Heat transfer and friction factor characteristics of annuli formed by the smooth inner tube and corrugated outer tube - An experimental study

The heat transfer characteristic in the annulus of a double pipe heat exchanger using the corrugated outer tube is analyzed with three corrugation pitches (10, 20, and 30 mm), three diameter ratios (0.53, 0.44, and 0.40), and Reynolds number range 3500-10,500. Tests are conducted for air as a working fluid. The heat exchanger with least pitch and diameter ratio is found to exhibit the highest Nusselt number and pressure drop. The maximum enhancement in the Nusselt number and friction factor is found to be 71% and 81%, respectively. In addition, correlations have been developed for Nusselt number, friction factor, and thermal performance factor.