Geometric effects of 45-degree elbow in horizontal air-water bubbly flow

The present study investigates the geometric effect of a 45-degree elbow on the development of local two-phase flow parameters and their distributions in horizontal two-phase flow. A round pipe with an inner diameter of 50.3 mm is used as a test section throughout the study. First, a 90 degree elbow is installed at L/D=206.6, then a 45-degree elbow is added at L/D=353.5 from the inlet, and local measurements are made at three different axial locations of L/D=342, 363 and 419. In total, 15 different flow conditions are investigated for the present analysis. At the measurement port just downstream of the 45-degree elbow (i.e., L/D=363), the local parameters are acquired in both the vertical and horizontal directions along the radius of pipe cross-section to capture geometric effects of the flow restriction. The local two-phase flow parameters acquired in the present study include void fraction, bubble velocity, interfacial area concentration and Sauter mean diameter. In view of one-dimensional transport, the local void fraction and interfacial area concentration are area-averaged and plotted along the axial direction. The characteristic geometric effects of the flow restrictions are clearly demonstrated in the distributions of the two-phase flow parameters and their development along the flow direction. The drastic changes in the interfacial area concentration across the elbow suggest that a 45-degree elbow induces significant changes in bubble interaction mechanisms.