Mouth-throat Geometry Research Articles

Numerical study on the effect of the realistic mouth-inhaler positions on orally inhaled drug delivery in pediatric intersubject upper airways

The relative position between the pediatric upper airway and the inhalation device during real inhalation administration has significant effects on the delivery efficiency of orally inhaled drugs. Morphological variability plays an important role in this process. However, the mouth-throat differences between adults and children were usually neglected because most of the commercial inhalation devices currently are designed for adults or older adolescents. The main objective of this study is to investigate these effects by four realistic pediatric mouth-throat (RMT) geometries. In addition, an idealized mouth-throat (IMT) model was developed to validate the numerical model and to compare with the RMT models. Computational fluid dynamics (CFD) simulations were performed to investigate the flow pattern and deposition pattern in these models and the results were compared with the cascade impactor experiments, replica experiments and in vivo results. No significant correlation (p > 0.1) between the relative position parameters and inhaler insertion depth can be noticed among the RMT models. Notably, significant variability in the inhaler posture was observed in RMT models, especially for the S4 model. Airflow structure shows that the RMT model has a complex onset of turbulence, reverse flow and subsequently vortex formation when compared with the IMT model. The oral cavity is the region with the largest deposition fraction (DF) and deposition efficiency (DE). The DF and DE of the oral cavity are negatively correlated to the position parameter (Lm) when mass median aerodynamic diameter (MMAD) of indacaterol 150 μg was utilized as the input particle parameter. The relative position between the inhaler and oral cavity has significant effects on the particle transport and deposition. Furthermore, in silico results overestimated the lung deposition in comparison to the in vivo and experimental results when MMAD was used as input. To resolve the disparity between the in silico and in vivo results, a modified prediction method based on the cascade impactor and original in silico results was proposed and a good correlation of the relative contribution of pulmonary absorption to total systemic exposure (flung) was found between the predicted and observed results. The findings of present work will provide useful information in understanding the particle transport and deposition in the pediatric airways for the design of inhaler.

The impact of actuator nozzle and surroundings condition on drug delivery using pressurized-metered dose inhalers.

The most commonly used method to deliver aerosolized drugs to the lung is with pressurized metered-dose inhalers (pMDIs). The spray actuator is a critical component of pMDI, since it controls the atomization process by forming aerosol plumes and determining droplet size distribution. Through computational fluid dynamics (CFD) simulations, this study investigated the effect of two different nozzle types (single conventional and twin nozzles) on drug deposition in the mouth-throat (MT) region. We also studied the behavior of aerosol plumes in both an open-air environment and the MT geometry. Our study revealed that spray aerosol generated in an unconfined, open-air environment with no airflow behaves distinctly from spray introduced into the MT geometry in the presence of airflow. In addition, the actuator structure significantly impacts the device's efficacy. In the real MTmodel, we found that the twin nozzle increases drug deposition in the MT region, and its higher aerosol velocity negatively affects its efficiency.

Effects of vocal fold adduction on the particle deposition in the glottis: A numerical analysis and in vitro assessment

BackgroundThe efficacy of inhalation therapy depends on the drug deposition in the human respiratory tract. This study investigates the effects of vocal fold adduction on the particle deposition in the glottis. MethodsA realistic mouth-throat (MT) geometry was built based on CT images of a healthy adult (MT-A). Mild (MT-B) and great (MT-C) vocal fold (VF) adduction were incorporated in the original model. Monodisperse particles range in size from 3 to 12 μm were simulated at inspiration flow rates of 15, 30 and 45 L per minute (LPM). The regional deposition of drug aerosols was performed in 3D-printed models and quantified using high-performance liquid chromatography. ResultsBoth the numerical analysis and in vitro experiments show that most particles are deposited in the mouth, pharynx and supraglottis, while few are deposited in the glottis and subglottis. For most cases in MT-A, the particle quantity in glottis is lower than 0.02 N/mm2 at 15 and 30 LPM while they increase dramatically at 45 LPM. It peaked at 0.347 N/mm2 for 5-μm particles at 45 LPM in MT-B and 2.324 N/mm2 for 6-μm particles at 30 LPM in MT-C. The lowest drug mass faction in the glottis in vitro were found at 15 LPM for MT-A and MT-C, and at 30 LPM for MT-B, whereas it peaked at 45 LPM for all MT models, 0.71% in MT-A, 1.16% in MT-B, and 2.53% in MT-C, respectively. ConclusionBased on the results of this study, larger particles are more likely to be deposited in the oral cavity, oropharynx, and supraglottis than in the glottis. However, particle deposition in the glottis generally increases with VF adduction and greater inspiratory flow rates.

