This paper presents the details of an experimental and numerical investigation of natural convection in a radial heat sink, composed of a horizontal circular base and rectangular fins. The general flow pattern is that of a chimney: i.e., cooler air entering from outside is heated as it passes between the fins, and then rises from the inner region of the heat sink. Parametric studies are performed to compare the effects of three geometric parameters (fin length, fin height, and number of fins) and a single operating parameter (heat flux) on the thermal resistance and the average heat transfer coefficient for the heat sink array. In addition, a correlation is proposed to predict the average Nusselt number for a radial heat sink. (C) 2010 Elsevier Ltd. All rights reserved.