Study On The Mechanism Of The Movement And Deposition Of Haze Particles In The Respiratory Tract

With the popularity of automotive and other industrial products, as well as the frequent occurrence of sand storm and other disasters, the world is facing an increasingly serious problem of air pollution now. The phenomenon of fog and haze occurs frequently, the prevalence of respiratory diseases increased significantly. The study of the mechanism of the movement and deposition of haze particles in human respiratory tract, is of great significance and theoretical value to the research of physiology and pathology. With the method of computational fluid dynamics, we established a gas-solid two phase flow model. At the same time, including the coupling mechanism of the cilia driven movement of mucus flow, the motion model of particles in mucociliary system was established, and the related numerical simulation was carried out. Not only discussed the mechanism of particle deposition in the macro field, but also had a research on the movement law of particles in the microcosmic field. Through the comparison with the existing experimental data and literature, proved the effectiveness and correctness of the model and the calculation method.Firstly, this paper expounded the basic theory of the computational fluid dynamics, established a gas-solid two phase model for the movement of particles in the respiratory tract, selected Large Eddy Simulation to describe the movement of air in the human airway, with the analysis of the force distribution of particles in the air stream, selected DPM model to track the trajectories of particles in the respiratory tract.Secondly, based on the physical model of human upper respiratory tract, established the rigid and flexible wall model of human upper airway. Had a research on the motion characteristics of air in the human airway, with the respiration intensity of 30L/ min and 90L/ min, in steady and circulation breathing model, and drew the following conclusions: due to the limitation of the geometrical structure of the respiratory tract, the airflow produced turbulent jet phenomenon at the glottis, and separated in supraglottic near the downstream of the tracheal wall with a backflow phenomenon; during the inspiration in the circulation breathing method, the axial airflow velocity increased in the respiratory tract, produced a more obvious phenomenon of the vortex in the pharyngeal and glottal downstream tracheal wall; airway wall had a displacement and deformation for the interaction between fluid and solid, in the floor of the mouth and throat, due to the phenomenon of expansion, the velocity of the flow declined.On this basis, had a research on the deposition rules of particles with size of 0.3um,2.5um and 6.5um, and considering the influence of different particle concentration on the particle deposition, which proved that : the size of particle diameter and the respiration intensity are the main two factors for the deposition of particles. The deposition mechanism of particle with different size is not the same, the turbulent diffusion and eddy entrainment are the main factors for the deposition of particles with size of 0.3um; inertial collision is the main factor for particle with the diameter of 6.5um; for the deposition of particle with size of 2.5um, the effect of inertial impaction and turbulent diffusion is very obvious.Finally, had a research on the deposition of PM2.5 in the bronchus area. Due to the movement rules of the cilia, established a movement model for the cilia; with the distribution of the mucus, established a mucus model with free surface boundary using the method of VOF. Considering the phenomenon of the cilia cluster, established the airway mucociliary system with the effect of the coupling between fluid and solid, to study the movement of the mucus layer and attached particles, the calculation results showed that the particles were effected by the “clear” mechanism in the Mucociliary system.