Inertial deposition of aerosols in bifurcating models during steady expiratory flow

The deposition of respiratory aerosols during the expiratory phase of breathing may be significant. However, only a limited number of studies have considered the effects of exhalation on aerosol deposition in bifurcating respiratory geometries. In this study, double bifurcation models of respiratory generations G3–G5 and G7–G9 were used to determine the deposition of aerosols in the size range of 1–7μm during steady exhalation. The geometries considered were based on standard and 30% constricted pediatric airway models. A previously tested CFD code was implemented to predict aerosol deposition under laminar flow conditions. Results indicated that deposition in bifurcating airways during expiration was a function of the Stokes number, which represents particle inertia, and the Dean number, which captures the strength of secondary flow conditions. For a Dean number of approximately 10, deposition was observed to decrease with increasing values of the Stokes number. Increasing the Dean number above approximately 100 resulted in a significant increase in deposition for constant Stokes number values. Existing algebraic correlations did not capture the effects of the Dean number on deposition during exhalation. As a result, novel correlations were proposed that predicted branch-averaged deposition efficiency as a function of both Stokes and Dean numbers. Implementation of these correlations into whole-lung models is suggested to improve the prediction of deposition during exhalation under laminar expiratory conditions in bifurcating airways.