Thermal-Fluid study of curved tubes in cross-flow

Three-dimensional simulations have been performed to investigate thermal performance by the external surface of curved circular tubes provided with concave and convex curvatures. The simulations were performed in Ansys-fluent software and results has been validated against the available results. The tubes were placed in a uni-directional free stream of air at a Reynolds number of 35000 which is within subcritical range for circular tube. The heat transfer capabilities of curved tubes have been compared with that of a straight tube of same diameter and height. A constant-heat-flux condition over the external surface has been used. The curved tubes have been designed such that it has vertical extensions at the end and curvatures at the middle section with curvature ratios of 0.075, 0.15, 0.225 and 0.3. Plots of coefficients of pressure, drag and lift, Nusselt number, heat transfer ratio and contours of pathlines were utilized to investigate the thermal behaviour around the tube surface. Results show the highest augmenting thermal performance exhibited by convex curved tube with curvature ratio 0.15 followed by curvature ratio of 0.225. Other reasonably better augmented heat transfer exhibited by concave curved tube with curvature ratio of 0.3. The present study also identifies augmenting, mitigating and insignificant zones around the tubes based on heat transfer rates. The results show an improvement in heat transfer when curved tube is used instead of straight tube which can be utilised in waste heat recovery recuperators.