Analysis of thermophysical properties of nanofluids using discrete particle modeling

Over the last decade a significant amount of research was committed to exploring the thermal transport properties of nanofluids. Several studies conducted over the period showed an enhancement of heat transfer properties in nanofluids when compared to that of the base fluids. However, the physical mechanism for the anomalous increase of heat transfer was not explained properly. A number of possible reasons have been proposed for such behavior, but a consensus has yet to emerge.;In this study, a discrete particle model was developed to predict the heat transfer properties of nanofluids and to understand the physical mechanisms behind the anomalous increase in heat transfer properties. The model solves for the fluid phase in Eulerian frame and particle phase in Lagrangian frame of reference. In order to predict the nanoparticle dispersion, Brownian force, thermophoretic force and van der Waals force were implemented to the particle equation.;Simulations performed to predict the heat transfer properties (i.e., the thermal conductivity and convective heat transfer coefficient) of nanofluids revealed that the heat transfer properties of nanofluids increase with an increase of particle volume fraction and decrease of particle size. Metallic nanofluids were observed to have better heat transfer when compared to that of nonmetallic nanofluids. The study indicated that particle dispersion, two-way interaction between fluid and particle temperatures and coagulation of particles were all necessary for the prediction of the thermal conductivity of nanofluids. However, the effect of particle dispersion on the anomalous increase in the convective heat transfer coefficient of nanofluids was found to be insignificant. The simulations performed using the multi-sized nanoparticles suspended in the fluid medium showed a significant difference in comparison with the single-sized nanofluids. The predicted thermal conductivity values were observed to be closer to the experimental value, when the simulation was performed with the multi-sized particles suspended in them.;The numerical model presented in this study showed good agreement with the experimental data. This model is an effective research tool, which provides information about the dynamics of multiphase systems at a microscopic level. Thus the model presented in this study will aid the research community in understanding the mechanism of heat transfer in nanofluids.