EXPERIMENTAL TECHNIQUES FOR MEASUREMENTS OF DROPLET EVAPORATION

New experimental techniques for droplet levitation and evaporation measurements are presented. A so-called ultrasonic levitator was used to position droplets in the size range between 0.5 and 2.2 mm at well defined points in space. Instantaneous droplet size measurements were performed by either a newly developed laser-shadow method or a CCD-camera. The laser-shadow method utilizes the intensity deficit in direct forward direction due to scattering and absorption of the illuminated droplet. Comparative measurements indicate a maximum droplet size error of less than 3%. Preliminary measurements of evaporation rates of single droplets show that pure liquids follow almost perfectly the well known D²-Law of evaporation, while water-sucrose and Ethyl-sucrose mixtures exhibit the expected non-linear behaviour. Finally, the influence of the ultrasonic field on evaporation rates was determined.