A CFD Investigation on the Aerosol Drug Delivery in the Mouth–Throat Airway Using a Pressurized Metered-Dose Inhaler Device

Inhalation therapy involving a pressurized metered-dose inhaler (pMDI) is one of the most commonly used and effective treatment methods for patients with asthma. The purpose of this study was to develop a computational fluid dynamics (CFD) model to characterize aerosol flow issued from a pMDI into a simulated mouth–throat geometry. The effects of air flow rate and cone angle were analyzed in detail. The behaviour of the multiphase flow initiated at the inhaler actuation nozzle and extended through the mouth–throat airway was simulated based on the Eulerian-Lagrangian discrete phase model, with the k-ω model applied for turbulency. We validated our model against published experimental measurements and cover the hydrodynamic aspect of the study. The recirculation we observed at the 90° bend inside the mouth–throat airway resulted in the selective retention of larger diameter particles, and the fluid flow patterns were correlated with drug deposition behaviour. Enhancing air flow rates up to three times reduced the aerodynamic particle diameters to 20%. We also observed that, as cone angle increased, mouth deposition increased; an 8° cone angle was the best angle for the lowest mouth–throat deposition.

Numerical study on the impact of mucus layer and inlet air-temperatures on the particle deposition in a highly idealized mouth-throat model using LES

Presence of mucus layer and inlet air temperature variations can significantly affect the extent of particle transport and deposition in the mouth-throat airway for aerosol drug delivery applications. In addition, higher inlet air temperature can lead to thermal injuries as well. The main goal of the present paper is to investigate these effects in a highly idealized mouth-throat geometry in detail. Large eddy simulation was performed to accurately predict the air flow-fields and a Lagrangian particle tracking model has been employed to capture the particle deposition efficiencies and patterns. The effects of three different inlet air temperatures (15 °C, 26.7 °C and 45 °C) and three different particle sizes (3 μm, 5 μm and 6 μm) have been studied for inlet flow rates of 15 L/min and 30 L/min with and without mucus layer in the present investigation. Detailed velocity and temperature fields, as well as, particle deposition efficiencies and patterns were analyzed and it has been found out that (a) the particle deposition efficiencies varied significantly with changes in inlet air temperature and flow rates, particle diameters and in the presence of mucus layer, (b) the presence of recirculation zones and secondary vortices determined the rate of particle deposition at different inhalation flow rates and inlet air temperatures, and (c) the changes in temperature distribution near the mouth-throat wall in the presence of mucus layer have a dominant effect on particle deposition as compared to inertial deposition. The findings of the present work will provide useful information in understanding the heat transfer effects on particle transport and deposition for the design of pulmonary drug delivery devices under the influence of various environmental and human factors.

Inhaler Spray Investigation Using High-Speed Phase-Contrast X-Ray and Schlieren Imaging.

