Particle Deposition Fraction Research Articles

Influence of Mesh Density on Airflow and Particle Deposition in Sinonasal Airway Modeling

There are methodological ambiguities in the literature on mesh refinement analysis for computational fluid dynamics (CFD) modeling of physiologically realistic airflow dynamics and particle transport in the human sinonasal cavity. To investigate grid independence in discretization of the (sino)nasal geometry, researchers have considered CFD variables such as pressure drop, velocity profile, wall shear, airflow, and particle deposition fractions. Standardization in nasal geometry is also lacking: unilateral or bilateral nasal cavities with and without paranasal sinuses have been used. These methodological variants have led to inconsistencies in establishing grid-independent mesh densities. The aim of this study is to provide important insight in the role of mesh refinement analysis on airflow and particle deposition in sinonasal airway modeling. A three-dimensional reconstruction of the complete sinonasal cavity was created from computed tomography images of a subject who had functional endoscopic sinus surgery. To investigate airflow grid independence, nine different tetrahedral mesh densities were generated. For particle transport mesh refinement analysis, hybrid tetrahedral-prism elements with near-wall prisms ranging from 1 to 6 layers were implemented. Steady-state, laminar inspiratory airflow simulations under physiologic pressure-driven conditions and nebulized particle transport simulations were performed with particle sizes ranging from 1-20 μm. Mesh independence for sinonasal airflow was achieved with approximately 4 million unstructured tetrahedral elements. The hybrid mesh containing 4 million tetrahedral cells with three prism layers demonstrated asymptotic behavior for sinonasal particle deposition. Inclusion of boundary prism layers reduced deposition fractions relative to tetrahedral-only meshes. To ensure numerically accurate simulation results, mesh refinement analyses should be performed for both airflow and particle transport simulations. Tetrahedral-only meshes overpredict particle deposition and are less accurate than hybrid tetrahedral-prism meshes.

CFD simulation of airflow behavior and particle transport and deposition in different breathing conditions through the realistic model of human airways

In this work, the airflow behavior and particle transport and deposition in different breathing conditions such as light breathing condition (15L/min), normal breathing condition (30L/min) and heavy breathing condition (60L/min) are investigated. The realistic geometry data was reconstructed from CT-scan images of the human airways with 0.5mm thickness of slices. The CT-scan images (DICOM files) are imported in the 3D-DOCTOR software and all slices were segmented. Then, the output has been imported in CATIA-V5 software. Finally, face, volume, mesh and extension tubes at inlet and outlets were created and then imported into ANSYS FLUENT 15. The Lagrangian approach is used to evaluating the transport and deposition of inhaled micro-particles. The presented results showed that for dp=5μm and 10μm, when flow rate =30Lmin and for dp=1μm, when flow rate =15Lmin, the particle deposition fraction have maximum amount. For flow rate =15Lmin and =30Lmin, the maximum deposition occurs in the zone number 1 and for flow rate =60Lmin occurs in the zone number 4. Also, the maximum pressure distribution happens when flow rate =60Lmin which would be acceptable. According to the results, the particles tended to go to the right branch and the minimum number of particles crossed the zone numbers 6 and 11.

Numerical Simulation of Particle Transport and Deposition in the Pulmonary Vasculature

To quantify the transport and adhesion of drug particles in a complex vascular environment, computational fluid particle dynamics (CFPD) simulations of blood flow and drug particulate were conducted in three different geometries representing the human lung vasculature for steady and pulsatile flow conditions. A fully developed flow profile was assumed as the inlet velocity, and a lumped mathematical model was used for the calculation of the outlet pressure boundary condition. A receptor-ligand model was used to simulate the particle binding probability. The results indicate that bigger particles have lower deposition fraction due to less chance of successful binding. Realistic unsteady flow significantly accelerates the binding activity over a wide range of particle sizes and also improves the particle deposition fraction in bifurcation regions when comparing with steady flow condition. Furthermore, surface imperfections and geometrical complexity coupled with the pulsatility effect can enhance fluid mixing and accordingly particle binding efficiency. The particle binding density at bifurcation regions increases with generation order and drug carriers are washed away faster in steady flow. Thus, when studying drug delivery mechanism in vitro and in vivo, it is important to take into account blood flow pulsatility in realistic geometry. Moreover, tissues close to bifurcations are more susceptible to deterioration due to higher uptake.

Respiratory Tract Deposition of Inhaled Wood Smoke Particles in Healthy Volunteers.

