Drag-reducing polymers were added to air and water flowing in a stratified configuration in a
horizontal 2.54 cm pipe. The interface was covered with large amplitude roll waves, that
have been called pseudo-slugs, over a range of flow conditions. The damping of small
wavelength waves causes a large decrease in the interfacial stress and, therefore, an
increase in the liquid holdup. At superficial gas velocities greater than 4 m/s the transition to
slug flow is delayed in that it occurs at larger liquid holdups. This observation is interpreted …