Enhanced Evaporation of Small, Freely Falling Water Drops Due to Surface Contamination

Abstract

Experimental evidence for enhanced evaporation of small (3?9 ? radius) water droplets is presented. Both ?pure? droplets and droplets contaminated with surface active materials that were dropped into air of known relative humidity (96?99%) at an ambient temperature of 29.9C evaporated. The rates of evaporation were determined by photographing the evaporating drops, measuring the distance they fell during a fixed time interval, and applying Stokes law. The contaminated droplets exhibited a rate of evaporation approximately 1.8 ?2 sec?1 faster than the ?pure? drops. This increase can be compared with rates for ?pure? drops of 1.9 and 5.7 ?2 sec?1 at 0.1 and 0.3C dew point depressions, respectively. It is suggested that this phenomenon is caused by the ejection of tiny spurts of water from the drop, this action being a result of the presence of foreign molecules adsorbed on the surface.