Research On The Sedimentation Of Aerosol Particles In Ventilating Ducts And The Air Duct Cleaning Interval

There are many reasons for the low indoor air quality,one of which is the sedimentation of dust in ventilating pipes of air-conditioning system.It can lower the performance of air-conditioning system and indoor air quality.The mastery of the law of flow and sedimentation of dusty air flow and the sedimentation law of dust particles in ventilating ducts of different structure can help comprehensively understand the behavior of the particles in ventilating duct which can be a guidance in theory but also in practice for implementing the mechanism of sediment process of particles in ventilating duct,predicting the effect of air supply of ventilating system, improving indoor air quality and preventing the sick building syndrome.This paper first reviewed the previous research findings,introduced the movement and sedimentation mechanism of particles in air duct,analyzed the movement law of air flow in air duct of air-conditioning system and demonstrated the classification and the main influencing factors of particle sedimentation.The mathematical model of the sedimentation velocity of particles was established.By analyzing and comparing the calculated particle sedimentation data,the factors related to dusty particles sedimentation such as dusty particle diameter,air supply velocity and the roughness concentration of the wall of duct were analyzed.(i) The sedimentation velocity increased as the particle diameter increased.Owing to the Brown diffusive force near the wall of duct,it also increased as the sub micron grade particle diameter decreased.(ii) For particles of which the particle diameter was greater than 1μm,the sedimentation velocity of dusty particles nearly increased linearly with air flow velocity in the logarithmic coordinate system.For particles of which the particle diameter was relatively small,the sedimentation velocity of dusty particles increased fast when air flow velocity was below 5m/s,but increased gently when air flow velocity reached 5m/s.(iii) The sedimentation velocity of dusty particles increased as the roughness concentration of the wall of duct increased,and decreased as the roughness concentration of the wall of duct decreased.At the end of this paper,the distribution of outdoor dusty particles of Xi'an city was analyzed.The cleaning interval of air ducts of the central air-conditioning system of a commercial building in Xi'an city was predicted.