Laminar natural convection in a two-dimensional square cavity of side length H due to two and three discrete heat source-sink pairs on the vertical sidewalls was numerically investigated. Main efforts were focused on the size and arrangement effects of the sources and sinks on the fluid flow and heat transfer characteristics. The sizes of sources and sinks were, respectively, H/4 for two sources-sinks pairs and H/6 for three sources-sinks pairs. The arrangement of the sources and sinks changes from the separated to staggered modes, i.e., first separately located on two sidewalls, then alternately located on two sidewalls, and finally alternately located oil one sidewall. The fluid flow, heat transfer, and heat transport characteristics were illustrated by streamlines, isotherms and averaged Nusselt number, and heatlines. It was found that the total heat transfer was closely related with the number of eddies in the enclosure. When the sources and sinks were split into smaller segments and/or arranged in a staggered mode, the number of eddies in the enclosure would increase and hence heat transfer was augmented. (c) 2008 Elsevier Ltd. All rights reserved.