Heat transfer enhancement in parabolic trough collector tube using Al2O3/synthetic oil nanofluid

Three-dimensional fully developed turbulent mixed convection heat transfer of Al2O3/synthetic oil nanofluid in a trough collector tube with a non-uniform heat flux was numerically studied. The effect of AL(2)O(3) particle concentration in the synthetic oil on the rate of heat transfer from the absorber tube was also investigated. Various nanoparticle concentrations (<5% in volume) at the operational temperatures of 300 K, 400 K, and 500 K were used in the current study. The heat flux distribution on the outer surface of the absorber tube was non-uniform in the circumferential direction but uniform in the axial direction. The heat flux in the circumferential direction was obtained using the Monte Carlo ray tracing technique. Three-dimensional Navier-Stokes mass, momentum and energy equations were solved using the FLUENT software. A second order discretization was used for the convective and diffusive terms and the SIMPLE scheme was applied for the velocity-pressure coupling. The outlet temperature of the absorber tube from the current numerical simulations was compared with existing experimental data. The absolute errors were found to be less than 3.8 degrees C. The current numerical results show that the convection heat transfer coefficient has a direct dependency on the volumetric concentration of nanoparticles in the fluid. In addition, the heat transfer enhancement due to the nanoparticles in the fluid reduces as the absorber operational temperature is increased. (C) 2014 Elsevier Ltd. All rights reserved.