Drag on Clusters of Submicron Spheres in Gravitational and Electrical Fields

Abstract

THE dependence of hydraulic and aerodynamic drag on particle shape has been of interest for a considerable time but theoretical work has greatly exceeded experimental results, especially for submicron particles. Fuchs¹ gave a concise summary of the position and Preining² and Vomela and Whitby³ have published mainly theoretical articles. Kunkel⁴ determined the drag on various configurations of steel balls glued together and falling in oil, and Megaw and Wiffen⁵ compared the diffusion coefficient of single and clustered submicron polystyrene spheres. Stöber et al.⁶ deduced that the Stokes diameter d_n of a cluster containing n spheres should be related to the diameter d₁ of a single sphere by the expression and confirmed its validity in an experiment in which single particles and clusters of submicron polystyrene spheres were centrifuged out of a spinning air stream. Stöber et al. also showed that, when expressed in terms of the Stokes diameter, Kunkel's results (in which the unit sphere was 0.12 cm diameter) agreed very well with those for submicron spheres in air.