Numerical investigation on turbulent heat transfer intensification using wavy-twisted elliptical tube; a novel swirling flow generator for designing heat exchangers and cooling passages

The present study deals with hydrothermal and thermodynamic characteristics of turbulent forced convective flow in a novel swirling flow generator. The geometry is an elliptical tube that not only is twisted around its central axis but also has a wavy-shaped structure, named wavy-twisted elliptical tube. The working fluid is considered to be water and the passage wall is subjected into a constant heat flux. The effect of Reynolds number(Re = 3,000, 4,500, 6,000, 7,500 and 9,000) and twist ratio(TR = 3.3 and 6.6) on flow pattern, velocity and temperature fields, Nusselt number, friction factor and thermodynamic efficiency is numerically investigated and some comparisons are made against conventional configurations such as wavy, twisted and plain elliptical tubes. As a wavy-twisted elliptical tube is applied instead of twisted elliptical tube, the swirling flow is affected by centrifugal forces and so an asymmetrical arrangement of dean voracities is created, leading to intensified secondary flow and greater temperature uniformity. Under this condition, the non-uniform, but powerful, ring-shaped coherent structures can be observed in wavy-twisted elliptical tube which is the main reason of heat transfer enhancement. The results reveal that the mean Nusselt number and friction factor in the wavy-twisted elliptical tubes are higher by 30%–88% and 59%–124%, respectively, compared to plain elliptical tubes. Among all the considered cases, the best thermal performance value is 1.44 which is related to the wavy-twisted elliptical tube with TR = 3.3, occurred at Re = 3,000. The use of wavy-twisted elliptical tube decreases overall entropy generation rate and improves the second law efficiency up to 69% in comparison with those values related to plain elliptical tube. The findings of the current simulations proved that the proposed configuration, i.e. wavy-twisted elliptical tube, can be applied in heat exchanger manufacturing industry instead of wavy or twisted tubes because of their extraordinary potential in heat transfer rate improvement.