Research On Heat Transfer Mechanism And Model Of Muti-hole Steam Jet Condensation

In the event of a breach or overpressure accident at an AP1000 nuclear power plant,the automatic depressurization system(ADS)will trigger at levels 1-3.Hightemperature,high-pressure steam is sprayed through muti-hole sprayers into the internal recirculation water tank(IRWST)in the safety shell,where it comes into direct contact with subcooled water and undergoes direct contact condensation(DCC).This prevents high-temperature,high-pressure steam from entering the safety shell and causing overpressure,which could threaten its structural integrity.The condensation heat transfer coefficient(HTC)of the steam release during DCC directly determines the condensation rate and thus affects the depressurization rate of the first loop.Therefore,a thorough investigation of the condensation heat transfer characteristics during steam release via DCC is crucial to ensuring the safe depressurization of the reactor.Existing research has primarily focused on the heat transfer characteristics and mechanisms of single-hole steam release DCC and the reliability of ADS systems,and most of the research on multi-hole steam injection is concerned with its pressure oscillation characteristics and overall temperature effect and there is less research on the mechanism of the heat transfer characteristics between holes.Based on this situation,this study constructed an experimental platform for multi-hole steam release DCC condensation and conducted steam release experiments for single-arm dual-hole,fivehole,and four-arm sixteen-hole sprayers.High-speed cameras and high-precision thermocouple arrays were used to obtain the steam flow patterns and steam temperature distributions during multi-hole steam release DCC.The experimental results showed that as the cooling water temperature increases,the steam plumes from multi-hole steam release DCC gradually interconnect to produce mutual shielding effects.Influenced by the mutual shielding effects between holes,the dimensionless penetration length of steam increases,and this study measured the dimensionless penetration length to be between 3.2 and 13.4.The axial temperature distribution of multi-hole steam release DCC exhibits a phenomenon of decreasing first,then slightly increasing,and then decreasing again.Based on the established dual-hole and five-hole HTC models,the heat transfer coefficient of multi-hole steam release DCC was calculated to be between 0.63 and 1.66 MW/m2℃.Due to the mutual shielding effects between holes,the HTC of five-hole sprayers is lower than that of dual-hole sprayers.In addition,based on the commercial finite element analysis software ANSYS,a three-dimensional model of the experimental platform for multi-hole steam release DCC was established.The steam flow patterns and steam temperature distributions obtained from the Mixture model calculations are consistent with the experimental values,with an overall steam temperature error of 5.4%.The average heat transfer coefficient obtained from simulation calculations was coMPared with experimental values,and the overall error was less than 20%,verifying the effectiveness of the simulation calculation model.The research in this paper provides important theoretical support for the mechanism research of the condensation heat transfer characteristics of multi-hole steam release and the study of the mutual shielding effects between holes.