Effects of curved inlet tubes on air flow and particle deposition in bifurcating lung models

In vivo bifurcating airways are complex and the airway segments leading to the bifurcations are not always straight, but curved to various degrees. Ho w do such curved inlet tubes influence the motion as well as local depositi on and hence the biological responses of inhaled particulate matter in lung airways? In this paper steady laminar dilute suspension flows of micron-pa rticles are simulated in realistic double bifurcations with curved inlet tu bes, i.e., 0 degrees less than or equal to theta less than or equal to 90 d egrees, using a commercial finite-volume code with user-enhanced programs. The resulting air-flow patterns as well as particle transport and wall depo sitions were analyzed for different flow inlet conditions, i.e., uniform an d parabolic velocity profiles, and geometric configurations. The curved inl et segments have quite pronounced effects on air-flow, particle motion and wall deposition in the downstream bifurcating airways. In contrast to strai ght double bifurcations, those with bent parent tubes also exhibit irregula r variations in particle deposition efficiencies as a function of Stokes nu mber and Reynolds number. There are fewer particles deposited at mildly cur ved inlet segments, but the particle deposition efficiencies at the downstr eam sequential bifurcations vary much when compared to those with straight inlets. Under certain flow conditions in sharply curved lung airways, relat ively high, localized particle depositions may take place. The findings pro vide necessary information for toxicologic or therapeutic impact assessment s and for global lung dosimetry models of inhaled particulate matter. (C) 2 001 Elsevier Science Ltd. All rights reserved.