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

我们小组之前研究了饱和蒸气压下从非沸腾状态到0.5至1 K之间的薄膜沸腾状态从平坦铜表面到液体^3He的传热特性，以及存在的薄边界层上的温差ΔT。在稳态条件下，测量铜表面和本体液体 ^3He 之间热通量 q^^· 的函数。在非沸腾状态和薄膜沸腾状态下，观察到 q^^·-ΔT 关系。曲线与其他液体相似，但是，在泡核沸腾状态下，数据不能用库塔特拉泽相关式来解释，即传热速率比相关式和观测到的 q^^・预期的大一个数量级以上。 -ΔT 曲线按其斜率细分为三个区域。液体 ^3He 在元素物质中具有最低的沸点和最小的表面张力，这些特征意味着没有预先存在的气泡核来刺激气泡...... 更多因此，液体^3He应该表现出独特的气泡形成过程，为了阐明泡核沸腾状态，我们通过高速相机（每秒500帧）观察了气泡的形成过程。）。我们构建了两种类型的低温恒温器和样品池，在 q^^・ = 8×10^<-5>W/cm^2 和体积下，气泡生长并离开表面的时间为 14 毫秒。液体^3He温度为0.7K，表面气泡的形状是类球体，这是由于液体^3He的低表面张力所致。另一方面，Bland等人观察到的氮气气泡是球形的。表面上的颈部较短，气泡生长和离开的时间比^3He长约20倍，这意味着^3He每次形成气泡的频率很高。在垂直方向上测量的平均气泡尺寸。随着热通量的增加，得到了热通量与单位时间气泡数之间的关系，曲线在I区到II区附近出现拐点。液体^3He中泡核沸腾的特征总结如下： (1)气泡形状呈类球体；(2)气泡生长速度比氮气快；(3)在热通量较大的区域，大的球状气泡覆盖表面，并形成气泡。增长率因此，气泡对表面附近液体的搅动变小，部分表面被薄膜覆盖，导致区域 II 的 q^^·-ΔT 曲线斜率平缓。