CFD Simulation On The Effects Of Indoor Airflow Pattern And Breathing Pattern On The Airborne Transmission Of Respiratory Infection

The structure of human respiratory system is complex and mainly consists of noses,pharynx,larynx,trachea,bronchi and lungs,which plays an important role in inhaling oxygen,heating and humidifying fresh air,excreting waste gas and intercepting some particles.Respiratory diseases include acute and chronic inflammations in upper and lower respiratory tracts.Two main ways for the spread of respiratory infection are through indoor air and via droplet nuclei.The deeper the droplets carrying pathogens deposit in the respiratory system and the longer they stay,the more harm is caused to the human body.Therefore,it is essential to simulate the airflow pattern and droplet deposition both in indoor environment and in respiratory system to assess the infection risk of respiratory diseases and provide reference for medical diagnosis and treatment.The CFD(computational fluid dynamics)simulation method is applied to conduct the research.The detailed geometric models of healthy adult body and respiratory system are collected and modified.The models and meshes of room,human body and respiratory system are built in the Gambit software.As a result,the interior and exterior environments for human body are integrated.The evaporation and movement of droplets exhaled from the standing infection patient is predicted by the Fluent software without considering the respiratory system.Impacts of ventilation system,indoor relative humidity(relative humidity,RH)and thermal plume on the simulation results are explored.It is found that the fine droplets(i.e.10 ?m)evaporate completely in a very short time regardless of ventilation type,while the RH variation only has little effect on deposition time for the large droplets(i.e.200 ?m).For the droplets of medium size(i.e.100 ?m),the displacement ventilation becomes an impediment to droplet evaporation,which is equivalent to a higher RH.And a transition from evaporation first to deposition first is also observed for middle droplets.Steady and transient state simulations are carried out to analyze the airflow pattern,pollutant distribution and droplet deposition inside and outside the susceptible individual's respiratory system.Effects of indoor airflow pattern,exhalation velocity of the source person,breathing condition of the susceptible person on airflow distributions in indoor environment and in respiratory system are discussed.When the source coughs,the exhaled jet can enter the breathing zone of another person,deviate the thermal plume and increase the infection risk,especially under displacement ventilation.It is found that the air distribution below the middle pharynx is hardly affected by indoor ventilation or source breathing.With dynamic respiration through noses,high velocity is discovered in the anterior part of nasal cavity,the narrow part of pharynx and the center of main trachea.With dynamic respiration through mouth,high velocity is discovered in the narrow part of oral cavity,followed by the narrow part of pharynx and the center of main trachea.With the same indoor ventilation and breathing flux,the respiration by nose is about 0.1 s later than the respiration by mouth.Overall,with a lower number of inhaled droplets,the respiration by nose is proved better than the respiration by mouth.This work studies the whole process of pathogen transmission of respiratory infections,including exhalation from source,delivery via air and droplet nuclei and inhalation into the susceptible.The simulations in this work have combined the indoor environment with the dynamic respiration to help predict and control respiratory infections in indoor environment and provide references for medical diagnosis and treatment of respiratory diseases.