Study On The Characteristics Of Steam Submerged Jets In The Presence Of Air

Compared with the dry-type containment,the pressure-suppression containment has the advantages of lower volume,fewer passive containment coolers and more efficient filtration and retention capacity of radioactive substances,showing an important application prospect.Condensation of mixed gas immersed jet is one of the most important thermal-hydraulic processes in the pressure-suppression containment after LOCA accident.At present,there are several pipeline layout design schemes for pressure suppression systems abroad: vertical,horizontal and porous,and the selection of pipe diameter,pipe length and submergence depth in the specific design is unknown.Therefore,in order to select reasonable design scheme and optimize design parameters of the pressure-suppression containment.In this paper,within the range of the thermal parameters of the pressure-suppression system after a LOCA accident,the following research works were carried out and completed for the possible arrangement modes:1.Visual experiments were carried out for vertical jet,horizontal jet and porous jet of air,steam and mixed gas.Three condensation regimes were identified: Chugging regime,bubbling regime and stable condensation regime.In Chugging regime,isolated bubble are intermittently generated and collapsed at the nozzle outlet,and subcooled water intermittently flows back into the nozzle.In bubbling regime,bubbles continuously form,grow and break away.In stable condensation regime,bubbles no longer appear,and the jet interface has a stable shape.Three interfacial shapes were observed: cone,expansion-contraction shape and double expansion-contraction shape.Finally,the transition boundaries among condensation regimes were determined.2.The trajectory analysis model of mixed gas jet at any angle was established.The influence of air mass fraction on the penetration length of mixed gas jet was determined,and the correlations of vertical and horizontal jet penetration lengths of mixed gas were established.The relative deviations between the predicted results and the experimental results are within 5% and 20%,respectively.In stable condensation regime of mixed gas jets,the parameters such as jet interface radius,expansion rate,fluctuation amplitude,fluctuation velocity and acceleration were analyzed.3.The characteristics of pressure oscillation and fluid oscillation were studied in time domain and frequency domain.The effects of different parameters on pressure oscillation intensity,pressure oscillation frequency,fluid oscillation probability,fluid oscillation amplitude and fluid oscillation frequency were discussed.In bubbling regime and stable condensation regime,the correlations for calculating the pressure oscillation frequency of steam jet and mixed gas jet were established,respectively.The analysis model of fluid oscillation was established,and the theoretical formulas of amplitude and frequency of fluid oscillation were obtained,which can well predict the experimental results.4.The formation and disappearance conditions of thermal stratification in pool were established,and the formation and disappearance mechanism of thermal stratification was analyzed.Near the boundary of Chugging regime,thermal stratification will be formed due to the sudden decrease of fluid oscillation intensity.The existence of a small amount of air can reduce the water temperature at the beginning of thermal stratification and increase the maximum temperature difference in pool.When the air mass fraction is higher than a certain value,the two-phase plume can make the pool completely mixed,and thermal stratification will no longer occur.The minimum air mass fraction for eliminating thermal stratification decreases with the increase of pipe diameter.