The condensational growth of spherical water microdroplets is studied in a laboratory setup and with a mathematical model. In the experiment, droplet clusters are kept in a freely levitated state within an upward-oriented flow of water vapor. In the presence of an electrostatic field of 1.5 • 10 5 V m -1 , droplet growth is accelerated by factors 1.5 to 2.0 as compared to conditions without any external electric field. Presumably water molecules in the ambient air are accelerated through the presence of the electric field. A kinetic model to predict the acceleration of condensational growth confirms this hypothesis to be feasible. The droplets themselves are polarized so that the deposition of steam molecules is facilitated in the electric field. The simplifications and limitations of the model are discussed.

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Horizontal oscillations of small droplet clusters (from one to four droplets) levitating over a locally heated water layer in upward vapor–air flow are investigated experimentally. These oscillations are caused by a complex dynamic interaction between the droplets and the nonsteady gas flow. The path of the center of the droplet cluster is similar to a random walk in a potential well. The vibrational spectra of clusters’ centers obtained by Fourier analysis showed several frequency peaks between f = 1.61 and 5.96 Hz found in all clusters, which shows that the cluster tends to oscillate as a whole. The possibility of decoupling of the aerodynamic interaction between the gas flow and the droplets and the interaction between individual droplets is discussed.

The condensational growth of water droplets in technical and natural systems varies with environmental conditions such as droplet size, droplet composition, air humidity, temperature, and turbulence. This contribution addresses the influence of external electrical fields on the condensation process. Although electrical fields exist in the atmosphere, for example in thunderstorm clouds, and although it is generally accepted that electrical fields exert an influence on the condensation process, no quantitative description of this influence at ambient temperatures exists. We present laboratory experiments and a theoretical model to further develop understanding of the influence of electric fields on condensation at various temperatures. The levitated droplet cluster technology is applied to study the kinetics of droplet growth in an external electric field at temperatures between 50 C and 70 C. The theoretical model is designed to mirror the experimental conditions as precisely as possible. Experimental and kinetic model results are in qualitative agreement in that the relative contribution of the electrically induced contribution to total condensation reduces with increasing temperature. Vice versa, the electrically induced condensation significance is expected to further increase with decreasing temperatures below 50 C. We expect that electrocondensation will be the dominating process at room temperatures and even more at temperatures near 0 C, at electric field strengths typical for clouds. Further studies are needed to extend the experimental and theoretical temperature range to conditions typical for clouds in the atmosphere.

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