Two-phase flow dynamics and PM_2.5 deposition in healthy and obstructed human airways during inhalation

Lately, there has been an unexpected increase in the global burden of diseases due to inhalation of ambient air contaminated with fine particulate matter (PM_2.5). The adverse effects due to inhalation of PM_2.5 are more exaggerated for patients with obstructive lung diseases such as Chronic obstructive pulmonary disease (COPD). In this study, numerical investigations were carried out on the effects of particle diameters and different Reynold numbers at the inlet on deposition patterns and fractions in COPD patients and healthy individuals. Three real and transient inhalation curves with average Reynolds numbers of 164.3, 362.4, and 606.4 were used to represent rest, light activity, and moderate exercise inhalation statuses. Four median diameters including 0.075 µm, 0.15 µm, 0.3 µm, and 0.6 µm were injected at the inlet of the control volume (G5–G8) of the Weibel’s lung geometry to represent the particle size distribution for a PM_2.5 concentration of 50 µg m^–3. Deposition fractions and patterns were obtained from tracking a total of 350031, 692596, and 833553 PM_2.5 particles corresponding to rest, light activity and, moderate exercise respectively. Deposition fractions (DFs) for the different sizes of PM_2.5 ranged between 0.12% and 1.18% in the healthy airway geometry and between 0.05% and 0.49% in the COPD case. The deposition patterns were skewed for a COPD case due to jet flow phenomena, skewed mass flow rates, and the induced dean vortices. While depositions at the carina regions could be attributed to inertial impaction, those along the bifurcations could be attributed to centrifugal forces, complex secondary flows, and inertial impaction. The effects of the deposition mechanisms varied between the two geometries, among different particle diameters and inhalation statuses.