Abstract

Low-Re-number turbulent flow and convective heat transfer of Al₂O₃-water nanofluid inside a helically corrugated channel (HCC) were examined numerically. The helically corrugated channel (HCC) was studied for the first time by analogy to a helically corrugated tube. The Reynolds number (based on the nanofluid properties) varies between 5000 and 10000. The nanoparticles volume fraction ranges from 0.1% to 5%. Also, the nanoparticle sizes of 20 nm, 40 nm, and 60 nm were considered. The two-phase mixture model was utilized in the simulations. The numerical results were compared with the experimental data. It was illustrated that a previously established correlation for the effective viscosity could be erroneous in certain circumstances. Hence, that model was amended carefully, and a correlation for nanoparticles with the mean diameter of 20 nm was presented. It was argued that the 20 nm nanoparticles slightly decrease the thickness of the velocity boundary layer. Besides, it was shown that there is a critical particle size above that the heat transfer decreases. Based on the present study, the recirculation region in the corrugation cavity has a significant impact on the turbulent mixing for Re ≥ 10000. Among the tested cases, the maximum ratio of Nusselt number was 1.413 for the particle size of 20 nm and the volume fraction of 5%, while the corresponding pressure drop ratio was 7.122.

摘要

_{Al 2} O ₃的低Re数湍流和对流传热- 对螺旋波纹通道 (HCC) 内的水纳米流体进行了数值检查。通过类比螺旋波纹管，首次研究了螺旋波纹通道 (HCC)。雷诺数（基于纳米流体特性）在 5000 和 10000 之间变化。纳米粒子的体积分数范围为 0.1% 到 5%。此外，还考虑了 20 nm、40 nm 和 60 nm 的纳米粒子尺寸。在模拟中使用了两相混合模型。将数值结果与实验数据进行了比较。它说明了先前建立的有效粘度相关性在某些情况下可能是错误的。因此，对该模型进行了仔细修改，并提出了平均直径为 20 nm 的纳米粒子的相关性。有人认为 20 nm 的纳米粒子会略微降低速度边界层的厚度。此外，表明存在临界粒径，传热会降低。根据目前的研究，波纹腔中的再循环区域对 Re ≥ 10000 的湍流混合有显着影响。在测试案例中，对于 20 nm 的粒径和体积分数，努塞尔数的最大比率为 1.413 5%，而相应的压降比为 7.122。