Modeling and experimental studies on mixing and stratification during natural convection in containments

Mixing and thermal stratification often occur in passive containment cooling systems. Currently, most of reactor system analysis codes do not use the thermal stratification to simplify the calculation. The 2-D or 3-D CFD methods require very fine grids and long running times. In this paper, a new code based on thermal stratification is used to solve heat transfer problems in large enclosures which can give good results in a short time without complex meshing. The models in the code provide the capability to simulate the containment. At the same time, a series of small scale model experiments with air injection are conducted to simulate the LOCA accidents. Simple variable method is adopted in the experiments to study the effects of four different factors on the flow field. The results of the experiments and the codes are compared to verify the validity of the code. Several typical conditions were calculated by a CFD code, and comparison between the running times of these two codes shows the advantage of the model used in the new code.