Flow dynamics between the inclined fins of a finned tube

An experimental program was undertaken to measure the local static pressure along an inclined fin's internal and external faces on a finned tube provided with these devices; the airflow was transversal to the tube. The fins inclination angle respect to the tube axis was 45°. The local static pressure on the tube surface between a pair of fins was also measured; the experimental results are presented and analysed in this paper. The analysis indicates the presence of volumetric streams (secondary flows) in the internal side channel formed by two inclined fins. On the external fin's face, the flow has a similar tendency as in the cylinder case but with a late detachment of the boundary layer in the fin's tip. With the local static pressure distribution measured, it was possible to evaluate the drag coefficient C_D for the internal and external faces of the inclined fins and on the tube surface as well, for a range of velocities (Re_d = 6-56 × 10³). The results of the drag coefficient computed for the inclined fins were compared against other authors' results, for a smooth cylinder and a sphere, and we can conclude that for the finned tube with inclined fins the aerodynamic resistance is nearly 1.5 times higher than the one encountered for a smooth cylinder case.