Local Deposition Patterns Research Articles

Anatomy matters: The role of the subject-specific respiratory tract on aerosol deposition — A CFD study

The COVID-19 pandemic is one of the greatest challenges to humanity nowadays. COVID-19 virus can replicate in the host’s larynx region, which is in contrast to other viruses that replicate in lungs only, i.e. SARS. This is conjectured to support a fast spread of COVID-19. However, there is sparse research in this field about quantitative comparison of virus load in the larynx for varying susceptible individuals. In this regard the lung geometry itself could influence the risk of reproducing more pathogens and consequently exhaling more virus. Disadvantageously, there are only sparse lung geometries available. To still be able to investigate realistic geometrical deviations we employ three different digital replicas of human airways up to the 7th level of bifurcation, representing two realistic lungs (male and female) as well as a more simplified experimental model. Our aim is to investigate the influence of breathing scenarios on aerosol deposition in anatomically different, realistic human airways. In this context, we employ three levels of cardiovascular activity as well as reported experimental particle size distributions by means of Computational Fluid Dynamics (CFD) with special focus on the larynx region to enable new insights into the local virus loads in human respiratory tracts. In addition, the influence of more realistic boundary conditions is investigated by performing transient simulations of a complete respiratory cycle in the upper lung regions of the considered respiratory models, focusing in particular on deposition in the oral cavity, the laryngeal region, and trachea, while simplifying the tracheobronchial tree. The aerosol deposition is modeled via OpenFOAM\\protect \\relax \\special {t4ht=®} by employing an Euler-Lagrangian frame including steady and unsteady Reynolds Averaged Navier–Stokes (RANS) resolved turbulent flow using the k-ω-SST and k-ω-SST DES turbulence models. We observed that the respiratory geometry altered the local deposition patterns, especially in the laryngeal region. Despite the larynx region, the effects of varying flow rate for the airway geometries considered were found to be similar in the majority of respiratory tract regions. For all particle size distributions considered, localized particle accumulation occurred in the larynx of all considered lung models, which were more pronounced for larger particle size distributions. Moreover, it was found, that employing transient simulations instead of steady-state analysis, the overall particle deposition pattern is maintained, however with a stronger intensity in the transient cases.

Computational modeling for the evaluation of suppressed scintillation yields in plastic scintillators using Geant4.

The yield of scintillation photons emitted from scintillators is considered to be proportional to the LET (linear energy transfer) which is energy distribution per unit length, in the low-LET domain, but not proportional in the high LET domain due to the suppression yield from the so-called quenching effect. Ogawa et al. proposed a computational method to estimate scintillation yield using Monte Carlo simulations considering the principle of the FRET (fluorescence resonance energy transfer) process, which is a phenomenon of energy transfer between fluorescent molecules. In their study, the track structure simulations could reproduce measured yields of scintillation. However, Ogawa et al.'s model was not suitable for estimating the scintillation yields when the particle energy was low when using condensed history simulations. Therefore, we propose a new method for estimating scintillation yields more accurately using Geant4 to improve the model calculations based on condensed history simulations. We simulated the local energy deposition pattern in a NE102A plastic scintillator to calculate the number of excitors in the microscopic volume for various nuclides (helium to argon ions). The suppressed scintillation yields were estimated using the model calculations of sequential FRET processes while considering the inactivation of the excitors selected as donors of the FRET process. The model calculations successfully reproduced the experimental scintillation yields within 10% error for the lighter ions up to neon. However, when the analysis was repeated for silicon and argon, the maximum error in the scintillation yields increased up to 27%. The proposed computational model for the evaluation of the suppressed scintillation yields emitted from NE102A scintillator irradiated with heavy ions using sequential FRET calculations with condensed history method returned simulated scintillation yields.

