Fluid elastic instability and vortex induced vibration parameters in finned tube arrays with P/D ratio 1.79

Abstract

Purpose This paper aims to analyze the effect of fin geometry on mechanisms of flow induced vibration. Finned tube arrays are used in a heat exchanger to increase its efficiency. Therefore, it is necessary to investigate the effect of geometric parameters of the fin fluid elastic instability and vortex shedding. In this paper, the effect of fin height, fin density and tube pitch ratio for parallel triangular tube array on fluid elastic instability and vortex shedding is analyzed. Design/methodology/approach Experimental analysis was carried out on a parallel triangular finned tube array with a pitch ratio of 1.79 subjected to water crossflow. The experimentation aims to study fluid elastic instability and vortex-induced vibration mechanism responsible for flow induced vibration for finned tube array. A fully flexible finned tube array of the copper tube was used with its base diameter of 19.05 mm and thickness of 2 mm. Over the tube surface, crimped fins of height 6 mm and the same material are welded spirally with fin density 8.47 mm and 2.82 mm. Experimental analysis was carried out on a test setup developed for the same. The results obtained for the finned tube array were compared with those for the plain tube array with the same base tube diameter. Findings For parallel triangular tube array of copper material, test results show that critical velocity increases with an increase in fin pitch density for low pitch tube array. Before the occurrence of instability, the rate of growth in tube vibrations is high for plain tubes compared to that with fin tubes. The results based on Owen’s hypothesis show vortex shedding before the occurrence of fluid elastic instability. The effect of fin geometry on vortex-induced forces is analyzed. For the tube array pattern understudy, the values of Conner’s constant K for coarse fin-tube and fine fin tube array are obtained, respectively, 6.14 and 7.25. Originality/value This paper fulfills the need for research on the effect of fin geometry on fluid elastic instability and Vortex shedding on a tube array subjected to water cross flow when the pitch ratio is less than two, i.e. with a low pitch ratio.

Investigation on vibration parameters in aluminum finned tube arrays subjected to water cross flow

“…For aluminum and steel tubes, this ratio is approximately same. The modal parameters obtained by free vibration testing of steel tubes of the same geometry as that of aluminum tubes used for experimentation are compared with the results obtained numerically, showing good agreement (Yadav and Mohanty, 2021c, d). The natural frequency obtained in still water for the plain tube and tube with 3 mm fin height is identical because the mass ratio is approximately same.…”

“…, 2018; Mitra et al. , 2009; Yadav and Mohanty, 2021c, d). Weaver and Yeung (1984) investigated the effect of tube mass on the instability threshold for various tube array patterns and concluded that fluid elastic instability is mass ratio independent.…”

Effect of fin density and fin height on flow-induced vibration behavior of finned tube arrays subjected to water cross flow

“…The water cross flow experiments with finned tube arrays are conducted, and research data are published by a few researchers in the recent past. Yadav and Mohanty (2021a) have conducted the experiments to investigate the effect of fin density, fin height and pitch ratio on the fluid elastic instability and vortex shedding behavior of parallel triangular tube arrays made of copper material. The effect of fin geometry and pitch ratio on the fluid elastic instability of parallel triangular finned tube arrays of steel material was studied by Yadav and Mohanty (2021b) by conducting experiments in water cross flow.…”

“…The effect of fin geometry and pitch ratio on the fluid elastic instability of parallel triangular finned tube arrays of steel material was studied by Yadav and Mohanty (2021b) by conducting experiments in water cross flow. The comparison of the results of the experiments conducted by Yadav and Mohanty (2021a, b) indicate that instability threshold is delayed for copper tube arrays compared to steel tube arrays. Desai and Pavitarn (2016, 2017) tested parallel triangular finned tube arrays in water cross flow to study their fluid elastic instability and vortex shedding behavior.…”