Abstract
An improved version of the Hewitt (differential) electric mobility analyzer was developed and its classifying characteristics were determined theoretically. The central mobility of the classified aerosol was found to be ( q c + q m )/4 πΛV, where q c and q m are the clean air and main outlet flows, respectively, Λ is a geometric factor, and Λ is the center rod voltage. The half-width of the mobility band was found to be ( q a + q s )/4 πΛV, where q a and q s are the aerosol and sampling outlet flows, respectively. These expressions were verified by the tests with a monodisperse aerosol of known size and low charge. A major advantage of this device is that the classified aerosol fraction remains airborne, ready for further use or analysis. Thus, one application of the device is the production of monodisperse test aerosols of known size, charge, and concentration by classification of a polydisperse aerosol. Other current applications include accurate measurement of particle electric mobility moments and high-resolution particle size analysis for polydisperse aerosols in the 0.005–1.0 μm size range.
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