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

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; I 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 mu m diameter) as well as nonspherical solid NaCl particles (.19-.85 mu m) 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%.