Experimental Study On Chugging Characters By Vertical Submerged Steam Jet Condensation With Non-condensable Gas

Large amount of high-temperature and high-pressure steam will be released into containment vessel and threaten its integrity as the Loss of Coolant Accident occurred.Therefore,it is necessary to provide pressure suppression facilities or equipments,such as the Pressure Suppression Pool,in order to suppress the rise of pressure and temperature by condensing steam,thereby ensuring the integrity of the containment vessel.This paper mainly focus on the direct contact condensation phenomenon,which is the representative phenomenon during the pressure relief in Pressure Suppression Pool.The experiments use 50 mm nozzle in diameter,with immersion depth of 300 mm.During the measurements,dynamic pressure sensors and thermocouples are used to measure pressure oscillation and temperature distribution of direct contact condensation under different water temperatures,steam mass flow rates and mass fractions of non-condensable gas.Analysis are based on previous investigations and experimental phenomena,including the pressure waveform,oscillation frequency and intensity,in-tube fluid and temperature oscillation,and thermal stratification which are characteristics of chugging and bubbling condensation phenomenon.In this experiment,according to the pressure waveform,oscillation frequency and intensity,and experimental phenomena,the condensing region contains three subregions: Chugging region,Transition Chugging region and Bubble Condensation Oscillation region.In chugging region,chugging jets,caused by in-tube steam condensation,produce the maximum intensity of pressure oscillation.In transition chugging region,steam condensation occurs at the nozzle in form of bubble collapse,creating the pressure oscillation.Moreover,in this region,chugging phenomenon occurs frequently,and the root mean square of pressure oscillation is the highest.In bubble condensation oscillation region,steam condensation occurs outside the nozzle,and the chugging phenomenon is no longer obvious.The reciprocation of the bubble interface and the rupture of the bubble mainly cause the pressure oscillation.In this region,pressure oscillation intensity and frequency reach to minimum,causing severe thermal stratification.The empirical correlation of oscillating frequency established by Aya that based on the bubble condensation model can well predict the characteristic frequency in this experimental condition,and the prediction error is within ±30%.When mixed with non-condensable gas,the chugging phenomenon is strongly suppressed,and the oscillation intensity is significantly reduced.However,small amount of non-condensable gas(the mass fraction is less than 4%)will exacerbate the thermal stratification.When the mass fraction rise over 4%,the mixing capacity increases and the thermal stratification disappears.