Experimental and computational studies of liquid aerosol evaporation

Abstract

The phenomenon of liquid aerosol evaporation was investigated both experimentally and computationally in this project. A vibrating orifice aerosol generator (VOAG) was utilised to generate a monodispersed stream of liquid droplets of a desired initial size. Three types of liquids, ethanol, hexane and water, of distinct volatilities were used. The droplets were allowed to travel through air at ambient temperature and pressure. The change in diameter of the droplets as evaporation occurs was measured dynamically using a variety of experimental techniques. Global sizing velocimetry (GSV) was applied to visualize the motion and change in diameter of droplets in real time so as to select an optimal set of operating conditions under which coalescence of droplets did not occur. A phase Doppler interferometer (PDI) was used to measure the Sauter mean diameter and axial velocity of droplets at various distances from the nozzle of the VOAG. The size and velocity profiles obtained were compared with calculations carried out using computational fluid dynamics (CFD) coupled with two different theoretical liquid evaporation models. It was observed that both liquid evaporation models produced similar droplets size profiles for ethanol and water, but a significant difference in the predicted sizes was observed for hexane. In general, a good qualitative agreement between the experimental and computational results was obtained. This represents the first report of a study involving direct comparisons of dynamic measurements of the size evolution of evaporating liquid aerosols with numerical predictions obtained from CFD calculations.