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Mechanisms and characteristics of micro-layer configuration in phase change heat transfer between liquid and vapor

液汽相变传热微层结构机理及特征

基本信息

批准号：
17360096
负责人：
UTAKA Yoshio
金额：
$ 10.18万
依托单位：
Yokohama National University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2005
资助国家：
日本
起止时间：
2005 至 2007
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-17360096/
关键词：
heat transfer phase change heat transfer boiling mini-channel nucleate boiling micro-layer laser extinction method 熱電熱

项目摘要

To elucidate the mechanism and characteristics of boiling heat transfer in a narrow gap micro-channel vaporizer, the experimental investigation concerning the micro-layer thickness that formed between the heating surface and vapor generated was performed. The micro-layer thickness was measured applying the laser extinction method for the channel gap sizes of 0.5, 0.3 and 0.15 mm. The configuration of thin liquid micro-layer distributions on the surface was clarified. The gap size, the rate of bubble growth and the distance from the incipient bubble site have an effect on the micro-layer thickness. The initial micro-layer thickness increased with increase of the velocity of bubble forefront to moderate value of the velocity. In the region of larger velocity, the thickness was constant for each gap. The distributions of the initial thickness of micro-layer on the surface were shown. Furthermore, the mechanism and characteristics of heat transfer was investigated quantitatively by analyzi … More ng the affecting factors such as the position of vapor bubble generated, the velocity of vapor forefront, the periods of the micro-layer dominant and the liquid saturation in a boiling cycle and so forth.The configuration of micro-layer formed under growing bubble in nucleate pool boiling was investigated. Micro-layer thickness was measured by specially devised measuring system applying the laser extinction method. The thickness of the initially formed micro-layer was decided uniquely. Furthermore, the study is carried out to elucidate the contribution of micro-layer on heat transfer on the basis of the measurement of configuration of micro-layer. The dominant factors determining the characteristics of micro-layer such as micro-layer thickness distribution, duration of micro-layer existence, the size of micro-layer area and so-forth were expressed by non-dimensional form on the basis of the similarity of bubble growth rate. Finally, the contribution of the evaporation from the micro-layer in nucleate boiling was shown. Less

为了阐明窄间隙微通道汽化器内沸腾换热的机理和特性，对加热面与产生的蒸汽之间形成的微层厚度进行了实验研究。微层厚度的测量应用激光消光法的通道间隙尺寸为0.5，0.3和0.15毫米。澄清了表面上的薄液体微层分布的配置。差距尺寸、气泡生长速率和距初始气泡位置的距离对微层厚度有影响。初始微层厚度随气泡前沿速度的增大而增大，当气泡前沿速度达到中等值时，微层厚度随气泡前沿速度的增大而增大。在速度较大的区域，每个间隙的厚度是恒定的。给出了表面微层初始厚度的分布。并通过数值分析，定量地研究了其传热机理和传热特性。 ...更多信息研究了沸腾循环中汽泡产生位置、汽峰速度、微层占优势的周期和液相饱和度等因素对微层形态的影响，并对池核沸腾中汽泡生长下形成的微层形态进行了研究。微层厚度的测量是通过专门设计的测量系统，应用激光消光法。初始形成的微层的厚度是唯一决定的。在此基础上，通过对微层结构的测量，研究了微层对换热的贡献。基于气泡生长速率的相似性，将决定微层特征的微层厚度分布、微层存在持续时间、微层面积大小等主导因素用无因次形式表示。最后给出了微层蒸发对核态沸腾的贡献。少