Frosting characteristic measurement and defrosting performance improvement

结霜特性测量和除霜性能改进

• 批准号: 17F17365
• 负责人: 党 超鋲
• 金额: $ 1.41万
• 依托单位: The University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for JSPS Fellows
• 财政年份: 2017
• 资助国家: 日本
• 起止时间: 2017-11-10 至 2020-03-31
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-17F17365/
• 关键词: Heterogeneous nucleation; droplet solidification; freezing front; trapped air bubbles; temperature distribution; frost and ice; 着霜; 除霜; 白色干渉計

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.

作为结霜和结冰的前提条件，本文首次对水滴的凝固过程进行了研究，设计了Hele-Shaw单元，并利用该单元对二维水滴的凝固特性进行了观测。包括非均匀成核、液滴形态、冻结前沿的演化、捕获的气泡以及液滴内部的温度分布等。通过定量地比较在冷冻-融化循环中使用泵送空气蒸馏水和新制备的蒸馏水的水滴的空气释放过程，本年度研究了冷冻的二维疏水型水滴中的气泡。首先，在熔化阶段，溶解空气从气泡中逸出，过冷度降低。对于新制备的蒸馏水滴，在表面温度从-20 ℃变化到-30 ℃的实验条件下，三个循环的成核都没有发生。其次，在冻融循环过程中，气泡尺寸变小，数量增多。第三，由于初始溶气量不同，两种水滴的总逸出气量有明显差异，但三个循环的总逸出气量比例相近，分别为15.87%和14.02%。最后，在三次冻融循环中，两种油膜包裹水滴的逸出空气含量、水滴温度下降持续时间和过冷度的变化趋势相同。