A new methodology for measuring filtration efficiency as a function of particle aerodynamic diameter using a monodisperse aerosol source

S. Payne*, M. Irwin, J. Symonds, Cambustion Ltd.; T. Johnson, University of Cambridge, UK

The Aerodynamic Aerosol Classifier (AAC) uses a centrifugal force and sheath flow between two concentric rotating cylinders to produce a truly monodisperse aerosol classified by aerodynamic diameter with a range from 25 nm to 6.8 ┬Ám. The instrument is unique in being able to produce a stream of particles of known finite aerodynamic diameter; other technologies such as impactors and virtual impactors provide either an upper or lower cut. Since the classification technique is independent of particle charge state, there are no losses in throughput associated with charging efficiency, and no multiple charging peaks such as those commonly associated with the differential mobility analyser (DMA).

Samples from two respiratory filtering half masks conforming to international standards for personal protective equipment were mounted in an in-line filter holder. These were placed downstream of the AAC which was run at a series of rotational speeds and sheath flows to select aerodynamic diameters from two atomised aerosol sources: sodium chloride (NaCl) and dioctyl sebacate (DOS). The upstream and downstream particle number concentrations were measured using a condensation particle counter (CPC). Tests at each particle size were run back-to-back replacing the AAC with a DMA long column, which was configured to select particles of the same aerodynamic diameter when converted from electrical mobility size space. This enabled direct comparison of transmission efficiency and filter penetration behaviour between the two methods of classification. It was found that...

Session: G5 - Filter Test Systems
Day: 14 March 2018
Time: 09:00 - 10:15 h

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