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The natural convective heat transfer inside a square enclosure containing Al2O3 and Cu nanofluids has been studied using Lattice Boltzmann method. A nonuniform sinusoidal heat flux was applied on one of the side boundaries. The calculated results and experimental data were in good agreement. Impacts of Rayleigh (Ra) number (105–107), nanoparticles solid volume fraction or SVF (0.01–0.1), and local oscillation wavelengths for wall heat flux (0.1, 0.5, and 1) on thermal and flow patterns have been studied. It was shown that an increase in SVF (0.01–0.1) and Ra number (105–107) for Cu nanofluids decreases the maximum wall temperature by 48.3 and 49.2%, respectively. In addition, for the same oscillation wavelength and Ra number, Cu-water nanofluid has about 30% higher rate of heat transfer compared to Al2O3-water. With an increase in SVF at low Ra number, the heat tends to be transferred at a constant rate. The enclosure containing Al2O3-water has lower absolute stream function values than Cu-water nanofluid by 26.6%. [ABSTRACT FROM AUTHOR]

Combined effects of hydrodynamic partial slip, thermal radiation due to solar energy, and nanoparticles volume fraction on natural convection and entropy generation of atmospheric ultrafine aerosols sample enclosed within a two-sided lid-driven cavity are studied numerically in the present contribution. Partial slip effect is taken into account along the two horizontal moving walls, and thermal radiation is considered through Rosseland approximation. The governing equations are solved using an accurate finite volume method based on SIMPLE algorithm. The impact of Brownian motion of nanoparticles is also considered in this study, whereby KKL (Koo-Kleinstreuer-Li) correlation is utilized for simulating the effective thermal conductivity and viscosity of nanofluid. The heatline visualization technique is also utilized to study the energy flux within the cavity. A comprehensive study is conducted on the controlling parameters, including partial slip coefficient (λ = 0 - 5), radiation parameter (Rd = 0 - 2), and nanoparticles volume fraction (ϕ = 0 - 4%), which influence the flow and heat transfer characteristics. Results show that the partial slip usually eliminates the effect of mechanical forces provoked by the moving lids. Moreover, thermal radiation homogenizes the medium thermally, which results in decreasing the average entropy generation. It is also observed that the effect of carbon-black nanoparticles on the atmospheric heat transfer manifests a wide variety of fashions mainly dependent on the presence or absence of thermal radiation due to solar energy. [ABSTRACT FROM AUTHOR]