Heat transfer in a turbulent flow tube integrated with tori as vortex generator inserts

In the present study, a new design improvement of conventional smooth tubes by inserting tori is proposed to enhance heat transfer with minimal increase of frictional penalty. Heat transfer and flow characteristics in different configurations are investigated by the numerical simulations. The effects of torus aspect ratio (AR) and torus inclination angle (alpha) on Nusselt number, friction factor, and performance evaluation criteria (PEC) are analyzed and discussed. The variations of average entropy generation rate (S-avgen) with AR and alpha are also presented. The results show that the tube integrated with tori can achieve higher average Nusselt number (Nu) and PEC than those of smooth tube. This is attributed to the improved fluid mixing, boundary layer disruption, and formation of vortex/swirl flow. Nu and average friction factor (f) increase while PEC decreases with the increase of AR. Significant enhancements of Nu and f around 1.93 to 3.36 and 4.76 to 29.05, respectively, are reported for the tori integrated tube over the smooth tube. The corresponding PEC varies from 0.94 to 1.42. All results support that torus is a favorable device for the performance improvement of tube heat exchanger.