Investigations On Aerosol Scrubbing Efficiency Under Pool Scrubbing Condition

When a severe accident occurs in a nuclear power plant,radioactive aerosols are generated and released into the containment atmosphere,posing a risk of leakage into the environment.The phenomenon of aerosol pool scrubbing is the process in which aerosols are injected into the liquid phase with the airflow and retained.The research of the scrubbing characteristics of aerosol has certain guiding significance for the radioactive assessment and mitigation measures in the later stage of severe accidents in nuclear power plants.This article combines experimental research and theoretical analysis to research the scrubbing characteristics of aerosol under pool scrubbing.The main research work completed is as follows:Firstly,experimental studies on the evolution of gas flow morphology and interface scale were conducted using high-speed photography at inlet pressure from 0 to 400 k Pa,steam molar fraction from 0 to 0.7,liquid phase subcooling from-30 to 30 ℃,nozzle diameter from 1.5 to10 mm,and apparent gas velocity from 0.05 to 0.5 m/s.Based on the flow pattern,the pool scrubbing process is divided into injection region and fully developed region.In the injection region,the flow pattern is divided into discrete globule and continuous jet based on the injection conditions.Based on the different flow patterns mentioned above,the scale and shape parameter prediction equations for globule,jet,and swarms have been established and improved.The research results indicate that an increase in nozzle diameter and nozzle inlet pressure will increase the diameter of the globule,while the influence of steam molar fraction on the diameter of the globule is relatively weak.When the liquid phase subcooling is less than 0,steam condensation phenomenon causes the diameter of the globule to decrease.The penetration length of the jet is positively correlated with the nozzle inlet pressure and steam fraction.The swarm diameter is approximately in the form of normal distribution.The peak number,maximum,Sauter average diameter and aspect ratio of bubbles are negatively correlated with the apparent gas velocity,and are less affected by other parameters.Then,an experimental study of scrubbing efficiency was conducted at inlet pressure from2 to 400 k Pa,submergence from 0.3 to 1 m,and nozzle diameter from 6 to 10 mm.Based on the transformation process of scrubbing efficiency and the gas flow pattern in the injection region,the injection conditions are divided into bubbling,subcritical jet,and critical jet conditions according to the nozzle inlet pressure.A criterion for judging the transition of bubbling and jet conditions based on the liquid phase Weber number is proposed.On this basis,the changes in scrubbing efficiency under bubbling,subcritical,and critical jet conditions at different submergences were further obtained.The scrubbing efficiency of aerosol under different flow patterns was quantitatively obtained,and the evolution mechanism of scrubbing efficiency was analyzed from the perspective of flow patterns.Subsequently,comprehensive experimental research was conducted on the parameters that affect the scrubbing efficiency of aerosol,such as system pressure,hydrophilicity of aerosols,steam fraction,and temperature difference between gas and liquid.The research results indicate that the scrubbing efficiency is positively correlated with the system pressure and gas-liquid temperature difference,and the scrubbing efficiency of hydrophilic aerosols is higher than that of hydrophobic aerosols.Based on the analysis and summary of experimental data,an empirical relationship equation that considers the effects of inertia,flow pattern,submergence,and temperature difference is proposed,with a predicted relative deviation range of-15% to +25%.Finally,based on the predicted relationship equations of characteristic parameters under various flow patterns established in this article,a calculation model for the scrubbing efficiency of aerosol under pool scrubbing conditions was established.This model comprehensively considers the scrubbing mechanism under the flow patterns of globule,jet,and swarm,and also adds condensation and thermophoresis effects.The scrubbing model was used to analyze the influence mechanism of various relevant parameters on the scrubbing efficiency of aerosol under the flow pattern of globule,jet,and swarm,and compared with the research results of domestic and foreign scholars.The results showed that the established aerosol scrubbing model could predict the scrubbing efficiency under different aerosol diameters,gas flow,and gasliquid thermal parameters.The model was validated with experimental data,and the relative deviation was mostly within ± 30%.