The first pressurised metered dose inhaler (pMDI) was introduced in 1956. Even with excellent inhaler technique typically only 20% of the dose deposits in the lungs where needed. It is hoped that a better understanding of the initial plume formation and expansion during dose release can help improve modelling, devices and ultimately transport to the lungs. We have used two high-speed imaging techniques to investigate the transient dose event. Synchrotron phase-contrast X-Ray imaging is a technique that is sensitive to variations in the refractive index of materials in the X-ray region. Similarly, Schlieren imaging is an optical technique sensitive to the refractive index gradients which are often present in pMDI plumes due to gas density variations. We have combined and synchronised both techniques to investigate three commercial pMDIs actuators during dose release for various actuator/formulation combinations. We have observed temporal phases of propellant flowing in the orifice channel. At early times flash boiling takes place and drives gas emission, steep plume density gradients and liquid jets/droplets at the orifice. Evaporating liquid is present in the sump long after the dose is finished. Regional counter-flow is seen in plumes emitted into a mouth-throat geometry. As the foamy liquid-vapour mixture is forced out of the sump and into the orifice the liquid walls of the bubbles break into fragments which are forced out of the sump and tend to form a liquid-gas flow in the orifice channel. The period of high density plume observed by the schlieren technique corresponds to flash-boiling-driven liquid exiting the orifice channel.

Biophysical model to predict lung delivery from a dual bronchodilator dry-powder inhaler

A biophysical lung model was designed to predict inhaled drug deposition in patients with obstructive airway disease, and quantitatively investigate sources of deposition variability. Different mouth-throat anatomies at varying simulated inhalation flows were used to calculate the lung dose of indacaterol/glycopyrronium [IND/GLY] 110/50 µg (QVA149) from the dry-powder inhaler Breezhaler®. Sources of variability in lung dose were studied using computational fluid dynamics, supported by aerosol particle sizing measurements, particle image velocimetry and computed tomography. Anatomical differences in mouth-throat geometries were identified as a major source of inter-subject variability in lung deposition. Lung dose was similar across inhalation flows of 30–120 L/min with a slight drop in calculated delivery at high inspiratory flows. Delivery was relatively unaffected by inhaler inclination angle. The delivered lung dose of the fixed-dose combination IND/GLY matched well with corresponding monotherapy doses. This biophysical model indicates low extra-thoracic drug loss and consistent lung delivery of IND/GLY, independent of inhalation flows. This is an important finding for patients across various ages and lung disease severities. The model provides a quantitative, mechanistic simulation of inhaled therapies that could provide a test system for estimating drug delivery to the lung and complement traditional clinical studies.

Evaluation of Bio-relevant Mouth-Throat Models for Characterization of Metered Dose Inhalers.

For inhalation drug characterization, the traditionally used USP induction port provides limited in vivo predictive capability because it does not adequately mimic airway geometry. In this study, various bio-relevant mouth-throat (MT) models, including Alberta Idealized Throat (AIT), and 3D printed large/medium/small-sized VCU (Virginia Commonwealth University) models were evaluated using two metered dose inhaler (MDI) drug products: a solution MDI containing beclomethasone dipropionate (BDP-MDI) and a suspension MDI containing fluticasone propionate (FP-MDI). For BDP-MDI, use of VCU large and small MT models resulted in a significantly higher MT deposition and lower fine particle fraction (FPF) compared with the other MT models. In the case of FP-MDI, the three VCU models resulted in higher MT deposition and lower FPF compared with the USP induction port and AIT. Overall, the in vitro testing results for the suspension MDI were more sensitive to geometric differences of the MT models than those for the solution MDI. Our results suggest that in vitro characterization of MDI products can be influenced by many factors, including the type of formulation, the MT geometry, shape, internal space volume, and the material used to make the MT models.

In silico assessment of mouth-throat effects on regional deposition in the upper tracheobronchial airways

