Vortex Shedding from Tube Banks with Closely Mounted Serrated Fin

Abstract

This paper focuses on the vortex shedding from tube banks with closely mounted serrated fin. The tube banks were installed rigidly in the test section of a wind tunnel. We measured the mean velocity, the velocity fluctuation spectrum, and the gap velocity in the model tube banks that had the same pitch ratio as a boiler heat exchanger. We found two types of vortex shedding with different Strouhal numbers S_t of 0.40 and 0.20 in the case of Reynolds numbers R_e in the range 2.8 × 10⁴ to 6.2 × 10⁴. Strouhal numbers were calculated by using the measured values of the vortex shedding frequency, the gap velocity, and the equivalent diameter. The vortex shedding for S_t = 0.40 was mainly formed within the finned tube banks and the other vortex shedding for S_t = 0.20 was in the wake of the finned tube banks. The Strouhal number of the vortex shedding inside the finned tube banks changed from 0.40 to 0.32 for R_e = 6.2 × 10⁴. The applicability of the equivalent diameter, obtained from a single circular cylinder with a serrated fin, to the finned tube banks was examined. The calculated Strouhal number of 0.32 agreed with a Strouhal number of 0.30 obtained from Fitz-hugh’s map for bare-tube banks. The Strouhal number of 0.20 is similar to that for vortex shedding from a circular cylinder.