Heat transfer enhancement is an important issue because of environmental effects and also cost reduction in any thermal installation. A combined propeller-type turbulator and Al₂O₃ nanofluid are considered for heat transfer enhancement in a horizontal circular tube. Three-dimensional governing equations using the two-phase mixture model with SST k–ε turbulent model are numerically solved to predict the behavior of different thermo-fluid parameters in a horizontal circular tube. In addition to studying the effects of these, both means on the heat transfer enhancement, an important discussion on their simultaneous effects are also presented. The effects of turbulator on the generation of swirl flow and also on the turbulent kinetic energy are shown and discussed for different nanoparticle volume fractions and different nanoparticle mean diameters. On one hand, the effect of inserting a turbulator on the thermal performance significantly dominates the effect of using a nanofluid. For instance, at the Z/D = 13.5, using combined nanofluid and turbulator the heat transfer coefficient 2.68 times augments while using only a turbulator it is 2.53 times enhanced. On the other hand, turbulator generates a radial gradient on the momentum forces. The latter significantly deteriorates the uniformity of the nanoparticles concentration. A higher nanoparticle concentration at the near-wall region where the sedimentation problem is taken placed is seen. Thus, it is recommended that nanofluid is not a suitable choice for simultaneous consideration with a propeller-type turbulator in such an application particularly when considering its physicochemical stability drawback. However, further experimental investigations must be carried out to verify such a conclusion and recommendation. It should be mentioned that agglomeration and sedimentation of nanoparticles on the wall surface have not been considered on the modeling of nanofluid physical properties.

中文翻译：

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螺旋桨式湍流器和纳米流体在圆管中增强湍流传热的数值研究

由于对环境的影响以及在任何热力装置中的成本降低，提高热传递是重要的问题。考虑将螺旋桨式湍流器和Al ₂ O ₃纳米流体组合用于增强水平圆形管中的传热。使用具有SST的两相混合物模型的三维控制方程ķ - ε数值求解湍流模型，以预测水平圆管中不同热流体参数的行为。除了研究这两种方法对增强传热的作用外，还对它们的同时作用进行了重要讨论。对于不同的纳米颗粒体积分数和不同的纳米颗粒平均直径，显示并讨论了湍流器对涡流产生以及湍流动能的影响。一方面，插入湍流器对热性能的影响明显支配了使用纳米流体的影响。例如在Z / D = 13.5，结合使用纳米流体和湍流器，传热系数提高了2.68倍，而仅使用湍流器，传热系数提高了2.53倍。另一方面，湍流器在动量力上产生径向梯度。后者显着降低了纳米颗粒浓度的均匀性。在放置沉淀问题的近壁区域看到更高的纳米颗粒浓度。因此，建议在这种应用中纳米流体不是与螺旋桨式湍流器同时考虑的合适选择，特别是考虑到其物理化学稳定性缺点时。但是，必须进行进一步的实验研究以验证这种结论和建议。