Regional deposition of inhaled medicines is a valuable metric of effectiveness in drug delivery applications to the lung. In silico methods are now emerging as a valuable tool for the detailed description of localized deposition in the respiratory airways. In this context, there is a need to minimize the computational cost of high-fidelity numerical approaches. Motivated by this need, the present study is designed to assess the role of the extrathoracic airways in determining regional deposition in the upper bronchial airways. Three mouth-throat geometries, with significantly different geometric and filtering characteristics, are merged onto the same tracheobronchial tree that extends to generation 8, and Large Eddy Simulations are carried out at steady inhalation flowrates of 30 and 60L/min. At both flowrates, large flow field differences in the extrathoracic airways across the three geometries largely die out below the main bifurcation. Importantly, localized deposition fractions are found to remain practically identical for particles with aerodynamic diameters of up to dp=4μm and dp=2.5μm at 30 and 60L/min, respectively. For larger particles, differences in the localized deposition fractions are shown to be mainly due to variations in the mouth-throat filtering rather than upstream flow effects or differences in the local flow field. Deposition efficiencies in the individual airway segments exhibit strong correlations across the three geometries, for all particle sizes. The results suggest that accurate predictions of regional deposition in the tracheobronchial airways can therefore be obtained if the particle size distribution that escapes filtering in the mouth-throat (ex-cast dose) of a particular patient is known or can be estimated. These findings open the prospect for significant reductions in the computational expense, especially in the context of in silico population studies, where the aerosol size distribution and precomputed flow field from standardized mouth-throat models could be used with large numbers of tracheobronchial trees available in chest-CT databases.

Characterization of aerosol Stokes number in 90° bends and idealized extrathoracic airways

Prediction of aerosol deposition in the respiratory system is important for improving the efficiency of inhaled drug delivery and for assessing the toxicity of airborne pollutants. Deposition is typically reported as a function of a global Stokes number which is based on a reference flow timescale, or the ratio of the characteristic flow length and velocity scales. In reality, however, particles experience varying flow timescales as they are advected through the airways, which motivates the use of an instantaneous Stokes number based on the local properties of the flow field. We then define the effective Stokes number as the time-average of the instantaneous value. This effective Stokes number thus encapsulates the flow history and geometric variability, and provides a more detailed account of the particle trajectory in the flow. Laminar and turbulent flows in a curved pipe are examined first and provide a simplified, or canonical, configuration of the flow in the upper airways. They are followed by a study of turbulent flow in an idealized mouth–throat geometry. Our results demonstrate that the effective Stokes number can deviate significantly from the traditional value based solely on the reference flow timescale. In addition, the effective Stokes number shows a clear correlation with deposition efficiency and can therefore be used to determine optimal aerosol release locations in order to minimize extrathoracic losses.

Inhalation of tobramycin using simulated cystic fibrosis patient profiles.

TOBI® Podhaler™ is a capsule-based drug-device combination (tobramycin inhalation powder [TIP] 28 mg capsules via unit-dose dry powder T-326 Inhaler [Podhaler™]) developed for treatment of Pseudomonas aeruginosa infection in cystic fibrosis (CF). We explored how inspiratory flow profiles and mouth-throat geometries affect drug delivery with the T-326 Inhaler. Inspiratory flow profiles were recorded from 38 subjects aged 6-71 who had CF and varying degrees of lung function impairment. Ten of the inspiratory flow profiles were simulated in the laboratory using a custom breath simulator to determine delivered dose (DD) from the T-326 Inhaler. In vitro total lung dose (TLDin vitro ) was measured using four anatomical throat models, ranging from a child to a large adult. Aerosol performance was assessed across a range of inspiratory flow profiles. Mean DD ranged from 88.8% to 97.0% of declared capsule content. TLDin vitro ranged from 54.8% to 72.4% of capsule content between the flow profile/throat options tested, and the mean TLDin vitro across the range of flow profiles and anatomical throats tested was 63 ± 5%. Our findings indicate that the T-326 Inhaler provides reliable drug delivery at flow rates likely to be achieved by a broad spectrum of patients with CF. Importantly, forceful inhalation was not required to achieve a robust TLDin vitro . Pediatr Pulmonol. 2016;51:1159-1167. © 2016 Wiley Periodicals, Inc.

