Numerical Simulation of the Natural Convective Heat Transfer of Nanofluids in a Square Cavity Based on Different Predictive Models for Single-Phase and Multiphase Flow Mixtures

The flow and heat transfer characteristics of nanofluids in a square cavity were simulated using single-phase and mixed-phase flow models, and the simulation results were compared with the corresponding experimental values. The effects of different prediction models for the thermal properties of nanofluids, Grashof number, and volume fraction on the Nusselt number were analyzed. The velocity and temperature distributions of the nanofluid and de-ionized water in the square cavity were compared, and the effects of the temperature and flow fields on the enhanced heat transfer were analyzed according to the field synergy theory. The results show that for the numerical simulation of convective heat transfer in water, both the single-phase flow models and multiphase flow mixing models had high prediction accuracy. For nanofluids, single-phase flow did not reflect the heat transfer characteristics well, and the simulation results of the single-phase flow model relied more strongly on a highly accurate prediction model for the physical parameters. The multiphase flow mixing model could better reflect the natural convective heat transfer properties of the nanofluids in a square cavity. The nanofluid could significantly improve the flow state in the square cavity, thereby facilitating enhanced convective heat transfer. When the concentration is 2% (Grashof number is 1 × 106), the average Nusselt number of the nanofluid is increased by 19.7% compared with the base fluid.