10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Coagulation of Polydisperse Primary Particles from Free Molecular to Transition Regime
Georgios Kelesidis, EIRINI GOUDELI, ETH Zürich
Abstract Number: 1322 Working Group: Aerosol Physics
Abstract Agglomeration of nanoparticles is encountered in both atmospheric and industrial processes as in volcanic plumes and aerosol manufacture of carbon black or fumed silica. Coagulation of polydisperse primary particles (PPs) in the transition regime is the dominant agglomerate growth mechanism in the low-temperature region of flame reactors and high-pressure environments of combustion engines. Even though the dynamics of coagulating spherical particles, such as self-preserving size distribution (SPSD) and coagulation rate are reasonably well-understood, there is significant uncertainty for fractal-like agglomerates. For the latter, coagulation rates have been proposed, their mobility and SPSDs have been determined. All these have been confined to agglomerates with monodisperse primary particles (PPs). Realistic agglomerates, however, consist of polydisperse PPs.
Here coagulation of nanoparticles of varying PP polydispersity (σg,PP = 1 – 3) in the absence of coalescence, sintering or surface growth is investigated by a discrete element method (DEM) (Goudeli et al., 2015) from the free molecular (Goudeli et al., 2016) to transition regime. The effect of PP polydispersity on agglomerate size (radius of gyration, mobility radius and volume-equivalent radius), morphology (fractal dimension, Df, mass mobility exponent, Dfm, and their prefactors) as well as on the attainment of the well-known asymptotic fractal-like structure (Df = 1.91 and Dfm= 2.15) and SPSD is investigated. Increasing the polydispersity of the constituent PPs from σg,PP = 1 to 3 does not affect but only delays the attainment of the asymptotic Df, Dfm and SPSD of the resulting agglomerates. Furthermore, the effect of PP polydispersity on agglomerate dynamics (coagulation rate and polydispersity) is elucidated quantitatively.
Such characteristics affect the environmental impact of agglomerates (climate forcing or visibility impairment by soot) or performance of gas sensors and catalysts.
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