Respiratory tract deposition of air pollution particles is a key to their adverse health effects. This study was aimed to determine the size-resolved deposition fraction (DF) of sooty wood smoke particles in the lungs of healthy subjects. The type of wood smoke investigated is typical for household air pollution from solid fuels, which is among the largest environmental health problems globally. Twelve healthy volunteers inhaled diluted wood smoke from incomplete soot-rich combustion in a common wood stove. The DF of smoke particles (10-500 nm) was measured during three 15-min exposures in each subject during spontaneous breathing. Lung function was measured using standard spirometry. The total DFs by particle number concentration were 0.34±0.08. This can be compared with DFs of 0.21-0.23 in healthy subjects during previous experiments with wood pellet combustion. For particle mass, the total DFs found in this study were 0.22±0.06. DF and breathing frequency were negatively correlated as expected from model calculations (p<0.01). The DF of the investigated sooty wood smoke particles was higher than for previously investigated particles generated during more efficient combustion of biomass. Together with toxicological studies, which have indicated that incomplete biomass combustion particles rich in soot and polycyclic aromatic hydrocarbons (PAHs) are especially harmful, these data highlight the health risks of inadequate wood combustion.

Physical activity, air pollution and the brain.

This review introduces an emerging research field that is focused on studying the effect of exposure to air pollution during exercise on cognition, with specific attention to the impact on concentrations of brain-derived neurotrophic factor (BDNF) and inflammatory markers. It has been repeatedly demonstrated that regular physical activity enhances cognition, and evidence suggests that BDNF, a neurotrophin, plays a key role in the mechanism. Today, however, air pollution is an environmental problem worldwide and the high traffic density, especially in urban environments and cities, is a major cause of this problem. During exercise, the intake of air pollution increases considerably due to an increased ventilation rate and particle deposition fraction. Recently, air pollution exposure has been linked to adverse effects on the brain such as cognitive decline and neuropathology. Inflammation and oxidative stress seem to play an important role in inducing these health effects. We believe that there is a need to investigate whether the well-known benefits of regular physical activity on the brain also apply when physical activity is performed in polluted air. We also report our findings about exercising in an environment with ambient levels of air pollutants. Based on the latter results, we hypothesize that traffic-related air pollution exposure during exercise may inhibit the positive effect of exercise on cognition.

Deposition pattern of inhaled radon progeny size distribution in human lung

One of the important factors controlling the distribution of radiation dose to the different portions of the human respiratory tract is the deposition pattern of radon progeny containing aerosol. Based on the activity size distribution parameters of radon progeny, which were measured in Minia University, the deposition behavior of radon progeny (attached and unattached) has been studied by using a stochastic deposition model. The attached fraction was collected using a low pressure Berner cascade impactor technique. A screen diffusion battery was used for collecting the unattached fraction. Most of the attached activities for 222Rn progeny were associated with aerosol particles of the accumulation mode. The bronchial deposition fraction of particles in the size range of attached radon progeny was found to be lower than those of unattached progeny. The effect of radon progeny deposition by adult male has been also studied for various levels of physical exertion. An increase in the breathing rate was found to decrease the fraction with which inhaled progeny were deposited in the bronchi. As the ventilation rate increases from 0.54 to 1.5 m3 h−1, the average deposition fraction of airway generation 1 through 8 are expected to decrease by 22% for 1.4 nm particles and by 38% for 150 nm particles.

Particle Deposition in Respiratory Tracts of School-Aged Children

Exposure to ultrafine particles poses a potential health risk to school children. While many studies have focused on measuring ultrafine particle (UFP) concentrations in environments where children are at risk of high exposure, few studies have examined the particle deposition in the respiratory tract of children. This study aims to examine the particle deposition in the respiratory tract of school children in different microenvironments. UFP size distribution data were collected in residential homes, school buses, school classrooms, and from school outdoor air in both rural and urban areas of South Texas. The size distribution data were input to the Multiple Path Particle Dosimetry model to calculate regional and total particle deposition fraction. A 24-hour-school-day exposure was simulated by adding the time children spend in each microenvironment. The maximum pulmonary deposition fraction occurs at a diameter ranging from 18 to 40 nm, depending on condition. Age mostly affected the pulmonary region and the total lung deposition with the highest deposition fraction observed for younger children. In addition, comparison of size-dependent regional deposition and particle concentration establishes an accurate depiction of children's exposure and dose profiles. While children only spend 4% of the day in the home source environment, that environment may account for up to 77% of total daily dose intake. Higher deposition fraction occurs at smaller particle size. Younger children show increased levels of particle deposition than older children. Exposure period does not correlate to daily percentage of dose intake. This research can be used to assess children's accumulative exposure to UFPs.

