抄録
The variations of void fraction, bubble diameter and bubble velocity are measured using an electrical resistivity probe when two-phase flow goes through the region of sudden area expansion in the vertical pipe (from 0.05m i.d. to 0.1m i.d.). Air bubbles in the size of 4 to 10mm are made by bubble generator and injected at the position of z=-4m. (z axis is along the vertical pipe and z=0m is taken as the position of sudden area expansion.) In this study two different radial void distributions in the pipe are considerd. One is called as sliding flow regime, which occurs when the bubble diameters are less than 5mm. The other is termed as coring flow regime, which takes place when the bubble diameters are greater than 5mm. At z=0.4m the void fraction has a similar distribution to that in the region before the area expansion. But for just after expansion, average bubble diameter increases by 20%. This shows that a part of bubbles just after expansion merge together, and then break up. The observation using CCD camera can also confirm the merging and breakup of bubbles
