Development of a new condensation model for the nearly-horizontal heat exchanger tube under the steam flowing conditions

A new condensation heat transfer model package was developed to improve the prediction capability of one-dimensional best-estimate safety analysis code in a nearly-horizontal tube. The new model package consists of a one-dimensional separated momentum conservation model, an interface shape prediction model, a flow regime prediction model, and a condensation heat transfer coefficient model. The condensation heat transfer coefficient model is composed of a convective heat transfer model and a film condensation model that considers the effects of interfacial shear stress resulting from a high convective steam flow. Therefore, it can mechanistically take into account the heat transfer phenomena that are generated in the upper and lower parts of the tube under separated flow conditions. The developed condensation heat transfer model package was evaluated and verified by using available experimental data obtained from horizontal and nearly-horizontal tubes under the air–water and steam–water conditions. From a quantitative point of view, evaluation results confirmed the improvement of the prediction performance of the new condensation heat transfer model package when there is no non-condensable gas and at sufficiently high pressure.