AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Potential Enhanced Particle Growth in the Transition Regime
HUI OUYANG, Ranganathan Gopalakrishnan, Christopher Hogan Jr., University of Minnesota
Abstract Number: 25 Working Group: Aerosol Physics
Abstract Interparticle van der Waals potentials play an important role in aerosol particle growth by coagulation and can enhance the growth rate in many circumstances by a factor of 2-3. In spite of this, such interactions are often unaccounted for in solutions to the general dynamic equation for particle growth, mainly due to the mathematical complexities involved in dealing with such potentials. In this work, we use a combination of dimensional analysis and mean first passage time simulations to develop an accurate yet simple approach to account for such interactions. Through these two approaches we show that for realistic van der Waals interactions that a dimensionless collision rate coefficient, H, can be expressed solely as a function of the diffusive Knudsen number, KnD, and that the dimensionless H(KnD) relationship effectively describes the collision rate (and hence coagulation rate) between particles with van der Waals forces accounted for in the mass transfer continuum, free molecular, and transition regimes. The observed relationship is compared to the more traditional predictions of flux matching theory, which are found to underpredict the collision rate for the largest van der Waals potentials. Using the newly developed collision rate function, the general dynamic equation for particle growth is solved used constant number Monte Carlo simulations. These simulations demonstrate that the dynamics of a coagulating and initially monodisperse system are solely dependent upon the ratio of the van der Waals energy to the thermal energy, the initial diffusive Knudsen number, and the initial Knudsen number.