AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Crossover from Ballistic to Epstein Motion
William Heinson, CHRIS SORENSEN, Amit Chakrabarti, Flint Pierce, Kansas State University
Abstract Number: 192 Working Group: Aerosol Physics
Abstract We present a simulation of particle aggregation in the free molecular regime that undergoes a crossover from ballistic to Epstein diffusive motion where the frictional coefficient is proportional to the aggregate cross sectional area. The simulation starts with a dilute system of monomers all with mean free path (persistence length) of l$_0. Persistence length of the aggregate l$_a is found from the product of the Langevin characteristic time t$_c and the Maxwell root mean square velocity v$_(rms) which is l$_a=t$_c v$_(rms) . We will show that l$_a=l$_0N$^(1/2 -2x) where x=0.46. As the aggregates grow, the aggregate persistence length becomes smaller and the aggregate motion between collisions becomes more diffusive like. The kinetics of aggregation and aggregate size distributions show the expected BLCA and Epstein like behavior at early and late times, respectively. A significant crossover regime is found between these limits. The aggregation kernel homogeneity exponent evolves in a nonmonotonic manner from one regime to another.