Numerical Analysis Of Spray Response Process In A Limited Space

The main function of the containment spray system is to limit the temperature and pressure of the internal environment of the containment not to exceed the allowable limit when the reactor loses water or the main steam pipeline breaks.At the same time,the spraying process will also affect the gas mixing phenomenon in the containment,and then affect the possibility of hydrogen explosion.The study on the dynamic and thermodynamic effects of spray response process in a limited space is helpful to master the influence law of spray on gas mixing characteristics and the rate of cooling and depressurization in a limited space environment,and provide reference for the design of spray system.In this paper,computational fluid dynamics software is used to simulate the spray response process in air-helium environment and air-steam environment in limited space respectively.On the basis of verifying the rationality of droplet movement and heat and mass transfer model,the effects of droplet diameter,spray flow rate and spray height on gas mixing characteristics and temperature and pressure changes in limited space environment are further analyzed.The effects of droplet diameter,spray flow rate and spray height on gas mixing trend and mixing time were studied by numerical simulation of the dynamic effect of spray response process in a limited space under air-helium environment.The results show that the droplet diameter has obvious influence on the gas mixing characteristics in the studied range,and the smaller the diameter,the better the gas mixing effect.The change of spray flow has little effect on the degree of gas mixing;The change of spray height has a great influence on the helium volume fraction in the area below the nozzle.The higher the spray height,the higher the helium volume fraction after full mixing.Through the numerical simulation of the thermodynamic effect of spray response process in a limited space in an air-steam environment,the effects of droplet diameter,spray flow rate and spray height on the cooling and pressure reduction rate are analyzed.The results show that,when other conditions remain unchanged,the droplet diameter has a significant influence on the temperature and pressure changes in the studied range.The smaller the droplet diameter,the greater the depressurization rate.Compared with the droplet diameter of 150 μm,the depressurization rate of 350 μm is reduced by 12.2%,and the depressurization rate of 0～100 s is reduced by 16.88%.The greater the spray flow rate,the higher the cooling and depressurization rate.Even if the flow rate changes little,the temperature and pressure change greatly with time.The higher the spray height,the larger the direct interaction area between droplets and steam,and the better the cooling and pressure reduction effect.The gas temperature,steam volume fraction and vertical velocity of droplets at different positions in the steady-state stage of air-steam environment are analyzed.In the steady-state stage,with the increase of the distance from the nozzle,the steam volume fraction first decreases and then increases.At the same height,the temperature in the center of the container is the lowest,and the farther away from the nozzle,the smaller the temperature difference in the cross section.The vertical velocity of droplets near the nozzle is logarithmically distributed with the nozzle distance.