Effect of angle of attack on the heat transfer coefficient for an annular fin

Wind-tunnel experiments were performed to investigate the sensitivity of the heat transfer coefficient for an annular fin to small angles of attack. Quasi-local measurements were made at three zones on the fin surface: (I) forward of the tube; (II) at the side of the tube; and (III) behind the tube, with separate measurements being carried out on the two faces of the fin. The angle of attack ranged from -2° to 2°. The heat transfer coefficient in zone (I) was highly sensitive to the angle of attack, increasing by about 50% on the face of the fin where leading-edge separation was activated as the arigle was varied from - 2° to 2°. The corresponding increases in zones (II) and (III) were about 10%. On the other hand, for any angle of attack in the investigated range, the two-face average for each zone was not very different from the heat transfer coefficient for zero angle of attack. Therefore, the overall heat transfer performance of an annular fin is not significantly affected by small departures of the angle of attack from zero. However, since the differences between the coefficients for the two faces were found to be significant, measurement of the coefficient at only one face may yield erroneous results for the overall performance.