Air-water two-phase flow in vertical tubes

In the present research, a two-phase flow system is designed, manufactured, assembled, and adjusted to study two-phase flow behavior isothermally. Test sections are tubes standing in a vertical position and are made of transparent acrylic with inner diameters of 40 mm and 70 mm. Two axial locations of 1.73 m and 3.22 m are chosen for data acquisition. Flow pattern maps are presented for both tubes. Effects of tube diameter and axial location on pattern transition boundaries are investigated. Air and water are chosen as working fluids. The ranges of air and water superficial velocities are 0.054–9.654 m/s and 0.015–0.877 m/s for the 40 mm diameter tube, but these values are 0.038–20.44 m/s and 0.036–1.530 m/s for 70 mm diameter tube. The results show that for both tubes, increasing axial location does not affect flow transition boundaries significantly. However, the slug pattern region shrinks considerably by changing the tube diameter from 40 mm to 70 mm. Using image processing techniques, recorded high-speed movies were investigated accurately. As a result, bubbly flow in the 40 mm tube can be divided into three sub-patterns: dispersed, agitated, and agglomerated bubbly. Also, two types of slug patterns are also recognized in the same tube diameter which are called small and large slugs. Semi-annular flow is observed as an independent pattern in the 70 mm tube that does not behave as known churn or annular patterns.

You can find the published work here: (Annals of Nuclear Energy)