Droplet Deposition Pattern Affected by Different Heating Directions

The coffee ring effect commonly exists in droplet deposition patterns, which fundamentally affects scientific research and industrial applications, like pharmaceutical purification, salt manufacturing, etc. Some researchers have tried different solutions to control the distributions of droplet deposition patterns, but most control deposits by adjusting droplet characteristics. In this work, droplet deposition patterns with different wettability are investigated by both localized and substrate heating. A whole process of droplet evaporation is recorded. The droplet generally evaporates from constant contact radius (CCR) mode to constant contact angle (CCA) mode, and CCR stage occupies the most of time. Experimental results show that, without any chemicals, laser induced local heating transitions particle deposition patterns from ring-like structure to dot-like patterns on a hydrophilic surface, driving most saline solvent to the center. Meanwhile, a hydrophobic surface is also investigated showing that the particles tend to assemble at the central area, but the pattern is slightly different compared to that on hydrophilic surface. In addition, physical mechanisms of local heating and heating from substrate are also explored in the present study.

Inhalation Exposure Analysis of Lung-Inhalable Particles in an Approximate Rat Central Airway.

Rats have been widely used as surrogates for evaluating the adverse health effects of inhaled airborne particulate matter. This paper presents a computational fluid and particle dynamics (CFPD) study of particle transport and deposition in an approximate rat central airway model. The geometric model was constructed based on magnetic resonance (MR) imaging data sourced from previous study. Lung-inhalable particles covering a diameter range from 20 nm to 1.0 µm were passively released into the trachea, and the Lagrangian particle tracking approach was used to predict individual particle trajectories. Overall, regional and local deposition patterns in the central airway were analyzed in detail. A preliminary interspecies data comparison was made between present rat models and previously published human data. Results showed deposition “hot spots” were mainly concentrated at airway bifurcation apexes, and a gravitational effect should also be considered for inertia particles when using a rat as a laboratory animal. While for humans, this may not happen as the standing posture is completely different. Lastly, the preliminary interspecies data comparison confirms the deposition similarity in terms of deposition enhancement factors, which is a weighted deposition concentration parameter. This interspecies comparison confirms feasibility of extrapolating surrogate rat deposition data to humans using existing data extrapolation approach, which mostly relies on bulk anatomical differences as dose adjustment factors.

Lung aerosol dynamics of airborne influenza A virus-laden droplets and the resultant immune system responses: An in silico study

Influenza A Virus (IAV) replications start from the deposition of inhaled virus-laden droplets on the epithelial cells in the pulmonary tracts. In order to understand the local deposition patterns and within-host dynamics of infectious aerosols, accurate information of high-resolution imaging capabilities, as well as real-time flow cytometry analysis, are required for tracking infected cells, virus agents, and immune system responses. However, clinical and animal studies are in deficit to meet the above-mentioned demands, due to their limited operational flexibility and imaging resolution. Therefore, this study developed an experimentally validated multiscale numerical model, i.e., the Computational Fluid-Particle Dynamics (CFPD) plus Host Cell Dynamics (HCD) model, to predict the transport and deposition of the low-strain IAV-laden droplets, as well as the resultant regional immune system responses. The hygroscopic growth and shrinkage of IAV-laden droplets were also accurately modeled. The subject-specific respiratory system was discretized using polyhedron-core meshes. By recreating both mouth and nasal breathing scenarios, simulations of isotonic IAV-laden droplets with three different compositions were achieved. It is the first time that parametric analysis has been performed to investigate how different exposure conditions can influence the IAV aerodynamics in the lung and the subsequent immune system responses. Numerical results show a higher viral accretion followed by a faster immune system response in the supraglottic region when IAV-laden droplets with the higher NaCl concentration were inhaled. Consequently, more severe symptoms and longer recovery are expected at the pharynx. Furthermore, local deposition patterns of IAV-laden droplets and post-deposition infection dynamics provide direct quantitative evidence to enhance the fundamental understanding of the underlying mechanisms for upper airway and lower airway infections.

Numerical investigation of particle deposition in a triple bifurcation airway due to gravitational sedimentation and inertial impaction

Focusing on the particle deposition due to gravitational sedimentation and inertial impaction, the transport and deposition of micron particles with various diameters (i.e., 1 to 7μm) have been simulated in a triple bifurcation airway at flow rates of 15 to 120L/min. The airway configurations for generation 11 to generation 14 are determined by matching the Stokes number St and the sedimentation parameter γ (Particuology, 2016, 28:102–113). Air flow distributions, local deposition patterns, and deposition efficiencies are compared between simulations with and without gravity. The results suggest that minimum deposition efficiency exists for large particles indicating the change of dominant deposition mechanism between sedimentation and impaction. Sedimentation governed particle deposition is also observed for small particles. A revised correlation for predicting DE as a function of Stokes number and sedimentation parameter is proposed for 5.78×10−4<St<0.226 and 1.54×10−4<γ<0.06. These findings could be utilized to design the drug particle property and inhalation waveform for the high-efficiency pulmonary drug delivery.

