| Resumo: |
Flow-induced vibration (FIV) is probably the most critical dynamic issue in the design of tube bundles in shell-and-tubes heat exchangers. This fluid-structure phenomenon may generate high amplitude vibration of tubes or structural parts, which leads to fretting wear between the tubes and supports, noise or even fatigue failure of internal components. Several test sections have been constructed in order to study FIV problems, however, the vibration properties of tubes in the tube bundle, principally those related with two-phase flow, have not been totally understood yet. In order to enhance the current understanding on these phenomena, the present research proposes an extensive review on the behavior of the dynamic parameters of tube vibration in tube bundles. Furthermore, the characteristics of turbulence-induced vibration mechanism, including the design guidelines to predict its severity, are analyzed. Such a study is complemented by an experimental campaign in which the databases of dynamic parameters and turbulence-induced vibration design guidelines found in literature are validated. For this, a 19 mm O.D. and 381 mm long tube was mounted in cantilever in a tube bundle with normal triangular configuration (τ = 1.26), which is subjected to upward air-water crossflow with void fractions from 30% to 95%. The dynamic response of this tube was measured by using piezoelectric microaccelerometers. The obtained results show good agreement with the database of dynamic parameters and turbulenceinduced vibration design guidelines. Further, the results allowed the redefinition of a design guideline, which led to understand fluid-structure interaction as a function of flow patterns and mass velocities. In addition, Kalman filtering techniques were used to estimate flow-induced forces based on output only. The results suggests the presence of forces with a periodic component of quasi-constant frequency, in transverse direction, for void fractions up to 50%. Furthermore, it was noticed that flow-induced forces are generally higher in parallel direction. |
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