Abstract This study experimentally investigated the local heat transfer characteristics of supercritical carbon dioxide, which was uniformly heated in horizontal circular smooth tubes with inner diameters of 1.0 mm, 0.75 mm and 0.5 mm. The experimental results illustrated heat transfer enhancement with an increase in fluid temperature before the pseudocritical point and a decline in heat transfer just after the pseudocritical point. Subsequently, the heat transfer coefficient increased again when the fluid temperature was sufficiently higher than the pseudocritical value due to the enhancement of turbulence resulting from the decrease in viscosity. In addition, the parametric effects of outlet pressure, heat flux, mass flux, inlet temperature, and tube diameter on local heat transfer were investigated. The system demonstrated the optimal heat flux with the highest thermal performance when the outlet fluid condition was close to the corresponding pseudocritical point, at which both the specific heat and Prandtl number attained peak values. With other parameters fixed, the system with a higher mass flux, lower inlet temperature, or smaller diameter exhibited higher heat transfer performance. A new empirical correlation developed on the basis of the experimental data can reasonably predict the local Nusselt number of supercritical carbon dioxide along the flow path in uniformly heated horizontal tubes.

中文翻译：

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超临界二氧化碳在均匀加热水平微型管中局部传热的实验研究

摘要 本研究通过实验研究了在内径为1.0 mm、0.75 mm和0.5 mm的水平圆形光滑管中均匀加热超临界二氧化碳的局部传热特性。实验结果表明传热增强，流体温度在伪临界点之前增加，传热在伪临界点之后下降。随后，当流体温度足够高于伪临界值时，由于粘度降低导致湍流增强，传热系数再次增加。此外，还研究了出口压力、热通量、质量通量、入口温度和管径对局部传热的参数影响。当出口流体条件接近相应的伪临界点时，系统表现出具有最高热性能的最佳热通量，此时比热和普朗特数均达到峰值。在其他参数固定的情况下，具有较高质量通量、较低入口温度或较小直径的系统表现出较高的传热性能。在实验数据的基础上开发的一种新的经验关联式可以合理地预测均匀加热水平管中沿流动路径的超临界二氧化碳的局部努塞尔数。具有较高质量通量、较低入口温度或较小直径的系统表现出较高的传热性能。在实验数据的基础上开发的一种新的经验关联式可以合理地预测均匀加热水平管中沿流动路径的超临界二氧化碳的局部努塞尔数。具有较高质量通量、较低入口温度或较小直径的系统表现出较高的传热性能。在实验数据的基础上开发的一种新的经验关联式可以合理地预测均匀加热水平管中沿流动路径的超临界二氧化碳的局部努塞尔数。