Laminar natural convection in rectangular enclosures divided by a single thin partition is studied numerically by the finite-element method. Special emphasis is given to enclosures with aspect ratios less than 1, although the results for aspect ratios of 1 have also been reported for comparison. The effect on flow structure and heat transfer of shifting the partition in the enclosure has also been investigated. While the Prandtl number is held at unity, the Rayleigh number is considered over a wide range, that is, from 103 to l06and the aspect ratio assumed the values of 1, 0.8, 0.5, and 0.4. © 1992 by Hemisphere Publishing Corporation.