Understand two-phase flow in process piping

TLDR: In this article, a mathematical model for predicting two-phase flow regime and a procedure for calculating pressure drop in process pipelines are presented, where the authors show that the two phases tend to separate and lag behind.

Abstract: Two-phase flow often presents design and operational problems not associated with liquid or gas flow. For example, several different flow patterns may exist along the pipeline. Frictional pressure losses are more difficult to estimate, and, in the case of a cross-country pipeline, a terrain profile is necessary to predict pressure drops due to elevation changes. The downstream end of the pipeline often requires a separator to separate the liquid and vapor phases, and a slug catcher may be required to remove liquid slugs. Static pressure losses in gas-liquid flow differ from those in single-phase flow because an interface can be either smooth or rough, depending on the flow pattern. Two-phase pressure losses may be up to a factor of 10 higher than those in single-phases flow; in the former, the two phases tend to separate and the liquid lags behind. Most correlations for two-phase pressure drop are empirical and, thus, limited by the range of data for which they were derived. Mathematical models for predicting the flow regime and a procedure for calculating pressure drop in process pipelines are presented.