Analysis of Experiments for In-Tube Steam Condensation with Noncondensable Gas at Low Pressure Using the RELAP5/MOD3.2 Code Modified with a Non-Iterative Condensation Model

摘要

The standard RELAP5/MOD3.2 code is modified using non-iterative modeling, which is a mechanistic model developed for easy engineering application to simulate steam condensation in the presence of noncondensable gases in a tube. To predict the liquid-side heat transfer coefficients in the modified RELAP5/MOD3.2 code, Nusselt's correlation is used for condensation in a vertical tube and Kim's correlation correlated with the Froude number is used for condensation in a horizontal tube. In the modified code the wall friction in a vertical tube is calculated using the two-phase friction factor correlation proposed by Collier and the interfacial friction factor is calculated using the empirical power-law relationship of Choi. Both the standard and the modified RELAP5/MOD3.2 codes are used to simulate two kinds of vertical in-tube experiments and a horizontally stratified in-tube experiment involving the condensation phenomenon in the presence of noncondensable gas. Two vertical in-tube experiments, PCCS (Passive Containment Cooling System) condensation and reflux condensation experiments, provide data on the steady-state behaviors with typical flow, pressure and air mass fraction conditions likely to be seen in a condensing tube of PCCS and in a U-tube of steam generator in mid-loop operation. The horizontally stratified in-tube experiment represents the direct-contact condensation phenomena in a hot leg of a nuclear reactor. The modeling capabilities of the modified code as well as the standard code for steam condensation in the presence of noncondensable gas are assessed using those three KAIST condensation experiments. The modified code gives better prediction over the data of the three condensation experiments than the standard code. Simulation results of PCCS and reflux condensation experiments show that the local heat transfer coefficients are well predicted with the modified code but they are under-predicted by the default model and over-predicted by the alternative model. The modified code well predicts the experimental void fraction using the two-phase wall friction factor correlation. Simulation results of horizontally stratified condensation experiments show that the modified code predicts the interfacial heat transfer coefficient better than the standard code