Effects of the configuration of winglet vortex generators on turbulent heat transfer enhancement in circular tubes

Rectangular winglet vortex generators (RWVGs) are put forward to intensify turbulent heat transfer in circular tubes. Two configurations of RWVGs, including parallel type (P-RWVGs) and V-shaped type (V-RWVGs), are considered. Numerical results demonstrate that P-RWVGs generate a single longitudinal vortex, while V-RWVGs induce multiple longitudinal vortices. Both the flow patterns above increase the turbulent kinetic energy of the fluid and thus enhance fluid mixing in the tube. The influences of the attack angle (a) and length ratio (LR) of RWVGs on the thermal-hydraulic performance are examined experimentally. The results indicate that an increase in the length ratio of RWVGs contributes to the augmented pressure drop and heat transfer for both P-RWVGs and V-RWVGs. The heat transfer rate and flow resistance for the tube with P-RWVGs are increased respectively by 54-118% and 152-568 % over those for the smooth tube, and the corresponding values for V-RWVGs are 60-118% and 141-644%, respectively. The overall thermal performance of the tubes with P-RWVGs and V-RWVGs rises with the pressure drop. Overall, P-RWVGs with the combination of LR0.2-alpha 75 degrees and V-RWVGs with the combination of LR0.2-alpha 45 degrees show the higher thermal performance under the same pressure drop than the other cases. (C) 2020 Elsevier Ltd. All rights reserved.