The effective thermal management of the heat generating components is important for job scheduling in multi core processors used in several electronic devices. In the present paper, natural convection in an enclosure with alternately active heat sources for different switch over time period is studied. Laminar, incompressible 2-D code with Finite Volume Method (FVM) has been used to solve the transient equations of continuity, momentum and energy. The study is limited for the Rayleigh number (Ra) varying from 10(3) to 10(6) and Prandtl number of 0.71. For the range of Rayleigh number and time period studied here, heat transfer is found to be more than that of the steady operation of a single heater for all switchover time periods. Some nonlinear characteristics on hydrodynamics and heat transfer are observed at higher Rayleigh numbers for longer switchover time period. The analysis also shows that the decrease in time period results in increase in heat transfer. (C) 2014 Elsevier Ltd. All rights reserved.