Scaling analyses for the open flashing-driven natural circulation system

Transient simulating and scaling analyses are carried out to reproduce the transient operating behaviors of the prototypical big-scale open natural circulation system, which is designed for the Passive Containment Cooling System (PCCS). Firstly, a transient numerical code to simulate the operating behaviors of the open natural circulation system is developed and validated. Than, an effective and simplified 1:1 height scaling analyses based on the steady-state flow are conducted to model the operating behaviors of the prototypical open natural circulation system. The scaling process consists of heat transfer scaling of the heat exchanger and the pressure resistance scaling of the riser and downcomer sections, the purpose of which is to keep the driven force and pressure resistance of the model same with those of the prototype by changing the dimensions of the pipes. When choosing the geometrical parameters of the heat transfer tubes, the Reynolds number of fluid inside the heat transfer tube has a great influence on the modeling results. Thus, the flow regime inside the tube in the model system should be the same as that in the prototype system when choosing the geometrical parameters of heat transfer tube. The dimensions of the riser and downcomer section are scaled separately to keep the pressure resistances of them in the model same with those in the prototype respectively. From the comparison results of the model and prototype it can be found that the scaling open natural circulation system can reproduce the transient operating behaviors of the prototype very well and the scaling method in this study can be used for the engineering applications.