Numerical Simulation Of The Particle Transport And Deposition In Human Tracheobronchial Airways

According to epidemiological study, the increase of airborne particle pollution is highly associated with the increase of occurrence and mortality of pulmonary and cardiovascular diseases. Pulmonary toxicology shows that the inhaled particles can do harm to human health by series of behaviors, such as deposition and absorption. Human respiratory system is the main way to expose to the particulate matter, part of which can be deposited in the human lung airways, and then cause some adverse health effects, such as chronic obstructive pulmonary diseases (COPD) and asthma. On the other hand side, inhaling aerosol therapy is recognized as a most promising route for treating the respiratory diseases worldwide. However, it's still unknown how to target the aerosol drug to the disease sites and improve the treatment effect. Thus knowledge of particle transport and deposition in human respiratory system is essential for quantitatively understanding the exposure risk and dose-health effect of particles, as well as for improving the inhaling therapy efficacy.Computational fluid dynamics (CFD) simulations were conducted in the triple-bifurcation geometry representing the human tracheobronchial tree to make the study. Three models were established, they are healthy planar, healthy nonplanar and obstructive planar triple-bifurcation airway models derived from the 3rd to 6th generation of Weibel A (1963) model. Euler and Lagrange methods were selected to simulate the airflow pattern and particle trajectory respectively. Three dimensional N-S equations and Newton's second law were taken as the control equations. Reynolds number, particle diameter, and deposition mechanisms were chosen as the major factors which influence the airflow structure and particle deposition pattern. Thus in this paper, the influences of these factors on the three physical models were computed and analyzed by changing the Reynolds number, particle diameter and deposition mechanisms.Research shows that achievement of the airflow structure is the basic knowledge for understanding the particle transport and deposition patterns. Airflow structures, including axial velocity and secondary velocity, can influence the particle deposition patterns. Particles mainly deposit at the inner wall of the tubes which experience the higher axial flow rate and stronger inward secondary velocity. For particles in different diameters, deposition efficiencies (DE) are in different increasing tendencies, and the deposition mechanisms are different. For the three different physical models, the characteristics of airflow and particle deposition are distinctly different from each other, due to the different configurations. For patients of obstructive airways, e.g. chronic obstructive pulmonary diseases (COPD), the efficacy of the inhaling therapy is highly affected by the aerosol diameter and the respiratory rate.