Abstract
Vibration behaviors of a U-tube bundle in air-water two-phase cross-flows are presented. A total of 39 prototypic U-bend tubes were arranged in a rotated square array with a p/d of 1.633, which is identical to U-bend tubes of the OPR1000 steam generator. The present experimental facility has 2-span U-tubes in contrast to 8-span U-tubes of OPR1000 steam generator. However, modal analysis showed that the major vibration modes and corresponding natural frequencies were almost the same as those of the full 8-span U-tubes. Twelve 3-axis accelerometers were installed inside the U-tubes to measure the vibration motions. Tube vibration responses, critical velocity for fluid-elastic instability, two-phase damping ratio, and hydrodynamic mass were obtained. Finally, the instability factor (K) of Connors' relation was evaluated based on the above measured parameters.
