scholarly journals Airflow and Particle Deposition in Acinar Models with Interalveolar Septal Walls and Different Alveolar Numbers

2018 ◽  
Vol 2018 ◽  
pp. 1-18 ◽  
Author(s):  
Jinxiang Xi ◽  
Mohamed Talaat ◽  
Hesham Tanbour ◽  
Khaled Talaat
Keyword(s):  
Deposition Rate ◽  
Particle Deposition ◽  
Orientation Angle ◽  
Structural Complexity ◽  
Particle Dispersion ◽  
Breath Holding ◽  
Complex Models ◽  
Tracking Model ◽  
Lagrangian Tracking ◽  
Collateral Ventilation

Unique features exist in acinar units such as multiple alveoli, interalveolar septal walls, and pores of Kohn. However, the effects of such features on airflow and particle deposition remain not well quantified due to their structural complexity. This study aims to numerically investigate particle dynamics in acinar models with interalveolar septal walls and pores of Kohn. A simplified 4-alveoli model with well-defined geometries and a physiologically realistic 45-alveoli model was developed. A well-validated Lagrangian tracking model was used to simulate particle trajectories in the acinar models with rhythmically expanding and contracting wall motions. Both spatial and temporal dosimetries in the acinar models were analyzed. Results show that collateral ventilation exists among alveoli due to pressure imbalance. The size of interalveolar septal aperture significantly alters the spatial deposition pattern, while it has an insignificant effect on the total deposition rate. Surprisingly, the deposition rate in the 45-alveoli model is lower than that in the 4-alveoli model, indicating a stronger particle dispersion in more complex models. The gravity orientation angle has a decreasing effect on acinar deposition rates with an increasing number of alveoli retained in the model; such an effect is nearly negligible in the 45-alveoli model. Breath-holding increased particle deposition in the acinar region, which was most significant in the alveoli proximal to the duct. Increasing inhalation depth only slightly increases the fraction of deposited particles over particles entering the alveolar model but has a large influence on dispensing particles to the peripheral alveoli. Results of this study indicate that an empirical correlation for acinar deposition can be developed based on alveolar models with reduced complexity; however, what level of geometry complexity would be sufficient is yet to be determined.

Micro/Nano-Particle Deposition in the Airway of a 6-Year-Old Child From Nostril to the Third Generation

2012 ◽  
Author(s):  
Erfan Keshavarzian ◽  
Pejman Farhadi Ghalati ◽  
Omid Abouali ◽  
Goodarz Ahmadi ◽  
Mohammad Hadi Bagheri
Keyword(s):  
Deposition Rate ◽  
Particle Deposition ◽  
Upper Airway ◽  
Nano Particles ◽  
Nano Particle ◽  
The Third ◽  
Breathing Resistance ◽  
Lagrangian Tracking ◽  
Lagrangian Tracking Approach ◽  
Airway Model

In the present study the transport and deposition of micro/nano-particles in the airway model of a 6 year-old girl was investigated. The realistic airway model includes the nasal cavity, larynx, pharynx, trachea and also bronchial airways up to third generations. This model was developed from a series of high resolution CT scan images. For low to moderate activities, the steady airflows through the entire model of the child’s upper airway passages were simulated. Micro particle trajectories and deposition in the range of 1–30 μm were evaluated using a Lagrangian tracking approach and Eulerian method was used to assess the deposition rate of the nano-particles in the range of 1–150 nm. The deposition of micro and nano-particles in the airway of a child was evaluated and the results were with those for the adults and the differences were discussed. As was expected, a higher breathing resistance was observed for the 6-year-old child compared to adults, which leads to a higher particle deposition rate. The results of this study for the flow field and micro/nano-particle deposition showed the important differences between children and adults. Therefore care should be given to reduce the risk of airborne toxicants on infants and children.

Effects of the laryngeal jet on nano- and microparticle transport and deposition in an approximate model of the upper tracheobronchial airways

2008 ◽  
Vol 104 (6) ◽  
pp. 1761-1777 ◽  
Author(s):  
Jinxiang Xi ◽  
P. Worth Longest ◽  
Ted B. Martonen
Keyword(s):  
Reverse Flow ◽  
Approximate Model ◽  
In Vitro Models ◽  
Deposition Density ◽  
Flow Features ◽  
Tracking Model ◽  
Induced Flow ◽  
Lagrangian Tracking ◽  
The Right

