Characteristics of particle transport in an expanding or contracting alveolated tube

Features of flow and particle transport in a single axisymmetric alveolated tube with 30 cells in the presence of wall motion are analyzed numerically for flow conditions typically found in the Aerosol Bolus experiments: the tracheal breathing flowrate of 250 ml/s and breathing period of 8 s. Different characteristics of particle transport between the alveolated and the straight tube are explained based on the details of flow and particle motion. For both expansion and contraction the axial motion of particles in an alveolated tube is smaller than in a straight tube due to the decelerated flow in the alveolated region. In an expanding alveolated tube particles get accumulated near the wall and some particles enter alveolus, which make dispersion larger than that in an expanding straight tube. In a contracting alveolated tube particles consistently move toward the tube center, and flow velocity profile is much blunter than the parabolic one, making dispersion smaller than in a contracting straight tube. In the presence of wall motion, the difference in particle transport between alveolated tube and straight tube becomes larger as Strouhal number is increased. Limitations and physiological implications of the results are discussed.