Development and Evaluation of a High-Volume Virtual Impactor with a Circumferential Slit Nozzle

SUSMITA ISLAM, Qingqing Fu, Li Li, Bernard Olson, Christopher J. Hogan, University of Minnesota

     Abstract Number: 82
     Working Group: Instrumentation and Methods

Abstract
One important application of virtual impactors is to increase the concentration of bioaerosols during sampling, as the analysis of biological agents requires sampled pathogen concentrations above the limit of detection for the assay utilized. To this end, virtual impactors designed for high aerosol flow rates and with submicrometer cut-off sizes are desirable for concentrating particles as part of bioaerosol sampling schemes, to collect large volumes of aerosol in small liquid volumes or small substrate areas.

In this study, we designed a high-volume virtual impactor with a circumferential slit nozzle, targeting a cut-off size of 0.65 µm when sampling an aerosol flow rate of 720 LPM with a minor flow of 72 LPM. Performance evaluations were conducted in an ASHRAE Standard 52.2-2017 wind tunnel using polydisperse oleic acid particles generated by an atomizer. Experimental results indicate that the 50% cut-off point of the impactor agrees well with numerical predictions. However, the particle collection efficiency curve is less sharp compared to that of conventional virtual impactors with round nozzles. To better understand particle losses and trajectories within the designed virtual impactor, we performed computational fluid dynamics (CFD) simulations coupled with particle trajectory analysis. The effects of manufacturing tolerances—such as varied width in acceleration nozzle and misalignment between the acceleration nozzle and receiving tube—will be discussed.