Computational fluid dynamics simulation of heat enhancement in internally helical grooved tubes

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A computational fluid dynamics (CFD) investigation was carried out to study heat-transfer enhancement in four helically grooved tubes with different pitches, and compared with a smooth tube. The simulations were performed in the Reynolds number range of 4000-20,000 in helical rectangular groove tubes of 2-m length and 7.1-mm diameter under a constant heat flux of 3150 W/m2. The predicted values for CFD in this current study were compared with previously published experimental data. The primary focus of this study involved evaluating the effect of groove pitch on heat transfer and friction factors. A thermal enhancement factor was defined to evaluate the performance of the internally grooved-tube models. The results revealed that by decreasing the pitch size from 130 mm to 7.1 mm at the same Reynolds number, both the Nusselt number and the friction factor increase. In addition, by increasing the Reynolds number for the grooved pipe, the Nusselt number increased as in the case of a smooth pipe. The highest Nusselt number was obtained for a smaller pitch size of 7.1 mm, but at the expense of a greater pressure drop compared to smooth tubes. An optimum value of the enhancement factor (η) was observed at about Re = 15,000 for all investigated grooves, and enhancement up to 20% was obtained for grooved tubes having a 7.1-mm pitch size. © 2016 Elsevier Ltd.