AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Calculating the Translational Friction Coefficient of DLCA Aggregates in the Transition Regime using Extended Kirkwood-Riseman Theory
JAMES CORSON, George Mulholland, Michael Zachariah, University of Maryland
Abstract Number: 120 Working Group: Aerosol Physics
Abstract Knowledge of the friction coefficient is crucial to predicting particle diffusional, phoretic, and electrostatic behavior in real-world applications involving aggregate particles. Our study focuses on predicting the friction coefficient in the transition regime for clusters of spherical particles. We present results of our extended Kirkwood-Riseman method for the translational friction coefficient of DLCA aggregates in the transition flow regime. The EKR method is based on Kirkwood-Riseman theory for the continuum regime, which considers the effects of the individual spheres in an aggregate on the fluid flow pattern. These effects are quantified using a hydrodynamic interaction tensor evaluated for each pair of spheres in the aggregate. Our EKR method replaces the continuum hydrodynamic interaction tensor and monomer friction coefficient with appropriate Knudsen-number-dependent expressions obtained by solving the Boltzmann equation with the Bhatnagar-Gross-Krook model in place of the Boltzmann collision operator. EKR calculations are in good agreement with published experimental data, results of direct simulation Monte Carlo calculations, and values obtained using the adjusted sphere method of Dahneke (1973) and Zhang et al (2012). Our results show that aggregates exhibit more continuum-like behavior as both the primary sphere size and number of spheres increases. The shift to continuum behavior is evident for large aggregates even when the primary sphere size is smaller than the gas mean free path. We introduce an analytical expression for the translational friction coefficient of DLCA aggregates as a function of the primary sphere size and the number of primary spheres. This expression is in good agreement with our EKR method for Knudsen numbers between 0.01 and 100.