Numerical Simulation Of Indoor Human Exhaled Particulate Matter Movement Distribution And Risk Assessment Of Respiratory Infectious Diseases

Respiratory infectious diseases are a serious threat to human health and social and economic development.The research found that aerosol particles formed by human exhalation are the main carriers of pathogens of respiratory infectious diseases,and the movement and distribution characteristics of particles are important factors affecting the spread of respiratory infectious diseases.Most respiratory infectious diseases break out in indoor environment,and human beings spend about 80% of time at indoors every day.Therefore,it is very necessary to master the movement and distribution law of particulate matter indoors,and its impact on the transmission of respiratory infectious diseases is important.In this thesis,the numerical simulation method based on the coupling of computational fluid dynamics(CFD)and discrete element(DEM)is used to explore the movement and distribution law of indoor human exhaled particulate matter under different working conditions.On the basis of obtaining the concentration distribution of particulate matter,the air infection risk assessment method based on dilution method is used to assess the transmission risk of respiratory infectious diseases at different indoor levels,to provide guidance for people’s cognition of the spread of indoor respiratory infectious diseases.This paper takes the office as the research object,creates a three-dimensional physical model.After a detailed analysis of the force on the particles,the CFD-DEM method is used to establish the mathematical model of gas-solid two-phase flow.The established mathematical model is used for numerical simulation according to the experimental research and simulation research of relevant literature to verify the rationality of the mathematical model.Then the thesis set up the grid division and grid independence of the physical model are verified.Firstly,based on the established and verified mathematical model,this thesis simulates the indoor air distribution under three air supply modes: opposite side up supply and down return,same side up supply and down return and up supply and top return.On this basis,it simulates the indoor movement and diffusion process of particles with different particle sizes of 10μm,20μm,50μm and 100μm respectively.The results show that the indoor flow field is evenly distributed and the average velocity of air flow in the personnel activity area is small.Under different air supply modes,the movement of particles varies greatly with time and spatial distribution.The particle pollution range of the air supply mode on the same side is wider than that of the air supply mode on the opposite side,and the deposition of particles on the ground is less in a short time.The upper air supply and top return air supply mode is conducive to the discharge of small particle size particles,and its particle discharge efficiency is higher than the other two air supply modes.Then,based on the above research of air supply mode,this thesis further discusses the influence of particle source location and air supply speed on particle movement,obtains the changes of indoor horizontal movement distance,longitudinal movement distance and rising height of human exhaled particles with time under different particle source location and air supply speed,and analyzes the horizontal distribution law of particles in different room heights.The results show that the horizontal plane of particles is different at the same time under different particle source location and air supply speed.The farther the particle source is from the air supply outlet,the lower the horizontal plane of the particles at the same time,and the longer the particles stay indoors.With the increase of air supply speed,the rising speed of particles increases continuously,and the time to move to the return air inlet is gradually shortened,so that particles can be quickly discharged outdoors.Finally,through the air infection risk assessment model,this thesis uses the particle concentration distribution obtained above to calculate the infection probability of lower respiratory tract infectious diseases in different air supply modes,particle source locations and air supply speeds,and uses the calculated infection probability to evaluate the transmission risk of respiratory tract infectious diseases at different indoor horizontal locations.The research shows that the average probability of respiratory infectious disease infection at each indoor position is the lowest under the mode of upper supply and top return air supply,so it should be given priority when setting the type of room air supply.With the increase of the distance between the particle source and the air supply outlet,the indoor space exposed to the risk area of disease infection is less.When the air supply speed is high,the risk of disease transmission is relatively small except for the location near the infected person.When the air supply speed is small,the risk of transmission is generally high in the areas exposed to the risk of disease infection.