Direct numerical simulations of flow in realistic mouth–throat geometries

The flow in a set of four realistic mouth–throat geometries at a flow rate of 30L/min is studied in order to determine the effect of intrasubject and intersubject variations on the mean flow patterns and the turbulence fluctuations. Direct numerical simulations (DNS) are performed, which fully resolve all the scales in the flow, without requiring a turbulence model. An immersed boundary method is applied on curvilinear grids which simplifies the task of grid generation for the complex extrathoracic geometries and allows the use of a structured grid solver which increases the efficiency of the numerical scheme. Inspection of the mean, responsible for the convective transport of particles, and the fluctuating component of velocity, responsible for turbulent dispersion, allows us to explain in vitro deposition data in the literature obtained in the same mouth–throat models. The results provide insight as to how geometric variation affects aerosol deposition and explain the scatter in deposition data observed in the literature. Geometric variation is shown to have a large impact on both the mean velocity profiles and the turbulence intensities. Examination of the flow fields in the various mouth–throat geometries allows us to address the origin of the dependence of deposition on Reynolds number, and provide the physical significance of the empirical Reynolds number correction previously proposed in the literature.

Does the United States Pharmacopeia Throat Introduce De-agglomeration of Carrier-Free Powder from Inhalers?

We hypothesize that the USP induction port may de-agglomerate carrier-free powder emitting from dry powder inhalers (DPIs). Aerosols emitting from a range of DPIs (Spinhaler®, Turbuhaler® and Osmohaler™) and induction ports (USP throat, straight tube, Alberta idealized mouth-throat geometry (AG)) were sized by laser diffraction. Total drug recovery was obtained by HPLC and fine particle fraction computed. Air flow patterns were simulated using Computational Fluid Dynamics (CFD). The straight tube did not de-agglomerate emitted powder. However, the USP throat and AG further de-agglomerated powders from the Spinhaler, but not the Turbuhaler and Osmohaler. While budesonide powder deposited similarly in all induction ports, deposition was significantly higher in the AG for both DSCG and mannitol. CFD revealed agglomerates impacting on the USP throat with higher localized velocity compared with the straight tube. CFD further showed a more complex flow pattern with high-velocity air jets in the AG, which explains the higher FPF for DSCG and the lower FPF for mannitol using the AG. The USP throat further de-agglomerated the emitted powder from the DPI when it did not sufficiently disperse the powder. Other tools such as laser diffraction may be used for cross-examining to avoid artifacts in the results.

Development of a stochastic individual path (SIP) model for predicting the tracheobronchial deposition of pharmaceutical aerosols: Effects of transient inhalation and sampling the airways

While a number of studies have considered the dynamics of ambient or environmental particles in the respiratory tract, far fewer have evaluated the transport and deposition of pharmaceutical aerosols from inhalers in the mouth-throat (MT) and tracheobronchial (TB) airways. The objective of this study was to develop a new stochastic individual path (SIP) modeling approach for simulating the MT and TB deposition of a pharmaceutical aerosol from a dry powder inhaler and to evaluate the effects of transient vs. steady state conditions and sampling of the airways. In the SIP approach, representative models of the MT and upper TB geometries are considered through the third respiratory bifurcation (B3; approximately lobar bronchi). Stochastic individual paths are then evaluated extending from B4 to the terminal bronchioles (B15) in which one branch of each bifurcation is continued and one is not. Three SIP geometries were considered extending into the lower right lung lobe through the end of the conducting airways. A commonly prescribed dry powder inhaler (DPI) was connected to the MT geometry and the deposition of drug mass from a realistic polydisperse pharmaceutical aerosol was evaluated. Predictions of deposited drug mass in the MT and upper TB geometries were found to be in good agreement with concurrent experimental results. Transient inhalation was shown to influence the deposition of particles in the MT and upper TB airways through B3, where the Womersley number is greater than 1. In contrast, transient conditions were found to have little influence on deposition in the TB region starting with B4, where steady state simulations provided a good representation of total, regional, bifurcation-averaged, and localized deposition. Furthermore, a single SIP model was shown to characterize both regional and highly localized deposition within a lung lobe assuming mean airway dimensions. The resulting SIP model provides a highly efficient method to simulate the regional and local deposition of pharmaceutical aerosols throughout the conducting airways. In comparison with performing fully transient simulations of all branches in the regions considered, the SIP modeling approach reduces computational effort by a factor of approximately 3×10 5 while predicting regional and local deposition values to within approximately 5%.

