Latent cold heat energy storage characteristics by means of direct-contact-freezing between oil droplets and cold water solution

Abstract

Flow and solidification characteristics of paraffin oil droplets (tetradecane with the melting point of 5.8°C, the latent heat of fusion of 229.1 kJ/kg and the density of 770 kg/m 3 at 6°C) ascending in a cold water solution are experimentally investigated. The tetradecane oil is injected from a cylindrical single hole nozzle into the cold water solution and it disperses and forms tiny oil droplets. The oil droplets ascend in the water solution by buoyancy and freeze by direct-contact heat exchange with the cold water solution. Finally, they are completely or partially frozen. The partially frozen oil droplet is composed of a frozen outer shell and unfrozen central core. As a result, it was found that the solidification fraction of the frozen oil droplets, defined as mass ratio of the solidified parts to the whole, increases with a decrease in injection oil temperature and water solution temperature. However, under a lower temperature condition, the injected oil freezes at the outlet of the nozzle, and the solidification fraction reduces with a decrease in injection oil temperature and water solution temperature. A method of data reduction for the solidification fraction is proposed and non-dimensional empirical equations to predict the solidification fraction are proposed in this study.