A Study On The Characteristic Of Outdoor Particles Penetrating Into The Indoor Room Through The Crack

Haze contains PM2.5 particles that can more easily get into the lungs through the respiratory system, and infiltrate into the blood through the alveolar, causing the health of the human body would get a great impact. As the main source of PM2.5 particles in the indoor is the outdoor air pollutant penetrating into the indoor through the crack of the door, the window and the wall. Therefore, it is significant to study the penetration law of outdoor pollutants entering the indoor air.This paper, aiming at the penetration process of contaminants through cracks. Firstly, test the penetration performance in the experiment. Secondly, use the theoretical method to analyze the main factors affecting the penetration of pollutants from outdoor into the indoor. Finally, according to the above research results, the numerical simulation method is applied to calculate the penetration rate of the actual pollutants penetrating into the indoor. The research contents and results are as follows:(1) In this paper, we set up an experimental platform to test the permeability characteristics of particulate matters and study the influence on penetration rate of four factors like pressure, crack height, inner surface roughness and particle size. In the experiment, the particle concentration is controlled at higher than 150μg/m3, the roughness is controlled in the range from 0μm to 20.5μm, the pressure difference is controlled from 2Pa to 10Pa, and the crack height is controlled from 0.3mm to 1mm.The experimental results show that the permeability of particles is concentrated in the range from 0.55 to 1.(2) Data analysis showed that the experimental deviation of the penetration rate was affected by the particle size and the deviation will be larger when the particle size becomes larger. The relationship between the permeability and the pressure difference is linear, meaning that the permeability becomes larger with the pressure difference and the correlation coefficient is generally bigger than 0.7. In addition, the permeability is inversely proportional to the particle size, that is, the penetration rate decreases with increasing particle size. The effect of crack height and surface roughness on permeability is relatively small compared with the pressure difference and the particle size.(3) According to the method of changing the single variable to derive the formula of the relationship between indoor and outdoor concentration and induce the formula to calculate the balance time how long concentration of the indoor and outdoor air and the formula of the minimum volume per hour of the indoor air to purify. Based on the research results above, this paper used the numerical simulation method to analyze the infiltration of particles penetrating through cracks into the room. The simulation is divided into four groups of working conditions including the condition of low wind speed and medium particle concentration, the condition of low wind speed and low particle concentration, the condition of medium wind speed and medium particle concentration, the condition of high wind speed and high particle concentration. The results show that the concentration of outdoor particulate matter plays a major role in the growth rate of indoor particle concentration. The calculation result shows that once the outdoor hazes, the concentration of indoor particles generally balance with the outdoor within 2-3 hours.