Dynamics and Measurement of Smokes. II The Aerodynamic Diameter of Chain Aggregates in the Transition Regime

Aerodynamic diameters of linear Fe2 O3 chain aggregates with up to 160 primary particles ranging in mean diameter from 0.035 to 0.12 μm were measured with a cylindrical aerosol centrifuge. Aerodynamic diameters closely follow the semiempirical expression were ρ/ρo is the ratio of particle density to unit density; DI and og are the mean diameter and geometric standard deviation of the primary particles, respectively; and n is the average number of primary particles in a chain found at the location corresponding to D AE. The coefficient k is a function of D I only. In the continuum limit (DI $$ 0.02 μm) κ appears to reach a constant value that is consistent with earlier measurements by Stöber et al. (1970). The results suggest a predominant settling orientation normal to the chain axis for centrifuge measurements. Values for the slip coefficient as a function of chain thickness and length are derived, and imperfections in the chain configuration are explained in terms of a coefficient X.