Numerical investigation of nanofluids forced convection in circular tubes

In this paper, developing laminar forced convection flow of a water-Al2O3 nanofluid in a circular tube, submitted to a constant and uniform heat flux at the wall, is numerically investigated. A single- and two-phase model (discrete particles model) is employed with either constant or temperature-dependent properties. The investigation is accomplished for size particles equal to 100 nm. The maximum difference in the average heat transfer coefficient between single- and two-phase models results is about 11%. Convective heat transfer coefficient for nanofluids is greater than that of the base liquid. Heat transfer enhancement increases with the particle volume concentration, but it is accompanied by increasing wall shear stress values. Higher heat transfer coefficients and lower shear stresses are detected in the case of temperature dependents models. The heat transfer always improves. as Reynolds number increases, but it is accompanied by an increase of shear stress too. Moreover a comparison with data present in the literature is carried out. (C) 2009 Elsevier Ltd. All rights reserved.