Two-phase lattice Boltzmann simulation of the effects of base fluid and nanoparticle size on natural convection heat transfer of nanofluid

摘要

The effects of two kinds of base fluid (H_2O and Ga) and three different nanoparticle radiuses (20 nm, 40 nm and 80 nm) on the natural convection heat transfer of a rectangular enclosure filled with Al_2O_3-H_2O and Al_2O_3-Ga nanofluid at different Rayleigh numbers (Ra = 10~3 and Ra = 10~5) are discussed based on a two-phase lattice Boltzmann method in this paper. It is found that Al_2O_3-Ga nanofluid shows a better heat transfer enhancement than Al_2O_3-H_2O nanofluid. Al_2O_3-Ga and Al_2O_3-H_2O nanofluid with the same smallest radius (r = 20 nm) can enhance the heat transfer by 86.0% and 24.5% compared with water respectively. It is also found that Al_2O_3-Ga nanofluid at low Rayleigh number (Ra = 10~3) shows the biggest heat transfer enhancement (shows a 4.4% increase for every nanoparticle radius decreasing 20 nm) compared with Al_2O_3-H_2O nanofluid. The enhancement ratio at low Rayleigh number is about 3-10.8% and 23.5-28.8% more than that at high Rayleigh number for Al_2O_3-water and Al_2O_3-Ga nanofluid respectively. In addition, the nanoparticle fraction distributions in the enclosure are also investigated.