Degradation of condensation heat transfer on a vertical cylinder by a light noncondensable gas mixed with air-steam mixtures

In this study, the experimental investigation result of steam condensation on a vertical tube in the presence of air and a light noncondensable gas is presented. This study aims at elucidating the effect of hydrogen that may be generated during the progression of a severe accident on the condensation heat transfer. Using helium as a simulant of hydrogen, a series of condensation tests were performed. A novel helium measurement system was introduced to analyze the composition of mixture gas. The condensation heat transfer coefficient was obtained under natural convection conditions on a 1 m long condenser tube having an outer diameter of 21.5 mm. A comprehensive experimental database was obtained to understand the parametric effect of the total mass fraction of noncondensable gases, molar concentration of helium in noncondensable gases, and wall subcooling degree. An empirical correlation for the degradation factor to account for the effect of a light noncondensable gas was proposed for application to the condensation model for the steam–air mixture based on the experimental data. The strategy to adopt the degradation factor was assessed against three steam–air–helium condensation tests. •A degradation of condensation heat transfer coefficient because of additional helium is identified.•The degradation factor to represent a deterioration of heat transfer coefficient is derived.•The derived degradation factor has a good agreement with previous experimental studies.