The effects of injection modes on instantaneous particle deposition in a realistic human nasal cavity.

To understand the instantaneous particle deposition in nasal cavity, effects of two injection models on particle deposition characteristic were discussed in this paper. Based on a realistic human nasal cavity geometry obtained from CT scans, a comparison of deposition pattern in the nasal cavity between single injection and continuous injection was investigated through the Lagrangian approach. The instantaneous airflow field was simulated with the tidal volume of 159 and 318 mL by two sine wave curves at inlet. For the case of single injection, particles have finished deposition in the first half of inhalation, and a negative correlation between the tidal volumes and deposition can be observed when the particle diameter was larger than 10 µm. Moreover, particles were mainly deposited in the turbinate area that was beneficial for aerosol therapy. The inertial parameter was not suitable to predict the particle deposition in the case of single injection. With respect to continuous injection, a reduction in total deposition caused by the deceleration process of inhalation can be observed after 1.5 s. The deposition was closely associated with the time-varying flow field, and particles were mainly deposited in the anterior region and turbinate area. Besides, the particle deposition increased with the inertial parameter for continuous injection. The results indicated that the injection modes had an influence on both the total deposition and local deposition pattern in the nasal cavity. Copyright © 2016 John Wiley & Sons, Ltd.

Design and Testing of Electric-Guided Delivery of Charged Particles to the Olfactory Region: Experimental and Numerical Studies

Neurological drugs delivered to the olfactory region can enter the brain via olfactory pathways and bypass the blood-brain barrier. However, clinical applications of the direct nose-to-brain delivery are rare because of the extremely low olfactory doses using conventional nasal devices. This poor bioavailability is mainly caused by two factors: the complex nasal structure that traps particles in the anterior nose and the complete lack of control over particle motions after their release at the nostrils. In this study, the feasibility of electric-guided delivery to the olfactory region was tested in an anatomically accurate nasal airway model both experimentally and numerically. The nose replicas were prepared using 3-D printing and could be dissembled to reveal the local deposition patterns within the nasal cavity. A test platform was developed that included a dry powder charging system and a particle point-release nozzle. Numerical modeling was conducted using COMSOL and compared to corresponding experiments. Compared to conventional nasal devices, electric-guidance of charged particles noticeably reduced particle losses in the anterior nose and increased depositions in the olfactory region. The thickness and relative permittivity of the wall were observed to affect the electric field strength and olfactory dosages. Consistent deposition patterns were obtained between experiments and numerical simulations in both 2-D and 3-D nose models. Two conceptual designs were proposed to generate, charge, and control aerosols. Results of this study indicate that it is feasible to use an electric field to control charged particles in the human nose. Both electric-guidance and point-release of particles are essential to achieve targeted olfactory delivery. Future studies to refine the aerosol charging and release systems are needed for further enhancement of olfactory dosages.

Effects of nostril orientation on airflow dynamics, heat exchange, and particle depositions in human noses

The orientation of the nostrils is thought to regulate airflow dynamics and associated functions of the nose. Previous studies have used different nostril orientations ranging from downward-directed (90°) to anterior-directed (0°). However, the influences of nostril orientation on nose functions have not yet been studied. The objective of this study is to systematically assess the influences of the orientation of the nostrils on airflow, heat exchange, and particle behaviors during inhalation by means of image-based modeling. Nose models with five different nostril angles were developed by modifying the vestibule of an anatomically accurate nose airway geometry reconstructed from magnetic resonance imaging. Large eddy simulations and a Lagrangian tracking model were used to simulate airflow dynamics and particle transport with a wide range of inhalation conditions (4–45 L/min) and particle sizes (1–20μm). Results showed that nostril orientation exerted a significant impact on superior/inferior meatus ventilating and sub-regional and local depositions. The downward-directed nose model has the highest flow flux to the superior meatus and lowest flux to the nasal floor. The turbulence intensity inside the main flow is negligible; however, there are substantial vortex formations in the near-wall region. The anterior-directed nose model has the strongest near-wall vortices in the valve vicinity, which is coincident with the location of the highest wall shear stress and heat exchange, and has a close correlation with local particle deposition patterns. Results of this study indicate that the actual nostril angle should be preserved to reliably predict respiratory functions of a pathological/postsurgical nose, or the delivered doses of a topical intranasal delivery.

