Stable cluster of identical water droplets formed under the infrared irradiation: Experimental study and theoretical modeling

Infrared irradiation of a droplet cluster has been used during several years as the main method of preventing coalescence of the cluster with a layer of water. The desired effect is achieved by suppressing the condensational growth of large droplets. In new experiments, it was first discovered that prolonged exposure to infrared radiation leads to asymptotic equalization of radii of various droplets. A theoretical analysis of the experimental results was carried out on the basis of the developed model for transient heat transfer. The suggested model includes the thermal effect of infrared radiation, the dynamics of the combined process of evaporation and condensation, as well as convective heat transfer with the surrounding humid air. When calculating the infrared heating of semi-transparent water droplets, the spectral composition of the external radiation is taken into account. The evaporation and condensation of water droplets is considered taking into account the kinetics of the process in the Knudsen layer and the vapor diffusion in the outer part of the boundary layer. Simple analytical relations are obtained for the asymptotic equilibrium parameters of small droplets. The numerical data for the time variation in the size of cluster droplets streamlined by a mixture of air and supersaturated water vapor are in good agreement with the results of laboratory measurements.