Numerical analysis on heat transfer enhancement of Al2O3 and CuO-water nanofluids in annular curved tubes
Mahmoud Abdelmagied
Abstract
Abstract The present investigation presents numerically the thermo-hydraulic performance of annular curved tubes in the turbulent flow region. The three-dimensional (3D) computational fluid dynamic (CFD) model was developed by using a commercial ANSYS 14.5 package to get additional insights on the thermo-hydraulic performance on a level of detail that is not always available in experiment results. The turbulent k-ε realize model was employed to examine the effect of Al 2 O 3 -water and CuO-water nanofluids on the heat transfer and fluid flow characteristics at different key design parameters. Three coil geometry shapes (including helical, spiral, and conical), five annular cross-section shapes (including circular, elliptical, square, rectangular, and triangular), and three cross-section areas were also investigated in this study. The numerical simulations were carried out at Reynolds numbers of 4700 to 26,700 and nanofluid volume concentrations, φ of 1%, 3%, and 5%, with constant wall temperature (CWT) heat transfer boundary conditions. The result showed that the addition of Al 2 O 3 (45 nm) and CuO (29 nm) nanoparticles to water improves the heat transfer coefficient by 48.8%, 25.7%, and 8.4% and 37.1%, 20%, and 8.7%, respectively, at φ of 5%, 3%, and 1%, while the penalty of pressure drop is approximately negligible. The heat transfer rate per unit pumping power for helical design achieved 21.6% and 5.34% higher than conical and spiral designs, respectively, for the same curvature ratio, cross-section area, and coil length. Also, the circular shape achieved a higher heat transfer enhancement than elliptical, square, rectangular, and triangular shapes by 4%, 14.6%, 17.8%, and 30.1%, respectively. The maximum thermo-hydraulic performance index reached 1.68 and 1.58 for both Al 2 O 3 -water and CuO-water nanofluids, respectively, at φ of 5%.