Abstract: Micro-scale modification surface are usually used to enhance the pool boiling heat transfer, but the characteristics and mechanisms that how the nano-scale affects the pool boiling is still not clear.A series of TiO₂ nanotube array surface with different diameters are fabricated by electrochemical anodization and the pool boiling heat transfer performance with saturated deionized water on different TiO₂ nanotube array surface were experimentally investigated in this paper. Different Ti surface were prepared and their pool boiling heat transfer performance were also investigated for comparison. Before and after each pool boiling experiment, the contact angle of pure water on the surface of each sample was observed to test the surface wettability. A high speed camera was used to record the bubble dynamic process in the experiment. The results showed that the pool boiling heat transfer performances with different TiO₂ nanotube array were quite different. But the enhanced effect was not monotonic variation with the diameter increasing, which indicates that the diameter is not the only one of most important points on the pool boiling performance. In fact, the diameters of the TiO₂ nanotube here were smaller than the cavity diameter, and it was difficult to generate cavity. As a result, very small bubble was not observed. Anyway, all TiO₂ nanotube array had good surface wettability, and they can significantly enhance the critical heat flux (CHF) as much as 116% of the Ti surface. But the high temperature and large interfacial velocity during pool boiling are detrimental to the TiO₂ nanotube array, and some TiO₂ nanotube array may be damaged after the CHF, which leads to a significant CHF decreasing in the next pool boiling experiment.

Key words: pool boiling, enhanced heat transfer, nanostructure, critical heat flux, bubble, phase change

摘要： 以多个不同管径的TiO₂纳米管阵列表面以及不同Ti表面作为换热壁面，以去离子超纯水作为工质，进行重复池沸腾实验。在实验前后进行了样品润湿性能测试实验，测量了超纯水在样品表面上的静态接触角；在实验中，使用高速摄像机观测气泡动力学过程。实验结果表明，管径不是对池沸腾换热性能产生重要影响的唯一主要因素，管径尺度的凹坑难以形成有效的汽化核心，不利于强化换热。实验中没有观察到大量微小气泡，证实没有大量有效的汽化核心。由于TiO₂纳米管阵列表面的润湿性能较好，其能明显提高池沸腾的临界热通量（CHF），最大增幅度可达116%。但部分样品在经历CHF后会出现脱落现象，脱落后，CHF明显降低。

关键词: 池沸腾, 强化换热, 纳米结构, 临界热通量, 气泡, 相变