A model of transient internal fl ow and atomization of propellant/ethanol mixtures
in pressurized metered dose inhalers (pMDI)
B. Gavtasha, H. K. Versteega, G. Hargravea, B. Myatta, D. Lewis b, T. Church b, and G. Brambillac
aWolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough University, Loughborough, United Kingdom; bChiesi Limited, Chippenham, Wilts, United Kingdom; cChiesi Farmaceutici SpA, Parma, Italy
A B S T R A C T
This article reports the extension to binary propellant/excipient mixtures of the multiphase model of transient internal flow and atomization in pressurized metered dose inhalers (pMDIs) of Gavtash and colleagues for propellant-only flows. The work considers different accounts of the effect of less volatile ethanol on the saturated vapor pressure (SVP), viscosity and surface tension of HFA-based pMDI formulations. Representation of the SVP of HFA/ethanol mixtures by Raoult’s law is compared
with the empirical model developed by Gavtash and colleagues as well as different theoretical mixing rules for surface tension and viscosity. For initial ethanol contents ranging from 0 to 20% by mass, the temperature, pressure and spray velocity were predicted to be almost independent of ethanol concentration when using the empirical SVP model of Gavtash and colleagues. The
predicted aerosol droplet size increases with increasing concentration of ethanol. These model predictions compare favorably with phase Doppler anemometry (PDA) measurements of pMDI sprays. Exploration of model predictions with different mixing rules suggest that variations of the dynamic viscosity could result in 0.7 mm droplet size change, and different surface tension models yield around 1.5 mm droplet size change. The findings of this work challenge the view that the increase of droplet size is caused by the low volatility of excipients such as ethanol. Instead, attention is focused on composition-dependent viscosity and surface tension as potential controlling parameters with significant effect on the droplet size of HFA/ethanol sprays.
Application of fractal theory to estimation of equivalent diameters of airborne
carbon nanotube and nanofi ber agglomerates
Bon Ki Ku and Pramod Kulkarni
Centers for Disease Control and Prevention (CDC), National Institute for Occupational Safety and Health (NIOSH), Cincinnati, Ohio, USA
A B S T R A C T
Understanding transport characteristics of airborne nanotubes and nanofi bers is important for assessing their fate in the respiratory system. Typically, diffusion and aerodynamic diameters capture key deposition mechanisms of near-spherical particles such as diffusion and impaction in the submicrometer size range. For nonspherical particles with high aspect ratios, such as aerosolized carbon nanotubes, these diameters can vary widely, requiring their independent measurement. The objective of this study was to develop an approach to provide approximate estimates of aerodynamic- and diffusion-equivalent diameters of airborne carbon nanotubes (CNTs) and carbon nanofi bers (CNFs) using their morphological characteristics obtained from electron micrographs. The as-received CNT and CNF materials were aerosolized using different techniques such as dry dispersion and nebulization. Mobility and aerodynamic diameters of test aerosol were directly deduced from tandem measurement of particle mobility and mass. The same test aerosol was mobility-classifi ed and subsequently collected on a microscopy grid for transmission electron microscopy (TEM) analysis. TEM micrographs were used to obtain projected area, maximum projected length, and two-dimensional (2-D) radius of gyration of test particles. Estimates of the aerodynamic diameter and the diffusion diameter were obtained by applying the fractal theory developed for aerosol agglomerates of primary spherical particles. After accounting for the particle dynamic shape factor, estimated aerodynamic diameters agreed with those from the direct measurements (using tandem mobility-mass technique) within 30– 40% for the agglomerates with relatively open structures while the diffusion diameters agreed within 40– 50%. The uncertainty of these estimates mainly depends on degree of overlapping structures in the microscopy image and nonuniformity in tube diameter. The approach could be useful in calculating approximate airborne properties from microscopy images of CNT and CNF agglomerates with relatively open structures.