Numerical investigation on particle deposition in a chamber with an attached-wall heat source

The deposition of particles in a chamber with an attached-wall heat source is investigated numerically by the random walk model of Lagrangian method. The particle trajectories are evaluated by tracking 4,000 particles with a density of 1,400 kg m−3. The purpose of the present paper is to study the effect of the heat source length on the deposition of particles (2.5 µm–10 µm) and the particle deposition pattern on the attached-wall surface above the heat source. Numerical results show that the particle deposition fraction increases with the heat source length and the increase of the heat source length can accelerate particle deposition onto the attached wall. It is also found that the particle deposition number on the attached-wall surface above the heat source is a function of the deposit position and the particle size.

Particulate Emissions from Commercial Handheld Sparklers: Evaluation of Physical Characteristics and Emission Rates

Ground level fireworks, such as sparklers, are commonly used by children during festive occasions and celebrations. Airborne particulate matter (PM) emissions from these fireworks are of serious health concern. However, to date no information is available on the PM emission characteristics from sparklers and their emission rates. In this study, three commonly used sparklers, namely, low smoke sparklers (LSS), colored sparklers (CS) and whistling sparklers (WS), were investigated for their PM emissions and emission rates. It was observed that WS (4.45 × 1011 s–1 or 3.24 × 1010 g–1) had higher emission rates compared to CS (2.9 × 1011 s–1 or 1.64 × 1010 g–1) and LSS (7 × 1010 s–1 or 1.68 × 109 g–1). A relatively large number of nanoparticles (NPs) were emitted from their burning. About 83% of PM emitted by WS and CS were in the nano size range (aerodynamic diameter (AED) < 50 nm) whereas LSS had 62% of total particles in the nano size range. In addition, particle deposition fractions into the lung were also estimated. It was found that CS and WS had higher deposition efficiency compared to that of LSS.

A fully Eulerian approach to particle inertial deposition in a physiologically realistic bifurcation

The investigation of aerosol flows in bifurcations is significant in biomedical applications, because this geometry resembles the branching airways of the lung. Most of the existing computational studies regarding aerosol flow in branching airways use Lagrangian description for the particulate phase, when particle inertial effects are taken into consideration. In the present study a fully Eulerian model is used for studying the transport and deposition of inertial particles under steady state inspiratory flow in the single physiologically realistic bifurcation created by generations G3-G4 of the human lung. In-house codes are used to create the geometry and the computational grid, obtain the fluid flow field and calculate particle concentration. Deposition fractions are calculated, concentration profiles are shown and deposition sites are indicated under different flow conditions (Reynolds number and flow asymmetry in the branches) and particles of various sizes (1–10μm). It is found that total particle deposition fraction is loosely dependent on fluid flow Reynolds number and our results are in agreement with experimental findings. Moreover, total deposition fraction does not change significantly between symmetric Q1/Q2=1 and asymmetric Q1/Q2=2 flow conditions, but is considerably lower for the totally obstructed case, Q2=0. On the contrary, deposition sites and particle concentration profiles depend on the various flow conditions. Apart from deposition at the bifurcation, which is present at all cases, deposition sites downstream the bifurcation move towards the outer bifurcation wall and daughter tube exit as Reynolds number increases. For the Q2=0, it is also shown that particles are trapped and deposit even in the obstructed daughter tube. In all studied cases, it is found that there is a particle-free region at the outer wall, at the beginning of the daughter tubes opposite the bifurcation. The straightforward formulation of deposition modelling and derivation of detailed concentration profiles along the bifurcation are major advantages of the fully Eulerian methodology used in the study.

Development of a rhesus monkey lung geometry model and application to particle deposition in comparison to humans

The exposure-dose-response characterization of an inhalation hazard established in an animal species needs to be translated to an equivalent characterization in humans relative to comparable doses or exposure scenarios. Here, the first geometry model of the conducting airways for rhesus monkeys is developed based upon CT images of the conducting airways of a 6-month-old male, rhesus monkey. An algorithm was developed for adding the alveolar region airways using published rhesus morphometric data. The resultant lung geometry model can be used in mechanistic particle or gaseous dosimetry models. Such dosimetry models require estimates of the upper respiratory tract volume of the animal and the functional residual capacity, as well as of the tidal volume and breathing frequency of the animal. The relationship of these variables to rhesus monkeys of differing body weights was established by synthesizing and modeling published data as well as modeling pulmonary function measurements on 121 rhesus control animals. Deposition patterns of particles up to 10 µm in size were examined for endotracheal and and up to 5 µm for spontaneous breathing in infant and young adult monkeys and compared to those for humans. Deposition fraction of respirable size particles was found to be higher in the conducting airways of infant and young adult rhesus monkeys compared to humans. Due to the filtering effect of the conducting airways, pulmonary deposition in rhesus monkeys was lower than that in humans. Future research areas are identified that would either allow replacing assumptions or improving the newly developed lung model.

