AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Investigation of Flowrate-dependent Performance of Bipolar Diffusion Chargers
Meilu He, Matthew Brown, SURESH DHANIYALA, Clarkson University
Abstract Number: 540 Working Group: Instrumentation and Methods
Abstract Bipolar diffusion chargers are widely used for differential mobility analyzer (DMA) based measurements of submicron aerosol size distributions. The knowledge of the exact charging efficiency of particles is critical to accurate calculation of size distributions from DMA measurements. If the particles can be assumed to be charged to steady state, the particle charging efficiency can be calculated following the theory of Fuchs (1963) or Hoppel and Frick (1986). The assumption of steady state charging, however, may not always be accomplished. The final nature of the charge distribution depends on the ion concentration in the neutralizer, particle residence time, and design of the charger. In this study, the charging efficiency of popularly used commercial 85Kr neutralizers with source strengths of 2 mCi and 10 mCi (TSI 3077 and 3077A) and a 210Po neutralizer are determined as a function of particle size (10 - 50 nm) and flowrate (0.1 – 6 LPM). The experiments show that the charging efficiency of the 2mCi neutralizer for particles smaller than 50 nm in diameter is strongly dependent on the aerosol flow rates through the neutralizer, with a minimum charging efficiency at a flowrate of 1 LPM. The increase in particle charging efficiency with decreasing flowrates below 1 LPM is consistent with earlier findings (e.g., Ji et al. 2004), but the higher charging efficiency for flowrates larger than 1 LPM is a surprising finding. Theoretical description of the performance of the different neutralizers explaining their flowrate dependent nanoparticle charging behavior will be presented.