Proposed linear energy transfer areal detector for protons using radiochromic film.

Radiation therapy depends on predictably and reliably delivering dose to tumors and sparing normal tissues. Protons with kinetic energy of a few hundred MeV can selectively deposit dose to deep seated tumors without an exit dose, unlike x-rays. The better dose distribution is attributed to a phenomenon known as the Bragg peak. The Bragg peak is due to relatively high energy deposition within a given distance or high Linear Energy Transfer (LET). In addition, biological response to radiation depends on the dose, dose rate, and localized energy deposition patterns or LET. At present, the LET can only be measured at a given fixed point and the LET spatial distribution can only be inferred from calculations. The goal of this study is to develop and test a method to measure LET over extended areas. Traditionally, radiochromic films are used to measure dose distribution but not for LET distribution. We report the first use of these films for measuring the spatial distribution of the LET deposited by protons. The radiochromic film sensitivity diminishes for large LET. A mathematical model correlating the film sensitivity and LET is presented to justify relating LET and radiochromic film relative sensitivity. Protons were directed parallel to radiochromic film sandwiched between solid water slabs. This study proposes the scaled-normalized difference (SND) between the Treatment Planning system (TPS) and measured dose as the metric describing the LET. The SND is correlated with a Monte Carlo (MC) calculation of the LET spatial distribution for a large range of SNDs. A polynomial fit between the SND and MC LET is generated for protons having a single range of 20 cm with narrow Bragg peak. Coefficients from these fitted polynomial fits were applied to measured proton dose distributions with a variety of ranges. An identical procedure was applied to the protons deposited from Spread Out Bragg Peak and modulated by 5 cm. Gamma analysis is a method for comparing the calculated LET with the LET measured using radiochromic film at the pixel level over extended areas. Failure rates using gamma analysis are calculated for areas in the dose distribution using parameters of 25% of MC LET and 3 mm. The processed dose distributions find 5%-10% failure rates for the narrow 12.5 and 15 cm proton ranges and 10%-15% for proton ranges of 15, 17.5, and 20 cm and modulated by 5 cm. It is found through gamma analysis that the measured proton energy deposition in radiochromic film and TPS can be used to determine LET. This modified film dosimetry provides an experimental areal LET measurement that can verify MC calculations, support LET point measurements, possibly enhance biologically based proton treatment planning, and determine the polymerization process within the radiochromic film.

Three-dimensional CFD Modeling of Wave Scour Around Side-by-Side and Triangular Arrangement of Piles with REEF3D

Sediment transport and resulting local scour in marine and coastal environments can lead to the failure of structures. The knowledge and understanding of erosion and sediment transport mechanisms and the correct prediction of the local scour magnitude is crucial for the structural design. In the current paper the complex physics of local scour under wave conditions are modeled. The numerical results are compared with experimental data, showing good agreement. The three-dimensional computational fluid dynamics model REEF3D is used to calculate the detailed flow field and the resulting sediment transport pattern around the vertical pile. The location of the free surface is represented using the level set method, which calculates the complex motion of the free surface in a realistic manner. For the implementation of waves, the CFD code is used as a numerical wave tank. In order to provide an accurate prediction of propagating waves, the convection terms of the Navier-Stokes equations and the level set method are discretized with the 5th-order Weighted Essentially Non-Oscillatory scheme. The pressure is solved on a staggered grid, ensuring tight velocity-pressure coupling. The numerical model employs a Cartesian grid and complex geometries are treated with an immersed boundary method based on ghost cell extrapolation. Sediment transport is implemented through standard bed-load and suspended load formulas. The resulting sediment discharges and concentrations are evaluated with the Exner equation, giving the local erosion and deposition pattern for each time step. For the geometric representation of the moveable sediment bed, the level set method is used.

