Stabilization of levitating clusters containing saltwater droplets

Abstract

The influence of salt (NaCl) dissolved in water on the behavior of levitating droplet clusters, including the formation of equilibrium clusters from saline water droplets during their infrared irradiation, is of interest for further laboratory studies of biochemical processes in individual droplets. Experimental results are presented which show for the first time that even a small salt concentration significantly affects the condensational growth of droplets and their equilibrium size, which is achieved only when the salt concentration is below a certain threshold value. The dependence of this concentration threshold on the surface temperature of the pure water layer under the levitating cluster has been determined. Calculations showed that a correct theoretical description of the evaporation of salt droplets during infrared heating should take into account the asymmetry of the problem related to non-uniform volumetric absorption of radiation and a higher salt concentration at the upper surface of the droplet. The proposed approximate model that takes into account the kinetics of water evaporation and salt diffusion appears to be insufficient to agree well with experimental data. The authors believe that a possible physical reason for the additional decrease in the intensity of evaporation from the upper surface of the droplet is the partial crystallization of salt near the droplet surface due to external infrared irradiation.