Abstract
Aerosol centrifuges give a continuously graded measure of particle aerodynamic diameters. Such information is necessary in assessing the health hazards of airborne particulate matter. Centrifuge performance, however, is affected by secondary flow patterns and gas density differences between the sampled aerosol and the instrument's winnowing gas. An ideal winnowing gas would be identical to the gas phase of the aerosol; therefore, operating conditions which are dependent upon physical properties of the winnowing gas will vary for different aerosols sampled. A mathematical description of fluid dynamics within centrifuges is developed here and dynamic similarity of flow shown to exist when Rossby and Ekman numbers characterizing motion are preserved. As a result of this theoretical analysis successful operating conditions can be predicted a priori rather than by laboratory calibration. The theory is substantiated by experimental data. Application of the theory will make centrifuges more versatile and assure accurate particle size assessment.