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Sensitivity analysis of the diffusion boundary layer steam condensation model   BIAN Haozhi1, SUN Zhongning1, ZHANG Nan1, MENG Zhaoming1, and DING Ming1   1. Fundamental Science on Nuclear Safety and Simulation Technology Laboratory, Harbin Engineering University, Harbin, China, 150001 (bianhaozhi@yeah.net)   Abstract: In loss of coolant accidents (LOCAs), steam condensation in the presence of air is of vital importance. This is due to the initial and long term containment residual heat removal are closely related to the condensation heat transfer efficiency. In related numerical analyses, the diffusion boundary layer condensation model has been developed for the containment thermal-hydraulic analysis. However, the sensitivity of this model to some influential factors has not been quantitatively evaluated. In the present work, by analyzing mechanisms of the condensation model, three factors were concluded to be influential on the steam condensation model. They are: the mass transfer caused by the large temperature gradient in the near wall region (Soret effect), the effect of various diffusion coefficients on the model accuracy (Diffusion coefficient effect) and the effect of the mass fraction gradient in the near wall region (wall treatment effect). The influence of these factors was evaluated delicately based on numerical analysis on the COPAIN facility. The results indicate that the Soret effect takes around 5% in the total mass transfer in the saturated group and can be more than 40% in the superheated group; the maximum relative difference among various diffusion coefficient equations is 26%, and the value varies with air mass fraction and wall sub-cooling; the automatic wall treatments can give reasonable predictions on condensation heat transfer performance, and the accuracy of different wall treatment methods various. Keyword: CFD; steam condensation; non-condensable gas; condensation model; sensitivity analysis
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