Tesis de Postgrado Acceso Abierto
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Thesis ESTUDIO NUMÉRICO DE LA INFLUENCIA DE LA DISPERSIÓN Y OVERLAPPING DE PARTÍCULAS PRIMARIAS EN LA MORFOLOGÍA DE AGREGADOS DE NANOPARTÍCULAS DE HOLLÍN(2017) Morán Cofre, José Carlos; Departamento de Industrias; Fuentes Castillo, Andrés HernánThe agglomeration of nanoparticles lead to the formation of aggregates, which morphology is poorlydescribed by using Euclidean geometry. Fractal geometry in the other hand allows a quantitatively descriptionof the morphology of such aggregates. The experimental application of this geometry is carried out basedon the thermophoretic sampling technique with the subsequent transmission electron microscopy (TEM)generation of digital images. These studies have reported several morphological charasteristics of theseaggregates including: polydisperse sizes and overlapping of primary particles, polydispersity in aggregatessize and number of primary particles.The aggregates mass and area was found to increase monotonically with primary particles polydispersity,which was demonstrated analytically for aggregates consisting of a large number of primary particles. Thekind of primary particle size distribution studied (normal or lognormal) limit the maximum polydispersitylevel they can describe and therefore its eect on aggregates morphology. The shape of the coordinationnumber distribution function was found to be very sensible to the polydispersity level of monomers withlognormal PPSD, the anisotropy coecient declined steadily when increasing monomers polydispersity,meanwhile the radius of gyration did not change considerably. For monomers size distribution normal, noconsiderable eects on morphology were found for the range of polydispersity analyzed. In the other handlarge anisotropy coecients were found when adding overlapping to primary particles.Experimental studies of soot morphology based on analysis of TEM images usually neglect the potentialeects of primary particle polydispersity and overlapping. In this study, fractal aggregates of dierent sizesconsisting of polydisperse and overlapping primary particles were numerically generated using a fractaldimension and prefactor relevant to soot. A total of 3600 two-dimensional projections for each conditionstudied was produced and analyzed using two TEM image analysis methods commonly used in the combustionand aerosol communities to evaluate the eects of primary particle polydispersity and overlapping on therecovered morphological parameters of soot. The method of Tian et al. 2006 performs better in recovering thenumber of primary particles in an aggregate, the fractal dimension and prefactor than the method of Brasilet al. 1999. The eects of primary particle polydispersity and overlapping are found to decrease slightlythe derived fractal dimension and to increase the derived prefactor. Overall, the recovered fractal dimensiondisplays a weak dependence on primary particle polydispersity and overlapping.
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