Abstract View
An Experimentally Validated Model of Diffusion Charging of Arbitrary Shaped Aerosol Particles
LI LI, Ranganathan Gopalakrishnan, The University of Memphis
Abstract Number: 187
Working Group: Aerosol Physics
Abstract
Experimental studies have shown that particle shape strongly influences the diffusion charging of aerosol particles exposed to low energy (~0.03 keV) bipolar/unipolar ions. It is expected that the highly non-spherical particles such as aggregates with low fractal dimension or cylinders with very high length to diameter ratios may acquire more charges than a spherical particle of the same mobility diameter – the most commonly used size metric for aerosol nanoparticles. This aspect warrants the need for an accurate model to predict the charge distribution of non-spherical particles. This work presents a Langevin dynamics (LD)-based approach to describe the collision kernel between a charged/neutral arbitrary shaped particle and an unlike/oppositely charged ion. The diffusion charging model including Coulombic and image potential interactions published by Li et al. (J. Aerosol Sci. 140: 105481) for spherical particles is generalized for arbitrary shapes following the approach suggested by Gopalakrishnan et al. (J. Aerosol Sci. 64: 60-80) using LD simulations of aggregate-ion collisions for attractive Coulomb-image potential interactions. This extended model for collisions between unlike charged particle-ion (bipolar charging) and the model for like charged particle-ion (unipolar charging) put forward by Gopalakrishnan et al. (J. Aerosol Sci. 64: 60-80) are validated by comparing against measured bipolar charge distributions from prior experimental work. Comparison to the data for fractal aggregates reported by Matti (Aerosol Sci. Tech. 42(4): 247-254) and Xiao et al. (Aerosol Sci. Tech. 46(7): 794-803) reveal that the LD-based models predict within overall 30% without any systematic bias. In the case of linear chain aggregates reported by Wen et al. (J. Aerosol Sci. 15(2): 103-122), the mean charge on each particle estimated by model is found to be in good agreement with the measurements. The comparison with experimental results supports the use of LD-based diffusion charging models to predict the bipolar and unipolar charge distribution of arbitrary shaped particles for a wide range of particle size, and gas temperature, pressure.
We thank The University of Memphis High Performance Computing Cluster for providing computational resources to carry out this research. Funding for this work was provided by US National Science Foundation (NSF) PHY Grant Award Number 1903432 under the Directorate of Mathematical & Physical Sciences.