Slug flow pressure loss subject to sudden and gradual contraction in horizontal pipelines

The aim of the present study is to investigate steady two-phase slug flow pressure loss in water pipelines with a contraction, based on model experimentation. Experiments were performed in a horizontal rectangular closed conduit with a sudden contraction and two types of gradual contraction. Results reveal that although the homogeneous flow model with vena-contracta predicts the steady two-phase flow pressure loss more accurately than the slip flow model with vena-contracta, it nevertheless overestimates the two-phase flow pressure loss multiplier. The two-phase flow pressure loss multiplier is a function of liquid Reynolds number, the mass quality and the contraction type. The recovery pressure was detected downstream of a sudden contraction, for both single- and two-phase flows, implying flow contraction. The ratio of pressure loss through the gradual contractions to that in a sudden contraction is significantly greater in a two-phase flow compared to that in a single-phase flow, and increases with the increase in the air-to-water rates ratio, approaching unity. Finally, applying dimensional analysis and using SPSS mathematical software and statistical analysis, relationships were derived for the two-phase flow pressure loss multiplier and the ratio of two-phase flow pressure loss in a gradual contraction to a sudden contraction as functions of governing dimensionless parameters.