PHASE-DOPPLER DIAGNOSTIC STUDIES OF PRIMARY AND TERTIARY AEROSOLS PRODUCED BY A HIGH-EFFICIENCY NEBULIZER

Two phase-Doppler instruments (a two- and a four-beam laser light-scat tering interferometer) are used for the diagnostic studies of aerosol produced by a pneumatically driven, high-efficiency nebulizer (HEN). T he new nebulizer (capillary i.d. = 79 mu m) is useful in plasma spectr ometries for nebulization of solutions at uptake rates of 10-1200 mu L /min. Diagnostic studies involve measurements on primary and tertiary aerosols prior to injection into a high-temperature plasma. Simultaneo us measurements are conducted on droplet size and droplet velocity dis tributions, size-velocity correlation, span of aerosols, droplet numbe r density, volume flux, and percent volume of aerosol droplets under 8 mu m. The four-beam interferometer (or the 2D phase-Doppler system) i s used to assess the axial and radial velocity components of the prima ry aerosol from the HEN. A broad range of droplet velocities is observ ed near the nebulizer tip for the primary aerosol, but most tertiary d roplets travel at nearly the same velocity, much slower than the prima ry droplets. The Sauter mean diameter (D-3,D-2) of the primary aerosol is found to increase both along the center line of the aerosol pathwa y and at the boundary of the spray. The D-3,D-2 of tertiary aerosol ge nerated by the HEN is approximately 2-3 mu m smaller than that of a co nventional pneumatic nebulizer (capillary i.d. = 422 mu m) over a wide range of solution uptake rate (10-1200 mu L/min). For the solutions t ested, the D-3,D-2 of tertiary aerosol from the HEN is not affected si gnificantly by solution viscosity and surface tension. The significanc e of these measurements and data for enhancing analytical performance indexes in plasma spectrochemical analysis are discussed.