Influences Of Fittings On Aerosol Deposition In Ventilation Ducts

With the improvement of China's comprehensive national power,the process of industrialization and urbanization continues to accelerate,the increasing social standard of living,and environmental issues are increasingly prominent.Aerosol particles,as an important factor affecting environmental conditions,have attracted much attention.The proportion of cities with 338prefectures above municipal level that meet the primary annual limit of PM_2.5 and PM₁₀0 is less than50%,and particulate matter has a certain degree of harm to human health.Centralized air conditioning systems are widely used in public places such as shopping malls and hospitals.They filter large particles through air filters to ensure the cleanliness of indoor rooms.However,for small particles,they will still enter the room with the airflow,while some are in the airflow.The sedimentary particles are deposited on the inner wall surface of each part of the air duct.These deposited particles are not only easy to breed a large number of microorganisms and bacteria,but when the amount of particles deposited in the pipeline is large,the deposited particles are prone to suspension and carry various pathogens.The air supply airflow enters the air-conditioned room,causing air-conditioning disease,which has an extremely adverse effect on the health of the working people in the air-conditioned room.The partial member is complicated by the structure compared with the straight pipe section of the duct.According to the basic principle of the aerosol,the local member is more likely to deposit particles.Due to the large size of the elbow in order to reduce the airflow resistance,a baffle is required,and there is little research on the deposition of the elbow particles with the baffle.Therefore,this paper adopts the numerical simulation method for several large-size 90°rectangular elbows commonly used in engineering,such as the inner oblique line right angle type elbow,the inner and outer right angle type elbow,the inner arc outer right angle type elbow and the inner and outer concentric Arc-shaped elbows,etc.,studied the deposition law of the particles on the inner wall surface.As a partial component that reduces the airflow speed,converts the dynamic pressure into static pressure and enhances the uniformity of the airflow,the static pressure box has almost no research on the deposition of the inner wall surface.Therefore,this paper will also explore the law of particle deposition on the inner wall of the static pressure box.The results show that the flow field tends to be more uniform after the implement of deflector while the spatial distribution of the deposition rate of the elbows is similar despite of the duct size and the flow velocity.Meanwhile,the deposition velocity at the inner surface of the elbows'inner circle is positively correlated with the duct width and the flow velocity inside the pipes.By contrast,the deposition velocity at the inner surface of the elbows'outer circle drops with the growth of the duct width but rises with the increase of flow velocity in the pipes.When the four types of elbows change the position of the elbow and the direction of the wind,the difference between the velocity field and the turbulent energy field is very small.Among them,the velocity distribution of the right-angled elbow is the most uniform,and the inner and outer concentric arcs are curved.The kinetic energy field is most evenly distributed.The change of the elbow position has little effect on the particle deposition of the vertical elbow,and the change of the inlet direction has a relatively large influence on the particle deposition.The three types of static pressure boxes have the inner wall surface of the tuyere.The amount of particle deposition is concentrated around the tuyere and shows a gradual decreasing trend to the surrounding area.The inner wall surface of the non-ducting port is mainly controlled by the turbulent energy of the airflow and the amount of particle deposition.The area where the turbulence is strong is large.Under the same particle diameter,the amount of particle deposition on the inner wall of the static pressure box 3 decreases as the gas flow rate increases;at the same gas flow rate,the deposition amount of the inner wall surface of the plenum box 3 increases with the increase of the particle diameter.