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首页> 外文期刊>International Journal of Heat and Mass Transfer >Investigation on the characteristics and mechanisms of unusual heat transfer of supercritical pressure water in vertically-upward tubes
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Investigation on the characteristics and mechanisms of unusual heat transfer of supercritical pressure water in vertically-upward tubes

机译：超临界水在垂直向上管中异常传热的特性及机理研究

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摘要

The heat transfer characteristics of supercritical pressure water in a vertically-upward optimized internally-ribbed tube was investigated experimentally to study the mechanisms of unusual heat transfer of supercritical pressure water in the so-called large specific heat region. The experimental parameters were as follows. The pressure at the inlet of the test section ranged from 22.5 to 29.0 MPa, and the mass flux of the fluid was from 650 to 1200 kg/m~2 s, and the heat flux on the inside wall of the tube varied from 200 to 660 kW/m~2. According to experimental data, the characteristics of heat transfer enhancement and also the heat transfer deterioration of supercritical pressure water in the large specific heat region was analyzed and based on the comparison and analysis of the current major theories that were used to explain the reasons for unusual heat transfer to occur, the mechanisms of heat transfer enhancement and deterioration were discussed, respectively. The enhanced heat transfer was characterized by the gently changing wall temperature, the small temperature difference between the inside-tube-wall and the bulk fluid and the high heat transfer coefficient in comparison to the normal heat transfer. The deteriorated heat transfer could be characterized by the sharply increasing wall temperature, the large temperature difference and a sudden decrease in heat transfer coefficient in comparison to the normal heat transfer. The heat transfer enhancement of the supercritical pressure water in the large specific heat region was suggested to be a result of combined effect caused by the rapid variations of thermophysical properties of the supercritical pressure water in the large specific heat region, and the same was true of the heat transfer deterioration. The drastic changes in thermophysical properties near the pseudocritical points, especially the sudden rise in the specific heat of water at supercritical pressures, might result in the occurrence of the heat transfer enhancement, while the covering of the heat transfer surface by fluids lighter and hotter than the bulk fluid made the heat transfer deteriorated eventually and explained how this lighter fluid layer formed.
机译：通过实验研究了垂直向上优化的内肋管中超临界压力水的传热特性，以研究所谓的大比热区域中超临界压力水异常传热的机理。实验参数如下。试验段入口压力为22.5〜29.0 MPa，流体的质量通量为650〜1200 kg / m〜2 s，管内壁的热通量为200〜200 kg / m 2。 660千瓦/米〜2。根据实验数据，在大比热区分析了超临界压力水的传热增强特性，并分析了超临界压力水的传热劣化，并在对现有主要理论进行了比较和分析的基础上，进行了解释。讨论了发生传热，传热增强和劣化的机理。与正常传热相比，传热增强的特征在于壁温缓慢变化，管内壁与散装流体之间的温差小以及传热系数高。与正常传热相比，传热恶化的特征在于壁温急剧上升，温差大，传热系数突然降低。据认为，大比热区中超临界水的传热增强是由于大比热区中超临界水的热物理性质迅速变化而产生的综合效应的结果，对传热恶化。伪临界点附近的热物理性质的急剧变化，特别是在超临界压力下水的比热的突然升高，可能导致传热的增强，而流体的传热表面比大量的流体最终使传热恶化，并解释了这种较轻的流体层是如何形成的。

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