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TOTAL SCATTERING AND ABSORPTION CROSS SECTIONS OF CARBONACEOUS SOOT PARTICLES

DOI: 10.1615/ICHMT.1995.RadTransfProc.230

Tiago L. Farias
IDMEC-Institute of Mechanical Engineering, Instituto Superior Tecnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001, Lisbon, Portugal

Maria da Graca Carvalho
Instituto Superior Técnico, Lisbon, Portugal

Umit O. Koylu
Dep. of Chem. Eng., Yale University, New Haven, CT, 06520; Department of Mechanical and Aerospace Engineering University of Missouri - Rolla Rolla, MO 65409-0050, USA

G. M. Faeth
Department of Aerospace Engineering, the University of Michigan, Ann Arbor, Michigan 48109-2140, USA

Abstract

The absorption and scattering properties of fractal-like soot aggregates were investigated emphasizing the effects of aggregate and particle polydispersity as well as variable refractive index within each primary particle. The computational calculations were performed using a general formulation for the internal electric field of an assembly of small spherical particles irradiated by an electromagnetic wave that takes into account multiple-scattering and self interaction effects. Numerical cluster-cluster simulations were used to construct aggregates having appropriate fractal properties and prescribed number of primary particles and particle diameter. In addition, theoretical results based on the Rayleigh-Debye-Gans approximation for mass-fractal aggregates (RDG/FA) were also obtained in order to evaluate its potentialities to treat optical properties of aggregated matter - such as soot. Over the range of study, it was concluded that aggregation plays an important role in the total scattering predictions while absorption seems to be independent of this effect. The influence of aggregate polydispersity seems to be more noticeable in the scattering predictions while absorption is more affected by particle polydispersity. Furthermore, the primary particle variable refractive index study has revealed that the coat refractive index appears to dominate the scattering patterns while the existence of an inner core region may be neglected. Finally the RDG/FA predictions generally agreed with the more exact calculations, confirming its applicability to predict the optical properties of both monodisperse and polydisperse populations of soot aggregates.

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