Experimental study of the characteristics of an upward two-phase slug flow in a vertical pipe

Characteristics of the slug flow, mean void fraction, liquid slug and Taylor bubble lengths; and structure frequency were all extracted from the void fraction time series. Average void fractions at nine axial positions have been measured on a 6 m long (and 34 mm diameter) pipe test section by using conductance probes. For the flow conditions used, bubbly (with spherical cap bubble), slug/plug and churn/semi-annular flow patterns were observed. These observations were also confirmed by using statistical numbers. Time series analysis of the mean void fraction and its corresponding PDFs show that the effect of the mixer on the flow becomes, practically, negligible from a distance of 95 pipe diameter. It was found that, generally, the structure velocity can be well predicted from other available correlations in the literature. The theoretical model of Brauner and Ullmann was used to estimate the liquid in slug void fraction. It was inferred that this model is able to predict well the liquid slug void fraction; thus, it can be considered as one of the useful methods for predicting such parameter and to ascertain slug flow regime. The total pressure gradient was found to decrease with increasing gas superficial velocity.