目的 探讨液滴撞击低温曲面时的动态行为及固化特征,对于电力输送、风力发电以及航空航天等领域增强设备运行安全及性能具有重要意义。方法 采用黄铜圆柱表面,使用半导体制冷技术将圆柱表面冷却至约-15 ℃,将液滴以不同高度撞击圆柱表面,采用高速摄影仪分析液滴的动态行为特征。在此基础上,分别探讨液滴撞击外部振动激励表面以及硅油浸泡表面时的动态行为特征,探究其对液滴铺展和冻结特性的影响。结果 随着液滴撞击We数的增加,液膜厚度从撞击位置向两侧显著降低,分布逐渐趋于均匀且铺展范围增加,并且液滴的最大铺展因子βmaxµWe0.477,液滴到达最大铺展因子对应的时间tmaxµWe0.306。当低温圆柱表面存在一定频率和振幅的振动时,振动使得液膜更多地集中在表面下方,铺展范围更大,液膜厚度更薄。当液滴撞击低温浸油圆柱表面时,由于表面的润滑性,液滴在表面上的铺展受到抑制,液滴铺展因子明显减小,并主要集中在表面上部,且最终覆冰厚度显著增加。当撞击We数超过某一临界值后液滴会发生分离现象。运用能量分析方法,建立了理论分析模型,分析了液滴撞击前后的能量特征。结论 施加振动,随着振幅增大液滴的铺展范围增大且液滴到达最大铺展因子的时间减小,βmax在振动的影响下增加了12%,冰层厚度相对减薄了16%。当液滴撞击浸油表面时,在撞击We数小于临界值情况下,冰层厚度增加了13%且变化更加平缓,βmax相对减小5%;当超过临界值时,液滴撞击浸油表面后发生分离,残余液滴在表面上半部分形成一层薄薄的厚度相对均匀的冰层。
Abstract
The work aims to explore the dynamic behavior and solidification characteristics of droplets impacting cold curved surfaces, which is of significant importance for improving operation safety and performance in fields such as power transmission, wind energy generation, and aerospace. In the experimental section, an untreated cylindrical surface was prepared, and the surface was cooled to approximately -15 ℃ with a semiconductor thermoelectric cooler. A droplet impacted the cylindrical surface from varying heights, and the dynamic behavior of the droplet was analyzed with a high-speed camera. Two methods, external vibration excitation and surface modification by silicone oil immersion were employed to investigate the effects on the droplet spreading and freezing characteristics. The dynamic behavior of the droplet impacting different surfaces was observed and studied. It was found that as the Weber number of the droplet increased, the liquid film thickness significantly decreased along the cylindrical surface on both sides of the impact location. The distribution of the liquid film thickness gradually grew more uniform, and the spreading range increased. The maximum spreading factor of the droplet, βmax, was found to obey the relationship βmaxµWe0.477, while the time to reach the maximum spreading factor tmaxµWe0.306 was obtained. When the droplet finally froze, the frozen area was large, and the ice thickness was thin. Next, external vibrations with different vibration frequencies and amplitudes were applied to the cold cylindrical surface. The results showed that the vibration caused the liquid film to concentrate mainly in the lower part of the surface, leading to a larger spreading range and thinner liquid film. The final frozen area of the droplet increased, but the ice thickness grew thinner. When the droplet impacting a low-temperature oil-infused cylindrical surface, the lubrication effect of the surface suppressed the spreading. The spreading factor of the droplet was significantly reduced, and a droplet separation phenomenon occurred when the Weber number exceeded a certain critical value. The final ice coverage area decreased and was mainly concentrated in the upper part of the surface, with the ice layer thickness significantly increasing. An energy analysis was conducted, considering the conversion of the droplet's kinetic and vibration energy into the deformation energy of the droplet during the spreading process. A theoretical analytical model was established. The experimental values obtained from repeated experiments were consistent with the theoretical predictions, thus validating the accuracy of the model. The effects of applied vibration excitation and silicone oil modification on energy changes were also analyzed. When vibration was applied, the time for the droplet to reach its maximum spreading factor decreased and the maximum spreading factor increased with the increase of vibration amplitude. The maximum spreading factor (βmax) increased by 12%, and the ice coverage area expanded, though the ice thickness was reduced by 16%. When the droplet impacted the low-temperature oil-immersed cylindrical surface at Weber numbers below the critical value, the final ice thickness increased by 13%, with a smoother variation, while βmax decreased by 5%. However, when the Weber number exceeded the critical value, a droplet separation occurred, and the residual droplet formed a thin, relatively uniform ice layer on the upper part of the surface.
关键词
液滴撞击 /
液膜 /
曲面 /
结冰 /
振动 /
注油表面
Key words
droplet impacting /
liquid film /
curved surface /
icing /
vibration /
oil-infused surface
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基金
国家自然科学基金资助项目（51776128）
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