Experimental study of vertical and horizontal two-phase pipe flow through double 90 degree elbows

This paper presents an experimental study of the characteristics of the two-phase flow through vertical and horizontal pipes connected using 90-degree elbows with an inner diameter of 101.6 mm. 66 flow conditions are performed in this experiment, covering bubbly, plug, slug, pseudo slug, and stratified flow for horizontal pipe, and bubbly, cap bubbly, churn turbulent, and falling film/annular flow for vertical pipe. A detailed flow regime analysis for both horizontal and vertical pipe flow are discussed. Flow regime maps for both horizontal flow and vertical downward flow agree with the existing maps (Mandhane et al., 1974; Qiao et al., 2017). The effect of the elbow on the flow regime transition is primarily discussed based on the experimental results and observations. The effect of elbow observed in this experiment mainly contributes to the large bubble breakup and the change of void distribution. Area averaged void fraction development is presented and the sharp drop of void fraction in vertical downward test section is observed which results from kinematic shock phenomenon. A frictional pressure drop analysis is also studied using Lockhart-Martinelli correlation and it is found that C = 40, 100, and 125 are correlated with the frictional pressure drop data for horizontal, vertical, and whole test sections with minimum differences. With the database, the drift flux model for vertical downward flow (Goda et al., 2003) is validated and the relative difference between model and data is 15.95%.