Local deposition fractions of ultrafine particles in a human nasal-sinus cavity CFD model

Ultrafine particle deposition studies in the human nasal cavity regions often omit the paranasal sinus regions. Because of the highly diffusive nature of nanoparticles, it is conjectured that deposition by diffusion may occur in the paranasal sinuses, which may affect the residual deposition fraction that leaves the nasal cavity. Two identical CFD models of a human nasal cavity, one with sinuses and one without, were reconstructed from CT-scans to determine the uptake of ultrafine particles. In general, there was little flow passing through the paranasal sinuses. However, flow patterns revealed that some streamlines reached the upper nasal cavity near the olfactory regions. These flow paths promote particle deposition in the sphenoid and ethmoid sinuses. It was found that there were some differences in the deposition fractions and patterns for 5 and 10 nm particles between the nasal-sinus and the nasal cavity models. This difference is amplified when the flow rate is decreased and at a flow rate of 4 L/min the maximum difference was 17%. It is suggested that evaluations of nanoparticle deposition should consider some deposition occurring in the paranasal sinuses especially if flow rates are of concern.

Deposition of micrometer particles in pulmonary airways during inhalation and breath holding

We investigated how breath holding increases the deposition of micrometer particles in pulmonary airways, compared with the deposition during inhalation period. A subject-specific airway model with up to thirteenth generation airways was constructed from multi-slice CT images. Airflow and particle transport were simulated by using GPU computing. Results indicate that breath holding effectively increases the deposition of 5μm particles for third to sixth generation (G3–G6) airways. After 10s of breath holding, the particle deposition fraction increased more than 5 times for 5μm particles. Due to a small terminal velocity, 1μm particles only showed a 50% increase in the most efficient case. On the other hand, 10μm particles showed almost complete deposition due to high inertia and high terminal velocity, leading to an increase of 2 times for G3–G6 airways. An effective breath holding time for 5μm particle deposition in G3–G6 airways was estimated to be 4–6s, for which the deposition amount reached 75% of the final deposition amount after 10s of breath holding.

Flow patterns and deposition fraction of particles in the range of 0.1–10 μm at trachea and the first third generations under different breathing conditions

The velocity field and deposition fraction of the particles in the trachea and the first third generations of tracheobronchial tree are investigated with CFD simulation. The air flow rate of trachea is considered to be in the range of 15–60l/min in accordance to four different activity levels of male adults. A physiologically realistic dichotomic airway bifurcation geometry with structured hexahedral meshes are constructed. The simulations with different hexahedral mesh densities have shown that the grid independent results will be reached with the average dimensionless distance of the first cell to the walls of y+≈0.5. The deposition fraction graph for particles in the range of 0.1–10μm diameter has a minimum in the range of 0.1–1μm particle diameter and after that it increases for larger particles. The results of the simulations under different breathing pattern have shown that deposition fraction significantly increases at higher Reynolds and Stokes numbers.

Comparison of Stochastic Lung Deposition Fractions with Experimental Data

Deposition fractions of inhaled particles predicted by different computational models vary with respect to physical and biological factors and mathematical modeling techniques. These models must be validated by comparison with available experimental data. Experimental data supplied by different deposition studies with surrogate airway models or lung casts were used in this study to evaluate the stochastic deposition model Inhalation, Deposition and Exhalation of Aerosols in the Lung at the airway generation level. Furthermore, different analytical equations derived for the three major deposition mechanisms, diffusion, impaction, and sedimentation, were applied to different cast or airway models to quantify their effect on calculated particle deposition fractions. The experimental results for ultrafine particles (0.00175 and 0.01) were found to be in close agreement with the stochastic model predictions; however, for coarse particles (3 and 8 μm), experimental deposition fractions became higher with increasing flow rate. An overall fair agreement among the calculated deposition fractions for the different cast geometries was found. However, alternative deposition equations resulted in up to 300% variation in predicted deposition fractions, although all equations predicted the same trends as functions of particle diameter and breathing conditions. From this comparative study, it can be concluded that structural differences in lung morphologies among different individuals are responsible for the apparent variability in particle deposition in each generation. The use of different deposition equations yields varying deposition results caused primarily by (i) different lung morphometries employed in their derivation and the choice of the central bifurcation zone geometry, (ii) the assumption of specific flow profiles, and (iii) different methods used in the derivation of these equations.

