Visualization of convective boiling heat transfer in single microchannels with different shaped cross-sections
Visualization of convective boiling heat transfer in single microchannels with different shaped cross-sections
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DOI：
10.1016/j.ijheatmasstransfer.2005.12.024
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发表时间：
2006-10
影响因子：
5.2
通讯作者：
T. Yen;M. Shoji;F. Takemura;Yuji Suzuki;N. Kasagi
中科院分区：
文献类型：
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作者：
T. Yen;M. Shoji;F. Takemura;Yuji Suzuki;N. Kasagi
可视化具有相似水力直径但不同形状横截面的透明单微通道中的对流沸腾，并同时测量局部传热系数。测试了两种类型的微通道：圆形 Pyrex 玻璃微管（210μm 内径）和方形 Pyrex 玻璃微通道（214μm 水力直径）。在微通道外壁溅射100 nm厚的半透明ITO/Ag薄膜，用于微通道的直接焦耳加热。流场可视化显示方形和圆形微通道中流型的半周期性变化。这种变化是因为有限的空间限制了气泡在径向方向的生长。在方形微通道中，成核气泡的数量和局部传热系数都随着蒸汽质量的降低而增加。角部充当活跃的成核腔，导致局部传热系数较高。相比之下，光滑玻璃圆形微通道中没有空腔，在较低的蒸汽质量下产生相对较小的传热系数。最后，方形微通道的传热系数较高，因为方形微通道中的角部充当有效的活性成核位点。
Convective boiling in transparent single microchannels with similar hydraulic diameters but different shaped cross-sections was visualized, along with simultaneous measurement of the local heat transfer coefficient. Two types of microchannels were tested: a circular Pyrex glass microtube (210μm inner diameter) and a square Pyrex glass microchannel (214μm hydraulic diameter). A 100-nm-thick semi-transparent ITO/Ag thin film sputtered on the outer wall of the microchannel was used for direct joule heating of the microchannel. The flow field visualization showed semi-periodic variation in the flow patterns in both the square and circular microchannels. Such variation was because the confined space limited the bubble growth in the radial direction. In the square microchannel, both the number of nucleation bubbles and the local heat transfer coefficient increased with decreasing vapor quality. The corners acted as active nucleation cavities, leading to the higher local heat transfer coefficient. In contrast, lack of cavities in the smooth glass circular microchannel yielded a relatively smaller heat transfer coefficient at lower vapor quality. Finally, the heat transfer coefficient was higher for the square microchannel because corners in the square microchannel acted as effective active nucleation sites.