Influence of Double-sided Rectangular-wing Tape Insert on Heat Transfer Enhancement in a Heat Exchanger Tube

The paper presents an experimental study of turbulent flow friction and heat transfer characteristics in a constant heat-fluxed circular tube fitted with double-sided rectangular-wing pairs in straight tapes. In the experiments, the winged tape was inserted into the test tube with a constant wing attack angle (?) of 45? in order to generate longitudinal vortex flows through the tube. The insertion of the winged tapes was performed with five ratios of wing-pitch to tube-diameter (PR=P/D=0.5, 1.0, 1.5, 2.0 and 2.5). The measurements were conducted for the airflow rate in turbulent regime, Reynolds number from 4200 to 25,000. The experimental results show that the Nusselt number increases with the rise in Reynolds number but decreases with the increment of wing-pitch ratio. The mean Nusselt number and friction factor are, respectively, up to 445% and 47.5 times over the smooth tube and the maximum thermal performance is 1.42. In addition, the winged tape with PR=0.5 provides the highest heat transfer and friction factor but the one with PR=1.0 yields the best thermal performance.