Numerical Heat Transfer Study of Turbulent Tube Flow through Winglet-pairs

A numerical investigation on heat transfer behaviors in a constant heat-fluxed round tube inserted with winglet vortex generators is conducted. Air as the working medium flows through the tube for Reynolds numbers (Re) between 4000 and 20,000. The effect of using the rectangular-winglet tape (RWT) on heat transfer characteristics in the tube is numerically examined. For comparison purpose, the trapezoidal-winglet tape (TWT) and delta-winglet tape (DWT) are also offered. The RWT parameters in this work include four relative winglet-to-tube heights or blockage ratios (BR=b/D= 0.1, 0.15, 0.2, and 0.25) while the TWT and DWT are only at BR= 0.2. All the winglet pairs are at a single attack angle (α= 45°) and pitch ratio (p/D=PR=4). The numerical results show that the Nusselt number (Nu) and friction factor (f) of the tube inserts are enhanced with increasing BR values. The Nu for the inserted tube is about 1.8-2.7 times above that for the smooth tube while the f is around 4.5-11 times higher. For the studied BR ranges, the highest thermal performance is 1.48 for the RWT with BR= 0.1 at lower Reynolds number.