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

AbstractA 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

Heat transfer enhancement in tubular heat exchanger with double V-ribbed twisted-tapes

An experimental work on heat transfer enhancement in a round tube by insertion of double twisted tapes in common with 30° V-shaped ribs has been conducted. Air as the test fluid flowed through the test tube having a constant wall heat-flux with Reynolds number (Re) from 5300 to 24,000. The combined vortex generators (called “V-ribbed twisted tape”) were obtained by incorporating V-shaped ribs into the edges of double co-twisted tapes having a similar twist ratio of 4. The effect of pertinent V-rib parameters such as four relative rib heights, (called “blockage ratio”, BR=b/D= 0.07, 0.09, 0.14 and 0.19) and a relative rib pitch, (PR=P/D=1.9) at an attack angle of rib, α=30° on thermal characteristics was investigated. The experimental results reveal that the heat transfer and pressure drop in terms of the respective Nusselt number and friction factor for the V-ribbed twisted tapes show the increasing trend with the rise of Re and BR. The V-ribbed twisted tape with BR=0.19 yields the highest heat transfer and friction factor. However, the maximum thermal enhancement factor is about 1.4 for the V-ribbed twisted tape at BR=0.09 but is around 1.09 for the twisted tape with no rib