Numerical Investigation Of Forced Convection Heat Transfer Of Nanofluids In Microchannels

As a new type of heat transfer fluid, nanofluid with higher thermal conductivity has potential application prospect in the field of heat transfer enhancement. Many researchers have conducted many studies on the convective heat transfer of nanofluid and obtained a lot of results. In the present study, the numerical simulations of forced convective heat transfer of Al₂O₃-water nanofluid in two-dimensional and three-dimensional microchannels are performed. The main research contents and results are as follows:（1） Forced convection heat transfer of Al₂O₃-water nanofluid in a microchannel is studied numerically. The wall temperature of middle section of microchannel is maintained at a constant temperature and the walls of inlet and outlet sections are thermally insulated. The effects of variable thermal properties and constant thermal properties of nanofluid, nanoparticles volume fraction j and the Reynolds number Re on the forced convective heat transfer of nanofluid are analyzed. The results show that when Re and j are kept at constant values, the heat transfer rate for nanofluid with variable thermal properties is higher than that for nanofluid with constant thermal properties. When Re has the fixed value, the heat transfer rate increases with the increase of nanoparticles volume fraction j. When j has the fixed value and Re is small, the heat transfer in microchannel is dominated by thermal diffusion and the heat transfer rate is lower. With the increase of Re, the heat convection is dominant and the heat transfer rate increases.（2） By considering nanoparticles sphericity, forced convection heat transfer of Al₂O₃-water nanofluid in a microchannel is studied numerically. T he effects of nanoparticles sphericity on forced convection of Al₂O₃-water nanofluid in the two-dimensional microchannel are analyzed. The results show that when Re and j are kept at fixed values, the heat transfer rate increases with the decrease of nanoparticles sphericity. When Re has the fixed value, nanoparticles volume fraction j has little effect on the heat transfer rate with the increase of nanoparticles sphericity. Meanwhile, when j has the fixed value, Re has little effect on the heat transfer rate with the increase of nanoparticles sphericity.（3） Forced convection heat transfer of Al₂O₃-water nanofluid in a 3-D circular microchannel is studied numerically. The wall of microchannel maintains a constant heat flux. The effects of the diameter of nanoparticles dnp, Re and solid volume fraction j on the forced convection heat transfer are analyzed. Results show that with the increase of Re, the heat transfer rate increases when nanoparticles volume fraction and diameter of nanoparticles have the fixed values. when Re and dnp are kept at the fixed values, the heat transfer rate increases with the increase of the volume fraction of nanoparticles. When Re and j are kept at the fixed values, the heat transfer rate increases with the decrease of nao particles diameter. By analyzing the combination effect of nanoparticles diameter and solid volume fraction on heat transfer, with the diameter of nanoparticles increases, solid volume fraction has little effect on the heat transfer rate with the increase of nanoparticles diameter.