Flow patterns and void fractions of phases during gas–liquid two-phase and gas–liquid–liquid three-phase flow in U-bends

Highlights: • New methods for calculating of void fractions are proposed. • Gas–liquid and gas–liquid–liquid flow patterns are distinguished. • New maps of two-phase and three-phase flow are proposed. • Flow maps system may also be applied for other geometries than the examined U-bends. -- Abstract: This paper presents the results of research regarding hydrodynamics of two-phase gas–liquid and three-phase gas–liquid–liquid flow in U-bends. The conducted research involved the observation of the forming flow patterns and determination of void fraction of the specific phases that were found to be present in the flow. On the basis of the results of experimental flow maps were created for such flow and a method of calculating void fractions of the phases was established. The testing was conducted in 180° pipe bends with the internal diameters of 0.016, 0.022, 0.03 m and the curvature radii of 0.11, 0.154, 0.21 m, respectively. The flowing media applied were air, machine oils Itherm 12 and LAN 15 as well as water