In the present paper, a proposal for enhancement of flow boiling is made by developing tubes with discrete internal structures inside the tube. Experiments have been conducted with R407C refrigerant. Heat flux from 5 to 12.5 kWm^-2 and mass flux from 40 to 200 kgm^-2s^-1 has been considered an experimental range in an in-house setup. The heat transfer characteristics of the newly developed tube with an internally microdimpled (IMD) tube and a tube with internal bidirectional tunnel structure (BTS) are compared with the commercially available micro-fin (MF) tube. It is observed that the heat transfer coefficient of R407C inside both the IMD and BTS tubes is better than that of the MF tube. Comparison of flow pattern of R407C inside an IMD tube has been made to confirm the fluidic facts behind enhancement. However, pressure drop is observed to be significantly less for IMD and BTS tubes compared to the MF tube. Overall performance of the newly developed BTS tube and the MF tube compared to the plain tube has been analyzed with the help of a performance index. The performance index of the BTS tube is found to be greater than one and much better than that of the MF tube for the experimental range considered. By increasing nucleation site density, it has been shown that a higher heat transfer coefficient can be achieved with moderate pressure drop.

中文翻译：

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通过在管内提供离散结构来增强R407C蒸发过程中的传热

在本文中，通过开发在管内部具有离散内部结构的管，提出了提高流动沸腾的建议。已经对R407C制冷剂进行了实验。从5到12.5 kWm ^-2的热通量和从40到200 kgm ^-2 s ^-1的质量通量在内部设置中被视为实验范围。将新开发的具有内部微凹痕（IMD）管和具有内部双向隧道结构（BTS）的管的热传递特性与市售的微翅片（MF）管进行了比较。可以看出，IMD和BTS管内的R407C的传热系数都比MF管的传热系数要好。比较了IMD管内R407C的流型，以确认增强作用背后的流体事实。但是，与MF管相比，IMD和BTS管的压降明显较小。借助性能指标分析了新开发的BTS管和MF管与普通管相比的总体性能。在所考虑的实验范围内，发现BTS管的性能指标大于MF管的性能指标，并且比MF管的性能指标好得多。通过增加成核位点密度，已经表明，在适度的压降下可以实现更高的传热系数。