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

液氦中气泡成核和生长的可视化研究 3

基本信息

批准号：
14540367
负责人：
FUJII Yoshiko
金额：
$ 1.34万
依托单位：
Okayama University of Science
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

项目摘要

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

先前从非沸腾状态研究了从平坦的铜表面到液体 ^3HE的传热特性，从我们组的饱和蒸气压在饱和蒸气压的下，在0.5和1 K之间煮沸。在稳态条件下，测量了铜表面和块状液体之间存在的温度差ΔT，这是热通量q ^^ ・的函数。在非沸腾状态和沸腾的状态下，观察到的Q ^^ ・-ΔT关系曲线与其他液体相似。但是，在核沸腾的状态下，数据没有用库特塔德兹的相关性来解释，即，传热速率超过一个阶的级数，大于相关性的预期，并且观察到的q ^^ ・-ΔT曲线被其斜率细分为三个区域。液体 ^3HE具有最低的沸点，并且元素物质之间的表面张力最小。这些特征意味着没有预先存在的气泡核心可以刺激……更多的气泡。该液体应表现出独特的气泡形成过程。为了阐明核沸腾状态，我们通过可视化方法观察到了气泡。气泡形成过程是通过高速摄像头（每秒500帧）进行的。我们已经构建了两种类型的低温恒温器和样品单元。气泡从表面生长和出发的时间在q ^^ = 8×10^<-5> w/cm^2和0.7k的散装液体^3He温度下为14 ms。表面上的气泡形状是球形的，这是由液体的低表面张力来解释的。另一方面，Bland等人观察到的氮气气泡在表面上有短颈，并且气泡生长和出发的时间比 ^3he长约20倍。这意味着 ^3HE每次具有高频率的气泡形成。随着热通量的增加，在垂直方向上测得的平均气泡尺寸增加了。每次获得热通量与气泡数之间的关系。曲线在从I区域到II区域的变化附近具有一个影响点。液体中核沸腾的特征 ^3HE的特征概述如下：（1）气泡的形状是球体样的；（2）与氮之一相比，气泡生长速率很快；（3）在大量热通量的区域中，大球体气泡覆盖了表面，并且气泡数的增加速率变为两倍。因此，气泡在表面近地表面的搅动变得更少，表面的某些部分被膜覆盖，从而导致区域II处的Q ^^ ・-ΔT曲线的柔和斜率。较少的