Experimental And Numerical Simulation Research Of Heat Transfer Characteristics Of Steam Jet Condensation Through Multi-hole Nozzle

Under accident conditions,the high-temperature and high-pressure steam of the primary circuit of the AP1000 reactor injects into the in-containment refueling water storage tank(IRWST)of the containment through the automatic depressurization system stage 1～3(ADS 1～3),and direct contact condensation(DCC)occurs in the IRWST,which can prevent the high-temperature and high-pressure steam from directly entering the containment and ensure the integrity of the containment.With the continuous injection of steam,the water temperature in the IRWST will gradually increase,and thermal stratification may occur in the IRWST,which is detrimental to the rapid decrease of the reactor core pressure and temperature.Besides,the heat transfer coefficient(HTC)in the steam inject process determines the condensation rate of the steam,which directly affects the cooling rate and depressurization rate of the primary side.Therefore,in-depth analysis of the heat transfer characteristics of steam jet condensation is essential for optimizing the nozzle design and ensuring the safety of the reactor.For automatic depressurization system and steam ejection behavior,at present,the domestic and foreign experiments are mainly aimed at the system design reliability verification,and focusing on the overall flow-characteristics in the IRWST during steam ejection.The research on local condensation characteristics is often restricted to the single-hole steam ejection model.However,there is very little attention to the effect between the holes during multi-hole ejection,and the limited research only focus the local temperature characteristics of the condensation of the double-hole mode,without the studied of the effect of the hole-to-hole effect on the overall flow characteristics in the water tank.And the mutual influence between adjacent arms during the four-arm model discharge is not considered.Therefore,it is urgent to conducts experimental research on steam discharge and condensation of multi-hole,four-arm and special-shaped sprayers.Based on the above research status,this paper adopts a full-scale water tank and multi-hole sprayer to conduct steam ejecting experiments,and use a high-speed camera and thermocouple matrix to obtain the flow pattern and temperature field in the ejecting process.The experimental results show that the steam mass flow flux and water temperature will affect the steam plume.The steam mass flow flux,the diameter of the holes,and pitch-to-diameter ratio P/d will affect the water temperature when the steam starts to connect between the adjacent holes and the intensity of the connection degree.When the steam is connected,the heat transfer efficiency of steam will be reduced,which is defined as the mutual shielding effect when the adjacent holes are connected.In this paper,the dimensionless penetration length and HTC are obtained by experimental measurement and semi-empirical formula calculation,and they are in good agreement.The dimensionless penetration length of steam ranges from 3.5 to 11.9,and the average HTC of the multi-hole sprinkler is between 0.4-2.0MW/(m2·K).This research obtain the thermal parameters in the process of the multi-hole steam ejection,analyze the heat transfer characteristics,and express the mutual shielding effect of the steam plume between adjacent nozzle holes.This is of great engineering value to optimizing the design of the multi-hole sprayer.Besides,this paper is based on the system code RELAP5 and COSINE to simulate the steam ejection process,and the temperature distribution obtained is roughly the same as that measured in the experiment.When using RELAP5 simulation,the maximum error is 7.13%,and the average error is 2.97%.It is verified that the system program can simulate the steam spraying process.However,there are still some differences between the simulated value and the experimental value.Based on the code COSINE is used to simulate the discharge condensation process,the model is revised and improved.The maximum error is 4.91%,and the average error is 1.89%.Which is in good agreement with the experimental results.This research provides a reference for the subsequent improvement of code COSINE and is of great significance to the development of system code.