In the last decade, a number of investigations have been conducted to identify the possible mechanisms that contribute to the enhanced effective thermal conductivity of nanoparticle suspensions (nanofluids). The Brownian motion of the nanoparticles in these suspensions is one of the potential contributors to this enhancement and the mechanisms that might contribute to this are the subject of considerable discussion and debate. In the current investigation, the mixing effect of the base fluid in the immediate vicinity of the nanoparticles caused by the Brownian motion was analyzed, modeled and compared with existing experimental data available in the literature. The simulation results indicate that this mixing effect can have a significant influence on the effective thermal conductivity of nanofluids. (c) 2007 Elsevier Ltd. All rights reserved.