Experimental and theoretical studies of aerosol agglomerates

Citation

Drayton, Paul Jeffrey (1997) Experimental and theoretical studies of aerosol agglomerates. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/r246-6h84. https://resolver.caltech.edu/CaltechETD:etd-01092008-092702

Abstract

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The behavior and properties of aerosol agglomerates were experimentally and theoretically probed. Brownian coagulation coefficient rates for titania aerosol agglomerates of mobility diameters from 20 nm to 250 nm were measured. The experimental results agree reasonably well with the predictions of Rogak and Flagan, with the smallest agglomerates showing some enhancement of the coagulation coefficient by electrical image and van der Waals forces.

In order to analyze the coagulation experiments, the bipolar diffusion charging of aerosol agglomerates was studied. The steady-state bipolar charge distribution of titania agglomerates with primary particle diameters of 6.5 [...] 3 nm, were measured using a Tandem Differential Mobility Analyzer (TDMA) system. The experimental results were compared to an extended Fuchs steady-state charge distribution. The agglomerates were more likely to carry multiple charges than the theory predicted. The extended Fuchs theory was found to be strongly dependent on the properties of the ions.

Alignment of non-spherical particles with the electric field in a DMA, can bias size measurements. To investigate this phenomenon, a theoretical study of agglomerate particle alignment was undertaken. The tendency of a particle to align with the imposed field was found to be characterized by the ratio of the Coulombic to the thermal energies, [gamma]. The electrical mobility ratio [phi], of a linear chain aggregate was calculated to develop the orientation theory. As the number of primary particles increases, [phi] reaches a maximum and then declines. Experimental observations of particle alignment were compared to the theoretical predictions with the experimental data showing alignment effects for [gamma] over 5.0.

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