Effect of the solid obstacles on the natural laminar convection in a vertical enclosure is numerically and analytically investigated in the present work, aiming to identify suitable arrangements for heat transfer enhancement in the electronic cooling units. Two categories of morphology were taken into considerations, being attached to the horizontal walls and being placed centrally in the space. Thermal Rayleigh number, number of obstacles, and solid thermal conductivity have been varied to observe inherent flow structures and thermal transport mechanism, regarding of different levels of solid-to-fluid volume ratios. Flow field, thermal field and heat transfer rates are respectively visualized through streamlines, isotherms and heatlines. Depending on a large set of numerical data and critical boundary layer analysis, correlations have been developed for these two fundamental configurations. Results demonstrate that average Nusselt number is an increasing function of Ra and Kr and a decreasing function of gamma and N-A (and N-B). Furthermore, average Nusselt number of enclosure B is greater than that of enclosure A when volume ratio is lower, while this phenomenon is contrary as the volume ratio and relative obstacles number increases. These two configurations of obstacles number are important to optimize the cooling efficient of electronic components. (C) 2016 Elsevier Ltd. All rights reserved.