Nuclear safety code modelling of condensation in stratified flow

Abstract

Stratified condensing flow is important in the safety analysis of nuclear reactor systems. In the present work, several models for condensation heat transfer were assessed with a view to improving the TRAC interfacial heat transfer modelling. Bankoff's experiments of condensing stratified flow (Lim et al. [1], Bankoff et al. [2]) have been chosen as a physical benchmark. Various published models including Bankoff's correlations were implemented into the code and the code predictions were compared with the experimental data. Most models did not yield satisfactory predictions; only the Bankoff model for countercurrent condensing flow was found to give good agreement between experimental and calculated results. As the heat and mass transfer across gas-liquid interface have a similar mechanism and the interfacial mass transfer coefficient is easier to evaluate, attempts have been made to infer the heat transfer coefficient from mass transfer coefficient using a Colburn-type analogy. The predictions of this mass transfer analogy model were found to be in excellent agreement with the experimental data of countercurrent condensing flow. It is suggested that such a method could be extended to other flow configurations.