Correlation of interfacial friction for countercurrent gas-liquid flows in nearly horizontal pipes

We previously developed a one-dimensional (1-D) computation method with parameters adjusted from CCFL (countercurrent flow limitation) data in hot leg and pressurizer surge line models to generalize the prediction method for CCFL in nearly horizontal pipes. In the 1-D computation method, the constant value for the interfacial friction coefficient of fi = 0.03 was used. On the other hand, many correlations for the interfacial friction coefficient in horizontal and inclined pipes have been proposed. In this study, therefore, we carried out 1-D computations for CCFL in nearly horizontal pipes with the diameter of D = 0.03-0.75 m and the length to diameter ratio of L/D = 4.5-63 by using some selected correlations for the interfacial friction coefficient, which are a function of the gas or liquid Reynolds number. As a result, we confirmed that the correlation of the interfacial friction coefficient in terms of the Reynolds number cannot be used for large Reynolds numbers but fi = 0.03 can be used for the wide range of diameters. To improve the correlation with the gas or liquid Reynolds number, we proposed a modified correlation.