Dispersion of aerosol bolus during one respiration cycle in a model of lung airways

The dispersion of an aerosol bolus for one complete respiration cycle is analyzed numerically, using a lung airway model with four successive bifurcations. Unsteady Navier–Stokes equation and diffusion equation are solved by CFX-F3D, an FVM commercial code. Reynolds number based on the inlet conditions is varied between 0.533 and 24, and Womersley number between 0.0915 and 0.495, which correspond to the flow conditions in the 10th to the 18th generations of Weibel model at typical conditions of bolus experiments (tracheal breathing rate of 0.25 l/s, respiration period of 8 s and 0.8 μm particle size). The dispersion characteristics during the inhalation period are seen the same as in steady inhalation, the total dispersion increasing monotonically with inhalation. When flow direction is reversed to exhalation, bolus dispersion decreases with exhalation at first, but comes to increase again at a rate almost equal to that for steady exhalation after a certain amount of exhalation. The maximum reduction of bolus dispersion after flow reversal is comparable to the increase of bolus dispersion in the last generation just before flow reversal.