Experimental investigation of heat transfer coefficients for reflux condensation in the presence of noncondensible gas

Abstract

In the Loss-of-RHR accident during mid-loop operation reflux condensation in U-tube riser is experimentally studied. The present experimental study handles with the reflux condensation in the presence of noncondensible gas in a vertical tube. The main interest is to investigate the parametric effects such as inlet air mass fraction, system pressure and inlet steam flow rate on reflux codensation heat transfer. The test facility is mainly composed of two parts: an air-steam mixture generation part and a reflux condensation part(test section). Air is used as a noncondensible gas. Experiments are performed under the system pressure of 1 ~ 2.5bar, inlet steam flow rate of 1.04 ~ 2.15kg/hr and inlet air mass fraction of 0 ~ 57.9%. From experimental results, several characteristics of parametric effects are confirmed. The presence of air causes a decrease in heat transfer coefficients and, as a result, increases the active condensation length. As the inlet steam flow rate increases, the active length slightly increases during reflux codensation. As the system pressure increases, the active condensation length somehow decreases with an increase in heat transfer coefficients in that zone. And the flooding limit for inlet mixture flow rate is much less than that of Wallis`` flooding formula.