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Compressible Flow-based Virtual Impactor towards Bioaerosol Sampling

MYEONG-WOO KIM, Jaesung Jang, Ulsan National Institute of Science and Technology, Korea

Abstract Number: 162
Working Group: Bioaerosols

Abstract
Airborne viruses and bacteria cause allergies and infectious diseases, and their sampling with high concentration and safe capture is an important issue for their rapid measurements. One way to concentrate airborne biological particles coming into the sampler is to pass them through a virtual impactor. Although it is a well-known device, most studies have been focused on one with micrometre-sized cut-off diameter. Only few studies have dealt with virtual impactors with submicron cut-off diameters (Sioutas et al, 1994; Lee et al, 2002).

In this study, we present a virtual impactor with 0.45 μm cut-off diameters for 12 litres per minutes (LPM) using computer (FLUENT 18.2) simulation and experiments. The nozzle diameter (D_n) of the virtual impactor was computed using the Stokes number at the minor to total flow rate ratio of 0.1 and the Stokes number of ~0.4 (Marple and Chien, 1980). Another important parameters are the collection probe diameter (D_c), the distance from the collection probe to the nozzle (S), and collection probe angle (Θ_c). Computer simulation was performed at the following conditions: D_C = 1.0-1.8*D_n, S= 1.2-2.0*D_n, and Θ_c= 5-30°. We observed from the simulation and experiments that the cut-off diameter was around 0.4-0.55 μm, and the separation efficiency reached more than 98% at the particle size larger than 1 μm. The separation efficiency depended on the ratio of D_c/D_n, and its slope decreased with increasing ratio of D_c/D_n. The virtual impactor showed the highest collection efficiency at D_c/D_n = 1.4, and the collection efficiency depended on the collection probe angle. The experimental results for the virtual impactor showed similar value with simulation results. The optimized collection efficiency showed more than 78.4% at particle size larger than 1μm. This will be used for bioaerosol samplers with high collection efficiency and high concentration for high throughput.

This work was supported by the National Research Foundation of Korea(NRF) grant (2020R1A2C1011583), by the ITRC(Information Technology Research Center) support program (IITP-2020-2017-0-01635) supervised by the IITP (Institute for Information & communications Technology Promotion), by Basic Science Research Program through the NRF funded by the Ministry of Education(2020R1A6A1A03040570), and the Institute of Civil Military Technology Cooperation funded by Defence Acquisition Program Administration and Ministry of Trade Industry and Energy of Korean government (UM19402RD4).