Forced convective heat transfer of fluid (with nanoparticles) in metal-foam duct is numerically investigated and the velocity and temperature fields are obtained. The effects of some key parameters on flow and heat transfer of nanofluid in porous media are analyzed. For nanofluid in porous media, the feasibility of field synergy principle on convective heat transfer is examined and the mechanisms for related heat transfer enhancement are discussed. Results show that both pressure drop and Nu number for nanofluid in metal foams increase with an increase in volume fraction of nanoparticles. But the increasing amplitude of pressure drop increases while the increasing amplitude of Nu number decreases, which implies that heat transfer enhancement with nanofluid cannot offset pressure drop increase. Field synergy principle for pure fluid convection cannot guide the analysis of the heat transfer enhancement for nanofluid in metal foams, which calls for the modification of existing field synergy principle. (C) 2014 Elsevier Ltd. All rights reserved.