Comprehensive Study of Fluidelastic Instability in Heat Exchanger Tube Arrays

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University of Guelph

Abstract

Flow-induced vibrations (FIV) play a pivotal role in the design and operation of nuclear steam generators as they can compromise their structural integrity and long-term performance. Fluidelastic instability (FEI) is the most critical mechanism contributing to FIV, as it can cause unexpected failures. The steam generator tube failure at San Onofre Nuclear Generating Station (SONGS) is one of the latest incidents that highlighted the urgency of understanding and addressing FEI. Engineers and researchers need to delve into the intricacies of FEI to enhance the design methodologies and operational guidelines. This study aims to enhance the understanding of FEI and its impact on the dynamic behavior of tube arrays in cross-flow, involving single-phase (air and water) and two-phase (refrigerant R123) flow. In the first phase, a comprehensive experimental program was performed in a wind tunnel facility to investigate the stability behavior of the four standard tube array configurations (parallel triangular, normal triangular, normal square, and rotated square). The impact of array flexibility, pitch ratios, and array size on the onset of FEI in both transverse and streamwise directions was investigated. The results were compared to the published data and the theoretical prediction. The second phase focused on investigating the stability in liquid water flows in flexible parallel triangular arrays with low mass-damping parameter and varied pitch ratios, and investigated the effect of support gap on fluidelastic response. The work illustrated the role of clearance and pitch ratio on the dynamic behavior of tube arrays. Finally, the research tackled tube array subjected to two-phase flow, with wide range of void fractions which demonstrated how streamwise FEI can evolve in arrays that are dynamically stable in the transverse direction. The findings emphasize the significance of array flexibility, pitch ratios, array size, and support clearances on the prediction of the stability threshold for transverse and streamwise directions. This study offers crucial insights that can aid in improving industrial process safety and reliability.

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Vibration, Structure Integrety, Flow-induced Vibration, Fluidelastic Instability, Streamwise FEI, In-Plane FEI, Nuclear Steam Generators, Tube Array, Two-Phase Flow

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