Effect of surfactant on two-phase flow patterns of water–gas in capillary tubes*

Flow patterns of liquid–gas two-phase flow were experimentally investigated. The experiments were carried out in both vertical and horizontal capillary tubes having inner diameters of 1.60 mm. The working liquid was the mixture of water and Sodium Dodecyl Benzoyl Sulfate (SDBS). The working gas was Nitrogen. For the water/SDBS mixture–gas flow in the vertical capillary tube, flow-pattern transitions occurred at lower flow velocities than those for the water–gas flow in the same tube. For the water/SDBS mixture–gas flow in the horizontal capillary tube, surface tension had little effect on the bubbly–intermittent transition and had only slight effect on the plug–slug and slug–annular transitions. However, surface tension had significant effect on the wavy stratified flow regime. The wavy stratified flow regime of water/SDBS mixture–gas flow expanded compared with that of water–gas.