Thermal-fluidic correlations for turbulent flow in a serpentine heat exchanger with novel wing-shaped turbulators

Turbulent flow structures and heat transfer in a 180-deg sharp turning two-pass internal coolant passage of a serpentine heat exchanger are explored experimentally. The coolant passage has a square cross-section with novel wing-shaped turbulators mounted on two sidewalls. The bulk Reynolds number (Re) and pitch ratio (Pi/D-H) are varied from 5,000 to 20,000 and 0.6 to infinity, respectively. It is observed from the Particle Image Velocimetry measurements that there are wing-induced Fujiwhara co-rotating vortices. This unique flow feature leads to an averaged Nusselt number ratio ((Nu) over bar /Nu(0)) up to 5.5 higher than the highest value of 4.4 reported previously based on the Infrared Thermography results. In addition, the elimination of wake vortices by the present wing-shaped turbulators results in the 61.5% to 66.8% reduction of friction factor ratio ((f) over bar /f(0)) compared with the louvered channel. From the thermal-fluidic regression analysis for Pi/D-H = infinity and 0.7, the dimensionless spanwise-averaged mean transverse velocity and cross-sectionally averaged vorticity magnitude have the high correlation coefficient (R >= 0.7) with the spanwise-averaged local Nusselt number ratio in both the first and second pass. From the standpoint of thermal performance factor (TPF), Pi/D-H = 0.7 is preferable to other values of Pi/D-H since it provides the TPF value of 1.68 higher than the previous reported value of 1.41 for 15 <= (f) over bar /f(0) <= 80. Finally, empirical correlations of (Nu) over bar /Nu(0), and (f) over bar /f(0) versus Re and Pi/D-H are proposed. (C) 2020 Elsevier Ltd. All rights reserved.