Rapid Solidification Process of a Water Droplet Due to Depressurization

摘要

This paper reports an experimental and numerical study of rapid solidification of a water droplet due to depressurization. During the experiment, a distilled water droplet was suspended on a thermocouple, which was also used to measure the droplet temperature, and the droplet surface temperature was captured by an infrared thermograph. The experimentally measured data indicates that freezing occurs from the droplet surface when the droplet temperature reaches a certain subcooling. A mathematical model was constructed to simulate the temperature transition and the temperature distribution within the sphere. The model considers the pressure reduction in the test vessel, the kinetic condition for undercooled solidification, and the heat transfers due to convection and sublimation at the ice surface. A coordinate transformation method was used to capture the two moving boundaries within the droplet, which are internal solidification interface and surface sublimation interface. The model-predictions agree well with the measured temperature data, demonstrating the soundness of the present model. The results show that the rapid solidification of a water droplet due to depressurization is a typical non-equilibrium phase transition, with a lower ambient pressure, the solidification speed will be faster, and the duration time for droplet center temperature keeps constant will be shorter.