Numerical Simulation Of Inhalable Particles Deposition In The Alveolus

Airborne particles in air, which may cause illness of the human respiratory tract such as bronchitis and emphysema, aggravate cardiovascular diseases and asthma attacks, and decrease lung function after being inhaled into body, have become a main factor for air pollution. On the other hand, more and more nebulizers are adopted to cure respiratory diseases such as asthma. Thus, good knowledge of airflow structure, movement, dispersion, and deposition of aerosols in the gas exchange region is very important. In order to effectively simulate the particle movement and deposition, direct numerical simulation (DNS) method is adopted and the particles are tracked in the frame of Lagrange. The contents of this thesis can be divided into the following three parts.The first part discusses the effects of alveolar contraction/expanding on the flow field and particles deposition. The results reveal that alveolar contraction/expanding makes the fluid in the alveolus and bronchiole exchange easily. The influence of alveolar contraction/expanding on the submicron particles is much larger than the Brownian force and thus the submicron particles are likely to move into the alveolar cavity and finally deposit on the alveolar wall.The second part explores the impact of the amount of alveolar elastic deformation on the flow field and particle transport and deposition. The results show that the effect of different alveolar elastic deformation on the flow field intensity and the streamlines distribution within the alveoli is almost negligible. The amount of alveolar elastic deformation has a small influence on the particle transport, but which has a great influence on the deposition of submicron particles (dp< 1.0μm). The amount of alveolar elastic deformation has a great influence on the deposition efficiency of submicron particles (dP< 0.1μm) and large-scale micron particles (dp≥5.0μm), specifically, large alveolar elastic deformation will decrease the deposition efficiency of 0.1μm particles and small alveolar elastic deformation will decrease the deposition efficiency of 5.0μm particles.The third part discusses the effects of particle size and the respiratory cycle on particles deposition. The results reveal that the submicron particles are dominated by Brownian force and which distribute evenly in the alveolar cavity. The deposition of small-scale micron-meter particles (1.0μm～2.5μm) are governed by the drag force, so this kind of particles are easy to be convective. The deposition of large-scale micron particles (5.0μm) are dominated by the gravity, so this kind of particles are easy to precipitate. The respiratory cycle has a strong influence on the transient distribution of mesoscale (1.0μm～2.0μm) particles. The larger the respiratory cycle is, the mainstream decay more slowly. But the respiratory cycle nearly has no effect on the particles deposition.