A circumferential slot virtual impactor for bioaerosol concentration

Abstract

A virtual impactor aerosol concentrator with a circumferential inlet slot has been built and tested. Circumferential slot virtual impactors (CSVIs) have low pressure losses, similar to linear slot impactors, but without particle losses due to end effects. The CSVI was designed using the results from a computational fluid dynamics study. The device has a total sampling flow rate of 10 to 30 L/min and a concentration factor of 10:1. CSVIs were built based on the CFD study design and tested with oleic acid droplets and polystyrene latex beads. The test results found a cutpoint Stokes number of 0.75 and 90% particle transmission at least 52X the Stokes cutpoint. At a flow rate of 10 L/min the cutpoint is 2.0 µm aerodynamic diameter (AD) and >90% transmission efficiency was found between 4 mm AD, and 22 µm AD. At the flow rate of 30 L/min the cutpoint is 1.2 mm AD and a >90% transmission efficiency was found between 2 and 10 mm AD. Performance and pressure drop curves were found for a variety of flow rates. The pressure drop across the CSVI at 10 L/min was 270 Pa (1.1 in H2O) with an ideal power consumption of 0.045 watts. At 30 L/min the pressure drop was 970 Pa (3.9 in H2O) with an ideal power consumption of 0.44 watts.