The effect of a linearly heated left sidewall on natural convection flows in a cavity filled with nanofluid-superposed porous layers is investigated numerically using the Galerkin finite element method. Two cases, which use the vertical and horizontal directions for the porous-nanofluid layers, are considered to investigate the natural convection in the flow inside a square enclosure. In both cases, the left wall is linearly heated, whereas the right wall is isothermally cooled. The horizontal walls are assumed to be thermally insulated. The Darcy-Brinkmann model is used to solve the governing equations in the porous layer. The results show that the nanofluid produces more enhancement of heat transfer compared to the base fluid. Increasing the Rayleigh number (Ra) values caused the intensity of the streamlines in case 2 to be stronger than that in case 1. Lower values of the thermal conductivity ratio (K-r) imply greater heat transfer enhancement than for the high thermal conductivity ratios. At the low values of the thermal conductivity ratio (K-r < 1) and Darcy number values (Da < 10(-3)), the heat transfer is more enhanced for case 2 compared to case 1 while higher Darcy number produced case 1 overcome case 2. (C) 2018 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.