Study of bubble nucleation and growth by visualization in liquid helium 3

从a flat copper surface to liquid ^3 He were studied previously from the non-boiling state to the film boiling one between 0.5 and 1 K under saturated vapor pressure by our group。The temperature difference\T across the thin boundary layer existing between a copper surface and bulk liquid ^3 He was measured as a function of heat flux q^^· under steady-state conditions。在一个非沸腾的国家和一个正在播放的电影中，观察到的q^^·-ΔT关系曲线与其他液体相似。在核沸腾状态下，数据没有被Kutateladze的相关性解释，这意味着，热转移率比预期的相关性和观察到的q^^·-ΔT曲线被细分到三个区域，被其斜率所细分。Liquid ^3 He has the lowest boiling point and the smallest surface tension among elem\substances。这些特征意味着，没有预先存在的泡沫核可以刺激泡沫的产生 ... More mation。Thus liquid ^3 He should exhibit a unique bubble formation process.如果要澄清核泡沫状态，我们就可以通过可视化方法观察泡沫。泡沫成型过程是由高速摄像机拍摄的（每秒500帧），我们有两种低温和样品电池。The time for a bubble to grow and depart from the surface was 14 ms at q^= 8×10^\-5>W/cm^2 and a bulk liquid ^3 He temperature of 0.7 K。表面上泡沫的形状是类似于球体的，是由液体的低表面张力解释的。在另一边，一个硝基气泡观察由布兰德等人拍摄。在表面上有一个短脖子，而到了气泡成长和分离的时间大约要长20次。这意味着^3他每小时都有很高的泡沫形成频率。在垂直方向上测量了平均气泡大小，因为热通量增加了。热通量和每小时泡沫数量之间的关系被发现的曲线在从区域I到区域II的变化点附近有一个转折点。液体中的核沸腾的特征特征^3他被概括为如下： （1）泡沫的形状是类似于小精灵的; （2）泡沫的增长率很快与一个氮元素相比较;（3）在热通量的一个较大数量的区域，较大的球形气泡覆盖表面，以及气泡数的增加率可能成为可能。因此，气泡式近表面的接近表面的接触是由气泡式的，表面的一些部分被覆盖在电影中，Q^^-ΔT曲线在区域II的温和斜率的结果。Less（低）

The heat transfer characteristics from a flat copper surface to liquid ^3He were studied previously from the non-boiling state to the film boiling one between 0.5 and 1 K under saturated vapor pressure by our group. The temperature difference ΔT across the thin boundary layer existing between a copper surface and bulk liquid ^3He was measured as a function of heat flux q^^・ under steady-state conditions. In the non-boiling state and the film boiling one, the observed q^^・-ΔT relation curves were similar to other liquids. However, in the nucleate boiling state, the data were not explained by Kutateladze's correlation, that is, the heat transfer rate was more than one order large than that expected from the correlation and the observed q^^・-ΔT curve was subdivided into three regions by its slope. Liquid ^3He has the lowest boiling point and the smallest surface tension among elemental substances. These features mean that there is no pre-existing bubble nucleus to stimulate the bubble for … More mation. Thus liquid ^3He should exhibit a unique bubble formation process. In order to clarify the nucleate boiling state, we have observed the bubble by a visualization method. The bubble formation process was taken by a high-speed camera (500 frames per second).We have constructed two types of cryostats and sample cells. The time for a bubble to grow and depart from the surface was 14 ms at q^^・ = 8×10^<-5>W/cm^2 and a bulk liquid ^3He temperature of 0.7K. The shape of bubble on the surface was spheroid-like, which was explained by the low surface tension of liquid ^3He. On the other hand, a nitrogen bubble observed by Bland et al.was spherical with a short neck on the surface, and the time for a bubble to grow and depart was about 20 times longer than ^3He. This means that ^3He has a high frequency of bubble formation per time. The average bubble size measured in the vertical direction increased as the heat flux increased. The relation between heat flux and bubble number per time was obtained The curve had an inflection point near the change from region I to region II.The characteristic feature of nucleate boiling in liquid ^3He are summarized as follows : (1)The shape of bubble is spheroid-like ; (2)The bubble growth rate is fast compared with one of nitrogen ; (3)In the region of a large quantity of heat flux, the large spheroidal bubble covers the surface and the increasing rate of bubble number becomes dully. So, the agitation of liquid near surface by bubble becomes less and some parts of surface are covered with film, which results in the gentle slope of q^^・-ΔT curve at region II. Less