Visualization of Defect Particle Transmission to the Major Flow of a Slit Virtual Impactor

Abstract

Convective transport behavior of monodisperse supermicron particles has been analyzed in a slit virtual impactor. Particle trajectories were visualized using video imaging of scattered light and fluorescence from particles traversing the separation region of the impactor. The collection efficiency of the major flow was measured on an individual-particle basis for bulk Stokes numbers ranging from 0.42 to 25. We present an analysis based upon the local Stokes number to explain the transmission frequency of particles significantly larger than the 50% cutoff diameter into the major flow. The transmission efficiency calculated from the local Stokes number exhibits good agreement with the measured collection efficiencies.