AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Effect of Fractal Dimension and Prefactor on Aggregate Heat Conduction in the Free-Molecular Regime
FENGSHAN LIU, Gregory Smallwood, National Research Council Canada
Abstract Number: 631 Working Group: Aerosol Physics
Abstract One of the importance processes during laser-induced incandescence of soot is heat conduction cooling shortly after the laser pulse. Soot in general appears as mass-like fractal structure in flames as a result of particle aggregation. There is a shielding effect in aggregate conduction cooling due to the partial blocking of some primary particles in the interior of the aggregate from collision with the surrounding molecules. There have been very few studies investigating the cooling rate of fractal aggregates and these studies were conducted for specific fractal dimensions and prefactors. Quantitative studies for the shielding effect over a range of fractal dimension and/or prefactor have not been reported in the literature.
In this study, direct simulation Monte Carlo (DSMC) calculations were carried out for several pairs of fractal dimension and prefactor to investigate how these fractal parameters affect the shielding effect. Fractal aggregates of different fractal dimension and prefactor were numerically generated using a combination of tunable particle-cluster and cluster-cluster aggregation algorithm.
DSMC calculations of aggregate heat conduction were conducted in the free-molecular regime. Results were presented as a correlation of the heat conduction equivalent sphere diameter.