Impact of space charge on neutralization efficiency of highly charged aerosols: analytical and numerical insights using bipolar ions

Abstract. We investigate the influence of space charge on aerosol discharging behavior, emphasizing its importance in understanding and optimizing aerosol neutralization processes. Our study introduces the concept of space charge-assisted ionization and the distribution of charged aerosols. Specifically, we consider the case of highly charged aerosols introduced into a cylindrical chamber containing a bipolar ion source. In this scenario, space-charge-induced motion is explicitly included in solving the dynamical equation using a computational fluid dynamics (CFD) approach. This method allows us to assess the efficacy of corona-based neutralizers for charged aerosols. Our exploration focuses on the effect of spatial ion heterogeneity induced by space charge. Our results demonstrate that the efficiency of charge neutralizers in mitigating high concentrations of charged aerosols is influenced by various factors, including aerosol charge concentration, magnitude of the charge, and design parameters such as flow rate, ion production rate, and neutralizer geometry. We observe that particles at the periphery of the chamber experience a significantly slower neutralization compared to those flowing along the axis. Consequently, the aerosol system as a whole exits the chamber with a residual charge. This incomplete neutralization, caused by space charge effects, alters the particle charge distribution, potentially affecting size distribution measurements using mobility sizing instruments. These findings underscore the need to bridge theoretical concepts with practical applications in aerosol science and technology, with broad implications for environmental monitoring and industrial processes. Furthermore, our coupled model offers potential for investigating processes involving charged aerosols in the atmosphere, where space charge effects are also significant.