超临界二氧化碳水平管内层流混合对流换热数值模拟

Numerical simulation of laminar mixed convection heat transfer of supercritical carbon dioxide in horizontal tube

为得到二次流对换热的强化作用,对恒壁温冷却工况下,超临界二氧化碳在水平微细圆管内的混合对流换热进行了数值模拟。分析了重力水平、冷壁面温度、入口雷诺数Re等参数变化时管道壁面的传热系数,管内浮升力引发的二次流、范宁摩擦系数沿管道的变化规律,引入相对二次流动能将二次流的强度定量表示出来。研究发现管内流体顶部温度高于底部,上母线传热系数远高于下母线且在超临界二氧化碳的拟临界温度附近达到峰值,二次流及范宁摩擦系数在入口区域变化最剧烈,重力加速度对管内流场产生重要影响。

To obtain the strengthening effects of secondary flow on heat transfer, laminar mixed convec- tion heat transfer of supercritical carbon dioxide in a miniature horizontal circular tube under constant wall temperature cooling condition was determined through numerical simulation. The distribution of the local heat transfer coefficient, the buoyancy-induced secondary flow, the Fanning friction factor variation along the pipe were analyzed under different gravity levels, cold wall temperature and the different inlet Reynolds number. The relative secondary flow kinetic energy were introduced to quantitatively express the intensity of the secondary flow. The result showed that top temperature was higher than bottom, the top generatrix heat transfer coefficient reached peak value near the critical temperature and much higher than the bottom gener-atrix, the secondary flow and the Fanning friction factor changed the most intensely near the entrance area, the gravity acceleration had an important impact on the flow field.