Power consumption and thermal performance of tube employing punched delta winglets

Abstract

The method of enhancing heat transfer (HT) by combining jets and main longitudinal vortex (MLV) had been proposed and proven effective. Based on this method, this article further explored the interference effect of VG structure on jets, MLVs, and other forms of vortices, as well as the corresponding HT mechanism. The punched delta winglet vortex generators (PDWVGs) applied in this work had three inclined angles (α=30°,60°,90°), three numbers (N=2,4,6), and three pitch ratios (PR=4.89,3.27,1.63). The secondary vortices number (Se values were used to measure the strength and position of different vortices, and the field synergy number (Fc) was also applied to measure the underlying causes of HT rate. The results confirmed that MLVs (induced by PDWVGs in core-flow region) were created, which improved the mixing rate of the air. It was worth mentioning that the structure of MLVs and jets was different at different α values, specifically when α>30°, the jets would carry away heat from the wall surface and would also collide with the reflux MLVs, suppressing the further formation of the reflux region. The Se values of different cases clearly demonstrate the morphology and intensity of mixed vortices. Within the studied parameter range, the biggest TEFof 1.29 was observed at N = 2, PR = 1.63, α = 30° at Re=9090.