Numerical and experimental study of the heat transfer process in a double pipe heat exchanger with inner corrugated tubes

In this study, 3-D numerical simulations were carried out to analyse the influence of geometrical parameters for eight spirally inner corrugated tubes at turbulent flow (Re = 25 x 10(3)) in a double pipe heat exchanger. As a novelty, different combinations of pitch and height in a 3-D inward corrugated tube numerical model were analysed and validated with an experimental setup. This had not previously been conducted in a double pipe heat exchanger. Furthermore, the numerical model included the entire geometry of the heat exchanger, with dimensions of the computational domain similar to those used in actual commercial applications. Grid independence analysis of the numerical solution was performed based on a 3-D unstructured tetrahedral mesh scheme, considering the Realizable k - epsilon turbulence model. Case 8, with the highest corrugation height (H/D=0.05) and the lowest helical pitch (P/D=0.682) presented the highest pressure drops in both inner and annular tubes, being 4.15 and 1.27 times higher in the inner tube and in the annulus side than in the smooth tube, respectively. Regarding heat transfer, Case 9, with the smallest helical pitch and an intermediate corrugation height (H/D=0.041) obtained the highest number of transfer units (NTU) value, which, under the experimental conditions of this work, resulted in an increase of 29% compared with the smooth tube. In Cases 7 and 9, the inner tubes showed optimal results when considering the combined influence of the enhanced heat transfer performance and pressure drop using the performance evaluation criteria (PEC).