狭隘間隙ミニチャネル沸騰系における薄液膜構造と伝熱特性

摘要

In the previous reports, the heat transfer measurement was performed in a mini-channel boiling system and the thickness of micro-layer that formed between the heating surface and generated vapor with the vapor growth was measured applying the laser extinction method for the narrow gaps and the process of bubble growth was recorded by using a high-speed camera simultaneously. The effects of gap size, the velocity of vapor bubble forefront and the distance from the incipient bubble site were investigated on the micro-layer thickness in a narrow gap mini-channel boiling system and the configuration of the thin liquid micro-layer distributions on the heat transfer surface was clarified. In this study, the mechanism and characteristics of heat transfer were investigated quantitatively by analyzing 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 on the basis of the measured data in the previous researches. The heat transfer characteristics were analyzed and the data calculated were coincided with the measured data in the boiling curve for the gap size of 0.5 mm measured in the previous report. Therefore, it was concluded that the boiling phenomena in a narrow gap mini-channel were quantitatively determined by the two kinds of characteristic periods of the micro- layer dominant and the liquid saturated and the characteristic factors shown above.%一般に沸騰現象は，気泡生成に関わる性質，気泡成長・離脱にともなうバルク液，生成蒸気，および蒸気と伝熱面の間に形成される薄液膜等の挙動が非定常的に複雑に影響し合う結果として伝熱特性が決定される．本研究の対象とする平行な平面伝熱面間の狭間隙からなるミニチャネル制限空間内で沸騰が生じる場合には，蒸気泡は両壁面に押しつぶされることにより扁平形状のまま急速に伝熱壁面上に拡がる．そのことに対応して蒸気泡・壁面間に形成される薄液険の蒸発速度が，伝熱量を決定するための特に重要な役割をもつことになろ．