수직 전열관 외벽에서 발생하는 증기-공기 혼합물의 응축 열전달에 대한 곡률효과 실험연구

Abstract

The impotance of the passive safety systems has increased to assure the safety of the nuclear power plant after the Fukusima nuclear power plant accident and recent earthquakes in South Korea. PCCS(Passive Containment Cooling System), one of the various safety systems to be introduced into next-generation nuclear power plant, ensures the safety of nuclear power plant by condensation heat transfer phenomenon in case of a LOCA(Loss Of Coolant Accident). This study focused on the experimental investigation of the curvature effect about the rate the of condensation heat transfer on a vertical condenser tube under natural convection condition. And, based on the experimental data, we develop a correction factor that considers the effect of tube diameter on the condensation heat transfer coefficient. Therefore, to investigate the condensation heat transfer coefficient in the presence of a noncondensable gas, an experimental study was performed on the single vertical condenser tube with 21.5 mm in outer diameter, 5 mm in thickness and 1000 mm in the effective heat transfer length. Experiment was measured at the pressure ranging from 2 to 5 bar, and the air mass fraction ranging from 0.1 to 0.8. Almost isothermal wall conditions are maintained and uniform concentration of gas mixture is also kept during the experiments to reduce the effect of noncondensable concentration along the height. The heat transfer coefficients from experiments were compared with previous JNU experiments on 40 mm in outer diameter and 10 mm in outer diameter, and the curvature effect was investigated using SPACE, a thermal hydraulic system analysis code. SPACE shows the predicted heat transfer coefficient constantly as the diameter changes, indicating that the curvature effect is not reflected. And the comparison with experiments data results shows that the heat transfer coefficient increases with the decreases in diameter. These changes are independent of air mass fraction and pressure, and there is a curvature effect on diameter.