Determination of Modal Parameters for Finned Heat Exchanger Tubes of Various Configurations

Abstract

Very first step in the analysis of fluid elastic vibrations of heat exchanger tubes is determination of modal parameters (natural frequency and damping ratios) of the tubes. Natural frequencies and damping ratios of the tubes are very important parameters as critical velocity at instability also depends on them. Lower natural frequencies are desired so as to achieve the fluid elastic instability with limited flow capacities of the pump. This paper presents part of the research work to analyze fluid elastic vibrations of finned tubes subjected to single and two phase cross flows of water and air-water. It consists of determination of modal parameters of finned tubes for two different fin pitches (2.54 and 6.35 mm). The work also consists of determination of modal parameters for finned tube attached with welded rods of 220 mm length to reduce natural frequencies. It helps to know how fin tube parameters affect the natural frequency and damping values and hence their proneness to fluid elastic vibration. Further, as a requisite for easy conduct of experiments on fluid elastic vibration analysis of finned tubes, it is found that, natural frequencies of 56 and 65 Hz of fin tubes are reduced to 14 and 17 Hz respectively when solid rods of 220 mm length are welded to them.

Effect of Fin Geometry on Flow-Induced Vibration Response of a Finned Tube in a Tube Bundle

“…These phenomena do not cause the tube failure, but it happens due to fluid elastic instability. FEI occurs when the free-stream velocity in a crossflow tube bundle exceeds the critical velocity and ultimately with any further rise in flow speed, the tube's magnitude of vibration grows exceptionally (Pettigrew and Taylor 2003 (a), Pettigrew and Taylor 2003 (b), Desai andPavitran 2013, Khushnood andNizam 2017).…”