Thermal performance augmentation in round tube with louvered V-winglet vortex generator

Abstract

The article is concerned with investigating the effect of insertion of louvered V-winglet (LVW) vortex generators on convection heat transfer and pressure loss in a tubular heat exchanger. A metal tape was adopted for supporting the 30° LVW elements placed periodically on the edges of the tape to create two pairs of streamwise counter-rotation vortex flows throughout the tested tube. The use of LVWs could help to promote the fast mixing of fluid flow, to break up the development of boundary layer and to induce the impinging jets resulting in the faster heat transfer rate. Air as a working fluid flowed into the tested tube at Reynolds number from about 4200–25,800. The purpose of employing the louver mounted on the winglet is to reduce the pressure loss with slightly deteriorating the strength of main vortices appearing behind the winglet. The winglet parameters were three different relative winglet pitches, (RP=0.5–1.5), six louver angles (θ = 10°–90°), at a fixed relative height (RB=0.2) and attack angle (α = 30°). Influences of the mentioned parameters on the friction factor and Nusselt number including the thermal performance were explored. The experimental result has shown that among the LVWs the case of RP = 0.5, θ = 10° provides the largest friction factor and Nusselt number owing to impingement flows induced from the vortices onto the heated wall in the rear region of the winglet. The investigation reveals that the highest thermo-hydraulic performance from the LVW is about 2.48 at RP = 1 and θ = 30°. To scrutinize the flow pattern and the mechanism of enhancing convection coefficient, a 3-dimensional simulation of turbulent tube flow through LVWs was performed and the simulated results were verified with available measurements. The empirical correlations for measured Nu and f data of the LVW were also offered.