Special heat transfer characteristics of supercritical CO 2 flowing in a vertically-upward tube with low mass flux
Special heat transfer characteristics of supercritical CO 2 flowing in a vertically-upward tube with low mass flux
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超临界CO 2 在低质量通量垂直向上管内流动的特殊传热特性
DOI：
10.1016/j.ijheatmasstransfer.2018.01.112
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发表时间：
2018
影响因子：
5.2
通讯作者：
Xianliang Lei
中科院分区：
文献类型：
--
作者：
Qian Zhang;Huixiong Li;Xiangfei Kong;Jialun Liu;Xianliang Lei
针对低质量流量下超临界CO2（S-CO2）传热研究较少的现状，在High-TaP-SCO 2实验回路上对低质量流量下S-CO2在直径16 mm管内的传热进行了实验研究。在7.5-10.5 MPa的压力范围、50-500 kg/m2 s的质量通量和5-100 kW/m2的热通量下收集基本数据。在低质量流量下，分析了热流密度、质量流量和压力对传热的影响。结果表明，随着热流密度的增加，低质量流率（G< 300 kg/m2 s）下的传热现象与正常质量流率（G≥ 300 kg/m2 s）下的传热现象完全不同。在较低的质量流量下的传热并没有恶化，而是随着传热系数的增加而增强，这是单相对流传热的约2.6倍。当质量流量从400 kg/m2 s降低到100 kg/m2 s时，传热增强了约5倍，并由劣化向增强转变。并对这种传热转变的机理进行了讨论。结果表明，较低质量通量下的特殊传热强化主要是由强浮力和高压力流体的共同作用引起的。基于目前的数据集，现有的Nusselt超临界流体的相关性进行了重新评估，这些相关性未能捕捉到在低质量通量下发生的传热增强。最后，提出了一个适用于低质量流量下S-CO2传热的修正关联式，误差在±20%以内，可用于S-CO2相关装置的设计。
Due to limited studies on heat transfer of supercritical CO2(S-CO2) at low mass flux, an experimental study was conducted on the High-TaP-SCO2 test loop to study heat transfer of S-CO2in a 16-mm diameter tube with low mass flux. Fundamental data were collected at a pressure range of 7.5–10.5 MPa, mass flux of 50–500 kg/m2s and heat flux of 5–100 kW/m2. The effects of heat flux, mass flux, and pressure on heat transfer at low mass flux were analyzed. Results showed that, with increasing heat flux, a completely different heat transfer phenomenon was observed at lower mass flux (G< 300 kg/m2s) compared to a normal mass flux (G≥ 300 kg/m2s). Heat transfer at lower mass flux was not deteriorated but rather enhanced with a rising heat transfer coefficient, which is about 2.6 times higher than single-phase convective heat transfer. With mass flux decreasing from 400 to 100 kg/m2s, heat transfer was enhanced about 5 times and turned from deterioration to enhancement. The mechanism of this heat transfer transition was further discussed. Results suggested that the special heat transfer enhancement at lower mass flux was mainly induced by the combined effects of strong buoyancy and highcpfluid. Based on the present dataset, existing Nusselt correlations for supercritical fluids were reevaluated, and these correlations failed in capturing the heat transfer enhancement occurring at low mass flux. Finally, a modified correlation for the heat transfer of S-CO2at low mass flux was proposed within ±20% error and is available for the design of relevant devices with S-CO2.