Combined inertial and gravitational deposition of microparticles in small model airways of a human respiratory system

Focusing on relatively small airways in terms of the medium-size bronchial generations G6–G9, the interplay of impaction and sedimentation on micron particle transport and deposition has been simulated. A commercial finite-volume code, enhanced with user-supplied programs, has been employed. Although impaction is still a dominant deposition mechanism for microparticle in medium-size airways under normal breathing conditions (say, Qin=15–30L/min), sedimentation may play a role as well. In turn, that can influence the local particle deposition patterns, efficiencies and fractions for a realistic range of Stokes numbers (0.001⩽St⩽0.33)(0.001⩽St⩽0.33). However, deposition due to sedimentation is significantly amplified during slow inhalation; for example, the gravitational deposition may become dominant in the ninth bifurcation (i.e., generations G8–G9) for relatively large microparticles (say, dp>5μm) at Qin=3.75L/min. The occurrence of sedimentation changes the location of the deposition “hot spots” and reduces the order of the maximum deposition enhancement factor. The use of analytical formulas based on inclined tube models for predicting gravitational deposition in local bronchial airway segments as well as the combination of deposition by sedimentation and impaction has to be carefully examined. As shown, more prudent is the use of curve-fitted correlations generated from experimentally validated computer simulation results as a function of Stokes number and sedimentation parameter.