Design and Performance Evaluation of Multi-Nozzle Virtual Impactors for Concentrating Particles

Abstract

This paper describes the development and performance evaluation of multi-nozzle virtual impactors used in concentrating aerosol particles. Four virtual impactors were designed: one single-nozzle and three multi-nozzle virtual impactors with 4, 12 and 18 nozzles, respectively. For each of the four designs, two kinds of nozzles were implemented, one that had a flat surface and the other a cut-out nozzle designed with consideration of airflow streamlines inside the impactor. Thus, a total of 8 models of virtual impactors were designed and fabricated to study the internal particle loss and concentration performance. Multi-nozzle devices were provided primarily for applications involving high-volume air sampling. Virtual impactors with cut-out nozzles yielded higher fractional collection efficiencies and lower internal losses than virtual impactors with flat nozzles. It is expected that significant flow turbulence will occur in the space between the acceleration nozzles and the collection probes. This may increase the internal losses arising from back-impaction on the acceleration nozzles and particle deposition on the collection probes with flat nozzles.