Effects of position and geometry of curved vortex generators on fin-tube heat-exchanger performance characteristics

Abstract

The thermal and fluid-flow characteristics of the rectangular-winglet, delta-winglet-upstream (DWU), and delta-winglet-downstream (DWD) curved vortex generators (CVGs) are computationally analyzed in this study. Polar coordinates based on the tube center are considered to define the CVG positions, thereby facilitating a parametric study of the effects of the position angle (α) and radial distance (r) of CVGs. The resulting heat-transfer enhancement, pressure loss, and flow patterns have been analyzed in detail. When CVGs are placed at α=30°, mixed vortices are generated, thereby improving the heat-transfer performance of the fin. In contrast, placing the CVGs near the rear of the tube reduces the wake size and increases heat transfer behind the tube. Furthermore, a secondary flow is induced enhancing the fine heat-transfer performance. However, the most of results obtained in this study reveal that CVGs are not superior to conventional VGs. Further, the realization of optimum heat-transfer performance using CVGs mandates certain position and geometry requirements to be satisfied. For example, as observed in this study, the DWU CVGs (α=105°, r/R=1.25) and DWD CVGs (α=30°, r/R=1.5) exhibit the highest heat-transfer performance improvements of 5.2% and 7.5%, respectively, compared to conventional VGs. However, this enhancement in heat-transfer performance is realized at the cost of a relatively small pressure loss.