The coupled thermal boundary layers adjacent to a partition in a differentially heated cavity are numerically investigated. The cavity is filled with water, which is initially quiescent but with an imposed temperature difference between the two sides of the vertical partition. The numerical results show that the development of natural convection flows in the partitioned cavity undergoes three main stages: an initial stage, a transitional stage and a steady stage. The transient features of the coupled thermal boundary layers adjacent to the partition as well as the overall natural convection flow in the partitioned cavity are described. and heat transfer through the coupled thermal boundary layers and the partitioned cavity is examined. (C) 2009 Elsevier Ltd. All rights reserved.