An Aerosol Generator for High Concentrations of 0.5–5-μm Solid Particles of Practical Monodispersity

Abstract

A continuous-flow, evaporation-condensation aerosol generator has been designed to produce particles of practical monodispersity of stearic acid in concentrations of over 1 g/m³ at flow rates > 6 L/min. Pure stearic acid containing a dissolved impurity is melt-sprayed and evaporated, producing a nuclei- vapor mixture. The mixture is recondensed and then quickly quenched into spherical, solid particles of a narrow size distribution. The condenser design is a straight, insulated glass tube of 5 cm in inner diameter and of 110 cm in length. A heating and flow straightening conditioning section previous to the condenser provides a relatively flat condensation front across the tube diameter, while the insulated condenser walls in free convection create a low radial temperature gradient, both of which enhance particle monodispersity with particle geometric standard deviations < 1.25. The dynamic condenser conditions for the suppression of homogeneous nucleation were investigated as a function of the ratio of the Grashof-Prandtl numbers product to the Reynolds number.