Performance enhancement of high temperature fin-and-tube heat exchanger employing winglet combined vortex generators

Abstract

The fin-and-tube heat exchanger (FTHE) has the advantages of high temperature resistance, compact structure and high efficiency, and has been regarded as the optimal choice for flue gas heat transfer. In this study, the novel winglet vortex generators (VGs) are proposed for the high temperature HTHE where the flue gas with the inlet temperature of 1233 K transfers heat to the water. The effects of the combined VGs and the winglet combined VGs on the flue gas thermal–hydraulic performances are numerically studied. Furthermore, three winglet shapes including the triangular, trapezoidal and rectangular are compared. Moreover, the variations of high temperature HTHE performances with the flue gas mass flow rate are investigated. Compared to the plain fins, the surface heat flux and pressure drop of the combined VGs fins are increase by 15.8 % and 78.9 %, respectively. The designed winglets in the wake region could further reduce the area of the “teardrops” after the tube. The rectangular winglet combined VGs are decided as the best structure, which could maximally increase the surface heat flux by 11.9 kW/m2 compared to the triangular winglet combined VGs, while the pressure drop is slightly increased. Compared to the plain fins, the Nu of the rectangular winglet combined VGs is maximally increased by 16.4 and the maximum hydrothermal performance factor (HTPF) is 1.14. The optimum flue gas mass flow rate is determined as 1 g/s for the designed structures. This work can provide valuable guidance for design and modification of the high temperature HTHEs.