10 mm垂直单管通道内超临界水传热弱化现象的实验与数值分析

超临界压力下的流体因拟临界点附近物性的剧烈变化，形成了非常奇特的传热现象。因流体密度突变，在低流量下会引起强烈的浮升力作用，对超临界流体的流动和传热均有极大影响。本工作通过实验获得10 mm单管内传热弱化现象的实验数据，并采用改进的低雷诺数湍流模型，使用数值方法模拟该传热弱化现象。计算结果表明，不同于以往传统的模型会高估壁面温度，改进的低雷诺数湍流模型能较好预测实验结果。数值模拟结果还揭示了浮升力对湍流剪切应力和速度分布的影响，进而引起传热弱化和传热恢复。

Experimental and Numerical Study on Convection Heat Transfer Deterioration of Supercritical Water in 10 mm Vertical Tube

The heat transfer at supercritical pressure is mainly characterized by the thermo-physical properties which vary strongly near the vicinity of pseudo-critical point. The strong variation of density leads to great buoyancy effect at low flow rate, which imposes great influence on supercritical fluid flow and heat transfer. The convection heat transfer deterioration of supercritical water in 10 mm vertical tube was studied, and an improved low Reynolds turbulent model was proposed in numerical study to analyze the heat transfer deterioration phenomenon. The calculation results of supercritical fluid heat transfer show that traditional turbulence models overestimate wall temperature, but the present model can predict wall temperature correctly. The numerical results also show the buoyancy effect on turbulent shear stress and flow velocity distribution, which leads to heat transfer deterioration and recovery.