2001 Volume 15 Issue 4 Pages 409-422
A ring-type obstacle, which simulated a spacer in Light Water Reactor or a flow obstruction supporting heat transfer tube, was set in an upward air-water two-phase flow within a vertical tube to investigate the effects of the obstacle on liquid film thickness. We measured the axial distributions of time varying liquid film thickness near the obstacle in the range of superficial water velocity of 0.06-1.6m/s and superficial air velocity of 0.5-36m/s and discussed the effects of the flow conditions and the distance from the obstacle on the liquid film thickness. The results are summarized as follows: (1) A reverse flow of liquid film has strong effects on the minimum film thickness near the obstacle. The axial distribution of the minimum film thickness near the spacer is different from that of the mean film thickness when the reverse flow of liquid film appears, however, these distributions are similar to each other when the reverse flow does not appear. (2) When the reverse flow appears, a liquid film may break down at the lower superficial air velocity as the superficial water velocity becomes higher.