Abstract An experimental investigation is conducted to determine the effect of dimpled depth on the condensation heat transfer coefficient and pressure drop of R-134a flowing inside dimpled tubes. The test condenser is a double tube heat exchanger where the refrigerant flows inside and water flows in the annulus. The inner tube is a 1500 mm long and 8.1 mm inside diameter. The experiments are carried out for one smooth tube and three dimpled tubes having dimpled depth of 0.5, 0.75, and 1.0 mm. For each test tube, several test runs are performed over mass flux range of 300–500 kg/m2s, heat flux range of 10–20 kW/m2, and condensing temperature range of 40–50 °C. The experimental results reveal that the dimpled tube presents the significant heat transfer enhancement and pressure drop penalty. The tube with the highest dimpled depth yields the highest heat transfer enhancement and pressure drop penalty up to 83% and 892% higher than those of the smooth tube, respectively. Additionally, the overall performance of dimpled tube is evaluated in term of efficiency index. The new correlations including the effect of dimpled depth, dimpled pitch, and helical pitch on the Nusselt number and friction factor of R-134a in dimpled tube are developed.

中文翻译：

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R-134a在不同凹陷深度凹陷管内流动的冷凝传热和压降实验研究

摘要 进行了实验研究以确定凹坑深度对凹坑管内流动的R-134a 的冷凝传热系数和压降的影响。测试冷凝器是一种双管换热器，其中制冷剂在内部流动，水在环形空间中流动。内胎长 1500 毫米，内径 8.1 毫米。对一根光滑管和三个凹坑深度分别为 0.5、0.75 和 1.0 毫米的凹坑管进行了实验。对于每个试管，在 300–500 kg/m2s 的质量通量范围、10–20 kW/m2 的热通量范围和 40–50 °C 的冷凝温度范围内进行多次测试运行。实验结果表明，波纹管呈现出显着的传热增强和压降损失。具有最高凹坑深度的管产生最高的传热增强和压降损失，分别比光滑管高 83% 和 892%。此外，凹坑管的整体性能是根据效率指数来评估的。新的相关性包括凹坑深度、凹坑节距和螺距对凹坑管中 R-134a 的努塞尔数和摩擦系数的影响。