湍流普朗特数对竖直圆管高热流超临界二氧化碳流动传热性能的影响

Effect of Turbulent Prandtl Number on the Performance of Supercritical Carbon Dioxide Turbulent Flow in a Vertical Round Tube With High Heat Flux

超临界二氧化碳(supercritical carbon dioxide,S-CO_(2))因其腐蚀性小、临界参数低、高效等优势,广泛应用于燃煤火力发电、聚光太阳能发电、核反应堆等领域。其中,S-CO_(2)通常处于高温高压高热通量的加热湍流状态。现阶段湍流模型主要针对亚临界、拟临界流动问题,对超临界流体流动适用性较差,因此,该文开展超临界工况下管内S-CO_(2)湍流流动传热研究。针对剪应力输运模型(SST湍流模型),建立均匀加热垂直上升管内S-CO_(2)多场耦合数值模型,并通过实验数据验证模型正确性。研究湍流普朗特数(Pr_(t))对湍流模型的影响,并探讨关键运行参数对管内壁温度的影响。结果表明,Pr_(t)对高温高压高热流S-CO_(2)湍流流动传热有重要影响。当Pr_(t)从1降低到0.65~0.70时,内壁温的平均相对误差可降低约3.16%,对流换热系数可增加25.21%。通过对Pr_(t)的修正可以有效提高SST湍流模型的准确性,结果可为高热流密度下S-CO_(2)循环的发展提供一定理论基础。

Supercritical carbon dioxide(S-CO_(2))is widely used in coal-fired thermal power generation,concentrated solar power generation and nuclear reactors because of its low corrosiveness,low critical parameters and high efficiency.In these conditions,S-CO_(2)is usually turbulent flow with high temperature,high pressure and high heat flux.At present,the turbulence model is mainly used for subcritical and near-critical flow problems,whereas it is not suitable for supercritical fluid flow.Therefore,a study is carried out on the characteristics of S-CO_(2)turbulent flow in a vertical tube under supercritical conditions far from the pseudo-critical point.A multi-fields coupled numerical model of S-CO_(2)in a round tube with uniform heating is developed and validated by our experimental data.The effect of the turbulent Prandtl number(Pr_(t))on the turbulence model is investigated,and the effect of key operating parameters is also discussed.The results show that Pr_(t)has an important effect on the heat transfer of the S-CO_(2)turbulent flow with high heat flux.For the SST turbulence model,when Pr_(t)is reduced from 1 to 0.65~0.70,the mean relative error(MRE)of the inner wall temperature can be reduced by approximately 3.16%and the convective heat transfer coefficient can be increased by 25.21%.The modification of Pr_(t)can effectively improve the accuracy of SST turbulence modeld.This paper also provides a theoretical basis for the development of S-CO_(2)cycle under high heat flux.