Heat transfer and entropy generation of turbulent forced convection flow of nanofluids in a heated pipe

摘要

Eulerian-Eulerian multi-phase mixture model is applied to numerically analyse the turbulent flow and heat transfer behaviour of water based Al_2O_3 and TiO_2 nanofluids in a pipe. The main goal of the present work is to investigate the effects of volume concentrations, Brownian motion and size diameter of nanoparticles on the flow and heat transfer. Analysis of entropy generation is presented in order to investigate the condition that optimises the thermal system. Results reveal that small diameter of nanoparticles with their Brownian motion has the highest heat transfer rate as well as thermal performance factor for x = 6%. Above all, the higher heat transfer rate is found while using the multi-phase model than the single-phase model (Saha and Paul [1]). Also, the optimal Reynolds number is found to be Re = 60 × 10~3 for x = 6% and d_p = 10 nm, which minimises the total entropy generation. Finally, it is showed that TiO_2-water nanofluid is the most energy efficient coolant than Al_2O_3-water nanofluid, and some new correlations have been proposed for the calculation of average Nusselt number.