Local Heat Transfer and Flow Structure on and Above a Dimpled Surface in a Channel
Local Heat Transfer and Flow Structure on and Above a Dimpled Surface in a Channel
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DOI：
10.1115/2000-gt-0230
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发表时间：
2000-05
期刊：
影响因子：
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通讯作者：
G. I. Mahmood;M. L. Hill;D. Nelson;P. Ligrani;H. Moon;B. Glezer
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文献类型：
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作者：
G. I. Mahmood;M. L. Hill;D. Nelson;P. Ligrani;H. Moon;B. Glezer
实验结果，测量上和以上的酒窝测试表面上放置的一个通道的壁，给出了雷诺数从1250到61,500和空气入口滞止温度的比表面温度范围从0.68到0.94。这些措施包括流动可视化，调查的时间平均总压和流向速度，空间分辨当地努塞尔数，这是使用红外热成像测量，结合能量平衡，热电偶，和原位校准程序。通道高度与凹坑印记直径的比率为0.5。流动可视化显示涡流体和涡对从凹坑脱落，包括一个大的上洗区域和从每个凹坑的中心区域发出的流体包，以及涡对和涡流体，在凹坑对角线附近形成。这些涡结构增加了每个凹坑下游边缘附近的局部努塞尔数，在每个凹陷内都略有增加，尤其是在每个凹坑下游的平坦表面上。这种增大分布在较大的表面积上，并且随着入口滞止温度与局部表面温度之比的减小而变得更加明显。因此，局部和空间平均传热增强变得更大，因为这个温度比降低。这是由于涡旋流体在将冷流体从通道的中心部分平流输送到靠近较热的凹陷表面的区域中的作用。
Experimental results, measured on and above a dimpled test surface placed on one wall of a channel, are given for Reynolds numbers from 1250 to 61,500 and ratios of air inlet stagnation temperature to surface temperature ranging from 0.68 to 0.94. These include flow visualizations, surveys of time-averaged total pressure and streamwise velocity, and spatially resolved local Nusselt numbers, which are measured using infrared thermography, used in conjunction with energy balances, thermocouples, and in situ calibration procedures. The ratio of channel height to dimple print diameter is 0.5. Flow visualizations show vortical fluid and vortex pairs shed from the dimples, including a large upwash region and packets of fluid emanating from the central regions of each dimple, as well as vortex pairs and vortical fluid that form near dimple diagonals. These vortex structures augment local Nusselt numbers near the downstream rims of each dimple, both slightly within each depression, and especially on the flat surface just downstream of each dimple. Such augmentations are spread over larger surface areas and become more pronounced as the ratio of inlet stagnation temperature to local surface temperature decreases. As a result, local and spatially averaged heat transfer augmentations become larger as this temperature ratio decreases. This is due to the actions of vortical fluid in advecting cool fluid from the central parts of the channel to regions close to the hotter dimpled surface.