In this paper, we assume that a nanofluid is a mixture consisting of a continuous base fluid component and a discontinuous nanoparticle component. Then, based on the analysis of Buongiorno in 2006 for critical slip mechanisms in nanofluids, we consider the effects of Brownian diffusion and thermophoresis of nanoparticles on heat and mass flux in nanofluid. With the coupled conservation equations, we analyze the heat conduction properties of general nanofluids under three conditions: 1) stationary fluid with uniform temperature, 2) stationary fluid under constant temperature boundary, and 3) stationary fluid under constant heat flux boundary. The results show that nanofluid effective thermal conductivity depends on the thermal conductivity of nanoparticle and basic fluid, particle concentration, particle size, particle distribution, Brownian and thermal diffusion, boundary condition and time. It indicates that the nanofluid effective thermal conductivity can be well predicted for stationary fluid with uniform temperature from classical effective medium theory such as Maxwell’s approach. However, the measurements applying steady or unsteady heat conduction methods for pure materials fail to predict correctively the effective thermal conductivity of nanofluid and are influenced by boundary conditions. Preliminary conclusions include approximate correlations of effective thermal conductivity of dilute nanofluids using steady state and quasi-steady state measuring methods.

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