The extent to which laryngeal-induced flow features penetrate into the upper tracheobronchial (TB) airways and their related impact on particle transport and deposition are not well understood. The objective of this study was to evaluate the effects of including the laryngeal jet on the behavior and fate of inhaled aerosols in an approximate model of the upper TB region. The upper TB model was based on a simplified numerical reproduction of a replica cast geometry used in previous in vitro deposition experiments that extended to the sixth respiratory generation along some paths. Simulations with and without an approximate larynx were performed. Particle sizes ranging from 2.5 nm to 12 μm were considered using a well-tested Lagrangian tracking model. The model larynx was observed to significantly affect flow dynamics, including a laryngeal jet skewed toward the right wall of the trachea and a significant reverse flow in the left region of the trachea. Inclusion of the laryngeal model increased the tracheal deposition of nano- and micrometer particles by factors ranging from 2 to 10 and significantly reduced deposition in the first three bronchi of the model. Considering localized conditions, inclusion of the laryngeal approximation decreased deposition at the main carina and produced a maximum in local surface deposition density in the lobar-to-segmental bifurcations (G2–G3) for both 40-nm and 4-μm aerosols. These findings corroborate previous experiments and highlight the need to include a laryngeal representation in future computational and in vitro models of the TB region.

Effect of Inhaling Patterns on Aerosol Drug Delivery: CFD Simulation

2008 ◽  
Author(s):  
Jinho Kim ◽  
Jim S. Chen
Keyword(s):  
Secondary Flow ◽  
Particle Deposition ◽  
Cfd Simulation ◽  
Dry Powder Inhaler ◽  
Upper Airway ◽  
Aerosol Deposition ◽  
Dose Inhaler ◽  
Breath Holding ◽  
Pharmaceutical Aerosols ◽  
Airway Model

Inhaled Pharmaceutical Aerosols (IPAs) delivery has great potential in treatment of a variety of respiratory diseases, including asthma, pulmonary diseases, and allergies. Aerosol delivery has many advantages. It delivers medication directly to where it is needed and it is effective in much lower doses than required for oral administration. Currently, there are several types of IPA delivery systems, including pressurized metered dose inhaler (pMDI), the dry powder inhaler (DPI), and the medical nebulizer. IPAs should be delivered deep into the respiratory system where the drug substance can be absorbed into blood through the capillaries via the alveoli. Researchers have proved that most aerosol particles with aerodynamic diameter of about 1–5 μm, if slowly and deeply inhaled, could be deposited in the peripheral regions that are rich in alveoli [1–3]. The purpose of this study is to investigate the effects of various inhaling rates with breath-holding pause on the aerosol deposition (Dp = 0.5–5 μm) in a human upper airway model extending from mouth to 3rd generation of trachea. The oral airway model is three dimensional and non-planar configurations. The dimensions of the model are adapted from a human cast. The air flow is assumed to be unsteady, laminar, and incompressible. The investigation is carried out by Computational Fluid Dynamics (CFD) using the software Fluent 6.2. The user-defined function (UDF) is employed to simulate the cyclic inspiratory flows for different IPA inhalation patterns. When an aerosol particle enters the mouth respiratory tract, its particles experience abrupt changes in direction. The secondary flow changes its direction as the airflow passes curvature. Intensity of the secondary flow is strong after first bend at pharynx and becomes weaker after larynx. In flow separation, a particle can be trapped and follow the eddy and deposit on the surface. Particle deposition fraction generally increases as particle size and inhaling airflow velocity increase.

Hybrid LES/RANS Model for Simulation of Particle Dispersion and Deposition

2018 ◽  
Author(s):  
H. Sajjadi ◽  
M. Salmanzadeh ◽  
G. Ahmadi ◽  
S. Jafari
Keyword(s):  
Turbulence Model ◽  
Particle Deposition ◽  
Computational Cost ◽  
Particle Dispersion ◽  
Distribution Functions ◽  
Wall Region ◽  
Rans Model ◽  
Turbulence Effects ◽  
Scale Turbulence ◽  
Les Model

Particle dispersion and deposition in a modeled room was investigated using the Lattice Boltzmann method (LBM) in conjunction with the hybrid RANS/LES turbulence model. For this new model a combination of LES and RANS models was used to reduce the computational cost of using the full LES in the entire domain. Here the near wall region was simulated by the RANS model, while the rest of the domain was analyzed using the LES model within the framework of the LBM. The k-ε turbulence model was applied in the RANS region. For using the k-ε model in the LBM framework, two additional distribution functions for k and ε were defined. For the LES region the sub-grid scale turbulence effects were simulated through a Smagorinsky model. To study the particle dispersion and deposition in the modeled room, particles with different sizes (diameters of 10nm to 10 μm) were investigated. The simulated results for particle dispersion and deposition showed that the predictions of the present hybrid method were quite similar to the earlier LES-LBM. In addition, the predictions of the hybrid model for the particle deposition and dispersion were closer to the LES simulation results compared to those of the k-ε model. It was shown that the Brownian excitation is very important for nanoparticles and the number of deposited particles for 10nm particles is higher than those for the larger 100nm and 1μm particles. The deposition rate for 10 μm particles is also high due to the inertial effects.

