Abstract

Vortex generators (VGs) are passive elements that contribute to enhance the heat transfer and produce a low pressure loss. Rectangular channels are the basic unit of many heat exchangers. Frequently, both are combined and therefore they are investigated intensively. Regardless, the influence of punched holes on the plate surface is often ignored when the thermohydraulic performance of rectangular channels has been studied. This work deals with a numerical study about the impact on the channel thermohydraulic performance of a delta winglet pair of perforated VGs punched on the channel surface. The VGs transversal pitch and the flow pattern in the common flow area were investigated for three configurations and sixteen different arrangements. The computational domain consisted of a plate centered in the middle of the rectangular channel. The numerical model was validated by comparison with published correlations for the entry region with isothermal walls as well as inside the laminar flow regime. Secondary flow was evaluated to explain the heat transfer enhancement. A performance evaluation criterion based on the similarity of pumping power was applied. All configurations studied enhanced the heat transfer and increased the pressure loss, with values up to 12.8% and 17.5% respectively. A reverse direction of rotation of vortices was found caused by the punched holes in two configurations, a result that was not found in the literature revised. A vortices inhibition caused by the punched holes was identified, which constitutes an important result and a novelty. For Reynolds numbers higher than 120, the application of VGs punched on the channel surface is advantageous. According to the performance evaluation criterion applied, the positive impact of VGs on the surface was increased with the Reynolds number, reaching values of 1.075 for the common flow up configuration with the punched holes behind and the highest VGs transversal pitch. (c) 2021 Elsevier Ltd. All rights reserved.