Gas–solid two-phase flow in a triple bifurcation lung airway model

Abstract Laminar oscillatory flow as well as micron-particle transport and wall deposition in a triple bifurcation airway model have been simulated using a validated finite-volume code with user-enhanced programs. Three realistic breathing patterns, i.e., resting, light activity and moderate exercise, were considered. Transient air flow, particle transport, and wall deposition results are shown and summarized in terms of regional particle deposition efficiencies (DEs). The effects of skewed inlet profiles on the flow field and particle deposition were recorded as well. Particle deposition may increase under cyclic flow conditions, i.e., DE-values are typically larger for cyclic flow than for steady flow evaluated at the mean flow rate of a given inhalation or exhalation pulse. While particles deposit mainly around the carinal ridges, i.e., flow dividers, during inspiratory flow due to direct impaction, they deposit on the tubular surfaces during exhalation because of strong secondary flows. Moreover, particle deposition during exhalation is much lower than for inhalation at the same local Stokes number. The comparisons of DEs among different lung generations or bifurcation areas for both cyclic inhalation and exhalation show that DEs in the third bifurcation region may be quite different from those at previous bifurcations due to upstream geometry and flow effects.