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

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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