Experimental study on the local convective coefficient distribution on a pipe surface with inclined fins

Experimental results for the convective coefficient distribution in both the inside and conical end zones of the extended surface in a finned pipe are presented for three different flow velocities. The devices were located in a physical model of a staggered square pitch arrangement in which the pipes were disposed very close together and exposed to a transverse air flow. The fin inclination angle with respect to the axis was γ° = 20°, the fin height H = 15 mm, the pipe diameter D = 28 mm and the distance between fins s = 8 mm. The results show that the convective coefficient distributions in the conical region and in the inside region of the fin are quite different. For three velocities of flow (u = 10-40 m/s) higher values of the convective coefficient were obtained in the conical region of the fin, near the junction of the fin with the pipe. On the other hand, the higher values in the internal face of the fin were located in wider regions of the lateral extremes of the fin. Only for Re ≈ 20 000 the zones with higher values of convective coefficient were located near the junction of the fin with the pipe. The heat transfer coefficient distribution on the pipe surface is very similar to the one obtained for a flat cylinder. From the experimental results, the formula to calculate the heat transfer of a tube with fins inclined in an angle of γ° = 20° was developed. This formula considers the separation between the tubes, the parameters of the fins and the arrangement of the bank of tubes.