| Summary: | This article used the lattice Boltzmann method to study the heat transmission of natural convective of nanofluids in a 2-D square cavity partially filled with porous medium. The nanoparticles volume fraction of Al2O3, Cu, and SiO2 were 0.5%, 1%, 1.5%, 2%, 3%, and 4%, which were mixed with water and 70% of ethylene glycol aqueous solution as the base fluid, and made up six kinds of nanofluids as the research object. Using nanofluids coupled double distribution lattice Boltzmann method model, this paper studied the rules of natural convection heat transfer of different nanofluids with the changing of Rayleigh number and the concentration of the nanoparticles in the 2-D square cavity partially filled with porous medium. The results showed that the average Nusselt number of the hot wall will increase with the increase of Rayleigh number number, and under different heat transfer conditions, there are two different critical Rayleigh numbers. In the case of different concentrations of the same concentration, the critical Rayleigh number is about 105, when Ra > Rac, the average Nusselt number of water is higher; when Ra < Rac, the average Nusselt number of, the average Nusselt number of ethylene glycol is higher. In the case of different concentrations of same particles, the critical Rayleigh number is between 105 and 106, there was also a critical Rayleigh number (Rac =105), when the Ra < Rac, the average Nusselt number of the hot wall will increase with the increasing of concentration; when the Ra > Rac, there is a slight decreasing in the average Nusselt number with the increasing of concentration. The critical Rayleigh number of water as the base fluid is smaller than that of ethylene glycol as the base fluid.
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