| Budget Amount *help |
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 1997: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1996: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
In this research, dynamic behavior of nanometer-sized aerosol particles and ion clusters was studied by measuring with the differential mobility analyzer (DMA) combined with a condensation nucleus counter (CNC) or an electrometer (EM) as a particle detector. The results obtained can be summarized below. At the first year, a theoretical and experimental study of mobility shift in the case of extremely fine particles requiring low electric fields for their classification when performing aerosol size measurements with the DMA has been carried out. As a result, it was made clear that the mobility shift is due to (i) diffusive mixing of trajectories of different-sized particles, and (ii) the existence of a space-charge field in addition to the applied field. Furthermore, the most important results can be summarized thus : (i) particles smaller than the average are classified at voltages smaller than the ideal ; (ii) particles larger than the average are classified at voltages larger than th
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e ideal ; (iii) larger aerosol concentrations lead to larger shifts ; (iv) mobility shifts occur even at low aerosol concentrations due to Brownian diffusion effects ; and (v) mobility shifts are important only in the first DMA,and can be safely neglected for the second. At the second year, particle size measurement were done using a tandem DMA system to accurately determine the size of the particles on the basis of the results of the first year. Penetration of nanometer-sized particles through a wire screen and a laminar flow tube has been carried out. The results obtained can be summarized thus : (i) the presence of electrical charges in the particles do not affect their penetration behavior ; (ii) the existing theories, Cheng and Yeh for wire screens and Gormley and Kennedy for tubes, are accurate for particles with Stokes-Einstein diameter down to 2nm ; and (iii) particles do not rebound from the metallic surfaces, i.e., all the particle-metal collisions are effective, Furthermore, an experimental study of charging and neutralization of aerosol particles by bipolar air ions has been carried out. As a result, if adequate value of ion mobility and mass are chosen, our experimental results agree very well with Fuchs'theory for particles larger than about 3nm. In the size range below 3nm, deviations are considerable and abrupt. Less
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