抄録
Natural circulation has been adopted as the way of passive heat removal by some evolutionary and innovative reactors. Sub-cooled boiling is of great importance to the stability of a natural circulation system. An analytical model of two-phase natural circulation system is developed and sub-cooled boiling is taken into consideration. Numerical simulation of both steady state and transient state natural circulation are carried out. Besides, flow oscillation in Nuclear Power Simulation System (NPSS) is studied. One dimension homogeneous flow model is used to solve the governing equations. And lumped parameter model is adopted to establish the wall energy conservation equation. The test section is divided into four parts: single phase liquid, partial sub-cooled boiling, fully developed sub-cooled boiling and saturated boiling. Different heat transfer correlations are employed to calculate the wall temperature and heat transfer coefficient. Fluid temperature, void fraction and wall temperature are obtained by a MATLAB code. The effects of heating power, inlet temperature and system pressure on flow rate are investigated by the steady state code. The transient analysis indicates that flow oscillation occurs when sub-cooled boiling takes place at the exit of the test section. The flow oscillation is enhanced when heating power or inlet temperature is increased before a certain value, the flow oscillation tends to disappear when heating power or inlet temperature is further increased. Increasing system pressure has a stabilizing effect on the flow oscillation.
