Focusing of aerosols into a particle beam at pressures from 10 to 150 Torr

Abstract

The study of aerosols including chemical analysis has been substantially advanced after the development of aerodynamic focusing lenses. Test results of 2 such lenses are presented; 1 operating at pressures between 15 and 80 Torr and the other at higher pressures between 30 and 175 Torr. The lenses consist of 7 single orifices separated by spacers and contained in a tube of about 10 cm in length. Orifice diameters range from 1.40 to .25 mm, while the exit holes (nozzles) are smaller. Laminar gas flow within a lens produces a narrow particle beam which is directed into a vacuum chamber for analysis of beam width and position, aerosol transport efficiency, linearity, and other parameters. The lenses were tested both with spherical monodisperse oil particles (.34-4 μm diameter) as well as nonspherical solid NaCl particles (.19-.85 μm) simulating larger particles with lower density. Both lenses produce narrow aerosol beams with diameters smaller than 4 mm about 90 mm downstream of the nozzle. Although nonspherical particles broaden the aerosol beam by a factor of 2-4, this fact allows a distinction between liquid and solid nonspherical aerosols. Beam characteristics are well reproduced when lenses are dis- and reassembled. The transmission of aerosols through each of the 2 lenses is a nearly linear function of the pressure. Transmission efficiencies have been measured to be above 90%.