Numerical study on flow structure and heat transfer in a circular tube integrated with novel anchor shaped inserts

This paper reports a numerical study of the thermal performance enhancement of a circular tube embedded with novel anchor-shaped vortex generators. The three-dimensional turbulent periodic flow in the tube subject to a constant heat-flux wall boundary condition is investigated. The fluid flow and heat transfer characteristics are presented for Reynolds number (Re) ranging from 3000 to 18,000. The influences of pitch ratios (PR = P/D = 1, 1.5, 2, and 2.5) and the anchor vortex wing aspect ratios (sigma = b/a = 0.4, 0.6, 0.8,1, and 1.2) on Nusselt Number (Nu), friction factor (/), and the thermal enhancement factor (TEF) are reported. The vortex flow induced by the anchor vortex generator (AVG) inserts leads to a better fluid mixing, thereby accompanied a high heat transfer rate. The results indicate that the presence of AVG inserts elicits a considerable enhancement of Nusselt number and friction factor, which are about 2.24-4.56 and 4.01-23.23 times of those in the corresponding smooth tube, respectively. The maximum TEF of 1.72 is obtained for b/a = 0.4 and P/D = 1 at Re = 3000. These results provide evidence that the AVG insert is a promising device for turbulent convection heat transfer enhancement in a heat exchanger tube.