Fine particulate matter (PM2.5) produced from traffic-loaded urban areas, combustion processes during industrial processes, and dust resuspension during mechanical disturbances may cause considerable health hazards when it is inhaled, owing to an enhanced accumulation of this particulate material in the lung. While the in-plane airway structures of human lungs are usually used in numerical models, a 3D out-of-plane layout that can geometrically represent triple bifurcations airways of the so-called Weibel model is developed in the present study with the presence of fine particles inside. For in-plane airways, the centerlines of all generations always lie on the same plane. In contrast, 3D out-of-plane is typical of the centerline of each descendant generation that rotates 90° to the centerline of its grandmother generation. Given three different breathing conditions, ranging between 15 L min–1 and 60 L min–1, the sizes of the deposition particles considered herein vary from 0.3 µm to 0.75 µm. The numerical results are discussed in terms of the airflow patterns (e.g., streamlines and velocity contours and vectors), the particle deposition patterns, deposition fractions (DFs) in different sections of the lung, the correlation between Stokes number and total DFs, and the correlation between the total DFs and the PM2.5 diameters. The predictions in Generations 8 to 12 (G8–G12) reveal that deposition fractions (DFs) increase with respiration frequency and intensity. It is also observed that the more anterior the bronchus is, the more significant the particle deposition is, regardless of the respiratory state. Also, the total DF tends to increase as the particle size decreases. This will lead to the development of subsequent tracheal atrophy.
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