Study of winglets vortex generators in a circular tube for thermal enhancement

Abstract

Vortex generators/turbulent promoters generate the vortices which reduce the boundary layer thickness and introduce a better mixing of the fluid to enhance the heat transfer. In this research, thermal performance of winglets longitudinal vortex generators (VGs) were investigated experimentally. Delta winglet VGs of different heights and attack angles were inserted inside a 1 m length copper tube. The experiments were conducted with VGs for an air flow range of Reynolds numbers from 6000 to 33000. The influence of the winglet VGs on heat transfer and pressure drop was investigated in terms of the Nusselt number and friction factor. Vortex generators were arranged repeatedly inside the tube 12 rows (N) with same pitch distance (P=L/N) and each row consists of 4 VGs in a circular pattern on the inner surface of the tube. So relative pitch ratio (PR=P/D) is 1.6 and three winglets blockage ratios (B=H/D) are 0.1, 0.2, 0.3 with respect to three winglets heights (H=5mm, 10mm and 15mm). Attack angles of the VGs were maintained 0°, 15°, 35° and 45° for B=0.3. The objectives of the study were to investigate the heat transfer enhancement and to identify the parameter which induces the highest thermal performance augmentation in the circular tube. Based on the experimental results, the best parameter for thermal performance enhancement (TPE) (η) is for B=0.1, with PR=1.6, β=45°. Nusselt number increased 2 times higher than that of the smooth tube. Friction factor decreased with Reynold number from 0.13 to 0.06.