PARTICLE DEPOSITION IN AIRWAY BIFURCATIONS .2. EXPIRATORY FLOW

In the present analysis, local inhomogeneities of particle deposition are examined in a bifurcation geometry under realistic expiratory flow conditions, considering the simultaneous effects of inertial impaction, gravitational settling, Brownian motion and interception. The airflow field within the bifurcation during expiration is obtained by solving the Navier-Stokes equations on a three-dimensional computer mesh with a finite-difference technique. Knowledge of the velocity field allows us to simulate the trajectories of aerosol particles entrained in the airstream with Monte Carlo methods. The spatial deposition pattern within the bifurcation is then determined by the intersection of particle trajectories with the surrounding wall surfaces. The effects of particle size, flow rate, inlet flow profile, and bifurcation geometry on the spatial deposition pattern are investigated. In most cases, hot spots are found downstream of the central bifurcation zone. Model predictions are compared with the available experimental data and with other theoretical results.