9. Random Turbulence Excitation in Single-Phase Flow
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Many process components such as heat exchangers operate with a single-phase fluid. As well, tubes near the inlet region and preheater of two-phase heat exchangers, such as a nuclear steam generator, are exposed to single-phase cross flow. In single-phase cross flow, three major mechanisms can lead to tube failure in a shell-and-tube heat exchanger: fluidelastic instability, periodic wake shedding, and random excitation forces. Both fluidelastic instability and periodic wake shedding can cause large amplitude vibrations in a tube bundle and quickly lead to catastrophic tube failure. However, random excitation forces cause comparatively small-amplitude vibrations that will not lead to short-term failure. These vibrations do, however, lead to continuous rubbing of a tube against its supports, thereby resulting in progressive damage to the tube as a result of fretting wear. As reactors age, it is increasingly important to be able to assess the effects of random excitation vibration to determine the maximum safe operating lifetime for each component. As well, the production of more reliable and longer lasting steam generators requires an accurate assessment of tube response to random excitation during the design process. To this end, it is necessary to have accurate design guidelines.