MC simulation of aerosol aggregation and simultaneous spheroidization

A companion article by Tandon and Rosner (1999) showed that Monte-Carlo (MC ) simulation methods can generate joint pdfs of particle volume, v, and sur face area a, for coagulating populations of suspended nonspherical particle s simultaneously sintering at finite rates. For continuum-regime Brownian c oagulation at times longer than the characteristic coagulation time, a "sel f-preserving" asymptotic pdf shape was shown to extend to these bivariate p opulations, using the rescaled volume v/(v) over bar (t) and rescaled area a/(a) over bar (t) as "similarity" variables. This article considers the co rresponding problem of coagulation in the "free-molecule" limit, relevant t o the atmospheric pressure flame experiments of Xing et al. This combinatio n of coagulation- and sintering-rate laws again leads to "self-preserving" rescaled jpdfs, explicitly time-independent for an isothermal environment a gain dependent on a Damkohler-like number, Dam(f) (ratio of coagulation tim e to fusion time). While flames are more complex than our idealized simulat ions, our present pdfs and associated "mixed moments, "capture important fe atures of experimental results as one approaches the flame, especially evol ution of a mean particle "shape factor," mean number of spherules per aggre gate, and narrowness of the spread of spherule sizes. This agreement, coupl ed with the versatility of MC-methods for multistate variable particle popu lation balances, encourages extensions leading to a versatile tractable, fo rmalism for the developing field of sol reaction engineering.