A small mixing-type unipolar charger for nanoparticles (SMUC) was developed to increase the charging efficiency and throughput by using a small charging chamber (0.5 cm 3 ) to reduce particle loss caused by electrostatic dispersion. -were estimated theoretically with and without electrostatic dispersion to clarify the effect of electrostatic dispersion on particle losses in the charging chamber. The measured f e for d p < 10 nm in the 0.5 cm 3 chamber is higher than the theoretical results without electrostatic dispersion, indicating that particle loss caused by electrostatic dispersion is reduced by use of the small volume charging chamber.
An aerosol neutralizer called the Mixing-type Bipolar Charger using Corona-Discharge at High Pressure (MBCCHP) was developed. In the MBCCHP, a corona discharge (High-Pressure Corona Ionizer; HPC Ionizer) induced by high frequency voltage (>100 Hz) at high pressure (>0.2 MPa) is used to generate bipolar ions at high concentration (1-3 × 10 9 ions/cm 3 ) that are then mixed with aerosol particles flowing in a charging chamber where no external electric field is present. The charging performance of the MBC-CHP was evaluated by comparing the measured and theoretical number ratios of positively and negatively charged particles to the total number of particles, and by comparing those of negatively charged to positively charged particles for an equilibrium charge distribution. The theoretical and measured results agreed well in the particle size range of 5-80 nm. Particle loss in the MBCCHP for the size range of 5-100 nm was less than 15%, and particle generation from the electrode due to spattering or from the carrier gas containing SO x due to chemical reaction was either negligible or not observed. The MBCCHP can effectively provide aerosol particles in the equilibrium charge state. Advantages include (1) no selective deposition of charged particles by an electric field, (2) no generation of new particles by reactive molecules, such as atmospheric pollution gases contained in a sample aerosol by chemical reactions with active species, such as OH radicals, produced by discharge, and (3) no effect of carrier gases of the sample aerosol on the ion properties.
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