| Human daily activities require constant intake of oxygen from Surrounding environment air,but industrial productions release large amounts of fine particulate matters into the environment,which is complex in composition and can move with the motion of air.Some of these particles enter the respiratory system along with the gas,causing respiratory diseases in humans.Respiratory diseases are common and frequent,posing a serious threat to human health.The study of the pathogenesis and effective treatment of respiratory diseases has received increasing attention in recent years.Therefore,the study of the airflow and particle motion in the respiratory tract under different health conditions has an important significance and implication in the academic research and clinical application.To interrogate the airflow and particle movement characteristics in the nasal cavity,this thesis is based on the commercial software platform Ansys Fluent,using the transition SST turbulent model in Computational Fluid Dynamics(CFD)to simulate the airflow in the nasal cavity under different conditions(respiratory intensity,temperature,relative humidity).The Discrete Phase Model(DPM)is used to analyze the movement status of particles in different sections of the nasal cavity when the force and density changed.The main innovations of this thesis include the following:(1)Based on clinical images and data,the geometric models of nasal cavity under different perforation states were constructed,and the influence of the change of airflow status on the relative humidity of nasal septum perforation site was simulated under real external condition.(2)For the particles in the nasal cavity,single-component liquid particles and multi-component particles with evaporable components were selected.Numerical simulations of the deposition and evaporation efficiencies of in the nasal cavity under different perforation conditions have been performed under varying temperature and relative humidity conditions.The main conclusions are:(1)The complex internal structure of the nasal cavity leads to the formation of sophisticated reversal and vortex structures.Perforations inside the respiratory tract produce significant vortex structures,and the impact of nasal septum perforations with a larger diameter(10mm)at the nasal valve region on the relative humidity of the nasal septum wall.The airflow patterns inside the respiratory tract is most significant among different perforation positions of the nasal septum.(2)For solid particles,as breathing intensity and particle size increase,the particle deposition efficiencies(DE)gradually increases.Compared to other perforated areas,small particle sizes are more likely to enter the lower respiratory tract when passing through larger diameter perforations(10mm)in the nasal septum.The deposition distribution of multi-component particles is similar to that of solid particles,with large particle sizes deposited primarily in the anterior nasal cavity,the middle nasal cavity,and the nasal septum.Perforations in the nasal septum lead to a decrease in particle DE in the middle nasal cavity,but with increasing breathing intensity,the presence of perforations in the nasal septum and the anterior nasal cavity results in a significant increase in particle deposition efficiencies.(3)The deposition of single-component liquid particles with a small diameter in the normal nasal cavity is greatly affected by temperature,with higher deposition efficiencies and lower evaporation rates at lower temperatures.When the particle size is larger(>2.5 μm),the effect of temperature on particle deposition is small,and the evaporation phenomenon gradually disappears.The motion of single-component liquid particles with diameters smaller than 5 μm in the normal nasal cavity is greatly affected by humidity conditions,with lower humidity making particles more likely to evaporate.The deposition of single-component liquid particles with diameters in the range of 1 to5 μm in the perforated nasal cavity is greatly affected by both temperature and humidity conditions. |
