Abstract
A supersonic virtual impactor with a Laval nozzle was numerically investigated into its performance as a separator or concentrator for ultra-fine aerosol particles down to nano-size range. Influences of the impactor geometry, such as shape of nozzle cross-section (rectangular and circular), clearance between nozzle exit and particle collection probe inlet, and probe geometry on the separation characteristics were numerically investigated. The effect of sheath flow along the nozzle wall and center was investigated into its effect on the separation characteristics and the particle wall loss.
The supersonic virtual impactor was designed to obtain the stagnation flow, which provided a distinct standing shock wave between the nozzle exit and the collection probe inlet. The smaller distance from the collection probe inlet to the standing shock wave was related to the cutoff size of particle. The sheath air flow improved the separation sharpness and the particle wall loss.