Tracer techniques for the assessment of material migration and surface modification of plasma-facing components

Tracer techniques were used in the TEXTOR tokamak to determine high-Z metal migration and the deposition of species used for plasma edge cooling or wall conditioning under different types of operation conditions. Volatile molybdenum hexa-fluoride, nitrogen-15 and oxygen-18 were used as markers in tokamak or ion cyclotron wall conditioning discharges (ICWC). The objective was to obtain qualitative and quantitative of a global and local deposition pattern and material mixing effects. The deposition and retention was studied on plasma-facing components, collector probes and test limiters. Optical spectroscopy and ex-situ analysis techniques were used to determine the plasma response to tracer injection and the modification of surface composition. Molybdenum and light isotopes were detected on all types of limiters and short-term probes retrieved from the vessel showing that both helium and nitrogen are trapped following wall conditioning and edge cooling. Only small amounts below 1×1019m−2 of 18O were detected on surfaces treated by oxygen-assisted ICWC.

Pediatric in vitro and in silico models of deposition via oral and nasal inhalation.

Respiratory tract deposition models provide a useful method for optimizing the design and administration of inhaled pharmaceutical aerosols, and can be useful for estimating exposure risks to inhaled particulate matter. As aerosol must first pass through the extrathoracic region prior to reaching the lungs, deposition in this region plays an important role in both cases. Compared to adults, much less extrathoracic deposition data are available with pediatric subjects. Recently, progress in magnetic resonance imaging and computed tomography scans to develop pediatric extrathoracic airway replicas has facilitated addressing this issue. Indeed, the use of realistic replicas for benchtop inhaler testing is now relatively common during the development and in vitro evaluation of pediatric respiratory drug delivery devices. Recently, in vitro empirical modeling studies using a moderate number of these realistic replicas have related airway geometry, particle size, fluid properties, and flow rate to extrathoracic deposition. Idealized geometries provide a standardized platform for inhaler testing and exposure risk assessment and have been designed to mimic average in vitro deposition in infants and children by replicating representative average geometrical dimensions. In silico mathematical models have used morphometric data and aerosol physics to illustrate the relative importance of different deposition mechanisms on respiratory tract deposition. Computational fluid dynamics simulations allow for the quantification of local deposition patterns and an in-depth examination of aerosol behavior in the respiratory tract. Recent studies have used both in vitro and in silico deposition measurements in realistic pediatric airway geometries to some success. This article reviews the current understanding of pediatric in vitro and in silico deposition modeling via oral and nasal inhalation.

Calculation of hygroscopic particle deposition in the human lung

Context: Inhaled hygroscopic aerosols will absorb water vapor from the warm and humid air of the human lung, thus growing in size and consequently changing their deposition properties.Objective: The objectives of the present study are to study the effect of a stochastic lung structure on individual particle growth and related deposition patterns and to predict local deposition patterns for different hygroscopic aerosols.Materials and methods: The hygroscopic particle growth model proposed by Ferron et al. has been implemented into the stochastic asymmetric lung deposition model IDEAL. Deposition patterns were calculated for sodium chloride (NaCl), cobalt chloride (CoCl2 · 6H2O), and zinc sulfate (ZnSO4 · 7H2O) aerosols, representing high, medium and low hygroscopic growth factors.Results: Hygroscopic growth decreases deposition of submicron particles compared to hydrophobic particles with equivalent diameters due to a less efficient diffusion mechanism, while the more efficient impaction and sedimentation mechanisms increase total deposition for micron-sized particles. Due to the variability and asymmetry of the human airway system, individual trajectories of inhaled particles are associated with individual growth factors, thereby enhancing the variability of the resulting deposition patterns.Discussion and conclusions: Comparisons of model predictions with several experimental data for ultrafine and micrometer-sized particles indicate good agreement, considering intersubject variations of morphometric parameters as well as differences between experimental conditions and modeling assumptions.

