The onset of droplet entrainment in annular downward flows

The point of onset of large disturbance waves and droplet entrapment has been determined for the annular downward flow of air‐water mixtures in a 24 mm ID tube. Experimental results are in a good qualitative agreement with the previous work by Webb and Hewitt 1 . These results indicate that1 the critical gas velocity at the onset of entrainment is lower than the value predicted by available correlations 2 the critical gas velocity continuously decreases at increasing the liquid Reynolds number 3 below a liquid Reynolds number of 270 no entrainment occurs even at gas velocities as high as 80 m/secA correlation for the critical gas velocity which is based on a simple physical model of atomization, is also proposed.