Vibration Behavior of Rotated Triangular Tube Bundles in Two-Phase Cross Flows

Abstract

The results of a series of tests describing the vibration behavior of several rotated triangular tube bundles subjected to two-phase cross flows are presented. Tube bundles with a pitch-to-diameter ratio of approximately 1.5 were tested over a broad range of void fractions and mass fluxes. Fluidelastic instability, random turbulence excitation, hydrodynamic mass, two-phase damping and local void-fraction were investigated. Well-defined fluidelastic instabilities were observed in continuous two-phase flow regimes. However, intermittent two-phase flow regimes had a dramatic effect on fluidelastic instability leading to lower than expected threshold flow velocities for instability. This effect was more pronounced in Freon two-phase flow than in air-water, and appeared well correlated to the transition between continuous and intermittent flow regimes. Generally, random turbulence excitation forces were much lower in Freon than in air-water. Although very dependent on void fraction, as expected, damping was quite similar in air-water and Freon.