Lagrangian/Eulerian model of coagulation and deposition of inhaled particles in the human lung

The primary objectives of the present study were to mathematically describe particle coagulation within the human respiratory tract and to analyze its impact on local particle deposition patterns for high concentrations of inhaled cigarette smoke particles. Coagulation mechanisms simulated were thermal motion, gravitational settling, laminar shear, turbulences, electrical charges, and inertial effects at airway bifurcations. To implement concentration dependent coagulation processes, the Lagrangian random walk deposition model IDEAL, simulating the paths of an individual particle, was modified by tracking the random path of an elemental air volume containing the full size distribution, thus adding an Eulerian element to the Lagrangian random path model. In this combined Lagrangian/Eulerian deposition model, the initial size distribution is continuously modified by coagulation, hygroscopic growth and deposition. For the specific inhalation conditions and the cigarette smoke size distribution assumed in this study, thermal diffusion is by far the greatest source of coagulation, with a minor contribution of laminar shear in peripheral airway generations.Number deposition, which comprises the loss of inhaled particles not only by deposition but also by coagulation, and mass deposition fractions were computed for different puff and breath-hold scenarios as a function of lung generation numbers. The main reduction of the number of inhaled particles in the respiratory tract occurs in the mouth due to coagulation, accompanied by a significant shift of the size distribution to larger particle diameters. In the lung, particle loss is caused primarily by deposition due to diffusion with a preferential deposition of smaller particle diameters. In the size range from about 250 to 500nm, the number concentration of particles in the exhaled air is higher than that in the inhaled air, indicating that the production of particles in this size range by coagulation is greater than the loss by coagulation to larger sizes and deposition.

Validating CFD predictions of highly localized aerosol deposition in airway models: In vitro data and effects of surface properties

Local deposition of pharmaceutical and environmental aerosols governs desorption, uptake, and biological response within the respiratory airways. Few studies have reported estimates of numerical microdosimetry and even fewer have compared these results with experiments. This study evaluated the effects of surface coating and roughness on the local deposition of inhaled coarse micrometer particles in an in vitro asymmetric double bifurcation geometry. The double bifurcation geometry is representative of airway generations 3–5 and includes mean asymmetry approximations from previous anatomical studies. Polystyrene latex 10μm monodisperse particles were delivered at a steady state tracheal flow rate of 60l/min (LPM) and mean local deposition patterns were resolved on a grid of 0.75mm squares using fluorescent microscopy. The three airway geometry surfaces tested were unaltered, coated with silicone oil, and sanded-coated. For the hard plastic in vitro models employed, coating the surface was shown to be important in order to prevent bounce and re-entrainment of the particles. Sanding the models altered the local deposition profile in an uncontrolled way and is therefore not recommended for future experiments. The best overall match between the in vitro results and CFD simulations was the coated experimental geometry and coarse wall roughness simulations. For this case, the relative error between the experiments and simulations for total deposition was 6%. On a local deposition basis, cumulative lines of deposition fraction in the x and y-directions showed reasonable agreement between the experiments and simulations. However, some evidence of post-deposition particle rolling or spreading was observed with the coated experiments at the second bifurcation. Comparing experimental and CFD results cell by cell, higher maximum deposition enhancement factors (DEFs) were observed for the in vitro cases, perhaps due to factors not included in the CFD simulations. This result implies that previously predicted maximum DEF values from CFD simulations may be conservatively low and that actual values with in vitro models or in vivo may be even higher than predicted. In conclusion, this study provides a valuable new dataset for understanding the effects of surface characteristics on local deposition, assessing hotspot magnitude in the tracheobronchial airways, and validating CFD predictions.

Tungsten migration studies by controlled injection of volatile compounds

Volatile tungsten hexa-fluoride was locally injected into the TEXTOR tokamak as a marker for material migration studies. The injection was accompanied by puffing N-15 rare isotope as a nitrogen tracer in discharges with edge cooling by impurity seeding. The objective was to assess material balance by qualitative and quantitative determination of a global and local deposition pattern, material mixing effects and fluorine residence in plasma-facing components. Spectroscopy and ex situ ion beam analysis techniques were used. Tungsten was detected on all types of limiter tiles and short-term probes retrieved from the vessel. Over 80% of the injected W was identified. The largest tungsten concentration, 1×1018cm−2, was in the vicinity of the gas inlet. Co-deposits contained tungsten and a mix of light isotopes: H, D, He-4, B-10, B-11, C-12, C-13, N-14, N-15, O-16 and small quantities of F-19 thus showing that both He and nitrogen are trapped following wall conditioning (He glow) and edge cooling.

