作出了展望.     

Effect of frequency and oscillation amplitude on moldability of alumina-foam-polystyrene bodies

Conclusions Molding alumina-foam polystyrene bodies at low vibration frequencies (1000 oscillations per minute) is not recommended. The high-frequency vibration (6000 oscillations per minute) with maximum amplitudes is of no great advantage over a frequency of 3000 oscillations per minute in relation to any reduction in the viscosity of the bodies. At a frequency of 3000 oscillations per minute and an amplitude of 1.0 mm the products have the maximum strength. The optimum moisture content of these bodies, facilitating immediate deshuttering of the freshly molded products is 22% using Soviet alumina, and 19% using Hungarian alumina.Translated from Ogneupory, No. 3, pp. 55–58, March, 1973.     

Combustion synthesis and the electric field: A review

This brief review discusses principles and some latest developments in electrically activated combustion synthesis. Processes discussed include field-activated combustion synthesis (FACS), field-activated pressure-assisted synthesis (FAPAS), reactive spark plasma sintering (R-SPS), electrothermal explosion (ETE), and electrostatic-field-activated combustion synthesis (EFACS). These processes have demonstrated clear benefits to the process of combustion synthesis through the application of electric field. Although a significant amount of works have been published in the area, there still remain some directions within the field where sustained research may provide even more scientific reward.