The prediction of critical velocity at instability threshold for shell and tube heat exchangers is important to avoid failure of tubes as a result of flow-induced vibrations due to water cross flow. The flow-induced vibration in finned tube heat exchangers is affected by various parameters such as fin height, fin pitch, fin material, tube array, pitch ratio, fin type, fluid velocity etc. In this paper, an experimental investigation of fluid elastic instability in shell and tube heat exchangers is carried out by subjecting normal square finned tube arrays of pitch ratio 1.79 to water cross flow.
The five tube arrays, namely plain array, two finned tube arrays with 3 fpi and 9 fpi fin density, and two finned tube arrays with 3 mm and 6 mm fin height are tested in the experimental test setup with water flow loop and vibration measurement system. The research objective is to evaluate the effect of fin density and fin height on the instability threshold. The critical velocity at instability threshold is determined to characterize the fluid elastic instability behavior of different tube arrays. The vortex shedding behavior of the tube arrays is also studied by determining Strouhal number corresponding to the small peaks before fluid elastic instability.
The fluid elastic instability behavior of the tube arrays was found to be the function of fin tube parameters. The experimental results indicate that an increase in fin density and fin height results in delaying the instability threshold for finned tube arrays. It is also observed that critical velocity at instability is increased for finned tube arrays compared to plain tube arrays of the same pitch ratio. The design modifications in the outer box have resulted in further reduction in the natural frequency. This enabled to reach clear instability for all the five-tube arrays.
The research data add the value to the present body of knowledge by knowing the effect of fin height and fin density on the fluid elastic instability threshold of normal square finned tube arrays subjected to water cross flow.
The authors gratefully acknowledge the financial assistance provided by AICTE, New Delhi, under Research Promotion Scheme (RPS) for fluid elastic vibration experiments. The authors thank Dr. David Weaver of McMaster University for his valuable guidance, proper direction and motivation that made the research possible in a real sense. The authors are also thankful to Dr. S.G. Joshi for his restless guidance and words of encouragement during the tenure of the research activity. The authors also express their sincere thanks to undergraduate and postgraduate students for their involvement and timely help.
Funding: The study was funded by the All India Council for Technical Education (AICTE), New Delhi under the Research Promotion Scheme (RPS) [Ref. No.: 8023/RID/RPS-37/2010-11].
Desai, S.R. and Sonare, M.N. (2023), "Effect of fin density and fin height on flow-induced vibration behavior of finned tube arrays subjected to water cross flow", Multidiscipline Modeling in Materials and Structures, Vol. ahead-of-print No. ahead-of-print. https://doi.org/10.1108/MMMS-08-2022-0163
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