Numerical Study On Sedimentation Characteristics Of Pollutant Particles At Air Duct Elbow

In the ventilation and air conditioning system,the 90° bend pipe,which changes the flow direction of air flow,is the most common local component of air duct,and also the part where particles are prone to settlement.In order to ensure the indoor input of clean and healthy air flow and ensure that there will not be a large number of particles settling in the air duct section in front of the filter of the air duct system,it is necessary to study the particle movement and settling characteristics at the elbow of the air duct.Therefore,this paper takes four types of bends commonly used in engineering as the research object and uses Fluent software to conduct numerical simulation research on them.The specific work content is as follows:Firstly,the influence significance of the factors affecting the particle settlement in the horizontal 90° bend pipe is analyzed by means of orthogonal test variance analysis.The results show that the significance order of the influencing factors is as follows: airflow velocity(significant)> elbow type(insignificant but influential)> elbow size(insignificant but influential).Then,the influence of airflow velocity on particle movement in five air ducts was investigated.The results showed that when the airflow velocity was 8m/s,the number of particles settling in the tube and the dimensionless settling velocity of particles with different particle sizes were the minimum.Then,by exploring four vertical arrangement forms of inner inclined line and outer right angle elbow,it is found that controlling the air velocity within a certain range can effectively control the particle settlement;different arrangement has little effect on the dimensionless relaxation time of particles.The result shows that the airflow velocity is recommended to be controlled at about 6m/s in the layout form one,in which the airflow enters horizontally and exits vertically,and in the layout form four,in which the airflow enters vertically and exits horizontally.In the arrangement form two,in which the airflow enters horizontally and flows vertically upward,and in the arrangement form three,in which the airflow enters vertically and flows horizontally,the airflow velocity is recommended to be controlled at about 8m/s,which is most conducive to reducing the settlement of particles flowing in the air duct.Finally,the proposed wind speed was set for the air duct of each layout form,and the air duct types with less particle settlement and lower dimensionless particle settlement velocity in different types of air duct were explored.The results show that the air flow in the air duct enters from the horizontal direction and flows out from the vertical direction.The inner and outer concentric arc-shaped bend pipe is used in the layout form two,in which the air flow enters and exits horizontally,and in the layout form four,in which the air flow enters and exits horizontally.The arrangement form of air flow entering vertically and flowing out horizontally is the form three.When using inner arc outer right angle elbow,it is more conducive to reduce the settlement of particles in the air duct.The research results of particle movement and settlement in 90° bend of air duct can provide technical reference for regular cleaning and disinfection of air duct in ventilation and air conditioning system.