Effects of Generation Time on Spray Aerosol Transport and Deposition in Models of the Mouth–Throat Geometry

For most newly developed spray aerosol inhalers, the generation time is a potentially important variable that can be fully controlled. The objective of this study was to determine the effects of spray aerosol generation time on transport and deposition in a standard induction port (IP) and more realistic mouth-throat (MT) geometry. Capillary aerosol generation (CAG) was selected as a representative system in which spray momentum was expected to significantly impact deposition. Sectional and total depositions in the IP and MT geometries were assessed at a constant CAG flow rate of 25 mg/sec for aerosol generation times of 1, 2, and 4 sec using both in vitro experiments and a previously developed computational fluid dynamics (CFD) model. Both the in vitro and numerical results indicated that extending the generation time of the spray aerosol, delivered at a constant mass flow rate, significantly reduced deposition in the IP and more realistic MT geometry. Specifically, increasing the generation time of the CAG system from 1 to 4 sec reduced the deposition fraction in the IP and MT geometries by approximately 60 and 33%, respectively. Furthermore, the CFD predictions of deposition fraction were found to be in good agreement with the in vitro results for all times considered in both the IP and MT geometries. The numerical results indicated that the reduction in deposition fraction over time was associated with temporal dissipation of what was termed the spray aerosol "burst effect." Based on these results, increasing the spray aerosol generation time, at a constant mass flow rate, may be an effective strategy for reducing deposition in the standard IP and in more realistic MT geometries.

Evaluation of the Respimat Soft Mist Inhaler using a Concurrent CFD and In Vitro Approach

The Respimat Soft Mist Inhaler is reported to generate an aerosol with low spray momentum and a small droplet size. However, the transport characteristics of the Respimat aerosol are not well understood. The objective of this study was to characterize the transport and deposition of an aerosol emitted from the Respimat inhaler using a combination of computational fluid dynamics (CFD) modeling and in vitro experiments. Deposition of the Respimat aerosol was assessed in the inhaler mouthpiece (MP), a standard induction port (IP), and a more realistic mouth-throat (MT) geometry at an inhalation flow rate of 30 L/min. Aerosols were generated using an albuterol sulfate (0.6%) solution, and the drug deposition was quantified using both in vitro experiments and a CFD model of the Respimat inhaler. Laser diffraction experiments were used to determine the initial polydisperse aerosol size distribution. It was found that the aerosol generated from the highly complex process of jet collision and breakup could be approximated in the model using effective spray conditions. Computational predictions of deposition fractions agreed well with in vitro results for both the IP (within 20% error) and MT (within 10% error) geometries. The experimental results indicated that the deposition fraction of drug in the MP ranged from 27 to 29% and accounted for a majority of total drug loss. Based on the CFD solution, high MP deposition was due to a recirculating flow pattern that surrounded the aerosol spray and entrained a significant number of small droplets. In contrast, deposition of the Respimat aerosol in both the IP (4.2%) and MT (7.4%) geometries was relatively low. Results of this study indicate that modifications to the current Respimat MP and control of specific patient variables may significantly reduce deposition in the device and may decrease high oropharyngeal drug loss observed in vivo.

Comparison of ambient and spray aerosol deposition in a standard induction port and more realistic mouth–throat geometry

For inhalation aerosols, it is well known that spray momentum and geometry characteristics can significantly influence deposition in the mouth–throat (MT) region. However, little is know about the quantitative influence of spray momentum on aerosol transport and deposition. The objective of this study was to evaluate the effect of spray momentum on deposition in a standard induction port (IP) and a representative MT geometry using capillary-generated aerosols. Capillary aerosol generation (CAG) was selected as a model spray aerosol system that has not been previously tested in a realistic throat geometry. To evaluate the effects of spray momentum, the transport and deposition characteristics of transient capillary-generated aerosols were compared with ambient particles of the same size inhaled at a steady flow rate of 30 L/min. To evaluate the influence of geometry, aerosols were considered in a standard IP and a more realistic MT model. A previously tested CFD model was employed to simulate aerosol transport and deposition for ambient and CAG spray aerosols in both the IP and MT geometries. Considering the capillary-generated spray, good agreement was observed for the deposition of drug mass between the in vitro experiments (IP—15.3%, MT—19.4%) and CFD model predictions without droplet evaporation (IP—14.7%, MT—20.8%). In all cases considered, deposition was increased for spray vs. ambient aerosols and in the MT geometry vs. the IP model. Based on CFD results for a representative polydisperse aerosol distribution, the deposition of ambient particles was highly sensitive to the geometry considered, with 2.9 times more deposition in the MT compared to the IP model. In contrast, deposition was less influenced by the geometry for a CAG spray aerosol, with only a 25–40% deposition increase in the MT. As a result, use of the simple IP model may provide a reasonable approximation of total MT deposition for systems with high spray momentum. However, the IP model may be less useful for evaluating the total MT deposition in systems with reduced spray momentum effects.