Computational analysis of deposition and translocation of inhaled nicotine and
acrolein in the human body with e-cigarette puffi ng topographies
Ahmadreza Haghnegahdara, Yu Fenga, Xiaole Chenb, and Jiang Linc
aSchool of Chemical Engineering, Oklahoma State University, Stillwater, Oklahoma, USA; bSchool of Energy and Environment, Southeast University, Nanjing, Jiangsu, China; cCollege of Light Industry, Zhejiang University of Science and Technology, Hangzhou, Zhejiang, China
A B S T R A C T
Recently, toxicants such as formaldehyde and acrolein were detected in electronic cigarette (EC) aerosols. It is imperative to conduct research and provide sufficient quantitative evidence to address the associated potential health risks. However, it is still a lack of informative data, i.e., highresolution local dosimetry of inhaled aerosols in lung airways and other systemic regions, due to the limited imaging resolutions, restricted operational flexibilities, and invasive nature of experimental and clinical studies. In this study, an experimentally validated multiscale numerical model, i.e., Computational Fluid-Particle Dynamics (CFPD) model combined with a Physiologically Based Toxicokinetic (PBTK) model is developed to predict the systemic translocation of nicotine and acrolein in the human body after the deposition in the respiratory system. In-silico parametric analysis is performed for puff topography influence on the deposition and translocation of nicotine and acrolein in human respiratory systems and the systemic region. Results indicate that the puff volume and holding time can contribute to the variations of the nicotine and acrolein plasma concentration due to enhanced aerosol deposition in the lung. The change in the holding time has resulted in significant difference in the chemical translocation which was neglected in a large group of experimental studies. The capability of simulating multiple puffs of the new CFPD-PBTK model paves the way to a valuable computational simulation tool for assessing the chronic health effects of inhaled EC toxicants.
Estimate of scattering truncation in the cavity attenuated phase shift PMSSA monitor using radiative transfer theory
Fengshan Liu, David R. Snelling, Kevin A. Thomson, and Gregory J. Smallwood
Measurement Science and Standards, National Research Council, Ottawa, Ontario, Canada
A B S T R A C T
The recently developed cavity attenuated phase shift particulate matter single scattering albedo (CAPS PMSSA) monitor has been shown to be fairly accurate and robust for real-time aerosol optical properties measurements. The scattering component of the measurement undergoes a truncation error due to the loss of scattered light from the sample tube in both the forward and backward directions. Previous studies estimated the loss of scattered light typically using the Mie theory for spherical particles, assuming particles are present only on the sampling tube centerline, and without accounting for the effects of sampling tube surface reflection. This study overcomes these limitations by solving the radiative transfer equation in an axisymmetric absorbing and scattering medium using the discrete-ordinates method to estimate the scattering truncation error. The effects of absorption coefficient, scattering coefficient, asymmetry parameter of the scattering phase function, and the reflection coefficient at the sampling tube inner surface were investigated. Under typical conditions of CAPS PMSSA operation of low extinction coefficients below about 5000 Mm ¡1 , the scattering loss remains independent of the absorption and scattering coefficients but is dependent on the scattering phase function and the reflection coefficient of the sampling glass tube inner surface. The proposed method was used to investigate the effects of asymmetry parameter and surface reflection coefficient on truncation for absorbing aerosol particles whose scattering phase function can be well represented by the Henyey-Greenstein approximation. The scattering loss increases with increasing the asymmetry parameter and the surface reflection coefficient.
Hygroscopic properties of potassium-halide nanoparticles
M. Giamareloua, M. Smithb, E. Papapanagiotoua, S.T. Martinb, and G. Biskos c,d
aDepartment of Environment, University of the Aegean, Mytilene, Greece; bSchool of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA; cFaculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, The Netherlands; dEnergy Environment and Water Research Center, The Cyprus Institute, Nicosia, Cyprus
A B S T R A C T
The hygroscopic properties of KBr, KCl, and KI nanoparticles having diameters from 8 to 60 nm were measured using a tandem Differential Mobility Analyzer. In all cases, the deliquescence and efflorescence relative humidity values increased with decreasing particle diameter. The associated growth factors also decreased with decreasing particle diameter, in agreement with predictions by Kohler theory. Overall, the theoretically predicted growth factors agreed well with the€ measurements, i.e., within §3% uncertainty. For KCl particles having sizes down to 15 nm, however, a dynamic shape factor of 1.08, corresponding to non-spherical crystalline particles prior deliquescence, was inferred for agreement between measurements and theory. By comparison, KBr and KI within the same size range warranted shape factors of unity, equivalent to a sphere. These results contribute to an understanding of nanosize behavior widely relevant to material sciences as well as atmospheric aerosol particles over the oceans.
