Bubble Behavior and Heat Transfer in Quasi-Steady Pool Boiling in Microgravity
Bubble Behavior and Heat Transfer in Quasi-Steady Pool Boiling in Microgravity
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DOI：
10.1007/s12217-009-9151-7
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发表时间：
2009-07
影响因子：
1.8
通讯作者：
Jianfu Zhao;Jing Li;Na Yan;Shuangfeng Wang
中科院分区：
文献类型：
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作者：
Jianfu Zhao;Jing Li;Na Yan;Shuangfeng Wang
在微重力条件下，对脱气FC-72在平板加热器上的池沸腾进行了实验研究。采用准稳态加热方法，控制加热电压随时间呈指数增长。与地面实验相比，气泡的行为有很大的不同，对换热有直接的影响。附着在表面上的小的初级气泡似乎能够抑制邻近区域空洞的激活，导致壁温随着热流的缓慢上升。对于高过冷度，聚结后的气泡表面光滑，尺寸较小。整个加热炉表面难以覆盖，形成一个特殊的渐变沸腾区域，核态沸腾和局部干区并存。没有观察到与核态沸腾向膜状沸腾转变相对应的转折点。相反，在低过冷度下聚结气泡的表面振荡可能会导致更多的活化形核位置，从而使表面温度保持不变，甚至随着热流密度的增加而下降。此外，还可以观察到向膜沸腾的突然转变。结果表明，在微重力条件下，换热系数和热流密度随过冷度或压力的增加而增大，与正常重力条件下的情况相同。但在微重力条件下，CHF值很低，可能只有类似压力和过冷条件下的三分之一左右。
Pool boiling of degassed FC-72 on a plane plate heater has been studied experimentally in microgravity. A quasi-steady heating method is adopted, in which the heating voltage is controlled to increase exponentially with time. Compared with terrestrial experiments, bubble behaviors are very different, and have direct effect on heat transfer. Small, primary bubbles attached on the surface seem to be able to suppress the activation of the cavities in the neighborhoods, resulting in a slow increase of the wall temperature with the heat flux. For the high subcooling, the coalesced bubble has a smooth surface and a small size. It is difficult to cover the whole heater surface, resulting in a special region of gradual transitional boiling in which nucleate boiling and local dry area can co-exist. No turning point corresponding to the transition from nucleate boiling to film boiling can be observed. On the contrary, the surface oscillation of the coalesced bubble at low subcooling may cause more activated nucleate sites, and then the surface temperature may keep constant or even fall down with the increasing heat flux. Furthermore, an abrupt transition to film boiling can also be observed. It is shown that heat transfer coefficient and CHF increase with the subcooling or pressure in microgravity, as observed in normal gravity. But the value of CHF is quite lower in microgravity, which may be only about one third of that at the similar pressure and subcooling in terrestrial condition.