Analysis of Experimental Data of Condensation in the Presence of Non-Condensable Gases by a CFD Code

This work analyses the condensation of steam in the presence of non-condensable gases and was performed in the frame of studies on the physical aspects relevant for the safety of nuclear reactors containments (EU NoE SARnet-2). Data from the CONAN experimental facility installed at the University of Pisa have been considered as a basis for comparison with calculated results. The main objectives of the work were to implement previously developed condensation models in the STAR-CCM+ CFD code and to make comparisons with the reference experimental data. The models used to describe condensation are three: two of them are based on the detailed description of steam diffusion through the air-steam layer close to the wall, with and without conjugated heat transfer, and the third makes use of the heat and mass transfer analogy, adopting correlations for evaluating overall mass transfer coefficients. The first and the second model make use of a fine mesh close to the wall, as it is required for a detailed estimate of the thermal and concentration gradients necessary to evaluate heat and mass transfer; the third model, instead, makes use of the wall function approach, with allowance for larger nodes close to the wall. The models provide good estimates of the observed condensation rates,