AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Numerical Evaluation of Fuch’s Bipolar Charging Theory Using Stochastic Ion Mass and Mobility in a Non-Equilibrium Neutralizer
JEAN DE LA VERPILLIERE, Jacob Swanson, Adam M Boies, University of Cambridge
Abstract Number: 517 Working Group: Aerosol Physics
Abstract The need for portable, non-hazardous, bipolar aerosol chargers has led to the recent development and commercialization of soft x-ray and AC corona neutralizers. In past work we have demonstrated that x-ray and AC corona neutralizers led to different charging characteristics relative to radioactive charging. Measurement of ions from different neutralizers indicated that each approach produces ions with different electrical mobility distributions, but the standard Fuchs charging theory failed to explain the observed charge distribution discrepancies between the neutralizers. The objective of this work is to investigate two modifications to the existing theory in order to improve the understanding of the mechanisms responsible for charging inside three commercially-available neutralizers.
The first modification considers that steady state is not reached within the neutralizer due to ion diffusion losses to the neutralizer wall. Transport equations for particles of each polarity and for ions are derived from charge conservation equations, and solved using a forward numerical method. An existing model developed by Alonso and Alguacil (2003) is extended to neutralizers of more complex geometries, relying on different ionizing sources.
The second modification incorporates a stochastic modeling approach to reflect the variety of ion mobilities and masses that are known to exist in any bipolar charging environment. Distributions of ion mass and mobility are incorporated from past experimental measurements and the Fuchs charging theory is numerically solved for multiple iterations using a Monte Carlo approach. The ion-aerosol attachment coefficients are derived stochastically and the effect of multiple ion species is evaluated relative to standard deterministic charging models.
Results of the numerical simulations are compared to the experimental trends to determine whether the physical explanations used to justify the theoretical modifications reduce the discrepancies observed between neutralizers.