表面纳米多孔热功能结构成形机理及孔径尺度效应研究

Surface heat functional structures are widely used in energy conversion and transmission applications. The development of surface heat functional structure has entered a new era of micro-nano scale, however, faces the challenges like lacking of in-situ technique and theory to fabricate nanoporous surface structure, insufficient study on the nano-scale effects of nanoporous structure, and imperfect understanding of the mechanism of heat transfer enhancement by nanostructure. . To address the issues above, an in-situ processing technology based on surface alloying and dealloying is proposed in this project for the fabrication of nanoporous structure on metal surface. The mechanisms of alloying and de-alloying on the surface are explored by typical analysis methods used in electrochemistry for materials science, and consequently achieves morphology controlling of formed nanoporous surface. Morphological characterization and infrared imaging technique are occupied to study the evolution of porous structure under hydrothermal condition, and establish the rules of physical and chemical properties’ change on surface driven by scale effects of porosity. We combine with the results of visualized boiling experiments and surface characterization, and further reveal the mechanisms of heat transfer enhancement come from nano-porous surface. . The proposed project will bring the breakthrough in in-situ fabrication technique and theory of nanoporous surface heat functional structures, acknowledging stability of nanoporous structure and its nano-scale effects, strengthening the understanding of the mechanisms of boiling heat transfer enhancement. This project is of great significance in both theory and practice for improving energy efficiency and solving the problem of high heat flux thermal control.

表面热功能结构广泛应用于热能转换与传递的各个环节。本项目契合表面热功能结构的微纳发展趋势，针对表面纳米多孔结构原位成形技术及理论欠缺，孔径结构尺度效应研究滞后及其强化传热机理认识不完善的现状，提出一种基于表面合金化/脱合金的表面纳米多孔金属结构原位成形技术，通过材料电化学分析方法探索合金层生长与脱合金孔径成形机理，实现对表面成形纳米多孔结构的微观形貌控制；利用形貌表征和红外成像技术手段，深入认识该纳米多孔热功能结构在水热条件下的孔径演化规律以及孔径尺度效应引起的表面物化性能变化规律；结合可视化沸腾实验结果与表面物化特征，进一步揭示表面纳米多孔结构的强化传热机理。本项目将在表面纳米多孔热功能结构原位成形方法与理论、孔径结构稳定性及尺度效应、沸腾强化传热机理等方面取得技术与理论突破；对提高我国能源利用效率、解决高热流密度热控制难题具有重大理论与应用意义。

微纳多孔表面热功能结构已成为提高热能转换与传递效率的重要手段和研究热点，为提高强化沸腾传热机理认识水平，推动纳米尺度表面热功能结构走向应用的技术突破，提高热能利用效率、解决微电子等领域热控制难题具有重要意义。本项目提出一种基于表面合金化/脱合金的纳米尺度表面热功能结构的简易加工成形方法，在基于电化学调控手段的纳米多孔金属结构的原位成形机理及工艺控制方面取得了重要成果；首次系统研究了沸腾水热环境下强化传热纳米结构的尺寸效应带来的稳定性问题，为表面纳米强化传热结构的开发提供了尺度设计准则；基于对气泡动力学研究，对于纳米多孔表面的强化沸腾传热机理取得更深入的认识。项目研究的重要结果具体如下：.1) 纳米多孔表面热功能结构的制备及原位成形机理:Cu-Zn表面合金化过程由反应扩散机制主导，热处理温度是核心控制参数；电化学腐蚀单相Cu0.4Mn0.6合金研究证实外加电势是控制脱合金动力学过程的关键，可通过调整电势调节脱合金成形的纳米多孔结构孔径尺度，该脱合金过程可用逾渗理论加以解释；在三电极电化学体系-0.5 V (MSE)条件下，可制得孔径20 nm左右的较均一纳米多孔铜材料。.2）纳米多孔表面热功能结构纳米尺度效应及水热稳定性研究：发现了纳米多孔铜结构在沸水环境中孔径持续粗化现象，通过SEM与EDS的持续追踪，发现该结构在水热条件下具有较好的化学稳定性，该纳米多孔铜结构的粗化过程可由表面扩散控制方程预测。.3）纳米多孔表面沸腾传热性能及强化沸腾传热机理研究：纳米多孔表面在全热流密度区间的表现都优于光滑表面；该纳米多孔铜表面的强化沸腾传热作用来自于表面润湿性改善和微观形貌改变的共同作用。气泡动力学上，纳米多孔结构带来气泡成核密度和脱离频率的明显提高可以很好地印证传热性能的强化现象。