Research On Condensation Characteristics Of Low Mass Flux Steam Jet Under Different Ambient Pressure

Direct contact condensation of steam jet immersed in subcooled water is one of the key thermodynamic and hydraulic phenomena in the operation of the suppression system after loss of coolant accident,which affects the pressure suppression capacity of the suppression system and thus affects the structural integrity of the containment.Therefore,many researchers have conducted a lot of research work on the steam jet condensation characteristics under atmospheric pressure conditions.However,with the application of suppression technology in small pressurized water reactor with higher design pressure of containment,these research results based on atmospheric pressure conditions may not provide beneficial support for the design and operation of small pressurized water reactor suppression system.Based on the above requirements,the condensation regime,vapor-liquid interface oscillation and pressure oscillation characteristics,condensation heat transfer characteristics and pool thermal stratification characteristics were systematically studied under different ambient pressure（0.1～0.4 MPa）,steam mass flux(10～90 kg·m^-2s^-1),water temperature（20～138℃）and pipe diameter（28～51 mm）conditions in this paper.The main research work completed is as follows:（1）Under different experimental parameters,four condensation regimes with typical phase interface and dynamic pressure signal characteristics were identified,which are chugging,nonperiodic condensation oscillation,periodic condensation oscillation and bubbling condensation.The condensation regime maps under different ambient pressure and pipe diameter conditions were established.It is found that chugging is more likely to occur under higher ambient pressure conditions,and the boundary range of chugging is broadened.Based on the principle of conservation of energy,the judgment criterion of chugging was given.The relative deviations between the predicted value and experimental value are within±10%.（2）The process of steam-water interface oscillation and condensation pressure oscillation is analyzed under different ambient pressure conditions.The characteristic parameters of the inner pipe steam-water interface oscillation in chugging regime are affected by many factors.The oscillation frequentness and amplitude increase with the increase of ambient pressure,and the oscillation frequency decreases with the increase of ambient pressure.In condensation oscillation regime,the steam bubble oscillation frequency decreases with the increase of ambient pressure at high ambient pressure conditions,but distorts with the change of ambient pressure at atmospheric pressure.The pressure oscillation intensity in the pipe increases with the increase of the ambient pressure.But in the pool,it increases with the increase of the ambient pressure at low water temperature conditions and decreases with the increase of the ambient pressure at high water temperature conditions.In chugging regime,the peak value of pressure oscillation in the pool and in the pipe increases with the increase of ambient pressure.The prediction formula of pressure oscillation frequency was established for the periodic condensation oscillation regime,and the deviation from the data obtained in this experiment was within±15%,and the deviation from the experimental data of other scholars was within±25%.（3）The condensation heat transfer characteristics of periodic condensation oscillation and chugging were studied under different ambient pressure conditions.The transient condensation heat transfer coefficient fluctuates sharply with the oscillation of the steam bubble interface,and the maximum and minimum values of the transient condensation heat transfer coefficient decrease with the increase of the ambient pressure.The average condensation heat transfer coefficient increases with the increase of steam mass flux and pool water subcooling,and decreases with the increase of ambient pressure.The dimensionless correlation expression of the average condensation heat transfer coefficient of the periodic condensation oscillation is established,and the prediction error of the experimental data under different ambient pressure conditions is within±25%.（4）The temperature distribution in the pool was studied under different ambient pressure conditions.It is found that there is a strong correlation between the thermal stratification of pool and the transition of condensation regime.The thermal stratification degree is affected by many factors.The higher the ambient pressure,the greater the thermal stratification degree of pool.In the process of pool remixing,the downward moving velocity of the thermocline increases with the increase of steam mass flux and pipe diameter,and decreases with the increase of ambient pressure,and the velocity also decreases with the thermocline moving down away from the nozzle.The prediction formula of thermocline moving down velocity was established,which is applicable to different ambient pressure conditions,and the relative deviation of the predicted results from the experimental data obtained by this experiment and similar experiments of other scholars was within±20%.