Effects of the position and perforation parameters of the delta winglet vortex generators on flow and heat transfer in minichannels

Abstract

Minichannel with delta winglet vortices generator (VG) is widely used in heat exchangers. However, there is limited research in the literature on using VG with holes in opposite wall surfaces within a channel, and there are few reports on whether the use of VG with holes in minichannel will necessarily enhance heat transfer. In this work, we consider two different VG arrangements placed on opposite walls of a channel and three parameters for opening hole diameter (0.05, 0.15, and 0.25mm). Additionally, three different pitch values (15mm∼30mm∼45mm) are examined. Under a Reynolds (Re) number ranging from 3000 to 5500, the influence of VGs placement and hole parameters on the flow and heat transfer performance through calculations of parameters such as Nusselt number (Nu), friction coefficient (f), and thermal performance factor (TPF) are evaluated. Furthermore, the vortex structures are checked using the Q method and secondary vortex strength (Se). The results are shown to demonstrate that different VG placements mainly affect the main longitudinal vortices (MLVs), secondary longitudinal vortices (SLVs), and induced corner vortices (ICVs) structures downstream of the VGs. As the opening area increases, the shape of both vortices downstream of the VGs is significantly suppressed due to the generation of a jet flow, and the ICVs may even disappear (r=0.25mm). Case 1 (the right angle of the triangular wing is close to the center of the channel) has a larger TPF value. The opening of the hole reduces the heat transfer performance compared to the non-punched case, and their Nu number and f value are reduced by 0.2%−6.9% and 0.1%−8.3%, respectively. Case 1 obtained the maximum TPF value at Re=3000, which is 1.15, and P=15mm.