Visual Study of Flow Pattern Evolution of Flow Boiling in a Microtube
Visual Study of Flow Pattern Evolution of Flow Boiling in a Microtube
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DOI：
10.1080/01457632.2011.556477
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发表时间：
2011-10
影响因子：
2.3
通讯作者：
Xin Fu;Peng Zhang;Caojin Huang;Ruzhu Wang
中科院分区：
文献类型：
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作者：
Xin Fu;Peng Zhang;Caojin Huang;Ruzhu Wang
应用高速摄影来可视化液氮在涂有一层透明氧化锡薄膜作为加热器的向上石英微管中流动沸腾的流动模式演变。所使用的管的内径约为1.33mm。直观地研究了成核位点激活的特征，这是流型演化的开始。在低热通量和小质量通量的情况下，仅激活单个成核位点。与传统的正常尺寸的管相比，离开的气泡很快就长大到管内径的尺寸，并且从气泡流到段塞流和环形流的转变发生得更早。在高质量通量和高过冷度的情况下，多个成核位点被激活。考虑了相邻成核位点之间的相互作用。发现段塞流和环形流抑制下游成核位点。气泡聚并是流型演化的关键因素之一，人们发现气泡聚并会对邻近成核位点带来较大的扰动。还证明了过冷液氮中气泡凝结的特性。还研究了沸腾危机之后的流动模式演变。在微管中观察到干燥后状态，例如倒泡、倒段塞和倒环形流。清楚地证明了与流型演变中的流动不稳定性相关的流动反转和液体夹带。
High-speed photography was applied to visualize the flow pattern evolution of flow boiling of liquid nitrogen in an upward quartz microtube coated with a layer of transparent indium tin oxide film as the heater. The inner diameter of the employed tube was about 1.33 mm. The characteristic of nucleation site activation, which was the beginning of the flow pattern evolution, was studied visually. In the case of low heat flux and small mass flux, only a single nucleation site was activated. The departed bubbles grew to the size of the inner diameter of the tube soon and the transition from the bubbly flow to slug and annular flow occurred earlier compared to the conventional normal-sized tubes. In the case of high mass flux and high subcooling, multiple nucleation sites were activated. The interaction between adjacent nucleation sites was considered. Slug and annular flow were found to suppress the downstream nucleation site. Bubble coalescence was one of the key factors for the flow pattern evolution, and it was found that the bubble coalescence would bring about great disturbance to the adjacent nucleation site. The characteristics of bubble condensation in the subcooled liquid nitrogen were also demonstrated. Flow pattern evolution beyond the boiling crisis was also investigated. Post-dryout regimes such as inverted bubbly, inverted slug, and inverted annular flow were observed in the microtube. Flow reversal and liquid entrainment, which were relevant to flow instability in the flow pattern evolution, were demonstrated clearly.