Effects of the Opening Area Ratio of a Ring-Type Obstacle on Liquid Film Thickness in Upward Gas-Liquid Two-Phase Flow in a Vertical Tube

A ring-type obstacle, which simulated a spacer in a light water reactor or a flow obstruction supporting heat exchanger tube, was set in an upward air-water two-phase flow in a vertical tube to investigate the effects of the obstacle on liquid film thickness in relation to the drypatch generation. We measured simultaneously the time varying liquid film thickness at several axially different locations near the obstacle under the conditions of the superficial water velocity ranging from 0.06 m/s to 0.4 m/s and the superficial air velocity from 0.5 m/s to 36 m/s and discussed the effects of the opening area ratio of the obstacle on the liquid film thickness. The results are summarized as follows : (1) The minimum film thickness near the obstacle becomes thinner as the clearance between the obstacle and the inner surface of tube becomes smaller. (2) The obstacle makes the disturbance wave smooth and it makes the base film thick downstream of the obstacle when the clearance is small.