An Eulerian-Lagrangian based direct numerical Simulations (DNS) model was developed to investigate the effective thermal conductivity of nanofluids. A two-way coupling term to resolve the temperature interactions between the solid particles and fluid field was considered. The model also considered various forces acting on the nanoparticles. Cu/water nanofluids with 100 nm particles and Al2O3/water nanofluids with 80 nm particles were simulated at different volume fractions and the effective thermal conductivity of nanofluids was calculated. The present results suggest that the particle conductivity and forces acting on nanoparticle are necessary while predicting the effective thermal conductivity of nanofluids. (C) 2009 Elsevier Ltd All rights reserved