| Passive containment cooling systems (PCCS) provide a new safety design for the nuclear industry that provides the safety-related ultimate heat sink for a new generation of inherently safe reactors such as Westinghouse's AP600 and AP 1000 and General Electric's SBWR and ESBWR. It uses only natural forces, such as gravity, natural circulation, and a small number of automatic valves to make the system work.; This research investigates experimentally mixed convection and heat transfer augmentation by forced jets in a large enclosure, at conditions simulating those of actual passive containment cooling systems and scales approaching those of actual containment buildings or compartments. The experiment is designed to measure the key parameters governing the heat transfer augmentation by forced jets and affecting the potential for ambient stratification, and to investigate the effects of geometric factors, including the jet diameter, jet injection orientation, interior structures, and enclosure aspect ratio. The tests cover a variety of injection modes leading to flow configurations of interest (jet impinging on a containment wall, buoyant plumes, and wall jets, etc.) that contribute to reveal the nature of mixing and stratification phenomena in the containment under accident conditions of interest. By nondimensionalizing the governing equations, the heat transfer of mixed convection can be predicted to be controlled by jet Archimedes number and geometric factors. Using a combining rule for mixed convection and appropriate forced and natural convection models, the correlations of heat transfer augmentation by forced jets are developed and then tested by experimental data. The effects of jet diameter, injection orientation, interior structures, and enclosure aspect ratio on heat transfer augmentation are illustrated with analysis of experimental results. The recirculation speed is theoretically evaluated through the enclosure mechanical energy balance and correlated to the heat transfer augmentation. Steady stratified temperature distributions are given in comparison with model simulations of BMIX++ code. |
