Effects of 90-deg vertical elbows on the distribution of local two-phase flow parameters

The present study focuses on developing a database to investigate the effects of 90-deg vertical elbows on the transport and distribution of local two-phase flow parameters in air-water bubbly flows. The experimental facility consists of both vertical and horizontal sections made out of 50.8-mm inner diameter pipes and interconnected via 90-deg glass elbows. Six different flow conditions within or near the bubbly flow regime at the inlet are investigated in the current study. A multisensor conductivity probe is employed to measure detailed local two-phase flow parameters at ten axial locations along the test section, within which 90-deg elbows are installed at L/D = 63 and 244.7 from the inlet. The data show that the elbow makes a significant impact on the two-phase pressure drop, bubble distribution, and bubble velocity. The bubbles moving across the vertical-upward elbow are entrained along the secondary flow streamlines leading to a bimodal distribution. For the test conditions investigated in the present study, this bimodal distribution is independent of the bubble distribution upstream of the vertical-upward elbow. In the case of the verticaldownward elbow, on the other hand, the large inertia of the axial liquid flow results in the bubbles migrating toward the inside of the elbow curvature.