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Experimental Characterization of Microfabricated VirtualImpactor Efficiency
Citation:
Cados, T., O. Mahdavipour, D. Fahimi, S. Khaledian, P. Solomon, I. Paprotny, L. Gundel, AND T. Kirchstetter. Experimental Characterization of Microfabricated VirtualImpactor Efficiency. 2015 AAAR Annual Meeting, Minneapolis, MN, Minneapolis, MN, October 13 - 16, 2015.
Impact/Purpose:
The National Exposure Research Laboratory (NERL) Human Exposure and Atmospheric Sciences Division (HEASD) conducts research in support of EPA mission to protect human health and the environment. HEASD research program supports Goal 1 (Clean Air) and Goal 4 (Healthy People) of EPA strategic plan. More specifically, our division conducts research to characterize the movement of pollutants from the source to contact with humans. Our multidisciplinary research program produces Methods, Measurements, and Models to identify relationships between and characterize processes that link source emissions, environmental concentrations, human exposures, and target-tissue dose. The impact of these tools is improved regulatory programs and policies for EPA.
Description:
The Air-Microfluidics Group is developing a microelectromechanical systems-based direct reading particulate matter (PM) mass sensor. The sensor consists of two main components: a microfabricated virtual impactor (VI) and a PM mass sensor. The VI leverages particle inertia to separate coarse and fine particles into two airstreams: a minor flow of 0.6 cc/min and a major flow of 5.4 cc/min. This presentation highlights the novel methods developed to experimentally evaluate the particle separation efficiency of the microfabricated VI.Experiments are carried out inside a well-mixed chamber. Polystyrene latex spheres (PSLs) are collected on membrane filters near the inlet of the VI and downstream of the VI’s major and minor flow channels. A microscope is used to imageand count PSLs on less than 10% of each filter, and the total number of particles collected on each filter is estimated usingan extrapolation model. The model is validated using three different methods, including collecting replicate samples andby comparing the mass concentration of PSLs in the chamber calculated from the number of PSLs on each filter to the massconcentration measured with a calibrated DustTrak aerosol monitor. The particle separation efficiency of the VI has thusfar been evaluated experimentally for 0.5, 1.5, and 2.5 micrometer (diameter) PSLs and compared to the efficiencypredicted using a computational fluid dynamics model. Counting particles on filters at the VI's inlet and outlet anddeposited within the VI's flow channels (wall loss) allows for a nearly complete mass balance to be obtained and calculation of the VI collection efficiency curve.
