Experimental study on wall condensation with noncondensables in steam-gas pressurizer

The condensation heat transfer in the presence of noncondensables is one of the predominant mechanisms to determine the thermal-hydraulic behavior of steam-gas pressurizer. With steam and nitrogen as the gaseous mixture in upper region, the steam-gas pressurizer pursues the passive operations of the integrated small nuclear reactors, excluding additional active systems. The differences in the operating principle of steam-gas pressurizer from, and the advantages of it over, the conventional steam pressurizer were described. In this study, an experiment on the condensation heat transfer in the presence of noncondensable gas under natural convection condition was carried out. Since most of prior condensation experiments were conducted at low pressure less than 0.5 MPa and thus the applicability of conventional well-known heat transfer correlations to high pressure range has not been confirmed, the research herein covered from atmospheric pressure up to 2.0 MPa for investigating the characteristics of the wall condensation with noncondensables at high pressure. Heat transfer data are obtained on the internally-cooled vertical tube comprised in a cylindrical chamber. The condensation heat transfer coefficient was evaluated with altering the system pressure and the fraction of nitrogen. The results revealed that the condensation heat transfer degraded with an increase of nitrogen mass fraction or a decrease of system pressure and the existing correlations failed to predict the heat transfer coefficient at high pressure. The detailed physical analyses on the change of heat transfer by those factors were performed. New correlation for condensation heat transfer has been developed including pressure, mass fraction of noncondensables and wall subcooling terms. (author)