Heat transfer intensification of turbulent forced convection by inserting discontinuous twisted tapes in a wavy tube; hydrothermal and thermodynamics analysis

Abstract

The current study presents a numerical investigation on turbulent hydrothermal characteristics in a wavy passage equipped with discontinuous twisted tapes. The working fluid is water and passage walls are kept under constant wall temperature. The effect of Reynolds number (Re = 2500, 4500, 6500, 8500 and 10500), twist angle (TA = 90∘ and 180∘) and inclination angle (IA = 15∘ and 30∘) on velocity fields and streamlines, temperature contours, Nusselt number, friction factor, turbulent kinetic energy (TKE), thermal performance factor (TPF), energy efficiency factor (EEF) and entropy generation rate are evaluated. More uniform temperature and velocity fields can be found as both wavy passage and twisted tape are simultaneously applied. Both heat transfer rate and pumping power rise with increasing Reynolds number, twist and inclination angles. Results reveal that the twisted tape play more remarkable role on Nusselt number and friction factor at lower inclination angle. The best value of EEF is detected 24.6% occurring for passage with IA = 15∘ and TA = 180∘ at Re = 2500. Among all considered cases, those of empty wavy passage with IA = 30∘ at Re = 8500 and 10500 provides negative values of EEF, referring to inefficient cases from energy viewpoint. The contribution of wavy passage and twisted tape on heat transfer enhancement is individually assessed and it is found that the best value of twisted tape involvement on enhanced heat transfer is 79.6% taking place for configuration with IA = 15∘ and TA = 180∘ at Re = 4500. Finally, based on CFD results, passages are examined from thermodynamics viewpoint and it is shown that the second law efficiency growths with increasing twist and inclination angles.