AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Direct Simulation Monte Carlo (DMSC) Calculation of the Low Reynolds Number Drag on Aerosol Aggregates
CHONGLIN ZHANG, Thaseem Thajudeen, Carlos Larriba, Thomas Schwartzentruber, Christopher Hogan Jr., University of Minnesota
Abstract Number: 75 Working Group: Aerosol Physics
Abstract The drag force experienced by aggregate aerosol particles at low Reynolds number governs aggregate motion and growth in a number of environments, and is therefore of critical importance. However, because of the morphological complexity of aggregates and the transition regime nature of gas molecule-particle momentum transfer for small particles, drag force prediction for aggregates is not commonplace. Here, we describe the use of direct simulation Monte Carlo (DMSC) for prediction of the drag force on model aggregates. In DSMC, the gas flow field is modeled by a number of interacting “simulation particles”, which impart drag to the particle. Unique about DSMC is that it permits simulation of gas flows in the transition regime, i.e. under conditions often encountered for aggregate aerosol particles with sizes in the 20-200 nm size range. Despite the suitability of DSMC for calculation of the drag force on aerosol particles, calculations suffer from high statistical variability for flow speeds which are small relative to the mean thermal speed of the background gas molecules. We discuss methods to address this statistical variability, and apply DSMC for drag calculation on spheres, dimers, and 20-mer aggregates with Knudsen numbers in the range 0.05-10. Results of calculations are compared to the drag force predicted from the results of dimensional analysis. Reasonable agreement (~10% difference) is found between DSMC calculated drag force and model predictions.