物-化耦合微纳米结构润湿性及促进滴状冷凝机理研究

The wettability appeared on the micro-nano structure is result from the coupling processes and synergistic effect of various physics-chemistry characteristics. Due to the diversity of coupling elements and the complexity of coupling modes, it is difficult to analyze the influence for physics-chemistry characteristics on wettability qualitatively. However, these characteristics play an vital role in understanding the mechanism of wettability and dropwise condensation. In this study, an extensive conjugate analysis towards the coupling elements and the coupling modes will be conducted based on combining the theory of extenics and the bionic multi-factor coupling principle, and the physics and mathematical models, including different physics-chemistry characteristics, can be established. According to these models, the current water molecules aggregation state and the micro-droplet wettability on its surface would be calculated by using the molecular dynamics simulation. By doing so, the relationship between the physics-chemistry characteristics of micro-nano structure and wetting property will be studied, and the optimized parameters of physics-chemistry characteristics base the mathematical model is obtained. By implementing the above strategy, we can successfully achieve hydrophobic micro-nano structure controlled preparation. Then, the influence of physics-chemistry characteristics to the growth, coalescing, and self-moving of droplets are studied by means of experiments. Finally, introducing primary physics-chemistry characteristics into heat transfer analysis, a numerical model to describe the heat and mass transfer process of dropwise condensation on micro-nano surfce is developed. The purpose of this study is to reveal the the microcosmic mechanism of hydrophobicity and promoting dropwsie condensation on physics-chemistry coupling micro-nano surface. The research work above can supply theory support and technology accumulation for the optimal design of laboratory research and industrial applications.

微纳米复合结构所呈现的润湿性是表面多种物理-化学特性相互耦合、协同作用的结果，耦元种类的多样性及相互耦联方式的复杂性导致物-化特性耦元影响润湿性机理的定量描述困难，但却极为关键。本课题拟将可拓学理论与多元耦合仿生原理相结合，通过对耦元及耦联方式的可拓共轭分析来辨识主次耦元、解析耦合机理，进而建立物-化耦合微纳米阵列模型。采用分子动力学理论模拟典型物-化耦合结构界面上微观液滴的聚集形态和润湿性能，构建物-化特性与润湿性函数关系，求解优化参数。以此为指导，设计制备物-化特性参数可控的微纳米疏水表面，并实验观察分析物-化特性参数影响冷凝液滴生成、融合、自迁移的依变规律。最后将微纳米物-化特性参数引入滴状冷凝传热分析，建立滴状冷凝传热模型。通过本课题的研究，能更全面客观的揭示物-化耦合微纳米结构润湿性及促进滴状冷凝作用机理，为微纳米仿生结构强化冷凝换热实验室探索和工业化应用提供技术储备和理论指导。

微纳米复合结构表面能够表现出独特润湿特性，在强化冷凝、沸腾等相变换热过程方面具有巨大的应用前景和研究价值。为此，本课题围绕表面微纳米结构强化相变换热这一研究目标，从宏观和微观角度对表面结构强化冷凝和沸腾换热过程进行了理论和实验研究。理论研究方面，将可拓学理论与多元耦合仿生原理相结合，同时引入分形理论到冷凝传热分析过程中，分别对液滴在不同疏水表面和液膜在不同槽型表面的分布规律进行理论分析和数值模拟，重要结论和进展如下：（1）基于分形理论的液滴分布模型更加符合液滴实际分布情况，利用该模型可计算较大接触角范围内冷凝液滴的分布函数和传热量，且模型计算值与文献数据及实验测量值吻合较好，误差小于15%；（2）提出利用渐开线槽表面减薄冷凝液膜，降低传热热阻，强化膜状冷凝换热的研究思路，液膜在该槽表面的温度及热流密度分布更加均匀，传热性能较其它槽型提高30%以上，这一结论也得到了实验证实。实验研究方面，项目首先实验探索了微纳米级余弦槽疏水表面强化滴状冷凝传热特性。结果表明，液滴在微槽表面疏水性和传热性能都呈现明显的各向异性，横向的静态接触角明显高于纵向接触角，竖直纵槽阻碍液滴的横向合并，但其对液滴脱落过程起到极大促进作用，传热性能较光滑表面提高30%-50%。其次，为了研究纳米结构差异性对冷凝传热性能的影响，利用不同方法方法制备了不同结构的纳米线、纳米片及纳米花等疏水表面。通过冷凝传热对比实验发现，纳米线和纳米花结构表面能够维持稳定滴状冷凝，且纳米花结构表面传热性能最佳。同时，我们还对微柱结构强化微重力沸腾换热进行了理论和实验研究，通过实验观测和理论建模，研究了气泡脱离后产生的尾流对后续气泡的动力学过程的影响规律。结果表明，大气泡脱离后，所形成的尾流持续时间、尾流影响空间都大于后续气泡，尾流效应将持续影响后续气泡等生长、合并和脱离等动力学过程。