PIV and IRT measurements of hydrothermal performance in a U-shaped heat exchanger with 3D printed detached curved ribs

Novel detached curved ribs are proposed in this study and their influence on turbulent thermofluidic features in a two-pass U-shaped square channel is experimentally investigated using particle image ve-locimetry (PIV) and infrared thermography (IRT). Due to their geometric complexity, the ribs are fabri-cated with the 3D printing technology-fused deposition modeling and mounted in line inside the channel with a hydraulic diameter (DH) of 45.5 mm. Examined parameters include the rib convergence angle (alpha), divergence angle (beta), clearance ratio (C/H), and Reynolds number, which are respectively in the range of (25 degrees, 35 degrees, 45 degrees), (30 degrees, 40 degrees, 50 degrees), (0.25, 0.38, 0.56, 0.75, and 1), and (5,0 0 0-20,0 0 0). The PIV and IRT results show that that the detached curved ribs accelerate the core flow and significantly strengthen the Dean vortices in the turn region, leading up to 70% enhancement in Nusselt number ratio ( Nu /Nu infinity) in that region compared with previous best results. Further parametric studies reveal that at alpha=25 and beta = 40 degrees, Nu /Nu infinity and Fanning friction factor ratio (f over line /f infinity) first increase and then decrease with increasing C/H, with the maximum thermal performance factor (TPF) of 1.4 occurring at C/H = 0.38, slightly higher than the previous highest data for f over line /f infinity= 10-50. Finally, empirical formulations of Nu /Nu infinity and f over line /f infinity with alpha, beta, C/H, and Re for the present design are proposed with an average difference of 2.24% and 4.95%, respectively.(c) 2022 Elsevier Ltd. All rights reserved.