Maximizing the singly charged fraction of sub-micrometer particles using a unipolar charger

Abstract

Particle charging via the mixing of aerosols with unipolar ions typically results in multiple charges on particles. Particle classification and sizing, based on the electrical mobility, ideally requires all the particles being singly charged to the performance enhancement. In this study, we explored the feasibility of maximizing the singly charged fraction of particles via the control of the N_it product in a unipolar charger. The feasibility was first investigated by modeling unipolar diffusion charging. It was found that the singly charged fraction of monodisperse particles could be maximized by the control of the N_it product. A corona-based unipolar charger was also constructed to study the maximization of the singly charged fraction of monodisperse particles. It was found that a wider range of ion concentration in the charging zone could be obtained by the variation of ion-driving voltage compared to that by changing the corona-discharge current. The maximum singly charged fraction of monodisperse particles in various sizes was characterized when the charger was operated at the flow rates of 1.5 and 3.0 lpm. It was evidenced that the current charger could be conditioned to achieve a higher singly charged fraction of particles than that by bipolar chargers in the particle size range of 20–200 nm, particularly in the ultrafine particle size range. The control of N_it product in the charging zone of a unipolar charger offers a simple and effective means to enhance the singly charged fraction of particles in a given size range.

Copyright © 2019 American Association for Aerosol Research

EDITOR:

• Pramod Kulkarni

Acknowledgments

We would like to thank the editor and three anonymous reviewers for valuable comments and suggestions to help improve this article.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

X.C. would like to thank the Chinese Scholarship Council (CSC) for the financial support of the State Scholarship Fund. X.C. and J.J. is grateful for partial financial support from the National Key R&D Program of China.