Particle Dispersion and Deposition in a Curved Duct

2009 ◽  
Author(s):  
C. M. Winkler ◽  
S. P. Vanka
Keyword(s):  
Particle Deposition ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Outer Wall ◽  
Particle Dispersion ◽  
Radius Of Curvature ◽  
Dean Number ◽  
Particle Volume ◽  
Particle Tracking Method ◽  
Dean Vortex

Particle transport in ducts of square cross-section with constant streamwise curvature is studied using numerical simulations. The flow is laminar, with Reynolds numbers of Reτ = 40 and 67, based on the friction velocity and duct width. The corresponding Dean numbers for these cases are 82.45 and 184.5, respectively, where De = Rea/R, a is the duct width and R is the radius of curvature. A Lagrangian particle tracking method is used to account for the particle trajectories, with the particle volume fraction assumed to be low such that inter-particle collisions and two-way coupling effects are negligible. Four particle sizes are studied, τp+ = 0.01, 0.05, 0.1, and 1. Particle dispersion patterns are shown for each Dean number, and the steady-state particle locations are found to be reflective of the Dean vortex structure. Particle deposition on the walls is shown to be dependent upon both the Dean number and particle response time, with the four-cell Dean vortex pattern able to prevent particle deposition along the center of the outer wall.

scholarly journals ANALYTICAL AND CFD INVESTIGATION OF TURBULENT DIFFUSION MODEL FOR PARTICLE DISPERSION AND DEPOSITION

1970 ◽  
Vol 40 (1) ◽  
pp. 39-53
Author(s):  
Alamgir Hossain ◽  
Jamal Naser
Keyword(s):  
Diffusion Model ◽  
Turbulent Diffusion ◽  
Particle Deposition ◽  
Fluid Velocity ◽  
Particle Diameter ◽  
Particle Dispersion ◽  
Homogeneous Distribution ◽  
Lower Velocity ◽  
Different Depths ◽  
Diffusion Particle

A 2D analytical turbulent diffusion model for particle dispersion and deposition at different heights across the pipe flow and circumferential deposition has been developed. This liquid-solid turbulent diffusion model presented in this paper has emanated from an existing gas-liquid turbulent diffusion model. Simultaneously a comprehensive 3D numerical investigation has been carried out to study the above making of multiphase mixture model available in Fluent 6.1. In both studies different particles sizes and densities were used. The deposition was studied as a function of particle diameter, density and fluid velocity. The deposition of particles, along the periphery of the wall and at different depths, was also investigated. Both studies showed that the deposition of heavier particles at the bottom of the pipe wall was found to be higher at lower velocities and lower at higher velocities. The lighter particles were found mostly suspended with homogeneous distribution. Smaller particles were also suspended with marginal higher concentration near the bottom of the wall. This marginal higher concentration of the smaller particles was found to be slightly pronounced for lower velocity. The larger particles clearly showed deposition near the bottom of the wall. These analogies of particles are well discussed with the ratio between free flight velocity and the gravitational settling velocity. Key Words: Multiphase flow, turbulence diffusion, particle deposition, horizontal flow.   doi: 10.3329/jme.v40i1.3472 Journal of Mechanical Engineering, Vol. ME40, No. 1, June 2009 39-53

Use of aerosols to estimate pulmonary air-space dimensions

1981 ◽  
Vol 51 (2) ◽  
pp. 465-476 ◽  
Author(s):  
J. Gebhart ◽  
J. Heyder ◽  
W. Stahlhofen
Keyword(s):  
Particle Deposition ◽  
Continuous Monitoring ◽  
Region Of Interest ◽  
Normal Subjects ◽  
Breath Holding ◽  
Experimental Conditions ◽  
Single Breath ◽  
Inhaled Particles ◽  
Respiratory Flow ◽  
Air Space

