Abstract Transient analysis of vertical heating and horizontal cooling rectangular single-phase natural circulation loop with various water-based hybrid nanofluids (Al2O3 + Ag, Al2O3 + Cu, Al2O3 + TiO2, Al2O3 + CNT, Al2O3 + Graphene) with 1% volumetric concentration is studied numerically. Temporal fluctuation and time required to attain the steady-state, transient mass flow rate and energy-exergy performance parameters (effectiveness and total entropy generation) using hybrid nanofluids are compared with water. The effect of power input and geometry parameter (diameter and height) of the loop on transient performances is studied as well. The result reveals that the fluctuation of mass flow rate and time required to attain the steady-state are less for hybrid nanofluids as compared to water. However, platelet and cylindrical shaped nanoparticles yield a lower stability as compared to spherical shaped. The mass flow rate is enhanced with hybrid nanofluids, except Al2O3 + CNT and Al2O3 + Graphene, as compared to water. The energy-exergy performance of hybrid nanofluids is higher than water. The maximum increment in mass flow rate is shown by Al2O3 + Ag hybrid nanofluid (3%), whereas Al2O3 + Graphene shows the highest increment in effectiveness (25.4%) and highest decrement in total entropy generation (14.3%) as compared to water. Smaller diameter and lower height of loop are found preferable for the flow stability.

中文翻译：

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使用混合纳米流体的单相自然循环回路的瞬态热工水力和性能特征

摘要 采用体积浓度为 1% 的各种水基混合纳米流体（Al2O3 + Ag、Al2O3 + Cu、Al2O3 + TiO2、Al2O3 + CNT、Al2O3 + 石墨烯）的垂直加热和水平冷却矩形单相自然循环回路的瞬态分析为数值研究。将使用混合纳米流体达到稳态、瞬态质量流量和能量-火用性能参数（有效性和总熵生成）所需的时间波动和时间与水进行了比较。还研究了回路的功率输入和几何参数（直径和高度）对瞬态性能的影响。结果表明，与水相比，混合纳米流体的质量流量波动和达到稳态所需的时间更小。然而，与球形纳米颗粒相比，片状和圆柱形纳米颗粒产生较低的稳定性。与水相比，除了 Al2O3 + CNT 和 Al2O3 + 石墨烯之外，混合纳米流体的质量流速得到提高。混合纳米流体的能量-火用性能高于水。与水相比，Al2O3 + Ag 混合纳米流体 (3%) 显示了质量流率的最大增量，而 Al2O3 + 石墨烯显示出最高的效率增量 (25.4%) 和最大的总熵生成减量 (14.3%)。发现较小的直径和较低的环高度对于流动稳定性是优选的。混合纳米流体的能量-火用性能高于水。与水相比，Al2O3 + Ag 混合纳米流体 (3%) 显示了质量流率的最大增量，而 Al2O3 + 石墨烯显示出最高的效率增量 (25.4%) 和最大的总熵生成减量 (14.3%)。发现较小的直径和较低的环高度对于流动稳定性是优选的。混合纳米流体的能量-火用性能高于水。与水相比，Al2O3 + Ag 混合纳米流体 (3%) 显示了质量流率的最大增量，而 Al2O3 + 石墨烯显示出最高的效率增量 (25.4%) 和最大的总熵生成减量 (14.3%)。发现较小的直径和较低的环高度对于流动稳定性是优选的。