Özet:
Fully developed turbulent forced convection ow of an Al2O3/water nano uid in a circular pipe under constant wall heat ux is investigated numerically, using nite volume method. Both single phase model and two phase models such as mixture and Eulerian are considered. Di erent correlations for nano uids thermophysical properties have been compared in the single phase formulation to investigate the Brownian e ect for both turbulent and laminar ow. The results given by the single phase and two phase models are compared to the experimental results in the literature. The heat transfer enhancement and the increase in the pressure drop of the nano uid are found to be more signi cant when the Reynolds number and/or the volume concentration are increased in accordance to experimental results. The single phase model is observed to give accurate predictions when direct correlations for nano uid properties are available from experimental data. The predictions given by the two phase Eulerian model are more accurate for dilute suspensions at low volume concentrations, however for higher concentrations, the two phase mixture model gives closer results to experimental data, when compared to the Eulerian model. It is also found that Brownian motion is e ective in heat transfer enhancement for both laminar and turbulent ow of nano uids. The heat transfer enhancement increases with increasing Reynolds number and volume concentration, while the pressure drop increase depends only on volume concentration. For both low and high volume concentrations, the heat transfer enhancement to pressure drop increase ratio is observed to be higher in the turbulent case compared to laminar ow.
