Thermo-hydraulic performance in heat exchanger tube with V-shaped winglet vortex generator

This article presents the influence of V-shaped winglet vortex generators (V-WVGs) inserted into a constant heat-fluxed tube on thermal characteristics. In the present experiment, two V-WVG types: V-shaped rectangular- and delta-winglets (V-RW and V-DW) were mounted periodically on both sides of a straight tape before insertion into the tube with four relative winglet pitches (P-R = P/D = 0.5, 1.0, 1.5 and 2.0) and three winglet blockage ratios (B-R = b/D = 0.1, 0.15 and 0.2) at a fixed attack angle (alpha = 45 degrees). Effects of geometric parameters of both V-WVGs on thermal performance enhancement were studied using air as tested fluid in a turbulence condition, Reynolds number (Re) ranging between 4130 and 25,900. The measured result has been shown that the V-RW performs higher rate of heat transfer as well as friction loss than the V-DW and the rise in B-R results in higher increase of the heat transfer rate and friction loss while the increment in P-R yields the reversing tendency for both V-WVG types. A new thermal-performance enhancement factor (TEF) has been introduced and it reveals that the V-DW has TEF in a range of 1.82-2.0 or around 3% above the V-RW where its peak regarded as the optimal point is at B-R = 0.15 and P-R = 1.0. Empirical correlations for the Nusselt number and friction factor to assess the real merits of a heat exchanger tube with V-WVGs are determined.