窄流道内受限汽泡聚合特征及泡底微观传热传质机理研究

Narrow channel is used widely as a component in heat transfer enhancement. But a bubble in the narrow channel is confined by the channel wall significantly due to the small dimension of the channel. So the characteristic of confined bubble coalescence in narrow channel is very distinct, and the confined bubble coalescence affects the heat and mass transfer significantly. However, the research focuses on confined bubble coalescence is very limit in the published literature. In this project, a visual experiment is going to be carried out in a test-section with observation from different views by high-speed cameras. In order to obtain a 3-D view of bubble coalescence, one observation is carried out normal to the heating wall, and the other one is parallel to the heating wall. In this experimental study, the bubble morphology during and after bubble coalescence, the motion of gas-liquid-solid triple contact line, the variation of bubble contact angle, the development of liquid layer and dry-out path beneath the bubble will be observed carefully. Based on the experimental result, morphological feature of confined bubble coalescence will be investigated, and define the expressions of those forces acting on the severe confined bubbles during moving and coalescing, and a control model for confined bubble coalescence will be established. Also, investigation will be carried out on the mechanism of trapping liquid to the bubble based during confined bubble coalescence, and analyze the micro heat and mass transfer beneath the coalescence bubble, on the vapor-liquid interface and in the influenced region around the bubble. A mechanism model will be proposed to depict the effect of confined bubble coalescence on heat and mass transfer in narrow channel. Based on the research carried out in this project, it is expected to achieve profound understanding on the complicated confined bubble coalescence behavior and the mechanism of resulting effect on heat and mass transfer.

窄流道作为一种强化传热元件有着广泛应用。由于流道尺寸小，汽泡行为会受到流道壁面的严重限制，使得窄流道内受限汽泡聚合特征鲜明，且对传热传质影响非常显著。而文献中针对受限汽泡聚合所开展的研究非常有限。本项目采用三面可视窄流道实验段，同步从正面和侧面用高速摄像机观察受限汽泡的聚合行为，获得受限汽泡聚合的立体演化特征，包括受限汽泡聚合过程中以及聚合后的形态演变、汽-液-固三相线的运动、汽泡接触角的变化、汽泡底部液膜和干斑的发展等微观参数；分析受限汽泡聚合的形态特征，明确严重受限条件下汽泡各个受力的表达，并建立描述受限汽泡聚合的控制模型；通过研究受限汽泡聚合时捕获泡间液体到聚合后汽泡底部并形成厚液膜的发生机制，分析聚合后泡底液膜、汽液界面以及汽泡周围影响区内的各部分微观传热传质，建立受限汽泡聚合影响传热传质的机理模型。通过本项目研究，有望揭示窄流道内复杂的受限汽泡聚合行为及其对传热传质的影响机理。

窄空间流道作为一种强化传热元件有着广泛应用。由于流道尺寸小，汽泡行为会受到流道壁面严重限制，使得窄空间流道内受限汽泡聚合特征鲜明，且对传热传质影响非常显著。本项目基于可视化实验研究，通过高速摄像机观察受限汽泡的行为特征，比较不同工况下的汽泡行为特征差异。另外，本项目还针对不同管径的竖直流道开展沸腾换热实验，探究空泡行为和流型演化特征，以及流动震荡特性。同时，通过可视化研究获得了到不同工况下环状流的液膜厚度，并分析了环状流液膜厚度与加热壁面换热系数之间的关系。最后，在不同管径的窄空间流道内开展了绝热气-水混两相流动的可视化实验研究，分析竖直流道内Taylor气泡的界面形态特征以及表面张力对其的影响机理。通过本项目研究，已发表SCI文章6篇（其中4篇已发表，2篇已收录），发表EI文章4篇（3篇已发表，1篇已收录），发表国际会议论文1篇。本项目培养硕士研究生3人（1人已毕业），培养博士研究生2人（在读，硕博连读）。