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 × 10 4 to 6.2 × 10 4. 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 × 10 4. 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.

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