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首页> 外文期刊>International Journal of Heat and Mass Transfer >Special heat transfer characteristics of supercritical CO_2 flowing in a vertically-upward tube with low mass flux
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Special heat transfer characteristics of supercritical CO_2 flowing in a vertically-upward tube with low mass flux

机译：超临界CO_2在垂直向上流动的低质量通量管中的特殊传热特性

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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/m2 s 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/m2 s) compared to a normal mass flux (G ≥ 300 kg/m2 s). 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/m2 s, 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.
机译：由于对超临界CO2（S-CO2）在低质量通量下的热传递的研究有限，因此在High-TaP-SCO2测试回路上进行了实验研究，以研究S-CO2在直径16 mm的低管中的传热。质量通量。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的热通量的条件下收集基本数据。分析了热通量，质量通量和压力对低质量通量下传热的影响。结果表明，随着热通量的增加，与正常质量通量（G≥300 kg / m2 s）相比，在较低的质量通量（G <300 kg / m2 s）下观察到完全不同的传热现象。在较低质量通量下的传热并未恶化，而是随着传热系数的增加而增强，传热系数比单相对流传热高约2.6倍。随着质量通量从400降低到100 kg / m2 s，传热提高了约5倍，并从恶化转为增强。进一步讨论了这种传热转变的机理。结果表明，在较低质量通量下的特殊传热增强主要是由强浮力和高cpfluid的共同作用引起的。基于当前数据集，重新评估了超临界流体的现有Nusselt相关性，这些相关性未能捕获在低质量通量下发生的传热增强。最后，提出了在低质量通量下S-CO2传热的修正相关性，误差在±20％以内，可用于设计S-CO2相关装置。

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