Nonequilibrium heat conduction in a nanofluid layer with periodic heat flux oil one side and specified temperature oil the other side is studied numerically. The energy equations for the nanoparticles and base fluid are nondimensionalized and the problem is described by four dimension less parameters: heat capacity ratio, volume fraction of nanoparticles, period of surface heat flux, and the Sparrow number. The Sparrow number is to describe the coupling between the energy equations for nanoparticles and base fluid. Nonequilibrium between nanoparticles and base fluid, as well as heat transfer enhancement in nanofluid, of three nanofluids (diamond-water, diamond-ethylene glycol, and copper-ethylene glycol) is investigated. The results showed that the nonequilibrium between the nanoparticles and base fluid exist for all three nanofluids at low Sparrow number and short period of surface heat flux. The results also showed that heat transfer in a liquid layer can be enhanced by adding nanoparticles to the base fluid, but the level of enhancement is not as high as those reported by using transient hot wire (THW) method. (c) 2008 Elsevier Ltd. All rights reserved.