Inertial Particle Deposition in a 90° Laminar Flow Bend: An Eulerian Fluid Particle Approach

A numerical model for the simulation of aerosol flows via an Eulerian–Eulerian, one-way coupled, two-phase flow description is presented. An in-house computational fluid dynamics code is used to simulate the gaseous (continuous) phase, whereas a modified convective diffusion equation models particle transport. The convective diffusion equation, which includes inertial, gravitational, and diffusive particle transport, is solved by computational fluid dynamics techniques. The model is validated by comparing the calculated laminar fluid flow and particle deposition fractions to analytical and experimentally studied aerosol flows in a laminar flow 90° bend of circular cross section available in the literature. Model predictions are also compared with numerical predictions of Eulerian-Lagrangian models. Particle concentration profiles at different cross sections are calculated, and deposition sites on the wall boundary are indicated. For the range of studied particle diameters, the Eulerian–Eulerian model predicts deposition fractions satisfactorily, being in good agreement with the experimental data.

ENERGY LEAKAGE PROBABILITY EFFECT ON IGNITION CONDITION IN AN INERTIAL CONFINEMENT FUSION PLASMA

For a weak to moderately coupled plasma, the charged particle stopping power dE/dx was recently calculated from first principles in Ref. 1 using the method of dimensional continuation.2 While the calculational techniques were imported from quantum field theory, the calculation itself lies squarely within the standard framework of convergent kinetic equations. By using these calculations, ignition condition regime in (D/Tx/3Hey) fusion fuel pellet is investigated, including energy deposition fraction of charged particles and neutrons in fuel pellet, bremsstrahlung and inverse bremsstrahlung radiation, inverse Compton scattering and thermal conduction losses.

INDOOR AIR QUALITY: SHS Plus Ozone Poses One Fine Particle Problem

Smokers might want to think about creating a no-ozone zone as researchers report that the gas can react with chemicals in secondhand smoke (SHS) to produce ultrafine particles less than 100 nm in diameter.1 “Given the very large surface area and the very high alveolar deposition fraction of such particles, their potential to cause health problems cannot be ignored,” says first author Mohamad Sleiman, a chemist with the Environmental Energy Technologies Division of Lawrence Berkeley National Laboratory (LBNL).

Calculation of aerosol deposition in human lung airways using Horsfield geometric model

Clinical investigation shows a dramatic relation between deposition of particles in lung’s pathways and respiratory system diseases. Particle deposition may also play a major role in drug delivery via respiratory system. Previous researches on symmetric and 5-lobe models for rat, dog, hamster and human show that, the deposition fraction of fine particles (between 0.1 and 0.7 μm) is minimum. A multi-path asymmetric 5-lobe model of Horsfield et al. is employed to construct the airway tree. Since the data are based on lung casting, asymmetric properties of the model are more realistic. Deposition of 0.01–10 μm particles is calculated during inhalation using published formulas in every branch. Here, we measured the deposition up to alveolar region. Accumulative deposition versus particle diameter predicts less deposition in comparison with symmetric models in as much as our model is asymmetric. The flow is divided based on distal volume. Particle deposition for 0.01 μm is in good agreement with other models but for 1 μm different trend in lower generations is observed. It is concluded that the asymmetric pattern gives different deposition fraction in all regions, since the distinctive geometric properties of the model is in some extent different from that of symmetric model. But, the accumulative deposition trend is similar in both symmetric and asymmetric models.

Effect of smoking parameters on the particle size distribution and predicted airway deposition of mainstream cigarette smoke

It is known that puffing conditions such as puff volume, duration, and frequency vary substantially among individual smokers. This study investigates how these parameters affect the particle size distribution and concentration of fresh mainstream cigarette smoke (MCS) and how these changes affect the predicted deposition of MCS particles in a model human respiratory tract. Measurements of the particle size distribution made with an electrical low pressure impactor for a variety of puffing conditions are presented. The average flow rate of the puff is found to be the major factor effecting the measured particle size distribution of the MCS. The results of these measurements were then used as input to a deterministic dosimetry model (MPPD) to estimate the changes in the respiratory tract deposition fraction of smoke particles. The MPPD dosimetry model was modified by incorporating mechanisms involved in respiratory tract deposition of MCS: hygroscopic growth, coagulation, evaporation of semivolatiles, and mixing of the smoke with inhaled dilution air. The addition of these mechanisms to MPPD resulted in reasonable agreement between predicted airway deposition and human smoke retention measurements. The modified MPPD model predicts a modest 10% drop in the total deposition efficiency in a model human respiratory tract as the puff flow rate is increased from 1050 to 3100 ml/min, for a 2-s puff.