An experimental comparison of delta winglet and novel type vortex generators for heat transfer enhancement in a rectangular channel and flow visualization with stereoscopic PIV


DOĞAN M. , İĞCİ A. A.

INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, vol.164, 2021 (Journal Indexed in SCI) identifier identifier

Abstract

Vortex generators (VGs) make a very important contribution to enhancement of heat transfer in many applications. In this study, the comparison of a novel type of vortex generator (NTVG) producing longitudinal vortex (LV) with delta winglet pair (DWP) in terms of improving heat transfer was investigated experimentally. VGs were placed on the bottom surface of the rectangular channel. In order to make a correct comparison, projected areas of each vortex generator were kept equal. The position of the DWP, which ensured that the thermal enhancement factor (TEF) was maximal, was determined from the literature and placed (CFU, common flow up) accordingly on the bottom surface of the channel. As a result of the experiments, the highest TEF for DWP was obtained at about 1.15 and the results were found to be compatible with the literature. The highest TEF value for the NTVG was obtained of about 1.34. Consequently, enhancement in the heat transfer by NTVG was obtained higher than that of DWP. The transverse pitch ratio, P-t (=P/W) where the highest thermal enhancement was provided, was determined for the NTVG. When the transverse pitch ratio P-t was 0.4, the highest TEF value was obtained. LVs generated by the NTVG were visualized by using the PIV (Particle Image Velocimetry) system. The single NTVG has capacity to be able to produce two longitudinal vortices. It was seen that CFD (common flow down) and CFU, flow arrangements were generated at the back of VG and between VGs, respectively. According to the experimental results obtained, we can suggest that using NTVG instead of DWP is more effective in improving heat transfer. (C) 2020 Elsevier Ltd. All rights reserved.