AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Performance Testing of Two Virtual Impactors
Maria D. King, John Haglund, Ahmad Kalbasi, Samuel Beck, Alexander Zuniga, PAUL A. SOLOMON, Texas A&M University
Abstract Number: 159 Working Group: Instrumentation and Methods
Abstract Virtual Impactors (VI) are used to separate particles in air into two size ranges based on the inertia achieved by the particles as they are accelerated through the inlet or acceleration nozzle. The air stream is typically split 90% / 10% to the major (fine particle)/minor (coarse particle) flow channels often with subsequent collection on filters. Nozzle design and particle deposition (wall losses) within the virtual impactor may affect the cutpoint (50% collection efficiency), slope of the collection efficiency curve, and wall losses within the VI leading to undesirable performance of the sampler.
This study focuses on the performance of two different virtual impactors using fluorescently labelled monodisperse particles in the size range of 0.5 to 10 micrometers to determine their collection efficiency. Regional wall losses were evaluated by wiping different areas of the VI to remove the deposited particles after each cycle. Two sampler designs with two different nozzle geometries are evaluated using fluorescent particles. A commercially available VI with a conical nozzle (Tisch Environmental) operating at 1000 L/min is evaluated for its collection efficiency and used as a basis for comparison. The second VI operates at 1000 L/min and is a redesign of the 1000 LPM sampler replacing the conical nozzle with a newly designed nozzle to achieve improved performance of the VI. The ratio of the collection and acceleration jet diameters and spacing between the two jets were maintained at classical values (in the range between 1.25 and 1.4). The different nozzle profiles play an important role in performance, with the newly designed nozzle expected to result in a steeper slope of the efficiency curve and reduced wall losses.