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

S. Payne*, M. Irwin, T. Johnson, J. Symonds, Cambustion Ltd., UK

In order to investigate filtration efficiency as a function of particle size, previous studies have made use of either impactors based on aerodynamic diameter or electrical mobility classifiers such as the Differential Mobility Analyser (DMA). Impactor devices provide a 50% size cut at specified particle diameters, meaning determination of size-dependent filtration efficiency is a resource-heavy task with large uncertainties. The DMA enables selection of sub-micron particle sizes but relies on the accurate charge-conditioning of input aerosol by a neutraliser dependent on radioactive or X-ray charging methods. Uncharged particles do not pass through the DMA which significantly limits the instrument’s transmission efficiency (particularly at particle sizes below 50 nm), and while the output aerosol contains particles of the same electrical mobility, it is not truly monodisperse due to the presence of multiple charges (particularly at particle sizes above a few hundred nm).

The Aerodynamic Aerosol Classifier (AAC) selects particle size by using a rotating cylinder to balance opposing centrifugal and drag forces for the desired aerodynamic diameter, so that particles move across a sheath flow to the outlet. This new principle of aerosol selection is independent of the aerosol charge state and only limited by diffusion and impaction losses. The benefits to filtration experiments are...

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

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