An experimental study on drift flux parameters for two-phase flow in vertical round tubes

Correlations which can correctly express the velocity difference between steam and water of two-phase flow are required for accurate predictions of the thermal-hydraulic transient behaviour for a pressurized water reactor (PWR) power plant during a small break loss-of-coolant accident (LOCA). A drift flux model is one of the typical models which describes the relative velocity between the two phases. A number of empirical expressions of the parameters for the drift flux model have been proposed based on experiments. It is necessary to confirm whether those formulas are applicable to the simulation of two-phase flow behaviour in a large scale apparatus such as the actual PWR plant. In this study, the experiments of cocurrent and counter-current steam-water two-phase flow using a large scale apparatus with 0.1023 m diameter tubes, and small scale apparatus with 0.0197 m diameter tubes were carried out. This paper presents the tube diameter effects on the drift flux parameters (Co = distribution parameter and Vgj = drift velocity). In addition, new empirical correlations of the drift flux parameters for the two-phase flow in large diameter tubes are proposed. A root mean square error of the predicted void fraction is 16.8% compared with 1353 experimental data.