Simulation of airflow and aerosol deposition in the nasal cavity of a 5-year-old child

As a human grows from birth to adulthood, both airway anatomy and breathing conditions vary that alter the deposition rate and pattern of inhaled aerosols. However, deposition studies have typically focused on adult subjects, results of which may not be readily extrapolated to children. Furthermore, because of greater ventilation rate per body weight, children receive a greater dose than adults and therefore are more susceptible to respiratory risks. This study is to evaluate the transport and deposition of respiratory aerosols in a nasal-laryngeal airway model based on MRI head images of a 5-year-old boy. Differences between this child and adults in nasal physiology and aerosol filtering efficiency will be emphasized. A validated low Reynolds number (LRN) k?ω turbulence model was employed to simulate laminar, transitional, and fully turbulent flow regimes within the nasal airways. Particle trajectories and deposition in the spectrum of 0.5–32 μm were evaluated using a well-tested Lagrangian tracking approach for inhalation flow rates ranging from sedentary (3 L/min) to heavily active (30 L/min) conditions. Simulation results of the inhalation pressure drop and particle deposition rate provided a reasonable match with existing experimental results in nasal airway casts of children. Much higher breathing resistance was observed in the 5-year-old child compared to adults. Furthermore, deposition patterns were sensitive to inhalation flow rate under low activity conditions. An empirical correlation of child nasal filtering efficiency was proposed for micrometer particles based on a wide range of test conditions. Results of this study demonstrate that significant child–adult difference exists in inhaled aerosol depositions, which should be taken into account for risk assessment of airborne toxicants on infants and children.     

Experimental measurements and computational modeling of aerosol deposition in the Carleton-Civic standardized human nasal cavity

Aerosol deposition in the novel, “Carleton-Civic” standardized geometry of the human nasal cavity was studied both numerically and experimentally. Inhalation flow rates varied from 30 to 90 L/min in the experiments, and aerosol droplets had diameters ranging from 1.71 to 9.14 μm (impaction parameters ranging from 123.3 to 2527.6 μm L/min). For the numerical simulations, both the RANS/EIM (Reynolds averaged Navier–Stokes equations for the gas phase and eddy-interaction random walk models for the particulate phase) and large eddy simulations were used. The mechanism of aerosol deposition in the standardized nasal cavity was dominated by inertial impaction. Deposition data from the standardized nasal cavity transected cited in vitro data based on individual subjects. The data also correlated very well with cited in vivo measurements but generally showed less aerosol deposition for a given value of the impaction parameter. Regional deposition characteristics within the nasal passages were also investigated both experimentally and numerically and new trends of regional deposition versus impaction parameter are discussed. These trends provide new insight into the general deposition behaviour of various sized aerosols within the human nasal cavity.     

Investigating particle emissions and aerosol dynamics from a consumer fused deposition modeling 3D printer with a lognormal moment aerosol model

ABSTRACT

Particle emissions from consumer-fused deposition modeling 3D printers have been reported previously; however, the complex processes leading to observed aerosols have not been investigated. We measured particle concentrations and size distributions between 7 nm and 25 μm emitted from a 3D printer under different conditions in an emission test chamber. The experimental data was combined with a moment lognormal aerosol dynamic model to better understand particle formation and subsequent evolution mechanisms. The model was based on particles being formed from nucleation of unknown semivolatile compounds emitted from the heated filament during printing, which evolve due to condensation of emitted vapors and coagulation, all within a small volume near the printer extruder nozzle. The model captured observed steady state particle number size distribution parameters (total number, geometric mean diameter and geometric standard deviation) with errors nominally within 20%. Model solutions provided a range of vapor generation rates, saturation vapor pressures and vapor condensation factors consistent with measured steady state particle concentrations and size distributions. Vapor generation rate was a crucial factor that was linked to printer extruder temperature and largely accounted for differences between filament material and brands. For the unknown condensing vapor species, saturation vapor pressures were in the range of 10^?3 to 10^?1 Pa. The model suggests particles could be removed by design of collection surfaces near the extruder tip.

Copyright © 2018 American Association for Aerosol Research     

Simulation of sprayed particle deposition in a human nasal cavity including a nasal spray device

Effective nasal drug delivery is highly dependent on the delivery of drug from the nasal spray device. Atomisation of liquid spray occurs through the internal atomizer that can produce many forms of spray patterns and two of these, hollow-cone and full-cone sprays, are evaluated in this study to determine which spray pattern produced greater deposition in the middle regions of the nasal cavity. Past studies of spray particle deposition have ignored the device within the nasal cavity. Using computational fluid dynamics (CFD), two computational models of human nasal cavity model were reconstructed from CT-scans, where the difference between the two models was the presence of the nasal spray device accounting for the airway blockage at one of the nostrils. Experimental measurements from Particle Droplet Image Analyser (PDIA) were taken in order to gain confidence in determining the initial particle conditions for the computational models. An airflow field is induced through a negative pressure flow condition applied at the pharynx instead of constant flow rates at the left and the right nasal cavities. Subsequent airflow patterns and its effects on particle deposition, with and without a spray device, are compared. Contours and streamlines of the flow field revealed that the presence of a spray device in the nasal vestibule produced higher levels of disturbed flow, which helped the dispersion of the sprayed particles. Particle deposition was found to be high in the anterior regions of the nasal cavity caused by its inertia. Evaluation of the two spray types found that hollow spray cones produced more deposition in the middle regions of the nasal cavity. This paper also demonstrates the CFD methodology used, which can help in better understanding the design of future atomizers for nasal spray use.     

