关键词: 池沸腾, 强化换热, 纳米结构, 临界热通量, 气泡, 相变

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