Nanoparticle transport and deposition in the large
conducting airways using CFD

Abstract: While the benefits and possibilities of nanotechnology have received
considerable attention, the adverse health effects that may follow with
widespread use have not until recently been illuminated. Recent studies
have shown that nanoparticles, due to their smaller size and thereby bigger
surface area and surface reactivity, can be more toxic than larger
particles of the same material. However, the risks associated with the use
of nanoparticles also depend on the extent of exposure. In this thesis, the
effects upon inhalation are studied. In vivo and in vitro studies would be
very cost-intensive and difficult to perform for the study of particle
transport and deposition in the human airways. Therefore, numerical
simulations are increasingly being carried out together with validating
experiments when possible.

The influence of particle size is studied on transport and deposition
patterns in a rigid, smooth-walled model of the human airways, extending
from trachea to the segmental bronchi. The morphometrical data is based on
the asymmetric lung model of Horsfield et al. (1971). Particle deposition
efficiency and localisation is compared for particles (density = 1950
kg/m^3) in the size range 0.015-100 micrometres at inspiratory flow rates
of 0.1-1.0 l/s, measured at trachea. The commercial Computational Fluid
Dynamics (CFD) software package ANSYS CFX 10.0 is used for analysis. A
Lagrangian multiphase model approach is employed, and one-way coupling is
used between the continuum and dispersed phase, which allows particle
tracking to be run as a Post-process. Steady, laminar, 3-dimensional flow
is simulated and forces included are drag and gravity. The sizes of
systematic errors are estimated, allowing analysis of accuracy of the
results. Particle size has substantial influence on deposition, regarding
both efficiency and localisation. Deposition mainly occurs by inertial
impaction, and gravity can be neglected at higher flow rates. Deposition
generally increases with increase in particle size and flow rate. The major
part of the larger microparticles are captured at the first bifurcation,
while smaller microparticles are deposited less efficient, but more
uniformly throughout the model. The nanoparticles essentially follow the
streamlines through the model, and only a few percent are deposited in the
region modelled. Deposition patterns are affected by geometrical asymmetry,
and local deposition fractions differ up to 25 % between bifurcation units
of the same generation.