Experimental Study of an Aerosol Size Selector

The apparatus described is a variant of the ''Cascade Centripeter'' of R.F. Hounam and R.J. Sherwood. Particles are separated according to size through inertia effect; the biggest particles are concentrated at the centre of the gas stream from a circular orifice and collected by a sampling probe placed immediately after the orifice and co-axial with it. The gas flow through the probe represents a small fraction of the total flow, while the particle flow may be a large or very large fraction of the total particle flow entering the instrument. The air passes in succession through a number of orifices of decreasing size. At each stage, the largest particle fraction is diverted into the probe whilst the fine fraction is directed to the next stage. One important characteristic of this apparatus is that it can be used for separating particles according to size while maintaining the aerosol state. By carefully dimensioning and grouping the different stages it is possible, with a given polydispersed aerosol, to isolate the large-particle fraction, the fine fraction or the intermediate fraction. (author)