(49d) Coagulation of Polydisperse Primary Particles in the Transition Regime | AIChE

(49d) Coagulation of Polydisperse Primary Particles in the Transition Regime


Goudeli, E. - Presenter, University of Melbourne
Kelesidis, G., ETH Zurich
Coagulation of polydisperse primary particles (PPs) in the transition regime is the dominant agglomerate growth mechanism in low-temperature regions of flame reactors and high-pressure environments of combustion engines. During flame synthesis of nanoparticles, small PPs coagulate in the free molecular regime to form fractal-like agglomerates. When agglomerates exit the flame high-temperature region, they start to coagulate in the transition regime, as their mean free path becomes comparable to their diameter of gyration, dg, or mobility diameter, dm. The estimation of the dm of evolving aggregates is not trivial, as it depends on their structure and the number/size of their constituent PPs, np. Scaling laws describing the dm of agglomerates consisting of monodisperse PPs have been developed in free molecular, transition and continuum regimes. However, these models overestimate the dm of mature soot aggregates up to 37% as they neglect PP polydispersity.

Here, an event-driven method [1] for agglomeration of polydisperse PPs is used to investigate the agglomerate structure and size distribution in the transition regime. The dm, increases with increasing geometric standard deviation of the PPs, σg,p, while the average dg is hardly affected by σg,p for small compact agglomerates. The broad agglomerate size distributions formed in the free molecular regime narrow down by coagulation in the transition regime, attaining a quasi-self-preserving size distribution, regardless of σg,p. A scaling law for the np is derived as function of dm and dg which can be coupled with method of moments or population balance models to assist aerosol reactor design.

[1] Goudeli, E., Eggersdorfer, M. L,. & Pratsinis, S. E. (2015). Langmuir, 31, 1320-1327.