Turbulent particle dispersion in arbitrary wall-bounded geometries: A coupled CFD-Langevin-equation based approach

A Lagrangian continuous random walk (CRW) model is developed to predict turbulent particle dispersion in arbitrary wall-bounded flows with prevailing anisotropic, inhomogeneous turbulence. The particle tracking model uses 3D mean flow data obtained from the Fluent CFD code, as well as Eulerian statistics of instantaneous quantities computed from DNS databases. The turbulent fluid velocities at the current time step are related to those of the previous time step through a Markov chain based on the normalized Langevin equation which takes into account turbulence inhomogeneities. The model includes a drift velocity correction that considerably reduces unphysical features common in random walk models. It is shown that the model satisfies the well-mixed criterion such that tracer particles retain approximately uniform concentrations when introduced uniformly in the domain, while their deposition velocity is vanishingly small, as it should be. To handle arbitrary geometries, it is assumed that the velocity rms values in the boundary layer can locally be approximated by the DNS data of fully developed channel flows. Benchmarks of the model are performed against particle deposition data in turbulent pipe flows, 90° bends, as well as more complex 3D flows inside a mouth-throat geometry. Good agreement with the data is obtained across the range of particle inertia.

A CFD model for particle dispersion in turbulent boundary layer flows

In Lagrangian particle dispersion modeling, the assumption that turbulence is isotropic everywhere yields erroneous predictions of particle deposition rates on walls, even in simple geometries. In this investigation, the stochastic particle tracking model in Fluent 6.2 is modified to include a better treatment of particle–turbulence interactions close to walls where anisotropic effects are significant. The fluid rms velocities in the boundary layer are computed using fits of DNS data obtained in channel flow. The new model is tested against correlations for particle removal rates in turbulent pipe flow and 90° bends. Comparison with experimental data is much better than with the default model. The model is also assessed against data of particle removal in the human mouth–throat geometry where the flow is decidedly three-dimensional. Here, the agreement with the data is reasonable, especially in view of the fact that the DNS fits used are those of channel flows, for lack of better alternatives. The CFD Best Practice Guidelines are followed to a large extent, in particular by using multiple grid resolutions and at least second order discretization schemes.

Experimental Measurement and Numerical Study of Particle Deposition in Highly Idealized Mouth-Throat Models

Particle deposition in the human mouth-throat is an important factor in evaluating efficiency of drug delivered by inhalation devices, such as pMDIs or DPIs. Current USP standard impactor induction ports (which serve as an in vitro representative of the adult mouth-throat) underpredict in vivo mouth-throat deposition. However, preliminary experimental data in the prototype geometry of a highly idealized mouth-throat has indicated that it is a promising replacement for the USP mouth-throat (Zhang et al. 2004). In this study, partial optimization design of the highly idealized mouth-throat was performed using computational fluid dynamics (CFD) simulations. The performance of six candidate highly idealized mouth-throat geometries, each with a straight tube inlet of inner diameter 17.3 mm, was evaluated experimentally by measuring monodisperse particle deposition efficiency. Gravimetry was used to determine particle deposition in these geometries. Monodisperse particles of di-2-ethylhexyl-sebecate (DEHS) oil ...