Geometric effects of 90-degree vertical elbows on global two-phase flow parameters

Geometric effects of 90-degree vertical elbows on global two-phase flow parameters, in particular pressure drop and flow regime transition are investigated. Pressure measurements are obtained along the test section over a wide range of flow conditions in both single-phase and two-phase flow conditions. A two-phase pressure drop correlation analogous to Lockhart-Martinelli correlation is proposed to predict the minor loss across the elbows. Flow visualization is performed to study the effect of elbows on the two-phase flow regime transition. Modified flow regime maps for horizontal and vertical-downward two-phase flow are obtained which demonstrate that downstream of the elbows flow regime transition boundaries deviate significantly from the conventional flow regime transition boundaries. (author)