Due to the low heat transfer efficiency of common heat exchange systems, an improved heat exchange system was developed. Enhanced tubes (elliptical tubes with a built-in turbulator) instead of a smooth tube were used and TiO2-water nanofluids were substituted for water to intensify the heat transfer. The influences of turbulator (presence or absence), axial ratios of elliptical tubes (Z=1.235, 1.471, 1.706), nanoparticle concentration (ω=0.0 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%), and Reynolds number (Re=400–12,000) on the flow and heat transfer properties of TiO2-water nanofluids were studied. Thermal and exergy efficiency were used to research the comprehensive thermo-hydraulic characteristics of these heat transfer enhancement technologies. The thermo-hydraulic properties of nanofluids all showed an increasing trend with the growing axial ratio, nanoparticle concentration and Reynolds number. Nanofluids (ω=0.5 wt%) in an elliptical tube (Z=1.706) with a built-in turbulator showed the best thermal performance, which could be increased by 33.8% in comparison with water at best. The thermal efficiency index increased first and then decreased with the Re. Nanofluids in elliptical tubes with a built-in turbulator can clearly promote heat transfer under the identical condition.

中文翻译：

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内置湍流器的不同轴比椭圆管中纳米流体的热工水力性能实验研究

由于普通热交换系统的传热效率低，开发了一种改进的热交换系统。使用增强管（带有内置湍流器的椭圆管）代替光滑管，并用二氧化钛-水纳米流体代替水以加强传热。湍流器（有无）、椭圆管轴比（Z=1.235、1.471、1.706）、纳米粒子浓度（ω=0.0 wt%、0.1 wt%、0.3 wt%、0.5 wt%）和雷诺数的影响(Re=400–12,000) 研究了 TiO2-水纳米流体的流动和传热特性。热效率和火用效率被用来研究这些传热增强技术的综合热工水力特性。随着轴比的增大，纳米流体的热工水力特性均呈增大趋势，纳米粒子浓度和雷诺数。具有内置湍流器的椭圆管（Z = 1.706）中的纳米流体（ω = 0.5 wt％）表现出最佳的热性能，与水相比最多可提高33.8％。热效率指数随着 Re 的增加先增加后减小。在相同条件下，内置湍流器的椭圆管中的纳米流体可以明显促进传热。