This study aims to investigate heat transfer and flow characteristics of ethylene glycol/water (EGW) and CuO–EGW nanofluids in circular tubes with and without trapezoid ribs. Nusselt number and friction factor in tubes with trapezoid ribs are analysed under a constant heat flux by changing rib bottom angles. This study compares the convective heat transfer coefficients of 6 vol.% CuO–EGW nanofluid and base fluid. It is found that under a constant Reynolds number, the Nusselt number and friction factor for CuO–EGW nanofluid and base fluid increase with an increase in the inclination angle. The Nusselt number for the CuO–EGW nanofluid in the tube with 75° rib bottom angle averagely increases by 135.8% compared to that in the smooth tube, and the performance evaluation criterion is 1.64.

中文翻译：

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梯形肋圆形管中纳米流体传热和流动特性的数值研究

本研究旨在研究带有/不带有梯形肋的圆形管中乙二醇/水（EGW）和CuO-EGW纳​​米流体的传热和流动特性。通过改变肋底角，在恒定热通量下分析具有梯形肋的管中的努塞尔数和摩擦系数。这项研究比较了6 vol。％CuO–EGW纳米流体和基础流体的对流传热系数。发现在恒定的雷诺数下，CuO–EGW纳米流体和基础流体的努塞尔数和摩擦系数随倾斜角的增加而增加。具有75°肋底角的管中的CuO–EGW纳米流体的Nusselt值与光滑管相比，平均增加135.8％，性能评估标准为1.64。