Experimental study of condensation heat transfer in the presence of noncondensable gas on the vertical tube

Abstract

After the Fukushima nuclear power plant accident, passive safety systems have drawn much attention as a strategy to mitigate the accident of nuclear reactors. Among them, the Passive Containment Cooling System (PCCS) removes the energy released to the containment building through the condensation heat transfer phenomenon in the event of the loss of coolant accident (LOCA) or the main steam line break (MSLB). The PCCS will be deployed to prevent overpressurization failure of the containment in an advanced PWR. The thermal performance of the PCCS is governed by the condensation heat transfer rate of the steam mixed with the noncondensable gas in the containment atmosphere. In this study, an experimental investigation of the steam-air condensation on an outer surface of a tube is conducted to obtain heat transfer data for the PCCS in which the heat exchanger assemblies consist of multiple vertical tubes. The condensation heat transfer coefficient is measured on a vertical tube of 40 mm in outer diameter and 1.0 m in length. In the experiments, nearly isothermal wall conditions are maintained and the stratification of gaseous mixture is also investigated. Experiments were carried out at the pressure ranging from 2 to 4 bar and the noncondensable gas mass fraction from 0.1 to 0.8. The measured heat transfer coefficients were compared with existing correlations. Based on the experimental results, a new empirical correlation is proposed in terms of Grashof number, Jacob number and Schmidt number.