Research On Mechanism Of Penetration And Transmission Of Indoor Ultrafine Particles

Under the condition of no obvious pollution indoors, the penetration of outdoor particle is the main source of indoor particulate matter. To evaluate the risk of human exposure to pollutants indoor, it is necessary to understand the influencing factors and transmission mechanism of particle penetration process. The mechanism and influencing factors of penetration and transmission of indoor ultrafine particles were studied by experimental method and numerical simulation. Also the pollutant diffusion rules within the crack were given in this paper.The measurement device with different size of the crack was set up and particle number concentration and mass concentration of two experimental boxes were measured by using fast mobility particle sizer (FMPS) and mass concentration sampling analyzer (DustTrak). The penetration rate and particle size spectrum evolution of different particles size were obtained. According to the research, when the particle size measured by instrument falls into the interval between 6 to 523nm, the penetration rate increases with the increase of particle size. The key influencing factor is Brown diffusion. The average penetration rate ranges from 0.51 to 0.98 under the condition of 4 Pa differential pressure,1 mm crack height and 43 mm length. When the length is 94 mm, the average penetration rate varies from 0.55 to 0.95. Particle penetration rate is decreased with the increase of slit length and reduce of pressure. Particle number concentration of inside has a linear correlation with that of outside. The ratio of indoor and outdoor (I/O) ultrafine particle number concentration ranges from 0.69 to 0.74, the correlation coefficient R2 reaches 0.99, which indicates that indoor particulate matter concentrations are largely related to the penetration of outdoor particles. The average I/O ratio of ultrafine particle mass concentration is 0.74, the correlation coefficient R2 reaches 0.98. PM1, PM2.5 and PM10 and total particle mass concentrations of outdoor have a negative correlation with penetration rates.Taking the influence of the subsidence mechanism such as Brownian diffusion, gravitational settling and Saffman lift into account, numerical simulation was calculated by Fluent software. Particle penetration rate reduces with the decrease of inlet pressure and particle size and the increase of slit length. The crack height is the dominant factor. When crack height changes, penetration rate changes accordance to the dominant factors at the same size particle subsidence to the wall. Small size particles are greatly influenced by Brown diffusion effect, however, gravitational settling plays a increasing dominant role when the particle size grows. In different shapes of pipes, particles of larger size are more likely to deposit in the entrance section of the pipeline, where the concentration of particles is the highest. Particles of smaller size flow with airflow movement. The deposit position is more decentralized with the increase of channel corner, thus decreases the channel blocking. Particle concentration in L type pipe and U type pipe are higher at the bottom of corner and the right pipe wall, because there is a vortex at the corner, the particles deposites more easily.