Prediction of Slug Frequency for Medium Liquid Viscosity Two-Phase Flow in Vertical, Horizontal, and Inclined Pipes

Several experimental studies have been conducted to investigate the effect of liquid viscosity on slug frequency in horizontal, vertical, and inclined two-phase flows. Analyses of these studies reveal that the slug frequency is positively related to superficial liquid velocity and liquid viscosity; the superficial gas velocity has a dual minor effect on slug frequency, with an initial increase for low superficial gas velocity and then a decrease for high superficial gas velocity; and the slug frequency increases with increasing flow deviation from horizontal. Also, the analyses reveal that for inclined viscous flow, the slug frequency and slug length follow the same inverse relationship shown in horizontal and vertical slug flows. In the literature, several models have been developed for predicting slug frequency in viscous horizontal flows, whereas only a few models exist for viscous vertical and inclined flows. In this study, we aim to develop models for prediction of slug frequency in two-phase flow of medium liquid viscosity (30 <= mu(L) <= 250 mPa.s). Dimensional analysis of four published experimental data sets (218 data points) indicates that slug frequency is related to two dimensionless numbers; namely, a modified Froude number and inverse viscosity number. As a result, three slug frequency closure models are proposed for vertical, horizontal, and inclined flows, using a combination of these two numbers. The proposed models are tested against the four data sets, and very good results are obtained, with correlation coefficients ranging from 0.96 to 0.97.