Removal Efficiency of Monodisperse and Polydisperse Submicron Particles in a Test Chamber by using a Negative Air Ionizer

• Main Authors: Yi-Ying Wu, 吳宜穎
• Other Authors: Kuo-Pin Yu
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/66263660742864286976

碩士 === 國立陽明大學 === 環境與職業衛生研究所 === 102 === Exposure to particulate matters (e.g., fine and ultrafine particles) is associated with a variety of adverse health effects, including cardiopulmonary, respiratory and allergy diseases. Because people nowadays spend most of their time in indoor environments, their health is closely related to the exposure to indoor aerosol particles. In general, indoor aerosol particles are polydispersely distributed. However, the behaviour of monodisperse particle is simpler and more easily proven by theoretical model. There were rare researches focusing on the deposition removal of monodisperse submicron particles (MSPs) enhanced by negative air ions (NAIs). Understanding the difference between the deposition removal of NaCl MSPs and polydisperse submicron particles (PSPs) enhanced by NAI has become an urgent work and is benificial to apply the theoretical model in real situation. The particle-removal experiments were conducted in a stainless steel test chamber (0.216 m3) under 50% relative humidity (RH). The factors affect the deposition removal of particles was evaluated in this study. These factors included the particle size distribution (MSPs and PSPs) and the freestream air velocity (FAV) which was set at 0.56, 1.20 and 2.0 m/s,corresponding to low, medium and high wind speed, repectively. Sodium chloride (NaCl) and oleic acid aerosols with sizes range from 30 to 300 nm were tested. PSPs were generated from an atomizer and the MSPs (30, 50, 100, 170, 300 nm) were generated by passing the PSPs through a differential mobility analyzer. The number concentration and size distribution of the submicron particles in the chamber were monitored in real time with the Scanning Mobility Particle Sizer (SMPS®). The data from SMPS was used to calculate the decay constant (k), enhancement factor of removal rate (EF) and removal effectiveness (H) of aerosol particles. The deposition removal efficiency of NaCl paritcles enhanced by NAI was higher than that oleic acid and is better under low wind speed. Because the coagulation coefficient of PSP was larger than MSP, the decay constant of PSP was higher than that of MSP. In the tested size region, decay constant decreased with the increase of particle size. In contrast, the EF increased with the particle size. The EF of NaCl MSPs was higher than NaCl PSPs, but in the cases of oleic acid particle, the EF of PSPs was higher. By operating NAI, the deposition rate of particles could be enhanced to as high as 80 times compared to that without NAI operating. The removal effectiveness (H) of NaCl MSP ranged from 92.5 to 95.8 % under the low wind speed. The removal effectiveness of 30 nm oleic acid particle (PSPs) was lowest (79.2 %) under high wind speed. Conclusively, NAI is effective in enhancing the deposition removal of submicron particles. Although, the interaction between particles and negative air ions in the chamber is complicated and is involved with diffusion, field charging and coagulation, the trend of decay constant measured in MSP and PSP experiment is corresponding to that predicted by theoretical model.