目的 探究超疏水表面在结霜初期液滴冷凝与冻结特性。方法 采用操作简便、成本低廉的二次喷涂法制备实验所需的超疏水表面。基于可视化低温实验平台,对裸铝表面、疏水表面及2种超疏水表面（超疏水A和B）的冷凝与冻结过程进行可视化研究,并系统探究了不同冷表面温度对超疏水表面冷凝特性（Tw=3、0、-3 ℃）及冻结特性（Tw=-3、-6、-9 ℃）的影响。结果 研究表明,在相同工况下,接触角越大的表面,其冷凝液滴半径越小,表面覆盖率越低,液滴冻结所需时间越长。与超B表面冻结所需时间相比,裸铝、疏水、超A表面冻结所需时间分别缩短了92.8%、70.3%、45.9%。超疏水表面由于液滴合并跳跃现象显著,部分液滴甚至弹跳并带走周围液滴滑落表面,形成大量干燥区域,进一步降低了表面覆盖率。液滴间距大于冰桥传播的临界距离,从而有效抑制了冰桥的扩展。结论 超疏水表面凭借其低表面能和独特的微纳结构,表现出较高的接触角和较低的铺展系数,显著提高了液滴成核势垒,延缓了液滴生长速率,降低了表面覆盖率。此外,由于超疏水表面低黏附性,导致表面存在液滴合并跳跃行为进一步抑制了冰桥传播,最终实现了显著的抑霜效果。
Abstract
The study of the condensation and freezing characteristics during the initial stage of frost formation on superhydrophobic surfaces is of paramount importance for understanding the mechanisms involved in frost suppression. The work aims to focus on studying the behaviors of condensation and freezing on superhydrophobic surfaces, which is critical for developing effective strategies to mitigate frost accumulation in various applications, including energy systems, aerospace, and transportation. In this study, a simple and cost-effective secondary spray coating method was employed to prepare the necessary surfaces for experimentation. This method allowed for the efficient fabrication of surfaces that exhibited the required hydrophobic and superhydrophobic properties, thereby facilitating a systematic investigation into their frost formation characteristics. Following the preparation of these surfaces, a visual low-temperature experimental platform was utilized to conduct a detailed study of the condensation and freezing behaviors exhibited on different wettability surfaces, including a bare aluminum surface, a hydrophobic surface, and two types of superhydrophobic surfaces designated as surfaces A and B. To explore the effects of varying cold surface temperatures on the condensation and freezing characteristics, a range of experimental conditions was established. For condensation characteristics, cold surface temperatures of Tw = 3, 0, and -3 ℃ were investigated, while for freezing characteristics, temperatures of Tw = -3, -6, and -9 ℃ were examined. The experimental findings revealed a consistent trend that under the same operational conditions, surfaces with larger contact angles were associated with smaller radii of condensed water droplets, lower surface coverage, and longer time periods required for droplet freezing. Compared with the freezing time of super B surface, the freezing time of bare aluminum, hydrophobic and super A surface was shortened by 92.8%, 70.3% and 45.9% respectively. The unique properties of superhydrophobic surfaces played a significant role in these observations. These surfaces were characterized by low surface energy and specific micro/nano structures that resulted in poor wettability and low spreading coefficients. Consequently, spherical droplets that formed on superhydrophobic surfaces frequently experienced merging and jumping phenomena. Some droplets could bounce off the surface while carrying adjacent droplets along with them, leading to the creation of numerous dry areas on the surface. This resulted in a significantly reduced surface coverage. Notably, the distances between droplets often exceeded the critical distance required for ice bridge formation, which effectively inhibited the propagation of ice bridges and thus contributed to frost suppression. Furthermore, the wettability of the surface had a profound impact on the nucleation barrier for droplet formation. It was observed that the larger the contact angle of the surface droplets, the higher the nucleation barrier became. This relationship resulted in slower growth rates of the droplets and a decrease in their coverage on the surface. Ultimately, these factors collectively enhanced the frost suppression capabilities of the superhydrophobic surfaces being studied. In summary, this study elucidates the intricate interplay between surface wettability, droplet dynamics, and thermal conditions, demonstrating how specifically engineered superhydrophobic surfaces can effectively mitigate frost formation. The insights garnered from this study not only deepen the understanding of frost suppression mechanisms, but also pave the way for future innovations in materials designed for frost resistance. Such advancements are essential for improving performance in various fields where frost control is critical.
关键词
超疏水表面 /
凝结 /
冻结 /
冰桥 /
可视化
Key words
superhydrophobic surface /
condensation /
freezing /
ice bridge /
visualization
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