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

为了阐明窄间隙微通道汽化器沸腾换热的机理和特点，对受热面与蒸汽之间形成的微层厚度进行了实验研究。采用激光消光法测量了通道间隙尺寸为0.5、0.3和0.15 mm的微层厚度。澄清了表面薄液体微层分布的形态。间隙大小、气泡生长速度和离气泡起始点的距离对微层厚度有影响。随着气泡前沿速度的增加，初始微层厚度逐渐增大，直至速度适中。在速度较大的区域，每个间隙的厚度都是恒定的。给出了表面微层初始厚度的分布。通过对气泡产生位置、蒸汽前沿速度、微层主导周期和沸腾循环中液体饱和度等影响因素的分析，定量探讨了气泡的传热机理和传热特性。研究了核池沸腾过程中气泡生长形成的微层结构。采用激光消光法对微层厚度进行了测量。初始形成微层的厚度是唯一决定的。在对微层结构进行测量的基础上，进一步阐明了微层对换热的贡献。在气泡生长速率相似的基础上，将决定微层特性的主要因素如微层厚度分布、微层存在时间、微层面积大小等以无量纲形式表示。最后，分析了微层蒸发对成核沸腾的贡献。少

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