Performance of a modified virtual impactor

Abstract

The performance of a modified virtual impactor with a clean air core in the center of an aerosol flow is described. With this feature, the modified virtual impactor has overcome the inherent disadvantage of conventional designs which have fine particle contamination in the coarse particle fraction. Furthermore, the separation efficiency of this impactor can be predicted from the efficiency curve of the conventional type virtual impactor and the ratio of clean air flow to the total flow rate. With a higher clean air flow, the 50% cutoff Stokes number slightly increases and the efficiency curve has better separation characteristics. Internal wall losses in the impactor are a function of particle size and reach a local maximum near the 50% cutoff size. © 1986 Elsevier Science Publishing Co., Inc.