Effect of Laryngopharyngeal Anatomy on Expiratory Airflow and Submicrometer Particle Deposition in Human Extrathoracic Airways

The objective of this study is to systematically assess the influences of the larynopharyneal anatomical details on airflow and particle behaviors during exhalation by means of image-based modeling. A physiologically realistic nose-throat airway was developed with medical images. Individual airway anatomy such as uvula, pharynx, and larynx were then isolated for examination by progressively simplifying this image-based model geometry. Low Reynolds number (LRN) k-w model and Langrangian tracking model were used to simulate the dynamics of airflow and particle transport for a wide range of exhalation conditions (4-45 L/min) and particle sizes (1 nm-1 μm). Results showed that pharyngeal anatomical details exerted a significant impact on breathing resistance and particle profiles. Abrupt pressure drop resulting from the uvula-related airway obstruction was observed. Even though the total deposition rate in the nasal airway is largely unaffected by the upstream effect, the local deposition patterns vary notably. Results of this study also indicate that the pressure drop appears to be an appropriate parameter to characterize the geometric variations for diffusive depositions. Inclusion of pressure drop (D0.5Q-0.62dp0.07) gives an improved correlation than using the conventional diffusion factor (D0.5Q﹣0.28).

Outer divertor of ASDEX Upgrade in low-density L-mode discharges in forward and reversed magnetic field: II. Analysis of local impurity migration

Part I (Aho-Mantila L. et al 2012 Nucl. Fusion 52 103006) presented a detailed analysis of outer divertor plasma conditions in low-density L-mode discharges in ASDEX Upgrade. In this paper, we analyse the local migration of carbon that originates from 13CH4 injected into these plasmas from the vertical outer target. Notable changes are observed in the local carbon deposition patterns when reversing the magnetic field in the experiments. Kinetic impurity-following simulations are performed using the 3D ERO code package with 2D background plasma solutions calculated with the SOLPS5.0 code package. The modelling shows that the measured changes are due to the changes in plasma collisionality, dissociation and ionization rates, and E × B drift of the impurities. These conditions affect the direction and rate of impurity migration inside and out of the divertor, having wider consequences on the global migration of impurities in a divertor tokamak. It is further shown that the migration pathways are largely determined by carbon ions and, hence, relevant for impurities in general. Neutral carbon and hydrocarbons are deposited only in the near vicinity of the injection, where they affect the local re-deposition efficiency. In this limited region, a perturbation of the local plasma conditions by the methane puff appears likely, yielding a significant uncertainty for interpreting the deposition efficiencies. The local deposition is largely influenced by the magnetic presheath electric field, the structure of which is the main uncertainty in the SOLPS5.0-ERO simulations.

Transport and Deposition of Micro-and Nano-Particles in Human Tracheobronchial Tree by an Asymmetric Multi-Level Bifurcation Model

Transport and deposition of particles in the upper tracheobronchial tree were analyzed using a multi-level asymmetric lung bifurcation model. The first three generations of tracheobronchial tree were included in the study. The laryngeal jet at the trachea entrance was modeled as an effective turbulence disturbance, and the study was focused on how to accurately simulate the airflow and predict the motion of the inhaled particles. Downstream in the lower level of the bronchial region, a laminar flow model was used, as smoother flow condition was expected. Transport and deposition of nano- and micro-scale spherical particles in the range of 0.01 μm to 30 μm were evaluated. The particle local deposition pattern and deposition rate in the lung bifurcation was discussed. The proposed multi-level asymmetric lung bifurcation model was found to be flexible, easy to use and computationally highly efficient. It was also shown that the selection of the anisotropic Reynolds stress transport turbulence model (RSTM) was appropriate, and the use of the enhanced two-layer model boundary treatment was needed for accurate simulation of the turbulent airflow conditions in the upper airways.