Freezing of a water droplet due to evaporation—heat transfer dominating the evaporation–freezing phenomena and the effect of boiling on freezing characteristics

One of the authors has proposed a novel transport/storage system for the waste cold from the gasification process of liquefied natural gas (LNG), which consists of an evaporator, a cold trap, and a pipeline. In order to estimate the performance of this system, one should know the pressure in the evaporator, in which evaporation–freezing of a PCM occurs, and in the cold trap, as well as the pressure drop of the pipeline due to the flow of low pressure vapor of the PCM. In this paper, the cooling/freezing phenomena of a water droplet due to evaporation in an evacuated chamber was experimentally examined, and the heat transfer dominating the evaporation-freezing phenomena was investigated in order to estimate the pressure in the evaporator. From the results, it was shown that the water droplet in the evacuated cell is effectively cooled by the evaporation of water itself, and is frozen within a few seconds through a remarkable supercooling state, and that the cooling rate of the water droplets were dominated by heat transfer within the droplet under the abrupt evacuation condition. The later result means that, in order to obtain an ice particle by evaporation–freezing, the surroundings of the water droplet should be evacuated at the pressure as low as the saturate pressure of water at the maximum supercooling temperature of the droplet.