A New Heat Transfer Correlation for Condensation in the Presence of Air and Its Implementation into RELAP5/MOD3.3

Passive safety systems utilized in most of the advanced nuclear reactors make use of the condensation phenomenon to cope with the design-basis accidents. The inhibiting effect of noncondensable gases on condensation is an extremely important phenomenon, and several experimental research studies have been performed in recent years. Moreover, some theoretical investigations, including assessment of system analysis codes and in this connection modeling of new correlations with a reasonable accuracy, also have been carried out. The experimental work conducted at the Middle East Technical University (METU) was undertaken to investigate the inhibiting effect of noncondensable gas on the condensation phenomenon. The constituted database covers the wide range of system parameters such as the mixture Reynolds number and the air mass fraction. In this study, a new heat transfer correlation is proposed defining condensation phenomenon in the presence of air and is modeled using the METU database. Both the mixture Reynolds number and the condensate Reynolds number are taken into consideration to simulate the possible effect of interfacial waviness. The suppression effect of air, which is accumulated at the condensate-mixture interface, on heat flux is considered by inclusion of air mass fraction. The mean deviation with respect to the experimental data is determined to be 19.4%. Furthermore, the correlation was tested on the RELAP5 code, and the accuracy is determined to be 20%. The overall performance of the correlation, as coded in the RELAP5 code, is satisfactorily good with respect to experimental data for local heat flux, heat transfer coefficient, air mass fraction, and wall subcooling degree. The results obtained by utilizing the correlation yielded much better results compared with the original RELAP5 model, namely Colburn-Hougen.