Laminar and turbulent natural convection flow in a two-dimensional tall rectangular cavity heated from the vertical side has been investigated numerically for aspect ratios of 20, 40 and 80. The finite volume method was used to solve the conservation equations of mass, momentum and energy for Rayleigh numbers from 10(2) to 10(8), the flow was considered either laminar or turbulent. For turbulent flow, four different turbulence models kappa-epsilon were compared along with their experimental results for a cavity with an aspect ratio of 30, it was found that the better approach was with the one reported by Ince and Launder turbulent model [N. Ince, B. Launder, On the computation of buoyancy-driven turbulent flows in rectangular enclosures, Int. J. Heat Fluid Flow 10 ( 1989) 110-117]. The average Nusselt numbers as a function of Rayleigh numbers for the aspect ratios range of 20-80 were calculated and compared with five convective Nusselt number correlations reported from the literature. Convective Nusselt number correlations for laminar flow in the range of 10(2) <= Ra <= 10(6) and for turbulent flow in the range of 10(4) <= Ra <= 10(8) were presented. This study will help to have more accurate heat transfer parameters for applications such as facade elements. insulating units, double-skin facades, etc. (c) 2004 Elsevier B.V. All rights reserved.