Heat transfer augmentation of internal flow using twisted tape insert in turbulent flow

Heat transfer augmentation of turbulent single-phase flow in a concentric tube heat exchanger with short-length twisted tape inserts was numerically examined herein. The twisted tape length ratios were 0.25, 0.5, 0.75, and 1.0. The twisted tape was comprised of an aluminum strip with a constant thickness, a pitch, and a width of 0.7, 35, and 12.6 mm, respectively. This study was conducted for heat exchangers with/without twisted tape inserts. The Reynolds numbers ranging from 4,500 to 18,500 were applied. The analyses showed an improvement in heat transfer and friction factor in each of the tube systems, and the results were used to determine the system that delivered the best performance. The correlations of Gnielinski and Petukhov were also used for validating the predicted Nusselt number and friction factor for the plain tube. The results indicated that heat transfer augmentation was elevated as the tape-length ratio increased. The respective highest average Nusselt number and friction factor obtained in this study were 0.51 and 2.84 times greater than that of the plain tube.