The motion and frequency of large disturbance waves in annular two-phase flow of air-water mixtures

Abstract

In annular two-phase flow large disturbance waves are nearly always observed. These travel rapidly along the surface of the liquid film and have a “milky” appearance as a result of light scattering by their extremely ruffled surface. The conditions under which these waves occur have been examined and measurements made of the wave velocity, separation and frequency. The formation of the waves appears to coincide with a transition in entrainment observed in earlier work. Measurements of wave movements made by means of a ciné film and by a conductance probe method are in satisfactory agreement. The mean velocity of the disturbance waves was about 4–10 ft/sec compared with an air velocity of 40–150 ft/sec and a mean water velocity in the liquid film of 1–3 ft/sec. Mean wave velocity increased rapidly with increasing air flow but was insensitive to changes in water rate. The frequency of the waves was insensitive to air rate but increased in proportion to the liquid rate, thus suggesting that the waves are transporting the liquid. For any set of conditions the wave velocities measured are not evenly distributed about the mean and a number of peaks occur in the histogram. These peaks appear in the same positions for a number of different flow rates and the existence of “preferred velocities” is therefore possible. Similar, but more equivocal, observations are made with respect to wave separation.