AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Charge Distributions of Arbitrary Shaped Particles Charged by the Unipolar Diffusion Charger in the EAD and NSAM
DREW THOMPSON, David Y. H. Pui, University of Minnesota
Abstract Number: 606 Working Group: Instrumentation and Methods
Abstract Unipolar diffusion chargers are commonly used in aerosol instrumentation, such as in exposure monitors where a particle concentration is inferred from the electrical current produced by the deposition of charged particles or as a charge conditioner in a differential mobility analyzer (DMA) where predictable charge distributions are needed for the determination of particle size distributions. However, it has been reported that particle morphology affects the ion-particle collision rate, which in turn would affect the performance of any aerosol instrument employing a unipolar diffusion charger. An expression for the charge distributions of arbitrary shaped particles charged by the opposed flow unipolar diffusion charger used in the Electrical Aerosol Detector (EAD) and the Nanoparticle Surface Area Monitor (NSAM) will be presented. The particle charge distribution was found using the analytical solution of the birth-and-death theory where the ion-particle collision kernel was calculated using a recently published expression for arbitrary shaped particles in the transition regime (Gopalakrishnan, Thajudeen, Ouyang, and Hogan. (2013) J. Aerosol Sci.; 64: 60). Calculated charge distributions for spherical and cylindrical particles are compared to that measured using a tandem DMA (TDMA) system after correcting for experimentally determined size-, shape-, and preexisting charge-dependent particle losses in the charger.