Investigations of In-Plane Fluidelastic Instability in a Multi-Span Tube Array – Part II: Tests in Two-Phase Flow

Tests to study Fluidelastic Instability in an array of U-bend tubes were recently completed in the Multi-Span U-Bend test rig at Canadian Nuclear Laboratories. These tests were sponsored by the Electric Power Research Institute and were designed to study In-Plane Fluid elastic instability of steam generator tubes in two-phase cross flow. This instability mechanism was first observed in previous experiments by Atomic Energy of Canada Limited. This mechanism was not thought to be a serious practical concern until 2012 when it caused severe damage to tubes in a new replacement steam generator in a nuclear power plant in the United States. In this study, tests were conducted both with flows of air and two-phase liquid/vapour Refrigerant 134a. The tube bundle consisted of 22 flexible U-bend tubes supported by a configurable flat-bar arrangement. Testing focused on the effects of support geometry and tube-to-support interaction. Data was recorded from 33 dynamic signals from accelerometers, displacement probes, force transducers, and void-fraction probes. Part I of this two-part series presented results of air tests. Part II presents results of tests using two-phase Freon refrigerant (R-134a) as the working fluid.