Flow topology, heat transfer characteristic and thermal performance in a circular tube heat exchanger inserted with punched delta winglet vortex generators

Abstract

To improve the heat transfer rate and thermal performance, the punched delta winglet vortex generators, DWVGs, were inserted in the middle of the circular tube heat exchanger. The effects of the flow attack angles and the flow directions were investigated numerically for the Reynolds number Re = 100–2000. The finite volume method and the SIMPLE algorithm were used to study. The results are reported in terms of the flow structure, heat transfer behavior and thermal performance evaluation and also compared with the smooth tube with no vortex generators. As the numerical results, the use of the DWVGs in the tube can improve the heat transfer rate and thermal performance by creating the vortex flow through the tested section. The rise of the flow attack angle results in the increasing strength of the vortex flows. The flow attack angle of 25° performs the highest heat transfer rate and thermal performance, while the flow attack angle of 0o gives the reversed results. The computational results reveal that the optimum thermal enhancement factor is around 2.80 at Re = 2000, α = 25°, with the winglet tip pointing downstream. The correlations on both the Nusselt number ratio and friction factor ratio for the DWVG in the tube heat exchanger are presented.