Natural convection of composite nanofluids based on a two-phase lattice Boltzmann model.

A two-phase lattice Boltzmann method (LBM) is used to study the natural convection heat exchange characteristics of Al2O3–H2O nanofluids and (Al2O3/Cu)–H2O composite nanofluids in a rectangular cavity in this paper. It can be found that the two-phase LBM is suitable for the study on natural convection heat exchange characteristics of nanofluids, and its correctness is verified. Firstly, the effects of temperature differences (∆T = 1 K and ∆T = 11 K), nanofluids volume fractions (φ = 0.01, 0.03 and 0.05) and kinds of fluid (water, Al2O3–H2O nanofluids and Al2O3/Cu–H2O nanofluids) on the free convection are researched. Then, temperature and streamline distributions of Al2O3/Cu–H2O nanofluids are investigated, respectively. Lastly, local Nusselt number and average Nusselt number distributions of different nanofluids along with Y direction are investigated. It can be found that Al2O3/Cu–H2O nanofluids show a larger enhancement than Al2O3–H2O nanofluids and water. Al2O3/Cu–H2O and Al2O3–H2O nanofluids can strengthen the heat transfer performance by 9.9% and 5% at the extreme compared with deionized water, respectively. Besides, the maximum enhancement ratio of Al2O3/Cu–H2O and Al2O3–H2O nanofluids is 9.8% and 4.5% at small temperature difference (ΔT = 1 K), respectively, which is greater than that (1.6% and 0.36%) at big temperature difference (ΔT = 11 K). [ABSTRACT FROM AUTHOR]