Single-breath inhalations of monodisperse aerosols were performed with a group of normal subjects to determine aerosol recovery from the human lung after periods of breath holding. Aerosols of monodisperse nonhygroscopic droplets of bis(2-ethylhexyl) sebacate of between 0.5 and about 2.5 micron diam were used for the inhalation. The inhalation apparatus allows continuous monitoring of particle number concentration and flow rate close to the mouth. Experiments were designed to find the optimum experimental conditions for the principal concept of Palmes et al (In: Inhaled Particles and Vapours. London: Pergamon, 1976, vol. II. p. 339-347) to evaluate pulmonary air-space dimensions by means of aerosols. The experimental results obtained for various respiratory flow rates (125, 250, and 500 cm3 X s-1), settling velocities of the particles (10(-3) to 1.5 X 10(-2) cm X s-1) and volumes of inspired aerosols (500, 1,000, and 2,000 cm3) are compared with the results derived from a mathematical model for the particle deposition during respiratory pauses. Monodisperse aerosols with particles between 1 and about 1.5 micron diam. inspired for breath holding into the lung region of interest, may provide optimum conditions for the sizing of air spaces by means of aerosols.

Improved Discrete Random Walk Stochastic Model for Simulating Particle Dispersion and Deposition in Inhomogeneous Turbulent Flows

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Amir A. Mofakham ◽  
Goodarz Ahmadi
Keyword(s):  
Random Walk ◽  
Turbulent Flows ◽  
Particle Deposition ◽  
Finite Size ◽  
Particle Dispersion ◽  
Concentration Profiles ◽  
Velocity Fluctuations ◽  
Point Particles ◽  
Deposition Velocities ◽  
Gradient Drift

Abstract The performance of different versions of the discrete random walk models in turbulent flows with nonuniform normal root-mean-square (RMS) velocity fluctuations and turbulence time scales were carefully investigated. The OpenFOAM v2−f low Reynolds number turbulence model was used for evaluating the fully developed streamwise velocity and the wall-normal RMS velocity fluctuations profiles in a turbulent channel flow. The results were then used in an in-house matlab particle tracking code, including the drag and Brownian forces, and the trajectories of randomly injected point-particles with diameters ranging from 10 nm to 30 μm were evaluated under the one-way coupling assumption. The distributions and deposition velocities of fluid-tracer and finite-size particles were evaluated using the conventional-discrete random walk (DRW) model, the modified-DRW model including the velocity gradient drift correction, and the new improved-DRW model including the velocity and time gradient drift terms. It was shown that the conventional-DRW model leads to superfluous migration of fluid-point particles toward the wall and erroneous particle deposition rate. The concentration profiles of tracer particles obtained by using the modified-DRW model still are not uniform. However, it was shown that the new improved-DRW model with the velocity and time scale drift corrections leads to uniform distributions for fluid-point particles and reasonable concentration profiles for finite-size heavy particles. In addition, good agreement was found between the estimated deposition velocities of different size particles by the new improved-DRW model with the available data.

Simulation of Submicron Particle Deposition in Laminar and Turbulent Stagnation Point Flows

1991 ◽  
Author(s):  
Salem Abuzeid ◽  
Ahmed A. Busnaina
Keyword(s):  
Brownian Motion ◽  
Stagnation Point ◽  
Deposition Rate ◽  
Particle Deposition ◽  
Aerosol Particles ◽  
Laminar Flows ◽  
Wafer Surface ◽  
Particle Sizes ◽  
Mean Flow ◽  
Gaussian Random Process

Abstract The two dimensional laminar and turbulence stagnation-point flow over a wafer surface within a cleanroom environment are numerically simulated. This study shows the relationship between particle capture area on the wafer and the particle size and flow conditions. The mean flow field is simulated using a two equation k-ϵ turbulence model. Trajectories of aerosol particles are evaluated by solving the corresponding Lagrangian equation of motion that includes effects of drag, gravity, lift force, Brownian motion and turbulence fluctuations. The Brownian motion is modeled as a white noise process and turbulence fluctuation is assumed to behave as Gaussian random process. Simulations are carried out for aerosol particles (of various sizes) released at different locations over the surface. Depositions of particles on the wall are evaluated and a capture area which varies with particle sizes is produced. The results show that Brownian motion becomes very significant when turbulence fluctuations start to disappear near the wall for particles smaller than 1 μm in diameter. The results also show that, deposition of particles in turbulent flows are usually higher than that in laminar flows for all particle sizes considered. The effect of fluid on particle deposition rate is predicted for fluid of air and water. The results show that, particles deposition rate in air is higher than that in water.

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