| 研究実績の概要 |
As the prerequisite of frosting and icing, solidification of water droplets was firstly investigated in this project.A Hele-Shaw cell was designed and used to observe the solidification characteristics of two-dimensional water droplets. including heterogeneous nucleation, droplet morphology,freezing front evolution, trapped air bubbles, and temperature distribution inside a droplet, etc.
Air bubbles in frozen two-dimensional hydrophobic type water droplets were investigated in this year by quantitatively comparing the air releasing process from water droplets during freezing-melting cycles using pumped air distilled water and new made distilled water. Firstly, the subcooling degree would decrease as the dissolved air escaped from the bubbles in the melting stage. For new made distilled water droplet, the nucleation for three cycles did not occur until the experimental condition of the surface temperature was changed from -20 oC to -30 oC. Secondly, during the freezing-melting cycles, the air bubbles become smaller in dimension, and more in total number. Thirdly, the total escaped air volumes for two water droplets are obvious different due to different air dissolved content at start, while the total proportions for three cycles are similar, at 15.87% and 14.02% for two water droplets. Finally, the escaped air content, water droplet temperature decrease duration, and the subcooling degree for two water droplets surround with oil show the same fluctuation trend in the three freezing-melting cycles.
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