Abstract Number: 667 Working Group: Instrumentation and Methods
Abstract Aerosol charging is an important step as a pretreatment to analysis, handling and measurement of aerosol. However, it is known that the charging efficiencies of bipolar chargers are not so high due to the neutralization process, while a unipolar charger suffers from generation of multiply-charged particles for large particles. In the application of aerosol chargers for the electrical mobility classifier, this contrary causes low particle throughput and/or contamination by classifying multiply charged particles having sizes greater than the target size. Therefore, it is desirable to develop a high-efficiency aerosol charger with suppression of multiply-charged particles.
In this study, we developed a new unipolar charger with an acceleration electric field in the aerosol charging area. The electric field is formed parallel to the aerosol flow so that charged particles are accelerated toward outlet before obtaining excess charge. The performance of the new charger was evaluated by measuring charge distribution and penetration of the particles. The number fraction of singly charged particles increased and the multiply charging was successfully suppressed by the present charger. The acceleration electric field in the aerosol charging area introduced in the present work would effectively affect to increase the fraction of singly charged particles and to suppress the fraction of multiply charged particles. At the optimum conditions, the fractions of singly charged particles were 85 and 50 % for 30- and 100-nm particles, respectively, while doubly charged fractions were 8 and 13 %.