Investigation On Condensation Of Steam In The Presence Of Air Outside A Vertical Smooth Tube

The passive containment cooling system (PCCS) is widely used in the next generation ofnuclear reactor systems to maintain the integrity of the containment after longer term postutmost accidents like LOCA and MSLB. Based on double concrete containment, thecondenser is one of the most essential equipment in the PCCS and its heat transfer capabilitydetermines the performance of the PCCS. In the steam condensation process, the presence oflarge amounts of non-condensable gases will lead to the serious deterioration of heat transfer,further research on steam condensation in the presence of air must be conducted.In this paper，an experimental investigation and a numerical simulation has beenconducted to determine the characteristics of the steam condensation outside the smooth tubein the presence of air. The experimental results show that the heat transfer coefficient of steamcondensation is proportional to the value of wall subcooling to the power of negative0.6; andit decreases exponentially as a function of the increase of the air mass fraction. Combinedwith a large number of experimental data, a wider scope of application of the empiricalcorrelation is obtained, empirical correlation associated with the experimental value of theerror within±10%.Additionally， condensation processes of steam in the presence of air has beensuccessfully modeled by applying a user defined function (UDF) added to the commercialcomputational fluid dynamics (CFD) package. Calculated profiles of temperature, airconcentration, and velocity components are compared to experimental results and discussed.The results indicated that there is a good agreement between the experimental results and themodel predictions. The simulation results show that the latent heat transfer is the dominantfactor of the total condensation heat transfer; it was found that both the latent and the sensibleheat transfer coefficient decreased with the increase of the air mass fraction, local latent heatcoefficient showed an upward tendency along the height direction of the heat transfer tubefrom bottom to top, and sensible heat transfer coefficient taken on an opposite trend. Inaddition, the numerical model was applied to the TOSQAN experimental facility, despitesome discrepancies, the general agreement between experimental and calculated results showsthat the proposed approach is adequate and could be applied to similar simulations.