Influence of corrugation shape on heat transfer performance in corrugated tubes using numerical simulations

In this paper, numerical simulations are carried out to analyse the influence of geometrical parameters on the heat transfer and flow patterns for six spirally corrugated tubes at turbulent flow (Re = 25 x 10(3)). Some previous studies are restricted to 2-D analyse or 3-D numerical simulations considering a reduced section length of the tubes as the computational domain in order to reduce the computation cost. The novelty of this paper is to perform a high cost numerical simulation using a computational domain with a length of the tube (I, = 2 m) and dimensions similar to those used in commercial applications. In addition, a new non-dimensional parameter, the corrugation shape factor (CSF) is proposed, which takes into account the width of the corrugation, a geometrical dimension obviated in other studies. A 3-D unstructured tetrahedral mesh was created, and a grid independence analysis of the numerical solution was performed. The Realizable k - epsilon turbulence model with enhanced wall treatment was proposed to model the turbulence. Simulations were validated with experimental data available in the open literature. Regarding the ratio between height and diameter (H/D), the Nusselt number augmentation seems to augment as the II/D increases for low values of II/D(H/D < 0.05), whereas it decreases for values of H/D > 0.05. Considering the cases with the same diameter, in all the analysed cases, the pressure drop and Nusselt number augmentation decrease linearly as the P/D increases as well as both parameters increase linearly as the H/D, SI and CSI, increase. The numerical results indicate that the augmentation of the Nusselt number and the friction factor (compared with the smooth tube) increases approximately linearly with the CSF in the range tested in this work (4 < CSF < 18), regardless of the tube diameter.