Phd records
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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenWed, 31 Jan 2024 19:42:24 +0000Aerosol dynamics of agglomerates
https://resolver.caltech.edu/CaltechETD:etd-07122007-131336
Authors: {'items': [{'email': 'steverogak@gmail.com', 'id': 'Rogak-S-N', 'name': {'family': 'Rogak', 'given': 'Steven Nicholas'}, 'show_email': 'YES'}]}
Year: 1991
DOI: 10.7907/PVDQ-PN74
<p>The mobility, charging, coagulation and mass-transfer properties of aerosol agglomerates were related to the particle and the background gas mean free path λ. The mobility-equivalent diameter d<sub>m</sub> of a self-similar cluster of spheres in the continuum regime λ<<d<sub>m</sub> was calculated to be proportional to the radius of gyration R<sub>g</sub> of the cluster for fractal dimension D<sub>f</sub>>1.3. Slender-body behavior is approached for D<sub>f</sub><1.3. In the free-molecule regime d<sub>m</sub><<λ, d<sub>m</sub> is nearly equal to the projected-area diameter d<sub>A</sub>. In the transition regime d<sub>m</sub>~λ, d<sub>m</sub> depends on both d<sub>A</sub> and R<sub>g</sub>. In general, there is a divergence of d<sub>A</sub> and R<sub>g</sub> as the agglomerate size increases, but it is very gradual for typical aerosol agglomerates, for which d<sub>m</sub>~d<sub>A</sub> in the transition regime.</p>
<p>The mass transfer of nanometer-sized <sup>211</sup>Pb clusters to TiO<sub>2</sub> agglomerates was investigated with an Epiphaniometer. The measured mass-transfer-equivalent diameters of the agglomerates were within 10% of d<sub>m</sub>. The lead cluster mean free path was nearly the same as λ. For an analogous phenomenon, the bipolar diffusion charging of agglomerates, it was found that the charging-equivalent diameter of the agglomerates was ~10% larger than d<sub>m</sub>.</p>
<p>These measurements were incorporated into a model describing the coagulation of agglomerates in the transition regime. Particles smaller than the primary particle diameter d<sub>1</sub> were assumed to coalesce rapidly, while large particles were assumed to be solid with a fractal structure. In the transition regime, the agglomerate mean free paths are much smaller than d<sub>m</sub> even when d<sub>m</sub>< λ. This leads to distinctly different dynamic behavior than predicted by previous models developed for the continuum or free-molecule regimes. The enhancement of coagulation over that of dense spheres is large for aerosols with median diameters slightly greater than d<sub>1</sub> but smaller for aerosols consisting of much larger particles.</p>
https://thesis.library.caltech.edu/id/eprint/2861