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Aerosol dynamics of agglomerates


Rogak, Steven Nicholas (1991) Aerosol dynamics of agglomerates. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/PVDQ-PN74.


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 dm of a self-similar cluster of spheres in the continuum regime λ<<dm was calculated to be proportional to the radius of gyration Rg of the cluster for fractal dimension Df>1.3. Slender-body behavior is approached for Df<1.3. In the free-molecule regime dm<<λ, dm is nearly equal to the projected-area diameter dA. In the transition regime dm~λ, dm depends on both dA and Rg. In general, there is a divergence of dA and Rg as the agglomerate size increases, but it is very gradual for typical aerosol agglomerates, for which dm~dA in the transition regime.

The mass transfer of nanometer-sized 211Pb clusters to TiO2 agglomerates was investigated with an Epiphaniometer. The measured mass-transfer-equivalent diameters of the agglomerates were within 10% of dm. 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 dm.

These measurements were incorporated into a model describing the coagulation of agglomerates in the transition regime. Particles smaller than the primary particle diameter d1 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 dm even when dm< 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 d1 but smaller for aerosols consisting of much larger particles.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:aerosol dynamics ; aggregates ; Environmental Science and Engineering
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Environmental Science and Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Flagan, Richard C.
Thesis Committee:
  • Flagan, Richard C. (chair)
  • Fultz, Brent T.
  • Gavalas, George R.
  • Morgan, James J.
  • Seinfeld, John H.
Defense Date:23 April 1991
Non-Caltech Author Email:steverogak (AT)
Record Number:CaltechETD:etd-07122007-131336
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2861
Deposited By: Imported from ETD-db
Deposited On:31 Jul 2007
Last Modified:21 Dec 2019 04:22

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