Inactivation of aerosolized surrogates of Bacillus anthracis spores by combustion
products of aluminum- and magnesium-based reactive materials: Effect
of exposure time
Worrawit Nakpana, Sergey A. Grinshpuna, Michael Yermakova, Reshmi Indugulaa, Tiina Reponena, Song Wangb, Mirko Schoenitzb, and Edward L. Dreizin b
aDepartment of Environmental Health, Center for Health-Related Aerosol Studies, University of Cincinnati, Cincinnati, Ohio, USA; bDepartment of Chemical, Biological, and Pharmaceutical Engineering, New Jersey Institute of Technology, Newark, New Jersey, USA
A B S T R A C T
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 wellestablished 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.
Inactivation of airborne viruses using vacuum ultraviolet photocatalysis
for a fl ow-through indoor air purifi er with short irradiation time
Jeonghyun Kima and Jaesung Janga,b
aSchool of Mechanical, Aerospace and Nuclear Engineering, Ulsan National Institute of Science and Technology, Ulsan, Republic of Korea; bDepartment of Biomedical Engineering, Ulsan National Institute of Science and Technology, Ulsan, Republic of Korea
A B S T R A C T
Many ultraviolet (UV)-based disinfection methods have been developed; however, these methods usually use the recirculating mode or need long irradiation periods due to its low photon energy. Vacuum UV (VUV) was recently found to be a promising light source, despite its ozone generation. In this study, we investigated photocatalysis reactions by VUV with short irradiation times (0.004–0.125 s) for simultaneously inactivating airborne MS2 viruses and degrading the generated ozone toward a flow-through air disinfection system with high flow-rates. We developed three effective shapes for the catalyst frame: 2 mm and 5 mm pleated, and spiral-type Pd-TiO2 catalysts. The 2 mm pleated Pd-TiO2/VUV photocatalyst exhibited the highest activity for simultaneous MS2 inactivation and ozone degradation, and the catalytic activity was effective regardless of relative humidity.
Considering the gas phase and catalyst surface effects, and the natural inactivation of VUVirradiated but live MS2 viruses, the 2 mm pleated Pd-TiO2/VUV and succeeding UV photocatalysis showed more than 90% in the overall inactivation efficiency with residual ozone of 35 ppb at an irradiation time of 0.009 s (flow-rate: 33 l/min). In contrast, most UV-based purifiers take longer
times for disinfection. This system has the potential for an alternative to conventional UV-based air purifiers.
Internally mixed nanoparticles from oscillatory spark ablation between electrodes
of different materials
Jicheng Feng a, Nabil Ramlawia, George Biskos b,c, and Andreas Schmidt-Otta,c
aFaculty of Applied Sciences, Delft University of Technology, Delft, The Netherlands; bFaculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, The Netherlands; cEnergy Environment and Water Research Center, The Cyprus Institute, Nicosia, Cyprus
A B S T R A C T
The increasing need for engineered alloy nanoparticles (NPs) in diverse fields has spurred efforts to explore efficient/green synthesis methods. In this respect, spark ablation provides a scalable and viable way for producing widely different types of mixed NPs. Most importantly, implementation of the spark has the great advantage to combine a wider range of materials, thereby allowing the synthesis of mixed NPs with virtually unlimited combinations. Here we show that polarity reversal of
spark discharges between two electrodes consisting of different materials enables synthesis of alloy NPs, while having a good potential to control the broadness of their composition distribution. A model developed in this work provides a tool for tuning the ablation ratio between the electrodes by adjusting the electric characteristics of the spark circuit. The ablation ratio is equal to the mean composition of the resulting NPs. The model predictions are in accordance with measurements obtained here and in earlier works. The unique way of producing alloy NPs by spark ablation shown in this work becomes especially useful when the starting electrode materials are immiscible at macroscopic scale.
