Numerical simulation of safety injection and natural circulation in two containers by smoothed particle hydrodynamics on the effects of filling levels and thermal diffusivities

Natural circulation is an important process in reactor thermal-hydraulics study. This process is simulated by Smoothed particle hydrodynamics method for a modeled system of circulation. A new kernel function of (-1, 5) power components has been proposed here and validated by the dam-break case. The modeled circulation system is composed of two containers of different heights. Three filling levels (Case A) and four thermal diffusivities (Case B) have been utilized to analyze their effects. Six vortex-criteria have been utilized to visualize the representative vortical motion of fluids inside the containers. Circulations of velocity and velocity-temperature, heat transfer amount, mean temperature and mean material derivative have been defined here to quantify the feature of natural circulations for the two cases. The results show that the filling levels affect mainly the process of setup, rather than the steady level of natural circulation. A high filling level has a considerable larger amount of heat transfer between the hot and cool fluids. The thermal diffusivity does not affect the process of the circulation level, whereas it has great effects on the mean as well material derivative of the temperature of fluids. For example, comparing the mean temperature of the fluid at the thermal diffusivity alpha = 0.02 to that at alpha = 2.79 (in Case B at t = 600 s), the mean temperature of cool fluids is about 15 degrees C lower at alpha = 0.02 than that at alpha = 2.79, whereas the mean temperature of hot fluids is about 7 degrees C higher at alpha = 0.02 than that at alpha = 2.79. In addition, the difference in the initial temperature of fluids and the difference in heights between two containers affect the natural circulation levels.