Factors affecting the diameter of ring-shaped deposition patterns in inertial impactors having small S/W ratios

Abstract

Inertial impactors are an important part of aerosol science where they are used to obtain particle size distributions in a wide range of practical and scientific applications. A shortcoming of these devices is that the number of bins in the resulting distribution is limited to the number of impactors in an impactor cascade. Recent work has shown that if the ratio of the nozzle-to-impactor distance (S) to the nozzle diameter (W) is very small, S/W ∼ O(0.01), the normally disk shaped particle impaction pattern becomes a ring. Under these conditions the ring diameter is proportional to the particle diameter, presenting an opportunity for developing impactors capable of sub-stage particle diameter sizing. Before such impactors may be developed, however, further information is required regarding how the diameter of the aforementioned rings vary with S/W and particle diameter. Herein, experiments are presented where ring-shaped deposition patterns are obtained for a range of particle diameters and S/W. These results are consolidated to provide a relationship between the relevant dimensionless variables: the Stokes number (dimensionless particle diameter), S/W, and dimensionless ring diameter. Computer simulations of particle trajectories under the experimental conditions are presented and are used to reveal the underlying mechanism of this effect. Finally, a discussion is presented of practical approaches for using these results to obtain high resolution particle size distributions from impactor cascades.

Copyright © 2021 American Association for Aerosol Research

EDITOR:

• Jingkun Jiang

Additional information

Funding

This material is based upon work supported by the National Science Foundation under Grant No. 1804304.