Design and optimization on symmetrical wing longitudinal swirl generators in circular tube for laminar flow

It is crucial to further improve the overall performance of heat exchanger tube and make it adapt to higher flux conditions. In this paper, a novel type of tube inserts, symmetrical wing longitudinal swirl generators (SWLSGs), was proposed and its thermal hydraulic performance was numerically investigated under laminar flow. The effect of four geometrical parameters (inclined angle (phi(1)), face angle (phi(2)), wing angle (phi(3)) and pitch ( P )) was explored. The results showed the mechanisms of heat transfer augmentation for SWLSGs could be divided into two main categories. The first one was that a longitudinal swirl flow with multi-vortexes would be formed by symmetrical wings. The other one was that SWLSGs had a structure similar to a deflector, which guided the cold water in the center to scour tube wall. This study found that the variation ranges of Nu/Nu0, f/f(0), and the efficiency evaluation criterion ( EEC ) were 5.00- 10.22, 4.05-14.20, and 0.71-1.35, respectively. Both exergy destruction of heat transfer and fluid flow increased as face angle and wing angle increased, and decreased as inclined angle and pitch increased. Exergy destruction minimization principle was adopted to optimize SWLSGs. After fitting function through artificial neural network, genetic algorithm was applied to obtain the Pareto front. The physical parameters of the compromised point on the Pareto front were phi(1) = 25.6 degrees, phi(2) = 142.0 degrees, phi(3) = 13.4 degrees, P = 64.7 mm, and EEC = 1.26. The EEC of the highest point of the ratio of the exergy destruction of heat transfer and fluid flow (REHF) was 1.48. The present work provided a new method for multi-parameter study of tube inserts, and proved that the exergy destruction as evaluation was an effective evaluation index for design and optimization. (c) 2022 Elsevier Ltd. All rights reserved.