超临界压力水在垂直上升内螺纹管中的传热特性

在压力22.5～30 MPa，质量流速430～1200 kg·m^-2·s^-1，内壁热负荷284～719 kW·m^-2范围内，对超临界压力水在均匀加热垂直上升内螺纹管内的传热特性进行了实验研究，得到了内螺纹管内超临界压力水的传热特性，分析了压力、热负荷和质量流速变化对内螺纹管壁温及传热系数的影响，探讨了拟临界区的传热机理，并给出了能用于工程实际的传热实验关联式。实验结果表明：垂直上升内螺纹管中超临界水具有良好的传热特性。在低焓值区内螺纹管壁温随焓增平缓增加，而在高焓值区壁温随焓增的升高明显。由于热物性的剧烈变化，超临界水在拟临界焓值区发生了明显的传热强化。压力与热负荷的增大以及质量流速的减小均会导致内螺纹管壁温的升高和传热系数的减小，使得传热强化现象削弱，甚至出现传热恶化。

Heat transfer characteristics of supercritical pressure water in vertical upward rifled tube

In the range of pressure from 22. 5 MPa to 30 MPa, mass flow rate from 430 kg·m-2·s^-1 to 1200 kg·m^-2·s^-1, and heat flux at inner wall from 284 kW·m^-2 to 719 kW·m^-2, an experiment was conducted under supercritical pressure to investigate the heat transfer characteristics of water in a vertical upward rifled tube.The temperature distribution in the tube wall was obtained.The effects of pressure, heat flux at inner wall and mass flow rate on heat transfer coefficient and temperature at inner wall were analyzed, the enhancement mechanism for heat transfer was discussed, and the corresponding empirical correlations were presented.The experimental results show that the supercritical pressure water in the vertical upward rifled tube presents very good heat transfer characteristics.The wall temperature in the rifled tube increases slowly with fluid enthalpy when the bulk temperature of fluid is lower than the pseudo-critical temperature and increases considerably when the bulk temperature is above the pseudo-critical temperature.At the temperature near the pseudo-critical temperature, the thermophysical properties of water under supercritical pressure change abruptly.Therefore, the heat transfer is enhanced in the pseudo-critical enthalpy region.With the increase of pressure and heat flux of inner wall and with the decrease of mass flow rate, the temperature of inner wall increases and the heat transfer coefficient decreases obviously, the enhancement on heat transfer is weakened and the heat transfer may be deteriorated.