2011 年 26 巻 4 号 p. 321-325
Novel bipolar and unipolar charger where particles and high concentration ions are mixed quickly by ion flow and aerosol flow into the charging chamber without an external electric field are developed. The advantage of this method is 1) particle deposition by thermal motion and electrostatic dispersion is very low, and 2) particles are charged at a high efficiency. The new method employs a high-pressure corona ionizer for ion generator, because this ionizer can generate high concentration bipolar and unipolar ions applying an ac or a dc high voltage. It is found that the bipolar charger named as Mixing-type Bipolar Charger using Corona-discharge at High Pressure (MBCCHP) can attain the equilibrium charge distribution for 5-100 nm-particles. It is also found that the unipolar charger named as Small Mixing-type Unipolar Charger (SMUC) with chamber volume of 0.5 cm3 can achieve high extrinsic charging efficiency in the size range of 5-40 nm. Previously, the highest extrinsic charging efficiency for 5 nm was about 10%. However, the SMUC attained about 40% of extrinsic charging efficiency for 5 nm. From the results of diesel exhaust measurements of constant and transient driving, it is found that the MBCCHP and SMUC are very useful chargers in field measurements of diesel exhaust as well as in laboratory experiments.