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

Highlights: • Curved vortex generators (CVGs) were evaluated in a fin-tube heat exchanger. • The position and geometry of the CVGs were parametrically studied. • The resulting wakes, vortices, and corresponding heat transfer were compared. • Delta winglet CVGs were found to provide improved heat transfer performance. 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 ($\alpha$) 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 $\alpha ={30}^{°}$, 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 ($\alpha ={105}^{°}$, $r/R=1.25$) and DWD CVGs ($\alpha ={30}^{°}$, $r/R=1.5$) 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.