The electrical capacitance of aerosol particles indicates their diffusion charging level, which is important for their classification by electrical mobility, precipitation (removal or collection) in electrical fields, and morphology characterization. A minimum potential energy method was used to calculate the electrical capacitance for agglomerates composed of equally sized spherical primary particles (PPs). By discretizing the particle surface using finite spherical elements, as net charge only resides on the surface of an isolated conductor, this method was extended to calculate the capacitance of arbitrarily shaped particles. Based on the capacitance, the charge of these particles was obtained by diffusion charging theory. In addition, the dynamics of capacitance and mean charge of agglomerate during sintering or coalescence (at constant particle volume) to aggregates and finally to compact structures was computed and found in agreement with sparse experimental data. Particle morphology strongly affects the capacitance and mean charge of fractal-like particles. For example, both decreased by 60% upon full coalescence or sintering of an agglomerate consisting initially of 128 PPs.
Bibliographical noteFunding Information:
This work was supported by National Science Foundation (NSF) Grant #1236107 , “GOALI: Unipolar Diffusion Charging of Spherical and Agglomerated Nanoparticles and its Application toward Surface-area Measurement”. The authors wish to acknowledge the University of Minnesota Supercomputer Institute for providing the computation time for this project. The research leading to these results has received funding in part by the Swiss National Science Foundation (Grant no. 148643 ) and the European Research Council under the European Union׳s Seventh Framework Program (FP7/2007–2013, ERC Grant agreement no. 247283 ).
- Agglomerates and aggregates
- Electrical capacitance and charge
- Spatial charge distribution