Modeling and measurement of aerosol deposition on a heated substrate

Formation of an inorganic film by chemical aerosol deposition has been investigated experimentally and theoretically. Carrier gas flow rate, nozzle-to-substrate distance and substrate temperature were chosen as major process variables. The experimental work has been carried out to find their effect on the deposition efficiency, film thickness and its distribution. Both the deposition efficiency and film thickness increased with the carrier gas flow rate and substrate temperature but decreased with the nozzle-to-substrate distance. Especially at higher deposition rates, the central part of the film has a concave surface like a bowl. Flow and temperature fields of the fluid phase in the region between the nozzle and substrate were calculated numerically. Particle trajectories and particle evaporation were simulated numerically. As a result, the evaporation of the aerosol particles occurred so abruptly that the aerosol-existing region has a clear boundary. The extent of the region was found to be a determining factor in the film deposition, which characterizes the process of the chemical aerosol deposition.     

Orientation of aluminum particles in the film formed by aerosol deposition: A mathematical model

A simple mathematical model predicting the orientation of flat aluminum particles in the operation of painting flat surfaces with metallic paints is developed. The model is additively composed of separate steps accounting for the collision and deformation of a single drop striking against a solid surface, coalescence between the drop and solid surface, relaxation of the drop after the collision and coalescence, and drying by evaporating its volatile components. The calculations made with the developed model for several paint samples showed the agreement between the calculated results and experimental data.     

Bioactive glass coating using aerosol deposition

This work demonstrates the successful deposition of bioactive glass (BG) 45S5 coatings on various metallic and ceramic substrates at room temperature under low vacuum condition by using aerosol deposition (AD). This room temperature and particle impact consolidation-based deposition method enabled us to deposit well-adhered and dense BG coatings directly on metallic and ceramic substrates. In vitro tests with human osteoblast-like cells on substrates with a 45S5 BG coating demonstrated high cell activity on the surfaces. All tested materials exhibited high in vitro biocompatibility as no inhibition in cell proliferation could be observed. The utilization of AD process for achieving non-crystalline BG coatings is promising for practical bio-medical applications, e.g., bioactive coatings on bioinert metallic and ceramic substrates.     

Refinement and testing of the drift-flux model for indoor aerosol dispersion and deposition modelling

The drift-flux approach for predicting aerosol deposition within enclosed spaces has been refined and implemented within a commercial computational fluid dynamics (CFD) solver. The drift-flux model is tested against a previously reported study of aerosol deposition within a ventilated chamber to illustrate the performance of the approach for unsteady particle concentrations. The model has been made more general by accounting for deposition to surfaces at any angle to the gravitational vector. The algorithms for the calculation of the deposition velocity have been revised to offer improved precision. The model shows good performance when compared with the measured particle concentration decay rates. Comparison with well-mixed models shows obvious differences from the measured and drift-flux CFD approach. The dependence of point concentration measurements of decay rates on sampling time is explored and the limitations for estimating steady-state deposition behaviour are highlighted. An important aspect of aerosol ventilation of incompletely mixed enclosed spaces is illustrated. The drift-flux approach is shown to perform very well at reproducing the unsteady particle concentration decay observed.     

Gravitational deposition of aerosol particles from a developing flow in a horizontal circular tube

Aerosol particle deposition due to gravitational settling in a horizontal circular duct is examined for steady laminar flow, which develops from a uniform velocity profile at the entrance to a parabolic velocity profile downstream. Numerical calculation methods, based on the analysis of the limiting trajectories of the particles, are used to determine the deposition efficiency as a function of the duct entrance length. The results show that the deposition for the limiting cases of very large or small settling approach the solutions for deposition in a slug or a Poiseuille flow, respectively. In addition, particle inertial effects were included and for relatively large inertia, the deposition rate was significantly affected.     

Deposition of micrometer-sized aerosol particles in infant nasal airway replicas

In vitro measurements of particle filtration were made for nasal geometries of 11 infants aged 3–18 months. The geometries were obtained from computed tomography (CT) scans of seven males and four female infants and replicas were built using rapid prototyping. Particles ranging in aerodynamic diameter from 0.8 to were passed through these replicas with simulated tidal breathing. Filtration was determined from particle counts upstream and downstream of the models using an electrical low pressure impactor (ELPI). Mathematical fits were constructed to predict the measured deposition based on the relevant parameters. The fractional deposition, η, is found to depend on the Reynolds number of the flow (Re), the particle Stokes number (Stk), and an airway dimension D defined as airway volume divided by airway surface area. This dependence is well captured by the formula η=1-(2.164*10⁵/(2.164*10⁵+(Re^1.118Stk^1.057(D/D_avg)^-2.840)))^0.8510. Here, D_avg is the average value of the dimension D for the group studied and is equal to 1.20 mm. Re and Stk also use the dimension D as the length scale in their definitions.     

