Natural-convection heat transfer in a cylindrical enclosure, heated partially from below by a disk-shaped heating surface and cooled pbm the top and the side, war investigated experimentally and numerically. Heat transfer measurements are presented for the range of Rayleigh numbers from 10(8) to 2 x 10(10). The total acceleration normal to the heating surface was varied from 1 to 100 times the standard gravitational acceleration. The heat flux was varied from 0.19 MW/m(2) to 1.5 MW/m(2). The test results were correlated by an equation of the form Nu(D) = 0.2 Ra-D(0.325) for Prandtl number 2 and aspect ratio 1. The flow field war studied numerically using FLUENT code.