Classification Performance of Two-Stage Virtual Impactor

Abstract

The classification performance of a newly constructed two-stage virtual impactor was studied both theoretically and experimentally. It is found that the classification characteristics of the first stage are well represented by the previous theory, which accounted for the effects of core and sheath air flows. It is also found that the classification characteristics of the second stage agree well with the theory based on potential flow calculations, to the extent that the flow rate ratio of core to total air flow is assumed to be determined by the critical trajectories of particles in the first-stage jet. The theory, however, must take into account the fact that the particles deviate to the center line in the acceleration zone. The separation characteristics, which affect the size distribution of the test aerosols produced by the impactor, are also found to be estimated by the individual separation characteristic of the first and the second stages.