Abstract View
Effect of Volume Fraction and Hydrodynamic Interactions on Aerosol Particle Coagulation Using Langevin Dynamics Simulations
ZHIBO LIU, Vikram Suresh, Ranganathan Gopalakrishnan, The University of Memphis
Abstract Number: 625
Working Group: Aerosol Physics
Abstract
Coagulation of aerosol particles at high concentration is modeled by tracking identical spheres in a periodic domain using Langevin Dynamics (LD) simulations. As the particle solid volume fraction is varied between 10-6-10-1, departing from the dilute coagulation regimes (ηv → 0), it is seen that the coagulation rate constant or collision kernel increases by a factor of ∼6 in the continuum regime (defined by the diffusive Knudsen number KnD → 0) and is practically unaffected by particle crowding (or high volume fraction) in the free molecular regime (KnD → ∞) of diffusional mass transport. We provide a parameterization for β across the entire KnD regime as a function of ηv, building on prior work on coagulation kernel development for dilute aerosols using Langevin Dynamics (Aerosol Sci. Technology 45(12): 1499-1509). The effect of hydrodynamic interactions on particle coagulation, calculated using the extended Kirkwood-Riseman approach developed by Corson et al. (J. Fluid Mechanics 855: 535-553), is parameterized as a function of the momentum Knudsen number KnD, providing a holistic description of the influence of free volume and particle-particle interactions on coagulation of dense aerosols. It is seen that hydrodynamic interactions are the strongest in the continuum regime of momentum transfer (Kn → 0) and vanish in the limit of Kn → ∞ (free molecular momentum transfer regime). The LD simulations allow the quantification of each parameter for a system of identical spheres. Preliminary results indicate the need to design particle coagulation measurements to understand the deviation of coagulation rate constants from the predictions of dilute models at high volume fractions and the precise role of hydrodynamic interactions in altering the coagulation kinetics. Further research on the inclusion of particle polydispersity, non-spherical shape and the associated rotational motion using LD simulations is underway.