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Comparison of convective heat transfer of turbulent nanofluid flow through helical and conical coiled tubes

机译：湍流纳米流体通过螺旋和锥形盘管的对流传热比较

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Application of nanofluid and coiled tubes are two passive methods for increasing the heat transfer. In the present study, the turbulent flows of water and nanofluid in coiled tubes heat exchanger were numerically studied. CuO-water nanofluid containing 1 vol% copper oxide nanoparticles was used and single-phase approach was considered for nanofluid flow. The effect of different geometrical parameters on Nusselt number was also investigated for both helical and conical coiled tubes. Water properties were defined as temperature dependent function, and constant wall temperature was employed as wall boundary condition. Simulation results were validated by available experimental and numerical data of heat transfer coefficient and pressure drop inside the helically coiled tube. The results show that for the helically coiled tubes, Nusselt number increased by tube diameter enhancement, while the increase of pitch circle diameter resulted in its decline. However, the variation of helical pitch exhibited a slight effect on the heat transfer. Moreover, for conical coiled tubes, increase helical pitch and cone angle reduced Nusselt number; while this parameter increased as the tube diameter increases. Addition of 1% copper oxide to water led to 8% heat transfer augmentation in the helically coiled tube. Also, using CuO-water nanofluid, the performance index was enhanced by 3.5 and 5% for helical and conical coiled tubes, respectively.
机译：纳米流体和盘管的应用是增加传热的两种被动方法。在本研究中，对盘管式换热器中水和纳米流体的湍流进行了数值研究。使用了含有1％（体积）氧化铜纳米粒子的CuO-水纳米流体，并考虑了单相方法进行纳米流体的流动。还研究了螺旋形和锥形盘管的不同几何参数对Nusselt数的影响。将水的性质定义为温度依赖性函数，并将恒定的壁温用作壁边界条件。通过现有的实验数据和螺旋盘管内部传热系数和压降的数值数据验证了仿真结果。结果表明，对于螺旋盘管，管直径的增加会增加Nusselt数，而节圆直径的增加会导致管数的减小。但是，螺距的变化对传热影响很小。此外，对于锥形盘管，增加螺旋螺距和锥角会降低Nusselt数;而此参数随管直径的增加而增加。在水中添加1％氧化铜会导致螺旋盘管的传热增加8％。同样，使用CuO-水纳米流体，螺旋和锥形盘管的性能指数分别提高了3.5和5％。

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