Experimental investigation of thermal performance of novel type vortex generator in rectangular channel

Abstract

Vortex generators are objects with geometries specifically designed to increase heat transfer. In this study, the thermal performance of a novel vortex generator that can generate longitudinal vortices in a common flow-down pattern was experimentally investigated with Reynolds numbers in the range of 5000–25,000. The vortex generators were placed on the base surface of the channel in such a way that they were mirror images of each other according to the geometric symmetry plane in the main flow direction. At a fixed inclination angle, the effects of the ratio of the transverse distance between two vortex generators in a row to the channel width (transverse pitch ratio) and the ratio of the longitudinal distance between two vortex rows to the channel height (longitudinal pitch ratio) on heat transfer were analyzed. First, the experiments were performed for a single row by increasing the number of the vortex generators in the row (2, 4, 6, and 8) so that the transverse pitch ratios were 0.50, 0.25, 0.16, and 0.12. According to the results, as the transverse pitch ratio decreased, the Nusselt number and friction factor increased, so the highest increases were realized at the transverse pitch ratio of 0.12, reaching 1.44 and 2.07 times greater values compared with the smooth channel, respectively. However, the highest thermal enhancement factor was obtained at the transverse pitch ratio of 0.16. Then, vortex generators were placed with an inline arrangement keeping the transverse pitch ratio of 0.16 constant, and the experiments were executed for longitudinal pitch ratios of 1, 1.5, 3, and 5. The results revealed that the Nusselt number and friction factor increase with the decrease in longitudinal pitch ratio, but the highest thermal enhancement factor value (1.59) was obtained at the longitudinal pitch ratio of 1.5. In addition, the experiments were also performed using a staggered arrangement, but the inline arrangement proved to be more efficient than the staggered arrangement in terms of thermal performance. The maximal thermal enhancement factor was achieved for the inline vortex arrangement at the transverse pitch ratio of 0.16 and longitudinal pitch ratio of 1.5.