Heat transfer by natural convection for a centered inner adiabatic circular cylinder inside a trapezoidal enclosure filled with Ag-water nanofluid superposed saturated porous-nanofluid layer is numerically investigated. The inclined left and right walls of the trapezoidal enclosure are insulated. The bottom wall is partially heated at isotherm hot temperature, while the top wall is maintained at isotherm cold temperature. Finite element technique is used to numerically solve dimensionless Navier-Stoke equations for the nanofluid and porous-nanofluid media between inner adiabatic circular cylinder and trapezoidal enclosure. The numerical results are validated with those of Kim et al. [2008] in terms of streamlines and isotherms to check the accuracy of the present program. The validation illustrates a favorable agreement between the present work and Kim et al. The following parameters are studied: Rayleigh number (103 ≤ Ra ≤ 106 ), Darcy number (10-1 ≥ Da ≥ 10-5), nanoparticle volume fraction (0 ≤ ph ≤ 0.1), and porous layer thickness (0 ≤ Yp ≤ 100%).

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