Two-dimensional numerical simulations are conducted to study forced convection flow of different water-based nanofluids (ZnO, Al₂O₃, and SiO₂) with volume fractions () = 0–5% and fixed nanoparticle size (d_p) = 20 nm for Reynolds numbers (Re) = 50–225 over a double backward-facing step with an expansion ratio (ER) = 2 under constant heat flux (q″ = 3000 W/m²) condition using the finite volume method. Results indicate that the local Nusselt number increases with volume fraction and Reynolds number for all working fluids. In comparison to water, the maximum heat transfer augmentation of about 21.22% was achieved by using water-SiO₂ nanofluid at Re = 225 with  = 5% and d_p = 20 nm. Under similar conditions, the Al₂O₃ and ZnO nanofluids demonstrated 14.23% and 11.86% augmentation in heat transfer in comparison to water. The skin friction coefficient decreases with the increase in Re for all working fluids. No significant differences are observed in the values of skin friction coefficient among all working fluids at a particular Re. These results indicate that the heat transfer enhancement has been achieved with no increased energy requirements. In addition, the velocity increases with the rise in Re, with SiO₂ nanofluid exhibiting the highest velocity as compared to other working fluids.

中文翻译：

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双后向阶梯通道中不同纳米流体的热性能比较研究：数值方法

二维数值仿真进行研究不同水性纳米流体的强制对流流动（氧化锌，铝₂ ö ₃和SiO ₂）与体积分数（）  = 0-5％和固定的纳米颗粒尺寸（d _p）= 20雷诺数 (Re) = 50–225，在膨胀比 (ER) = 2 的双后向台阶上，在恒定热通量 ( q ″ = 3000 W/m ² ) 条件下，使用有限体积法的nm 。结果表明，对于所有工作流体，局部努塞尔数随着体积分数和雷诺数的增加而增加。与水相比，使用水-SiO ₂实现了约 21.22% 的最大传热增强纳米流体在RE = 225  = 5％和d _p  = 20纳米。在类似条件下，与水相比，Al ₂ O ₃和 ZnO 纳米流体的传热增加了 14.23% 和 11.86%。对于所有工作流体，表面摩擦系数随着 Re 的增加而降低。在特定 Re 下，所有工作流体之间的皮肤摩擦系数值没有观察到显着差异。这些结果表明在没有增加能量需求的情况下实现了传热增强。此外，速度随着 Re 的增加而增加，与其他工作流体相比，SiO ₂纳米流体表现出最高的速度。