Ring-shaped deposition patterns in small nozzle-to-plate distance impactors

Experiments were carried out in an impactor, where the distance between the impactor nozzle and the impactor plate was small, much less than one nozzle diameter in separation. The aerosol deposition patterns in this impactor were investigated for aerosols in the 3–15 μm diameter range. Ring-shaped deposition patterns were observed where the internal diameter and thickness of the rings were a function of the particle diameter. Specifically, the inner diameter and ring thickness were correlated to the Stokes number, Stk; the ring diameter decreased with Stk, and the ring thickness increased with Stk. At Stk∼0.4 the ring closed up, leaving a mostly uniform disk deposition pattern. These ring patterns do not appear to correspond to patterns previously described in the literature, and an order of magnitude analysis shows that this is an inertially dominated process.
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