Experimental evaluation of the Nukiyama-Tanasawa equation for pneumatic nebulisers used in plasma atomic emission spectrometry

Abstract

Drop size distributions for aerosols generated pneumatically were measured by means of a laser Fraunhofer diffraction system. The Sauter mean diameters of these aerosols were compared with those predicted by the Nukiyama-Tanasawa equation. In this study the following variables were considered: dimensions and design of the nebuliser nozzle, solvent nature and gas and liquid flow-rates. These parameters include all the variables contained in the Nukiyama-Tanasawa equation. Three main conclusions can be drawn from the results obtained: (i) in all situations predictions of the mean drop size made using the Nukiyama-Tanasawa equation are greatly in excess of the experimental results; (ii) under a given set of experimental conditions the Nukiyama-Tanasawa equation predicts that aerosols will be produced with larger mean diameters for some organic solvents than for water, whereas it is found experimentally that mean diameters for water aerosols are always larger than for organic solvents, and correlate well with their surface tension values; (iii) the nebuliser performance (i.e., its ability to generate as fine an aerosol as possible) increases as the nebulising gas cross-sectional area becomes, smaller, and also, though to a lesser extent, as the liquid cross-sectional area becomes smaller.