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

为了阐明窄缝微通道汽化器内沸腾换热的机理和特点，对受热面与产生的蒸汽之间形成的微层厚度进行了实验研究。用激光消光法测量了0.5、0.3和0.15 mm沟道间隙下的微层厚度。阐明了薄液微层在表面的分布形态。气隙大小、气泡生长速度和气泡起始位置的距离对微层厚度有影响。初始微层厚度随着气泡前沿速度的增加而增加，达到中等速度时，微层厚度也随之增加。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情况。并通过…分析对其传热机理和传热特性进行了定量研究进一步研究了汽泡位置、汽相前沿速度、微层占优周期、沸腾周期内液体饱和度等因素对沸腾过程的影响。采用激光消光法，利用专门设计的测量系统对微层厚度进行测量。初始形成的微层的厚度是唯一确定的。在此基础上，通过对微层结构的测量，阐明了微层对换热的贡献。根据气泡生长速率的相似性，将决定微层厚度分布、微层存在时间、微层面积大小等微层特性的主导因素用无量纲形式表示。最后，给出了微层蒸发对核态沸腾的贡献。较少

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