The flow theory and air flow structures in symmetric double-bifurcation airway models assuming steady laminar, incompressible flow, unaffected by the presence of aerosols, has been described in a companion paper (Part 1). The validated computer simulation results showed highly vortical flow fields, especially around the second bifurcations, indicating potentially complex particle distributions and deposition patterns. In this paper (Part 2), assuming spherical non-interacting aerosols that stick to the wall when touching the surface, the history of depositing particles is described. Specifically, the finite-volume code CFX (AEA Technology) with user-enhanced FORTRAN programs were validated with experimental data of particle deposition efficiencies as a function of the Stokes number for planar single and double bifurcations. The resulting deposition patterns, particle distributions, trajectories and time evolution were analysed in the light of the air flow structures for relatively low (ReD1 = 500) and high (ReD1 = 2000) Reynolds numbers and representative Stokes numbers, i.e. StD1 = 0.04 and StD1 = 0.12. Particle deposition patterns and surface concentrations are largely a function of the local Stokes number, but they also depend on the fluid–particle inlet conditions as well as airway geometry factors. While particles introduced at low inlet Reynolds numbers (e.g. ReD1 = 500) follow the axial air flow, secondary and vortical flows become important at higher Reynolds numbers, causing the formation of particle-free zones near the tube centres and subsequently elevated particle concentrations near the walls. Sharp or mildly rounded carinal ridges have little effect on the deposition efficiencies but may influence local deposition patterns. In contrast, more drastic geometric changes to the basic double-bifurcation model, e.g. the 90°-non-planar configuration, alter both the aerosol wall distributions and surface concentrations considerably.

Deposition patterns and efficiencies of a dilute suspension of inhaled particles in three-dimensional double bifurcating airway models for both in-plane and 90 deg out-of-plane configurations have been numerically simulated assuming steady, laminar, constant-property air flow with symmetry about the first bifurcation. Particle diameters of 3, 5, and 7 microns were used in the simulation, while the inlet Stokes and Reynolds numbers varied from 0.037 to 0.23 and 500 to 2000, respectively. Comparisons between these results and experimental data based on the same geometric configuration showed good agreement. The overall trend of the particle deposition efficiency, i.e., an exponential increase with Stokes number, was somewhat similar for all bifurcations. However, the deposition efficiency of the first bifurcation was always larger than that of the second bifurcation, while in general the particle efficiency of the out-of-plane configuration was larger than that of the in-plane configuration. The local deposition patterns consistently showed that the majority of the deposition occurred in the carinal region. The distribution pattern in the first bifurcation for both configurations were symmetric about the carina, which was a direct result of the uniaxial flow at the inlet. The deposition patterns about the second carina showed increased asymmetry due to highly nonuniform flow generated by the first bifurcation and were extremely sensitive to bifurcation orientation. Based on the deposition variations between bifurcation levels and orientations, the use of single bifurcation models was determined to be inadequate to resolve the complex fluid-particle interactions that occur in multigenerational airways.

Transport and deposition of ultrafine particles in straight, bent and bifurcating tubes are considered for different inlet Reynolds numbers, velocity profiles, and particle sizes, i.e., 1 nm⩽dp⩽150 nm. A commercial finite-volume code with user-supplied programs was validated with analytical correlations and experimental data sets for nanoparticle depositions, considering a straight tube, a tubular 90° bend, and a G3-G5 double bifurcation with both planar and nonplanar configurations. The focus is on the airflow structures as well as nanoparticle deposition patterns and deposition efficiencies, which were analyzed for planar and nonplanar bifurcating lung airway models representing part of the upper bronchial tree. Deposition takes place primarily by Brownian diffusion, and thus deposition efficiencies increase with decreasing nanoparticle size and lower inlet Reynolds numbers. Deposition in the nonplanar configuration differs only slightly from that in the planar configuration. When compared with axisymmetric inlet conditions, the more realistic, skewed inlet velocity and particle profiles generate nearly axisymmetric deposition patterns as well. This work may elucidate basic physical insight of ultrafine particle transport and deposition relevant to environmental, industrial and biomedical studies.