Abstract Three types of helical microtube coil namely circle, oval and elliptical are introduced and evaluated both experimentally and numerically. Al2O3-water, ZnO-water at three volume fractions ( ϕ ) of 1.0%, 1.5% and 2% are considered as working fluid as well as the base fluid (water). Different values of pitch are tested with constant pitch/diameter ratio of 1 for all geometries. The numerical simulations are presented the flow structures of helical microtubes in terms of velocity, isotherms, and vorticity contours. Compared to straight coil, the findings show that helical microtube curvature swirls are an important phenomenon to increase heat transfer. In addition, it shows that the heat transfer and friction loss increase as volume fractions of nanofluids and Reynolds number increase. The experiments have also uncovered that the use of helical microtube augment the heat transfer ratio considerably and greatest enhancement ratio was realized by employing circle form with ϕ = 2% of alumina nanofluid. Over ranges of considered flow, alumina nanofluid was better than ZnO-water nanofluid and the best thermal performance of 3.1 was recorded with using it at ϕ = 2% at Reynolds number of 1800. Besides, new empirical correlations were proposed and reported based on experimental data.

中文翻译：

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使用纳米流体在壳式和螺旋微管换热器中增强传热的实验和数值研究

摘要 介绍了圆形、椭圆形和椭圆形三种类型的螺旋微管线圈，并通过实验和数值进行了评估。Al2O3-水、ZnO-水在三个体积分数 ( ϕ ) 为 1.0%、1.5% 和 2% 时被认为是工作流体和基液（水）。对于所有几何形状，使用恒定的节距/直径比 1 测试不同的节距值。数值模拟显示了螺旋微管在速度、等温线和涡度等值线方面的流动结构。与直盘管相比，研究结果表明螺旋微管曲率漩涡是增加传热的重要现象。此外，它表明传热和摩擦损失随着纳米流体的体积分数和雷诺数的增加而增加。实验还发现，螺旋微管的使用显着提高了传热比，并且通过采用φ = 2% 氧化铝纳米流体的圆形形式实现了最大的传热比。在考虑的流量范围内，氧化铝纳米流体优于 ZnO-水纳米流体，在 φ = 2% 和雷诺数为 1800 时使用它记录了 3.1 的最佳热性能。此外，基于实验提出并报告了新的经验相关性数据。