Turbulent hydrothermal characteristics in a double-pipe heat exchanger with an internal twisted elliptical tube (TET) are investigated. The impacts of aspect ratio (AR = 1.4–2), uniform twist pitch (p = 100 mm-400 mm), and non-uniform twist pitch (five cases) on flow stream characteristics and heat transfer of parallel and counter-flows are investigated numerically. Utilizing a TET with a non-uniform twist pitch as an innovative approach yields noteworthy results, particularly in contrast to the traditional use of TETs with uniform twist pitch, owing to the longitudinal asymmetry. The outcomes depict that the pressure drop and heat transfer augment as the uniform twist pitch declines and the AR rises. The counter-flow has a more significant average Nusselt number than the parallel-flow by about 2–4 % without increasing the friction factor. Still, in some cases of non-uniform twist pitch, the average Nusselt number of the parallel flow is even 4 % higher than the counter-flow. The case with p = 100–200–400 mm (three parts with various twist pitches) and parallel-flow exhibits the most significant performance evaluation criterion (PEC) among the non-uniform twist pitch. As the aspect ratio increases from AR = 1.4 to AR = 2, the PEC factor in the counter-flow mode increases; however, there is an out-of-trend point at AR = 2 for the parallel-flow mode. The PEC factor augments about 8.47 % and 6.16 % for the counter-flow and the parallel-flow modes, respectively. The growth of TET twist pitch by 300 % reduces PEC by about 13.3 % in the counter-flow. The most significant PEC value is 1.166, which belongs to the case with the counter-flow condition and p = 100 mm.

中文翻译：

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双管换热器中均匀和非均匀内扭曲椭圆管的应用

研究了具有内部扭曲椭圆管（TET）的双管换热器中的湍流水热特性。长径比（AR = 1.4–2）、均匀扭距（p = 100 mm-400 mm）和不均匀扭距（五种情况）对平行流和逆流的流流特性和传热的影响为进行了数值研究。使用具有不均匀捻距的 TET 作为一种创新方法会产生显着的结果，特别是与传统使用具有均匀捻距的 TET 相比，由于纵向不对称。结果表明，随着均匀扭曲节距的减小和 AR 的增加，压降和传热增加。在不增加摩擦系数的情况下，逆流的平均努塞尔数比并流的平均努塞尔数高约 2-4%。尽管如此，在某些捻距不均匀的情况下，平行流的平均努塞尔数甚至比逆流高 4%。 p = 100–200–400 mm（具有不同捻距的三个零件）和平行流的情况在非均匀捻距中表现出最重要的性能评估标准（PEC）。随着长径比从AR=1.4增加到AR=2，逆流模式下的PEC因子增加；然而，对于并流模式，在 AR = 2 处存在一个偏离趋势的点。逆流和并流模式的 PEC 系数分别增加约 8.47% 和 6.16%。 TET 捻距增长 300%，逆流中 PEC 降低约 13.3%。最显着的 PEC 值为 1.166，属于逆流条件且 p = 100 mm 的情况。