Two-phase frictional pressure loss in horizontal bubbly flow with 90-degree bend

The two-phase pressure drop due to the minor loss in horizontal bubbly two-phase flow is studied. In particular, geometric effects of a 90-degree elbow is of interest in the present study. Experiments are performed in air-water two-phase flow near atmospheric pressure condition in round glass tube with inner diameter of 50.3mm. Along the test section, 90-degee elbow is installed at L/D=206.6 from the two-phase mixture inlet. Experiments are performed in 15 different flow conditions and the local static pressures are measured at five axial locations. Characteristic pressure drop due to the elbow is clearly demonstrated in the profiles of local pressure data along the axial direction. It is also found that the elbow effect propagates and is more significant further downstream than immediate downstream of the elbow. The overall two-phase frictional pressure loss between L/D=0 and 329 can be predicted well with the Lockhart-Martinelli correlation with parameter C=25, which is higher than the generally accepted value of C=20. A correlation for the two-phase pressure loss, including the minor loss due to the 90-degree elbow is developed by employing the approach analogous to that of Lockhart-Martinelli's. The newly developed correlation suggests that the modified parameter, C=65 fits best with the experimental data. In addition, the two-phase minor loss factor for the 90-degree elbow is found to be k=0.58, 50% higher than that recommended for single-phase flow.