ABSTRACT

We numerically examine the thermal performance of a round tubular heat exchanger featuring a combination of three passive techniques for heat-transfer enhancement: (i) center-cleared twisted-tape inserts, (ii) tube corrugations, and (iii) nanofluids. We consider three geometric tape parameters – the central-clearance width (C), the tape width (W), and the 180° tape pitch (H) – across a range of Reynolds numbers (500 ≤ Re ≤ 1250). For both water and a representative nanofluid (Al₂O₃-water), increasing W or decreasing C or H is found to increase the heat transfer coefficient at all Re. Switching from water to one of four water-based nanofluids − Al₂O₃-water, CuO-water, Cu-water, and TiO₂-water – is found to improve the heat transfer rate sufficiently to overcome any associated rises in pressure drop, resulting in thermal efficiencies higher than those of water. The highest thermal efficiency coefficient (η = 1.157) occurs with the Cu-water nanofluid at the smallest Re (500), whereas the lowest thermal efficiency coefficient (η = 1.115) occurs with the CuO-water nanofluid at the largest Re (1250). Across the entire Re range, increasing the volume concentration of Al₂O₃ nanoparticles (from ϕ = 2 to 5%) is found to increase the coefficients of heat transfer and thermal efficiency. This study provides new insight into how the heat transfer capabilities of a tubular heat exchanger can be enhanced by combining center-cleared twisted-tape inserts, tube corrugations and nanofluids.

摘要

我们在数值上研究了一种圆管式换热器的热性能，该换热器结合了三种用于增强传热的被动技术：（i）中心清除的扭曲带插入物，（ii）波纹管和（iii）纳米流体。我们考虑三个几何参数磁带-中央-间隙宽度（Ç），带子宽度（w ^），并且180°带间距（ħ） -在一系列的雷诺数（500≤的 重新 ≤1250）。对于水和代表性的纳米流体（Al ₂ O _3-水），发现增加W或减少C或H都会增加所有Re的传热系数。。发现从水转换为四种水基纳米流体之一-Al ₂ O _3-水，CuO-水，Cu-水和TiO _2-水–可以充分改善传热速率，以克服任何相关的压降升高，导致热效率高于水。Cu-水纳米流体在最小Re（500 ）时出现最高的热效率系数（η= 1.157），而CuO-水纳米流体在最大Re（1250）出现最小的热效率系数（η= 1.115 ） 。在整个Re范围内，增加Al ₂ O ₃的体积浓度发现纳米粒子（from = 2到5％）会增加热传递系数和热效率。这项研究提供了新的见解，说明如何通过结合中心清理的扭曲胶带，管形波纹和纳米流体来增强管状热交换器的传热能力。