An experimental study on the vibration induced by a two-phase air-water crossflow in a normal triangular tube bundle
Ricardo Álvarez-Briceño1; Fábio Kanizawa1; Gherhardt Ribatski1; Leopoldo P. R. de Oliveira1
1 University of São Paulo
doi:10.20906/CPS/COB-2015-0530
Resumo
Flow - Induced Vibration (FIV) is probably the most critical dynamic issue in the design of shell and tubes heat exchangers. This fluid - structure phenomenon may generate high amplitude vibration of tubes or structural parts, which leads to clashing between internal components, noise or even its fatigue failure. Many test benches have been constructed to study this phenomenon, however, some vibration mechanisms, mostly those related to multiphase flow, are not yet fully understood. Therefore, in this work, an experimental study on the vibration induced by a two-phase air - water vertical counter gravity crossflow in a tube bundle is presented. For this purpose, a 19mm OD stainless steel tube was flexibly mounted as a cantilever-beam in a test section. The dynamic response of the tube was measured by using piezoelectric microaccelerometers installed at its free-end. The surrounding rigid tubes were installed in order to complete a normal triangular pattern with pitch-to-diameter ratio of 1.26. This paper presents tests in air and water single-phase flows aiming at addressing the mode shapes and resonance frequencies of the dynamic structure. Also, damping was calculated by using the half-power bandwidth method. The influence of flow velocity on vibration amplitudes and frequencies was analyzed. Finally, tests for two - phase air - water flow were carried out; the influence of void fraction on vibration amplitude, resonance frequencies and damping was checked; damping results were compared with published results of previous FIV experimental tests performed.
Palavras-chave: cantilever-beam; flow - induced vibration; multiphase flow; void fraction; resonance frequency