Mouth-throat Geometry Research Articles

Experimental Measurements of Particle Deposition in Three Proximal Lung Bifurcation Models with an Idealized Mouth-Throat

In this paper, particle deposition in three idealized proximal lung bifurcation models with an idealized mouth-throat were investigated experimentally. These bifurcation models included (1) a small symmetric bifurcation, (2) an intermediate asymmetric bifurcation, and (3) a large symmetric bifurcation. An idealized mouth-throat geometry (the "Alberta geometry") was used as the inlet to these bifurcation models. Monodisperse aerosol particles of DEHS (di-2-ethylhexyl-sebecate) oil with mass median diameters in the range of 2.5-7.5 microm were employed at steady flow rates of 30-90 L/min. Particle deposition measurements were conducted by gravimetry. The results show that particle deposition in the mouth-throat and trachea accounts for the major portion of total deposition in the entire models used, and particle deposition fraction in the proximal lung bifurcations is lower compared with that deposited in the regions upstream (the mouth-throat and the trachea). Total particle deposition efficiency increases with increasing either inertial parameter or Stokes number. Total particle deposition varies appreciably from model to model. The laryngeal jet is the key factor dominating particle deposition within the trachea. An effect of Reynolds number on particle deposition efficiency in the trachea is observed. In addition, particle deposition in the bifurcation region is influenced little by the upstream flow condition, and therefore the effect of the laryngeal jet on deposition seemingly does not propagate to the bifurcations downstream.

In vitro intersubject and intrasubject deposition measurements in realistic mouth–throat geometries

This paper presents regional and total deposition measurements in several realistic mouth and throat geometries and demonstrates the effects of intrasubject and intersubject variations in geometry on deposition efficiency. A set of seven geometries that span the range of key dimensions of a larger set of 80 geometries were studied at flow rates of 30 and 90 l/ min and particle diameters of 3– 6.5 μm . The models were obtained using magnetic resonance imaging scans. Gamma scintigraphy and gravimetry were used to determine deposition. The models were subdivided into regions corresponding to the mouth, oropharynx, larynx and trachea. The results indicate that both total and regional deposition exhibit large intersubject differences, but also show some intrasubject difference. A mean equivalent diameter D mean = 2 V/πL (where V is mouth–throat volume, L is centerline path length), and corresponding velocity U mean=4 Q/ πD mean 2 (where Q is inhalation flow rate) are used as the length and velocity scale in defining a Stokes number, Stk. In addition, an effect on deposition due to flow Reynolds number, Re was noticed. When plotted vs. Stokes number with inclusion of this Reynolds number effect, the total deposition data from all the different geometries collapse onto essentially a single curve, given by: η=100– 100/(11.5 Stk 1.912 Re 0.707+1) for the parameter range explored, where η is the percent of inhaled aerosol depositing in the mouth–throat.

Particle deposition measurements and numerical simulation in a highly idealized mouth–throat

A new highly idealized mouth–throat that mimics in vivo deposition in the human oropharynx is proposed in the present study. Deposition of aerosols with mass median diameters of approximately 2.5, 5.0, and 6.0 μm is studied experimentally in the proposed highly idealized mouth–throat and two standard USP throats (described in the United States Pharmacopeia, 1995 and 2000, respectively) for steady inhalation flow rates of 30, 60 and 90 l/min . Gravimetry is used to measure aerosol deposition in these geometries. Both USP throats show curves of total deposition efficiency that are far below the in vivo average curve (J. Aerosol Med. 2(3) (1989) 285), revealing the inadequacy of the USP throats in replicating realistic mouth–throat geometries. On the contrary, the new proposed highly idealized mouth–throat geometry follows the in vivo average curve and is therefore an excellent candidate for use as a standard in the pharmaceutical field, replacing the available and inadequate USP throats. In addition to the above measurements, numerical simulation of aerosol deposition using computational fluid dynamics (CFD) techniques is also performed. Reynolds averaged Navier–Stokes (RANS) equations with a k– ω turbulence model are used to solve the primary flow and a Lagrangian random-walk eddy interaction model with near-wall correction (J. Aerosol Sci. 35 (2004) 1) is applied in the tracking of individual particles in the highly idealized mouth–throat. The total deposition results obtained from CFD simulation show relatively good agreement when compared with the measured data.

Improved numerical simulation of aerosol deposition in an idealized mouth–throat

The deposition of monodisperse particles (1.0– 26.0 μm diameter) in an idealized mouth–throat geometry has been studied numerically. The continuous phase flow is solved using a RANS (Reynolds averaged Navier–Stokes) turbulence model at inhalation flow rates of 90.0 and 30.0 l/ min . The particulate phase is simulated using a random-walk/Lagrangian stochastic eddy-interaction model (EIM). Without near-wall corrections in the EIM, poor agreement is seen with experimental data on deposition. However, when a new near-wall correction in the EIM is implemented, the particle deposition results in the idealized mouth–throat geometry are in relatively good agreement when compared with measured data obtained in separate experiments.

On the suitability of k– ε turbulence modeling for aerosol deposition in the mouth and throat: a comparison with experiment

Deposition of a polydisperse aerosol (MMD=4.8 μm, GSD=1.65) in a replica of a human mouth–throat is measured experimentally and compared to predicted results using computational fluid dynamics (CFD). The mouth–throat geometry represents an idealized, average mouth–throat. Experimental values of the fraction η of aerosol depositing in this mouth–throat are obtained using a radiolabelled, nebulized aerosol generated with a Pari LC+ nebulizer. Gamma scintigraphy is used to measure amounts of aerosol depositing at laminar (2 l min −1) and turbulent (28.3 l min −1) flow rates. Deposition is predicted computationally using a commercial CFD code (TASCflow) for these two flow rates. For the turbulent case, the standard k– ε turbulence model was used with the most common eddy lifetime model for turbulent particle dispersion [Gosman and Ioannides (1983) J. Energy 7, 482–490]. Good agreement between experiment and simulation is found for laminar flow (experiment: η=15.7±0.3%, simulation η=16%), but not for turbulent flow (experiment: η=25.6±0.7%, simulation η=65%). Measured and predicted pressure drops agree well for laminar flow (experiment: 0.26±0.02 Pa, simulation: 0.25 Pa), but differ less dramatically for the turbulent case than does deposition (experiment: 25.2±0.5 Pa, simulation: 22.3 Pa), indicating that accurate prediction of particle deposition in this geometry requires more accurate prediction of the fluid dynamics than can be obtained with the present turbulence model