Transport and Deposition of Spherical Particles and Fibers in an Improved Virtual Impactor

Flow velocity in an improved virtual impactor was calculated for a Reynolds number of 4000 using a finite-element method. The governing equations of motion for spherical particles and fibers were used along with flow field information to calculate transport and losses in the impactor. The calculated separation efficiency and loss fraction for spherical particles agreed with experimental results reported in the literature. For fibers, separation efficiency curves were obtained in terms of fiber Stokes number and aspect ratio. The calculated collection efficiency curve moved to higher Stokes numbers with increasing fiber aspect ratio. All fiber sizes showed significant losses at the tip of the collecting probe of the impactor. As a result, the separation efficiency never reached 100%. The computational approach illustrated here can be used for predicting separation characteristics, which will lead to improved and cost-effective design of the impactor.