Abstract:

The condensation heat transfer of FC-72 in a narrow rectangular channel with four kinds of elliptical pin-fin surfaces and a flat surface under microgravity condition was studied by visualization experiments. The effects of microgravity on condensate distribution, steam-liquid interface, condensation substrate temperature, inlet steam temperature and heat flux were analyzed. The results showed that the steam-liquid interface in the narrow rectangular channel was unstable, fluctuated and climbed along the lateral wall in microgravity. No obvious changes were observed in liquid film on the condensing surface after the release of drop cabin. For unsteady state, the condensation substrate temperature increased slightly, and there was a certain delay. After the release of drop cabin, the change of flow pattern in steam generator coil improved the heating efficiency, which resulted in a sharp rise in inlet steam temperature. For pulsating state, the change of substrate temperature was similar to that of unsteady state, but there was no obvious change in inlet steam temperature. For quasi-steady state, the temperature at some temperature measuring points jumped a little bit, but the inlet steam temperature had no obvious change. Furthermore, the heat flux decreased sharply in microgravity, falling by 18.8%.

Key words: microgravity, elliptical pin-fin, condensation, interface, temperature, two-phase flow

摘要：

对微重力条件下矩形窄通道内FC-72蒸气在4种不同参数的椭圆形针肋表面和平板表面上的冷凝传热进行了可视化实验研究，分析了微重力对冷凝表面冷凝液分布、气-液界面、入口蒸气温度、冷凝基底温度、热通量以及冷凝传热系数的影响。结果表明，微重力条件下，矩形窄通道内气-液界面出现不稳定，并有波动和沿侧壁爬升现象。落舱释放前后，冷凝表面液膜形态并未观察到明显变化；对于非稳态状态，冷凝基底温度出现小幅升高，并有一定的滞后，落舱释放后蒸气发生器盘管内流型的转变提高了加热效率，从而导致入口蒸气温度急剧升高；对于脉动状态，基底温度变化情况与非稳态状态相似，但入口蒸气温度并无明显变化；而对于准稳态状态，基底个别测温点温度发生阶跃，入口蒸气温度并无明显变化，热通量和冷凝传热系数发生急剧下降，降幅分别达18%和20%。

关键词: 微重力, 椭圆形针肋, 凝结, 界面, 温度, 两相流