Advanced Powder Technology, Vol.29, No.4, 890-903, 2018
Effects of curvature ratio on forced convection and entropy generation of nanofluid in helical coil using two-phase approach
Applying nanofluid and helical coils are two effective methods for thermal performance enhancement. Combination of these techniques could improve the energy efficiency of thermal equipment dramatically. In this study, a numerical analysis of nanofluid flowing in helical coil with constant wall temperature boundary condition was performed to evaluate nanofluid superiority over the base fluid. Forced convective heat transfer and entropy generation of aqueous Al2O3 nanofluid with temperature dependent properties were investigated. Eulerian two-phase mixture model was employed for nanofluid modeling and governing mass, momentum, energy, and volume fraction equations were solved using finite volume method. Simulations covered a range of nanoparticle volume fraction of 1-3%, Reynolds number from 200 to 2000, and curvature ratio of 0.05-0.2. In order to evaluate the heat transfer performance, a parameter referred as thermo-hydrodynamic performance index was applied. Also, entropy generation analysis was performed to examine the efficiency of the helical coil and nanofluid. The results demonstrate that performance index enhances by decreasing the Reynolds number and the increasing nanoparticle concentration. The best thermo-hydrodynamic performance can be obtained at low Reynolds number, high nanoparticle volume fraction, and large curvature ratio. Increasing curvature ratio decreases the ratio of local entropy generation by nanofluid to the base fluid. So, utilization of water based Al2O3 nanofluid in higher curvature ratio is more efficient from irreversibility point of view. (C) 2018 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.