Modeling of Friction Pressure Drop for Sodium Two-Phase Flow in Round Tubes

摘要

As sodium boiling can play an important role in assessing the safety of the sodium-cooled fast reactor (SFR), the thermal-hydraulic code TRACE is currently being extended at PSI for the simulation of sodium two-phase flow. An important aspect specifically addressed in the current paper is the accurate modeling of the pressure drop in round tubes. In the case of two-phase flow, the total pressure drop can be calculated as the sum of the liquid and gas friction losses, the acceleration term, the hydrostatic pressure drop, and the singular pressure losses.This work reports on the selection of physical models for the prediction of the pressure drop, with an emphasis on the two-phase friction pressure drop. The general approach applied is that of using a two-phase friction multiplier as suggested by Lockhart-Martinelli. Thus, in more specific terms, this study presents a review of the available correlations used for predicting the two-phase wall friction pressure drop. To study their validity when applied to liquid metal boiling situations, the correlations have been implemented in the extended TRACE code. An experiment investigating steady-state sodium boiling in a tubular section has been selected to confirm the validity of the physical models used in the numerical study. The quality of the correlations has been estimated quantitatively by comparing their predictions with the test data for different experimental conditions. The assessment results, together with recommendations as regards the "best" correlation, are presented in the paper.A similar study is planned for modeling of the singular pressure drop in tube bundles due to either grid spacers or wire wrappers in sodium two-phase flow. This should complete the models implemented in TRACE for two-phase sodium flow modeling.