低流量下等高差自然循环系统倒流现象实验研究

自然循环系统由于具有固有安全性而被广泛应用于核电站中。等高差自然循环系统是一种特殊的系统，其加热段与水箱之间是通过上下水平段连接。在低流量条件下，这类自然循环系统会发生水箱冷水倒流至上水平段的现象，目前对该现象的研究并不常见。对等高度差自然循环系统的上水平段倒流特性进行了可视化实验研究。实验结果表明，上水平段倒流长度随流量的增加而减小，随着加热段出口流体与倒流流体温差的增大而增加。研究发现，上水平段倒流现象主要受加热段出口流体惯性力和与倒流流体形成的浮升力共同影响，并且倒流现象的发生可以通过Richardson数来判定。

Experimental research on reverse flow phenomenon in natural circulation with equal height difference under low flow rate

Natural circulation systems are widely used in nuclear power plants due to their inherent safety. Natural circulation system with equal height different is a special system, because its heating section and water tank are connected by upper and lower horizontal loops. However, the phenomenon that the water in water tank reversely flows to the upper horizontal loop will be occurred in this kind of natural circulation system under low flow rate conditions. The studies of this phenomenon are not common. The reverse flow characteristics of upper horizontal loop is researched by visualization experiments. The results show that the reverse flow length in the upper horizontal loop decreases with the increase of flow rate, and increases with the increase of temperature difference between the outlet fluid of heater and the reverse flow fluid form water tank. It is found that the reverse flow in the upper horizontal loop is mainly affected by the inertia force of the hot water and the buoyancy force formed by the hot water and the reverse flow fluid. In addition, the reverse flow phenomenon in the upper horizontal loop can be judged by Richardson number.