Heat transfer enhancement in a novel internally grooved tube by generating longitudinal swirl flows with multi-vortexes

In this paper, turbulent flow characteristics and heat transfer performance in a novel internally grooved tube are analyzed numerically. The objective of this work is to enhance heat transfer performance without causing a considerable increase in the pressure drop by generating longitudinal swirl flows with multi-vortexes according to the optimum velocity field obtained from the heat transfer optimization. Visualization of the flow in the grooved tubes shows that longitudinal swirl flows with multi-vortexes are generated in the inclined grooved tube but not in the straight grooved tube. This kind of flow pattern results in a long flow path and relatively intense flow mixing between the wall and the core flow regions, which significantly improves the synergy between the velocity and temperature fields, and thereby enhances the heat transfer performances. Moreover, entropy generation analysis shows entropy generation number decreases with the increment of groove inclination angle as the inclination angle is no more than 30°, while beyond this inclination angle entropy generation number starts to increase. The minimum entropy generation number and maximum overall thermal-hydraulic performance are achieved with the groove inclination angle of 30° at the lowest Reynolds number. Therefore, we conclude that groove inclination angles have a profound effect on the heat transfer performances, and the mechanism of heat transfer enhancement is mainly due to the effect of the longitudinal swirl flows with multi-vortexes generated in the grooved tube.