Measured deposition of aerosol particles on a two-dimensional ribbed surface in a turbulent duct flow

Neutron activatable tracer-labelled particles were used to study the aerosol deposition for both smooth and ribbed surfaces of a duct under turbulent flow conditions. Spatial distribution of aerosol deposition along the horizontal upward-facing ribbed surface was experimentally determined. For four particle sizes in the range 0.7–7.1 μm, pronounced aerosol deposition was observed on the frontal and top surfaces of the ribs, and particle deposition enhancement, on the ribbed surfaces relative to a smooth surface, as high as seven times was observed. The presence of repeated square ribs on the duct surface caused a pressure increment of 3.2, relative to a smooth duct. Efficiency ratios (pressure drop-weighted aerosol deposition enhancement) greater than unity were evaluated for the four particle sizes studied.     

Deposition of micrometer-sized aerosol particles in neonatal nasal airway replicas

The nasal aerosol filtration properties of infants 0–3 months old have been quantified through in vitro measurements. Computed tomography (CT) scan data was obtained of seven individuals with ages of 5–79 days. Nasal airway replicas based on these images were manufactured using rapid prototyping. Deposition in the replicas was measured using an electrical low pressure impactor (ELPI) to measure the concentration of aerosol particles in the inertial regime. Comparing the difference in concentration when sampling through the model versus sampling through a blank line gave the deposition fraction. Deposition was measured for particles with aerodynamic diameters between 0.53 and 5.54 μm. Nonlinear least squares curve fitting was performed to collapse intersubject variability and represent the data with a single curve. To achieve satisfactory intersubject variability collapse, a non-dimensional pressure drop, the Euler number (Eu), was required in addition to the Reynolds number (Re) and the particle Stokes number (Stk) where the dimensionless parameters are evaluated with a length scale, D, defined as the airway volume divided by the airway surface area. The equation describing the deposition fraction, η, is η = 1- (14590 / (14590 + Stk^1.2201Re^1.7742Eu^1.5772))^0.3687. An analysis of the expected intersubject variability in in vivo deposition was also performed, yielding a method for predicting variance in neonatal nasal airway deposition.

Copyright © 2018 American Association for Aerosol Research     

Exact analysis of aerosol deposition during steady breathing

Using a trumpet lung model, a transport equation is derived for an aerosol breathed into and out of the human airways. The partial differential equation is solved exactly using the method of characteristics. From this solution, the deposition of particles along the airways is obtained for steady breathing with and without pause. The total and regional depositions for particle sizes ranging from 0.01 μm to 10 μm aerodynamic diameter are calculated for Weibel's lung model, and they compare satisfactorily with the existing experimental data. The effects of the rest lung volume and breathing pattern on the total and regional depositions are also determined in order to explain the observed intersubject variability. Comparison between the present results with that recommended by the Task Group on Lung Dynamics shows that the present pulmonary deposition is considerably lower. while the tracheobronchial deposition differs only slightly.     

Plasma resistance of quartz with a glass coating layer by aerosol deposition

ABSTRACT

To improve the plasma resistance behaviour, glass frits of SiO₂–Al₂O₃–Y₂O₃ with various powder sizes were coated onto quartz substrates by the aerosol deposition (AD) method. The thickness and microstructure of the coating layers were observed using a surface profiler and scanning electron microscopy. Plasma resistance was measured via the quartz substrate, after exposure to an inductively coupled plasma etcher. The coating layers were densely formed on the quartz substrates without additional heat treatment, and the layer thickness changed for the glass frit size distribution and AD process conditions. The SiO₂–Al₂O₃–Y₂O₃ glass coating layer showed a higher plasma resistance than quartz. Furthermore, the AD coating layer was evenly etched after plasma exposure. This study improves the lifetime of plasma chamber components in the semiconductor industry.     

Fragmentation and film growth in supersonic nanoaggregate aerosol deposition

Aerosol deposition with gas phase-synthesized chain-like nanoaggregates can yield dense coatings from the impaction of particles on a substrate; however, dense coating formation is not well understood. Here, we study coating consolidation at the single nanoaggregate level. Flame spray pyrolysis-made tin oxide nanoaggregates are mobility (size) filtered, accelerated through a de Laval nozzle, and impacted on alumina substrates. TEM images obtained from low velocity collection and supersonic deposition are compared via quantitative image analysis, which reveals that upon supersonic impact nanoaggregates fragment into smaller aggregates. This suggests that fragmentation is a key step in producing coatings denser than the depositing nanoaggregates themselves. We supplement experiments with detailed particle trajectory calculations, which show that the impact energies per atom during nanoaggregate deposition are below 0.2 eV/molecule. These results suggest that fragmentation can only occur at locations where nanoaggregates bonded by van der Waals and capillary interactions.