Physics of the Microchannel Flow Boiling Process and Comparison With the Existing Theories
Physics of the Microchannel Flow Boiling Process and Comparison With the Existing Theories
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微通道流动沸腾过程的物理原理及其与现有理论的比较
DOI：
10.1115/1.4036655
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
Moghaddam, Saeed
中科院分区：
文献类型：
--
作者：
Bigham, Sajjad;Moghaddam, Saeed
在本研究中，对不同生长阶段的气泡进行了六个基准实验，以评估现有微通道流动沸腾传热模型/假设的假设。结果表明，由于薄膜蒸发和瞬态传导传热机制，气泡沸腾过程引发了局部表面热通量的峰值。表面热通量的增强仅限于成核位置处气泡与表面接触区域的非常小的区域，限制了气泡沸腾过程的整体传热贡献。随着气泡-表面接触面积变大，这两种传热机制的贡献增加。随着气泡长度的增加，微层蒸发机制的激活时间显着增加，而瞬态传导机制的激活时间保持相对不变。当微通道大部分被气泡占据时，薄膜蒸发机制成为主要的传热方式。结果清楚地表明，在未被气泡覆盖的表面区域活跃的单相传热机制受层流理论控制（对于此处介绍的测试条件）。实质上，尚未观察到由于气泡生长和流动而在液相中产生可测量的增强效应。与现有微通道流动沸腾模型的比较表明，三区流动沸腾模型可以定性描述本实验中观察到的传热事件，但无法准确预测传热机制的大小。
In this study, six benchmark experiments are conducted on bubbles at different growth stages to evaluate the assumptions of the existing microchannel flow boiling heat transfer models/hypothesis. The results show that the bubble ebullition process triggers a spike in the local surface heat flux due to the thin film evaporation and transient conduction heat transfer mechanisms. This enhancement in the surface heat flux is limited to a very small area at the bubble–surface contact region at the nucleation site limiting the overall heat transfer contribution of the bubble ebullition process. The contribution of these two mechanisms of heat transfer increases as the bubble–surface contact area becomes larger. As the bubbles length increases, the time period of activation of the microlayer evaporation mechanism substantially increases while that of the transient conduction mechanism remains relatively unchanged. When the microchannel is mostly occupied by bubbles, the thin film evaporation mechanism becomes the dominant heat transfer mode. The results clearly indicate that single-phase heat transfer mechanism active at surface regions not covered by bubbles is governed by the laminar flow theory (for the test conditions presented here). In essence, a measureable enhancement effect in the liquid phase due to bubbles growth and flow has not been observed. A comparison with the existing microchannel flow boiling models suggests that the three-zone flow boiling model can qualitatively describe the heat transfer events observed in this experiment but fails to accurately predict the magnitude of the heat transfer mechanisms.
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