| The nasal cavity is the first portion for air flowing from the ambient atmosphere to the lung. It prevents the harmful masses such as the dusts and the bacteria from entering the lung. Also it can moisten and warm air, so the air becomes cleaner, warmer and moistened as it flows through the nasal cavity. It is obvious that the nasal cavity has a very important function in the whole respiratory system. When the nasal cavity has the pathological changes, the airflow may be blocked and the serious patients may die for breathing trouble. However, it's hard to investigate the airflow state and pressure distribution quantitatively in human nasal cavity for its complicated three-dimensional structure and due to inaccessible instrument as well. It is necessary to study the airflow state and the moistening and warming process of the nasal cavity by mechanical approaches.According to the detail anatomic data and the CT data of the nasal cavity, starting from the nasal entrance and picking up the twenty sections data of the nasal cavity in turn, the author built the nasal complex three-dimensional model by using the 3dsmax software. The finite elements were plotted in ANSYS. The detail airflow patterns of the biggest inspiration and a whole respiratory period were numerically simulated. It was confirmed that at the biggest breathing the airflow was laminar. The airflow pattern in the nasal cavity was determined mainly by its complicated three-dimensional structure. Numerical computations show that airflow mainly passes through the nasal floor (between the inferior and the middle turbinate), and the resistance at the nasal floor is the smallest. At the different time in one respiratoryperiod, the distributions of the airflow field and the pressure are very similar. During expiration, the peaks of velocity are bigger than inspiration, and the flow is more uniform in the turbinate region.Assuming the physical parameters, such as density, specific heat, viscosity coefficient, conductivity and diffusion coefficient do not change with temperature, and based on the airflow distribution in the nasal cavity, the author solved the convection-diffusion thermal equation to obtain the temperature field from the nostril to the laryngeal. The influence of the change of airflow temperature in the entrance on the temperature distribution in the nasal cavity was also discussed.The saturate process of moisture in the nasal cavity is actual the convection-diffusion mass transfer process. The style of control equation is the same as the convection-diffusion thermal transfer equation. By transforming the thermal conductivity equation, the mass diffusion coefficient is equivalent to the thermal conductivity coefficient, and the concentration of water vapor is equivalent to the temperature, then the mass transfer equation for water vapor was obtained. The author solved the equation to discuss the influence of the change of airflow moisture in the entrance on the moisture distribution in the nasal cavity.The results show that the temperature in the nasal cavity often kept between 30-33 despite the temperature changing greatly. It is obvious that the nasal cavity has very good function to warm cold air. When the moisture is 60% in the nostril entrance, its average is above 90% in the laryngeal.The results of this research may lead to meaningful understanding of the distribution of airflow along the nasal cavity under physiological and pathological conditions and may offer a theoretical foundation for the further theoretical study and clinical research of airflow and its resistance in normal and blocked nasal respiratory passages. |
