Deposition of Inhaled Particles in Bifurcating Airway Models: II. Expiratory Deposition

Abstract

Deposition efficiency of aerosol particles in the bifurcating airways during expiratory phase was investigated by using single bifurcation tube models with different branching angles (θ=15, 30 and 45°) for both symmetric and asymmetric branching geometry. Monodisperse oleic acid droplets (3, 5, and 7 μm dia) tagged with uranine were used as test aerosols, and flow regimes were maintained in Reynolds number of 566-5945. Deposition pattern within the branching tube model was also determined by eluting uranine tracer from different sections of the model. Particle deposition occurred principally in a short section of the parent tube immediately proximal to the bifurcation and increased with increasing flow rate, particle size, or branching angle. Deposition efficiency was uniquely correlated with Stokes number (St_k) and monotonically increased with a single parameter, √Stk.sinθ. These results and the mechanism of expiratory deposition in the branching airways were discussed in conjunction with previous results for inspiratory flow and theoretical predictions.