Modelling of necking and primary particle polydispersity in soot aggregates and their effects of the scattering matrix
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Date
2023
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Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2023.
Abstract
Soot has complex morphological characteristics such as aggregate and primary particle polydispersity, and necking. Modelling these structures and their e↵ects on the optical behavior is challenging attributed to the complex morphology and the corresponding formation mechanism. In this study, a comprehensive analysis of the impacts of necking and polydispersity in aggregate and primary particle size is conducted to identify their e↵ects on scattering matrix elements. Aggregate representations are generated via tunable fractal generation algorithms using particle-cluster and clustercluster aggregation, based on typical morphological parameters of flame-soot. Di↵erent necking models are evaluated quantitatively based on measured scattering matrix elements derived from an experimental study in the literature. Polydispersity in aggregate and primary particle size are implemented through log-normal distribution functions. Scattering matrix elements are calculated via discrete dipole approximation and multisphere T-matrix method. The impacts of the considered structures on the scattering matrix elements are presented, and the volume variation-based approach is evaluated for representing the impact of necking. According to the results, the impacts of necking and primary particle polydispersity are similar and dominated by the resultant volume change, whereas that of aggregate polydispersity is more complicated. Accordingly, the volume variation-based approach performs well in representing the e↵ect of necking on the scattering matrix for the specified cases. The deficiency of the volume variationbased approach is discussed as well, and an enhancement is proposed to increase its accuracy.