This paper discusses the conjoint effect of circular fin turbulators and alumina (Al₂O₃) nanofluid on the thermal performance of a helically wound coil-in-shell heat exchanger used for waste heat recovery. An experiment was conducted using three different coils: two with circular fin turbulators brazed to the annular coil surface at 45° and 90° orientations and one plain coil without a fin. The coil side fluid was Al₂O₃ nanofluid (0.05%, 0.1%, and 0.15% by volume concentrations) flowing in the coil under laminar and turbulent (500 ≤ Re ≤ 5500) conditions, while the hot air at different flow velocities from 1 to 3 m/s (i.e., 4500 ≤ Re_h ≤ 13,500) was used as the shell-side fluid. The experiment revealed that the Nusselt number increased by 43.96% and 69.66% and the thermal-hydraulic performance increased by 16.92% and 35.71% for the 90° and 45° fin orientations, respectively, at 0.15% concentration of Al₂O₃ nanofluid and hot air velocity of 3 m/s. Furthermore, the thermal-hydraulic performance showed a nearly two-fold increase with 45° fin orientation/Al₂O₃ nanofluid combination. Based on the experiment, correlations were developed for the Nusselt number, friction factor, and thermal-hydraulic performance in the laminar and turbulent regimes, which are fairly in agreement with acceptable limits.

中文翻译：

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环形翅片管和氧化铝纳米流体增强螺旋壳式换热器的热性能－实验研究及相关性发展

本文讨论了圆形翅片湍流器和氧化铝（Al ₂ O ₃）纳米流体对用于废热回收的螺旋缠绕壳管式换热器的热性能的联合影响。使用三种不同的线圈进行了实验：两个带有圆形鳍状湍流器，以45°和90°的方向钎焊到环形线圈表面，一个带有无鳍的普通线圈。盘管侧的流体是Al ₂ O ₃纳米流体（按体积浓度计为0.05％，0.1％和0.15％）在层流和湍流（500≤Re≤5500）条件下在盘管中流动，而热空气以不同的流速从1至3 m / s（即4500≤Re _h≤13,500）用作壳侧流体。实验表明，在浓度为0.15％的Al ₂ O ₃纳米流体和90％翅片方向上，对于90°和45°翅片取向，Nusselt数分别增加43.96％和69.66％，热工液压性能分别增加16.92％和35.71％。热风速度为3 m / s。此外，热液压性能显示出随着45°鳍片取向/ Al ₂ O ₃纳米流体组合的增加近两倍。在实验的基础上，建立了层流和湍流状态下的努塞尔数，摩擦因数和热工液压性能的相关性，这与可接受的范围相当吻合。