Heat transfer and fluid flow analysis in double-tube heat exchangers with novel self-join winglet vortex generators

Heat exchangers are crucial in industrial applications, as improving their working performance can significantly reduce carbon emissions and promote economic development. The improvement of heat exchangers can be achieved through heat transfer enhancement technologies, which aim to optimize heat transfer or minimize flow resistance. Among various enhancement techniques, winglets can induce multi-longitudinal vortices to improve heat transfer under lower pressure drop conditions. However, previous studies pay less attention to the variation of vortex interaction. Furthermore, unlike the tube side, the shell side has two walls that influence fluid flow and vortex interactions. Therefore, a novel self-join winglet vortex generator is proposed to investigate the variation mechanism of vortex interactions on both the tube and shell sides. In this work, ANSYS Fluent software is used to conduct a steady simulation of the effect of winglet structure and arrangement on the variation of vortex structures. Meanwhile, experimental studies of thermal performance are conducted to verify the reliability of numerical models and to summarize the heat transfer and fluid flow characteristics. Results indicate that boundary vortices contribute to enhance mixing uniformity of fluid flows. Furthermore, the dissipation intensity of boundary vortices increases with increasing included angles. As the curved ratio increases, the disturbance distribution in the high-speed region shifts toward the boundary layer, because the variation of curved ratio adjusts the region of vortex development. Due to wall limitations, the movement distance of boundary vortices increases. Compared with plain tubes, the Nusselt number increases by 1.90-2.32 times and 1.40-2.20 times in circular and annular tubes, respectively, while the friction factor increases by 2.23-5.10 times and 2.64-3.91 times in circular and annular tubes, respectively. The maximum thermal enhancement factor reaches 1.63 and 1.52 in the circular and annular tube, respectively. The novel winglet exhibits significant improvement in heat transfer and flow structure. These findings provide valuable guidance for the efficient application of novel winglet vortex generators in heat exchangers, thereby providing strategies to enhance working performance and improve flow fields on both tube and shell sides.