ABSTRACT In the present research work, heat transfer and friction characteristics of in-line elliptical tubes are studied experimentally and numerically with the aiming to enhanced the thermal performance. The elliptical tubes with an aspect ratio (AR) of 0.35 and 0.50 and with circular tubes of the aspect ratio of 1 are selected for Reynolds number (Re) ranging from 5000 to 21000. The results indicate that the elliptical tube shows higher heat transfer rate with a significant reduction in the friction factor for the entire range of Reynolds number. The superior performance of the elliptical tube is often due to the aerodynamic cross-section profile of the tubes which promotes better heat transfer with a reduction in the frontal area of the tubes. The study is performed for the two different pitch to major axis ratios (PR) of 1.25 and 1.5, respectively. The results show that at a pitch ratio of 1.25 the elliptical tube with an aspect ratio of 0.50 leads to the superior heat transfer rate, while at pitch ratio of 1.50 elliptic tubes with an aspect ratio of 0.35 indicate better thermo-hydraulic efficiency relative to 0.50.

中文翻译：

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直列椭圆管横流换热器热性能提升

摘要 在目前的研究工作中，对直列椭圆管的传热和摩擦特性进行了实验和数值研究，旨在提高热性能。雷诺数(Re)在5000~21000范围内选择长径比(AR)分别为0.35和0.50的椭圆管和长径比为1的圆管。结果表明椭圆管具有较高的传热率在整个雷诺数范围内，摩擦系数显着降低。椭圆管的卓越性能通常是由于管的空气动力学横截面轮廓，这促进了更好的热传递，同时减少了管的前部面积。该研究是针对 1.25 和 1.5 的两种不同的螺距与长轴比 (PR) 进行的，分别。结果表明，在螺距比为 1.25 时，纵横比为 0.50 的椭圆管具有较高的传热率，而在螺距比为 1.50 时，纵横比为 0.35 的椭圆管相对于 0.50 表明更好的热工水力效率.