Reflux Condensation Heat Transfer of Steam-Air Mixture under Turbulent Flow Conditions in a Vertical Tube

Abstract

Under certain hypothetical accident circumstances in a pressurized water reactor, reflux condensation in the steam generator U-tubes may be an effective heat removal mechanism. Non-condensable gas (air) may be present in the reactor coolant system and is well known to inhibit steam from condensing. In a previous study, local condensation heat transfer coefficients for reflux condensation with air were measured, and an empirical correlation intended for a laminar flow of steam-air mixtures was developed, which was a function of the partial pressure ratio, (P steam =P air). In this study, heat transfer coefficients measured under turbulent flows were used to modify the empirical correlation for improved prediction accuracy. The modified empirical correlation considers convection and is proportional to ðP steam = P air Þ 0:75 Re g 0:8 where Re g is the steam-air mixture Reynolds number. The correlation was verified against the data of Moon et al. and then incorporated into the transient analysis code RELAP5/SCDAPSIM/MOD3.2. The temperature distributions of the steam-air mixture calculated by the code for six reflux condensation tests are shown to agree well with the measured results.

Evaluation of Non-condensable Gas Recirculation Flow in Steam Generator U-tubes during Reflux Condensation

“…Temperature measurements provide the local saturation pressure, and the steam mass flow rate can be calculated from the partial pressure of steam, P steam (T g ), assuming a Gibbs-Dalton mixture of steam and an ideal non-condensable gas. Then the local heat flux can be obtained (for details, see Nagae et al, 2005Nagae et al, & 2007a. In Eq.…”

“…Therefore, in our study, we carried out condensation heat transfer experiments in the presence of a non-condensable gas in a collaborative study at Purdue University (Vierow et al, 2003) and derived an empirical correlation mainly for laminar flow . Moreover we conducted additional condensation heat transfer experiments, especially at high flow rates of a non-condensable gas, and improved the empirical correlation for turbulent flow conditions (Nagae et al, 2007a). In this article, we summarize the major results.…”

“…The same function of (P steam /P air ) 0.75 for laminar flow ) is used for turbulent flow, and the constants a and exponent b for Re g are determined by the least mean square method. The modified empirical correlation by Nagae et al (2007a) …”

“…As for gas velocity, steam Reynolds number gave better results than steam-air mixture Reynolds number for limited data . However, steam Reynolds number is not suitable for the additional data (Nagae et al, 2007a). Therefore, the empirical correlation for the interfacial heat transfer coefficient was reevaluated using the Reynolds number of the steam-air mixture, Re g .…”

“…In order to evaluate reflux condensation heat transfer characteristics in SG U-tubes in the presence of a non-condensable gas, experiments were conducted for condensation heat transfer of steam-air mixture under countercurrent flow in a vertical tube having an inside diameter of 19.3 mm and with pressure range from 0.1 to 0.4 MPa (Nagae et al, & 2007a.…”