Internally mixed nanoparticles from oscillatory spark ablation between electrodes
of different materials
Jicheng Feng a, Nabil Ramlawia, George Biskos b,c, and Andreas Schmidt-Otta,c
aFaculty of Applied Sciences, Delft University of Technology, Delft, The Netherlands; bFaculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, The Netherlands; cEnergy Environment and Water Research Center, The Cyprus Institute, Nicosia, Cyprus
A B S T R A C T
The increasing need for engineered alloy nanoparticles (NPs) in diverse fields has spurred efforts to explore efficient/green synthesis methods. In this respect, spark ablation provides a scalable and viable way for producing widely different types of mixed NPs. Most importantly, implementation of the spark has the great advantage to combine a wider range of materials, thereby allowing the synthesis of mixed NPs with virtually unlimited combinations. Here we show that polarity reversal of
spark discharges between two electrodes consisting of different materials enables synthesis of alloy NPs, while having a good potential to control the broadness of their composition distribution. A model developed in this work provides a tool for tuning the ablation ratio between the electrodes by adjusting the electric characteristics of the spark circuit. The ablation ratio is equal to the mean composition of the resulting NPs. The model predictions are in accordance with measurements obtained here and in earlier works. The unique way of producing alloy NPs by spark ablation shown in this work becomes especially useful when the starting electrode materials are immiscible at macroscopic scale.
Optimization of centrifugally spun thermoplastic polyurethane nanofi bers
for air fi ltration applications
N. A. Serhat Gundogdua, Yasin Akgula,b, and Ali Kilic a
aTEMAG Labs, Istanbul Technical University, Gumussuyu, Istanbul, Turkey; bMetallurgical and Materials Engineering, Karabuk University, Karabuk, Turkey
A B S T R A C T
While our knowledge of fiber formation by using conventional nanofiber spinning techniques has increased to a considerable extent, there are still few studies on centrifugal spinning either in academia or in the industry. Centrifugal spinning is a comparatively new method of producing fibers having nano- or microscale diameters. In this study, three main parameters (nozzle orifice diameter, rotational speed, polymer concentration) of centrifugal spinning were optimized to produce air filter media from thermoplastic polyurethane nanofibers. The effect of concentration of polymer solution was found to be a major contributor in TPU fibers optimization estimating 77.5%. After the optimization studies, the average fiber diameter of nanofiber sample produced at optimum conditions (22G needle as an orifice, 4000 rpm, and 10 wt% concentration of polymer solution) was 205 § 84 nm. Aerosol filtration performance of the produced webs was analyzed. Filtration efficiency of the optimized sample was found to be 99.4% for 0.3 mm particle size at an expense of 98 Pa pressure drop.
The effect of electric-fi eld-induced alignment on the electrical mobility
of fractal aggregates
James Corsona, George W. Mulhollanda, and Michael R. Zachariaha,b
aDepartment of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland, USA; bDepartment of Chemistry and Biochemistry, University of Maryland, College Park, Maryland, USA
A B S T R A C T
We study the effects of electric field strength on the mobility of soot-like fractal aggregates (fractal dimension of 1.78). The probability distribution for the particle orientation is governed by the ratio of the interaction energy between the electric field and the induced dipole in the particle to the energy associated with Brownian forces in the surrounding medium. We use our extended
Kirkwood–Riseman method to calculate the friction tensor for aggregates of up to 2000 spheres, with primary sphere sizes in the transition and near-free molecule regimes. Our results for electrical mobility versus field strength are in good agreement with published experimental data for soot, which show an increase in mobility on the order of 8% from random to aligned orientations. Our calculations show that particles become aligned at decreasing field strength as particle size increases because particle polarizability increases with volume. Large aggregates are at least partially aligned at field strengths below 1000 V/cm, though a small change in mobility means that alignment is not an issue in many practical applications. However, improved differential mobility analyzers would be required to take advantage of small changes in mobility to provide shape characterization.
